1
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Bossaert M, Moreno AT, Peixoto A, Pillaire MJ, Chanut P, Frit P, Calsou P, Loparo JJ, Britton S. Identification of the main barriers to Ku accumulation in chromatin. Cell Rep 2024; 43:114538. [PMID: 39058590 PMCID: PMC11411529 DOI: 10.1016/j.celrep.2024.114538] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2024] [Revised: 05/29/2024] [Accepted: 07/09/2024] [Indexed: 07/28/2024] Open
Abstract
Repair of DNA double-strand breaks by the non-homologous end-joining pathway is initiated by the binding of Ku to DNA ends. Multiple Ku proteins load onto linear DNAs in vitro. However, in cells, Ku loading is limited to ∼1-2 molecules per DNA end. The mechanisms enforcing this limit are currently unclear. Here, we show that the catalytic subunit of the DNA-dependent protein kinase (DNA-PKcs), but not its protein kinase activity, is required to prevent excessive Ku entry into chromatin. Ku accumulation is further restricted by two mechanisms: a neddylation/FBXL12-dependent process that actively removes loaded Ku molecules throughout the cell cycle and a CtIP/ATM-dependent mechanism that operates in S phase. Finally, we demonstrate that the misregulation of Ku loading leads to impaired transcription in the vicinity of DNA ends. Together, our data shed light on the multiple mechanisms operating to prevent Ku from invading chromatin and interfering with other DNA transactions.
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Affiliation(s)
- Madeleine Bossaert
- Institut de Pharmacologie et Biologie Structurale (IPBS), Université de Toulouse, CNRS, Université Toulouse III - Paul Sabatier (UT3), Toulouse, France; Equipe Labéllisée la Ligue contre le Cancer 2018
| | - Andrew T Moreno
- Department of Biological Chemistry and Molecular Pharmacology, Blavatnik Institute, Harvard Medical School, Boston, MA 02115, USA
| | - Antonio Peixoto
- Institut de Pharmacologie et Biologie Structurale (IPBS), Université de Toulouse, CNRS, Université Toulouse III - Paul Sabatier (UT3), Toulouse, France; Equipe Labéllisée la Ligue contre le Cancer 2018
| | - Marie-Jeanne Pillaire
- Institut de Pharmacologie et Biologie Structurale (IPBS), Université de Toulouse, CNRS, Université Toulouse III - Paul Sabatier (UT3), Toulouse, France; Equipe Labéllisée la Ligue contre le Cancer 2018
| | - Pauline Chanut
- Institut de Pharmacologie et Biologie Structurale (IPBS), Université de Toulouse, CNRS, Université Toulouse III - Paul Sabatier (UT3), Toulouse, France; Equipe Labéllisée la Ligue contre le Cancer 2018
| | - Philippe Frit
- Institut de Pharmacologie et Biologie Structurale (IPBS), Université de Toulouse, CNRS, Université Toulouse III - Paul Sabatier (UT3), Toulouse, France; Equipe Labéllisée la Ligue contre le Cancer 2018
| | - Patrick Calsou
- Institut de Pharmacologie et Biologie Structurale (IPBS), Université de Toulouse, CNRS, Université Toulouse III - Paul Sabatier (UT3), Toulouse, France; Equipe Labéllisée la Ligue contre le Cancer 2018.
| | - Joseph J Loparo
- Department of Biological Chemistry and Molecular Pharmacology, Blavatnik Institute, Harvard Medical School, Boston, MA 02115, USA.
| | - Sébastien Britton
- Institut de Pharmacologie et Biologie Structurale (IPBS), Université de Toulouse, CNRS, Université Toulouse III - Paul Sabatier (UT3), Toulouse, France; Equipe Labéllisée la Ligue contre le Cancer 2018.
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2
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Xiong Y, Han W, Xu C, Shi J, Wang L, Jin T, Jia Q, Lu Y, Hu S, Dou SX, Lin W, Strick TR, Wang S, Li M. Single-molecule reconstruction of eukaryotic factor-dependent transcription termination. Nat Commun 2024; 15:5113. [PMID: 38879529 PMCID: PMC11180205 DOI: 10.1038/s41467-024-49527-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2023] [Accepted: 06/09/2024] [Indexed: 06/19/2024] Open
Abstract
Factor-dependent termination uses molecular motors to remodel transcription machineries, but the associated mechanisms, especially in eukaryotes, are poorly understood. Here we use single-molecule fluorescence assays to characterize in real time the composition and the catalytic states of Saccharomyces cerevisiae transcription termination complexes remodeled by Sen1 helicase. We confirm that Sen1 takes the RNA transcript as its substrate and translocates along it by hydrolyzing multiple ATPs to form an intermediate with a stalled RNA polymerase II (Pol II) transcription elongation complex (TEC). We show that this intermediate dissociates upon hydrolysis of a single ATP leading to dissociation of Sen1 and RNA, after which Sen1 remains bound to the RNA. We find that Pol II ends up in a variety of states: dissociating from the DNA substrate, which is facilitated by transcription bubble rewinding, being retained to the DNA substrate, or diffusing along the DNA substrate. Our results provide a complete quantitative framework for understanding the mechanism of Sen1-dependent transcription termination in eukaryotes.
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Affiliation(s)
- Ying Xiong
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong, China
- School of Physics, University of Chinese Academy of Sciences, Beijing, China
| | - Weijing Han
- Songshan Lake Materials Laboratory, Dongguan, Guangdong, China
| | - Chunhua Xu
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China
| | - Jing Shi
- Department of Pathogen Biology, School of Medicine & Holistic Integrative Medicine, Nanjing University of Chinese Medicine, Nanjing, China
- Department of Pathology of Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou, China
| | - Lisha Wang
- Songshan Lake Materials Laboratory, Dongguan, Guangdong, China
| | - Taoli Jin
- Songshan Lake Materials Laboratory, Dongguan, Guangdong, China
| | - Qi Jia
- Songshan Lake Materials Laboratory, Dongguan, Guangdong, China
| | - Ying Lu
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China
| | - Shuxin Hu
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China
| | - Shuo-Xing Dou
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China
- School of Physics, University of Chinese Academy of Sciences, Beijing, China
| | - Wei Lin
- Department of Pathogen Biology, School of Medicine & Holistic Integrative Medicine, Nanjing University of Chinese Medicine, Nanjing, China.
- Jiangsu Collaborative Innovation Center of Chinese Medicinal Resources Industrialization, Nanjing, China.
- State Key Laboratory of Natural Medicines, China Pharmaceutical University, Nanjing, China.
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China.
| | - Terence R Strick
- Institut de Biologie de l'Ecole Normale Supérieure, PSL Université, INSERM, CNRS, Paris, France.
- Equipe Labellisée de la Ligue Nationale Contre le Cancer, Paris, France.
| | - Shuang Wang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China.
- Songshan Lake Materials Laboratory, Dongguan, Guangdong, China.
| | - Ming Li
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong, China
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3
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Fortea E, Lee S, Chadda R, Argyros Y, Sandal P, Mahoney-Kruszka R, Ciftci HD, Falzone ME, Huysmans G, Robertson JL, Boudker O, Accardi A. Structural basis of pH-dependent activation in a CLC transporter. Nat Struct Mol Biol 2024; 31:644-656. [PMID: 38279055 PMCID: PMC11262703 DOI: 10.1038/s41594-023-01210-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2023] [Accepted: 12/22/2023] [Indexed: 01/28/2024]
Abstract
CLCs are dimeric chloride channels and anion/proton exchangers that regulate processes such as muscle contraction and endo-lysosome acidification. Common gating controls their activity; its closure simultaneously silences both protomers, and its opening allows them to independently transport ions. Mutations affecting common gating in human CLCs cause dominant genetic disorders. The structural rearrangements underlying common gating are unknown. Here, using single-particle cryo-electron microscopy, we show that the prototypical Escherichia coli CLC-ec1 undergoes large-scale rearrangements in activating conditions. The slow, pH-dependent remodeling of the dimer interface leads to the concerted opening of the intracellular H+ pathways and is required for transport. The more frequent formation of short water wires in the open H+ pathway enables Cl- pore openings. Mutations at disease-causing sites favor CLC-ec1 activation and accelerate common gate opening in the human CLC-7 exchanger. We suggest that the pH activation mechanism of CLC-ec1 is related to the common gating of CLC-7.
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Affiliation(s)
- Eva Fortea
- Department of Physiology and Biophysics, Weill Cornell Medical School, New York, NY, USA
- Department of Anesthesiology, Weill Cornell Medical School, New York, NY, USA
| | - Sangyun Lee
- Department of Anesthesiology, Weill Cornell Medical School, New York, NY, USA
| | - Rahul Chadda
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO, USA
| | - Yiorgos Argyros
- Department of Anesthesiology, Weill Cornell Medical School, New York, NY, USA
- Department of Biochemistry, Weill Cornell Medical School, New York, NY, USA
| | - Priyanka Sandal
- Department of Molecular Physiology and Biophysics, The University of Iowa, Iowa City, IA, USA
| | - Robyn Mahoney-Kruszka
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO, USA
| | - Hatice Didar Ciftci
- Department of Physiology and Biophysics, Weill Cornell Medical School, New York, NY, USA
- Tri-Institutional Training Program in Chemical Biology, New York, NY, USA
| | - Maria E Falzone
- Department of Anesthesiology, Weill Cornell Medical School, New York, NY, USA
- Department of Biochemistry, Weill Cornell Medical School, New York, NY, USA
| | - Gerard Huysmans
- Department of Physiology and Biophysics, Weill Cornell Medical School, New York, NY, USA
- Erasmus University, Jette, Belgium
| | - Janice L Robertson
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO, USA
| | - Olga Boudker
- Department of Physiology and Biophysics, Weill Cornell Medical School, New York, NY, USA.
- Howard Hughes Medical Institute, Chevy Chase, MD, USA.
| | - Alessio Accardi
- Department of Physiology and Biophysics, Weill Cornell Medical School, New York, NY, USA.
- Department of Anesthesiology, Weill Cornell Medical School, New York, NY, USA.
- Department of Biochemistry, Weill Cornell Medical School, New York, NY, USA.
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4
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Gilhooly NS, Kowalczykowski SC. Specific anchoring of large topologically closed DNA for single-molecule protein:DNA interactions. BIOPHYSICAL REPORTS 2024; 4:100144. [PMID: 38390466 PMCID: PMC10881311 DOI: 10.1016/j.bpr.2024.100144] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/12/2023] [Accepted: 01/22/2024] [Indexed: 02/24/2024]
Abstract
Single-molecule and bulk biophysical approaches to study protein-DNA interactions on surface-immobilized nucleic acid templates typically rely on modifying the ends of linear DNA molecules to enable surface-DNA attachments. Unless both strands are constrained, this results in topologically free DNA molecules and the inability to observe supercoiling-dependent biological processes or requires additional means to micromanipulate the free DNA end to impose rotational constraints or induce supercoiling. We developed a method using RecA protein to induce the formation of a circularized compliment-stabilized D-loop. The resulting joint molecule is topologically closed, surface anchorable, and stable under microfluidic flow. Importantly, the method obviates the need for subsequent manipulation of surface-tethered DNA; tethered molecules remain supercoiled and retain accessibility to DNA-binding proteins. This approach adds to the toolkit for those studying processes on DNA that require supercoiled DNA templates or topologically constrained systems.
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Affiliation(s)
- Neville S Gilhooly
- Department of Microbiology and Molecular Genetics and Department of Molecular and Cellular Biology, University of California, Davis, Davis, California
| | - Stephen C Kowalczykowski
- Department of Microbiology and Molecular Genetics and Department of Molecular and Cellular Biology, University of California, Davis, Davis, California
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5
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Małecka EM, Woodson SA. RNA compaction and iterative scanning for small RNA targets by the Hfq chaperone. Nat Commun 2024; 15:2069. [PMID: 38453956 PMCID: PMC10920880 DOI: 10.1038/s41467-024-46316-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2023] [Accepted: 02/18/2024] [Indexed: 03/09/2024] Open
Abstract
RNA-guided enzymes must quickly search a vast sequence space for their targets. This search is aided by chaperones such as Hfq, a protein that mediates regulation by bacterial small RNAs (sRNAs). How RNA binding proteins enhance this search is little known. Using single-molecule Förster resonance energy transfer, we show that E. coli Hfq performs a one-dimensional scan in which compaction of the target RNA delivers sRNAs to sites distant from the location of Hfq recruitment. We also show that Hfq can transfer an sRNA between different target sites in a single mRNA, favoring the most stable duplex. We propose that compaction and segmental transfer, combined with repeated cycles of base pairing, enable the kinetic selection of optimal sRNA targets. Finally, we show that RNA compaction and sRNA transfer require conserved arginine patches. We suggest that arginine patches are a widespread strategy for enabling the movement of RNA across protein surfaces.
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Affiliation(s)
- Ewelina M Małecka
- Thomas C. Jenkins Department of Biophysics, Johns Hopkins University, 3400 N. Charles St.,5, Baltimore, MD, 21218, USA.
- Laboratory of Single-Molecule Biophysics, International Institute of Molecular and Cell Biology in Warsaw, Trojdena 4, Warsaw, 02-109, Poland.
| | - Sarah A Woodson
- Thomas C. Jenkins Department of Biophysics, Johns Hopkins University, 3400 N. Charles St.,5, Baltimore, MD, 21218, USA.
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6
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Bossaert M, Moreno A, Peixoto A, Pillaire MJ, Chanut P, Frit P, Calsou P, Loparo JJ, Britton S. Identification of the main barriers to Ku accumulation in chromatin. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.01.03.574002. [PMID: 38260538 PMCID: PMC10802386 DOI: 10.1101/2024.01.03.574002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2024]
Abstract
Repair of DNA double strand breaks by the non-homologous end-joining pathway is initiated by the binding of Ku to DNA ends. Given its high affinity for ends, multiple Ku proteins load onto linear DNAs in vitro. However, in cells, Ku loading is limited to ~1-2 molecules per DNA end. The mechanisms enforcing this limit are currently unknown. Here we show that the catalytic subunit of the DNA-dependent protein kinase (DNA-PKcs), but not its protein kinase activity, is required to prevent excessive Ku entry into chromatin. Ku accumulation is further restricted by two mechanisms: a neddylation/FBXL12-dependent process which actively removes loaded Ku molecules throughout the cell cycle and a CtIP/ATM-dependent mechanism which operates in S-phase. Finally, we demonstrate that the misregulation of Ku loading leads to impaired transcription in the vicinity of DNA ends. Together our data shed light on the multiple layers of coordinated mechanisms operating to prevent Ku from invading chromatin and interfering with other DNA transactions.
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Affiliation(s)
- Madeleine Bossaert
- Institut de Pharmacologie et Biologie Structurale (IPBS), Université de Toulouse, CNRS, Université Toulouse III - Paul Sabatier (UT3), Toulouse, France
- Equipe labélisée la Ligue contre le Cancer 2018
| | - Andrew Moreno
- Department of Biological Chemistry and Molecular Pharmacology, Blavatnik Institute, Harvard Medical School, Boston, Massachusetts 02115
| | - Antonio Peixoto
- Institut de Pharmacologie et Biologie Structurale (IPBS), Université de Toulouse, CNRS, Université Toulouse III - Paul Sabatier (UT3), Toulouse, France
- Equipe labélisée la Ligue contre le Cancer 2018
| | - Marie-Jeanne Pillaire
- Institut de Pharmacologie et Biologie Structurale (IPBS), Université de Toulouse, CNRS, Université Toulouse III - Paul Sabatier (UT3), Toulouse, France
- Equipe labélisée la Ligue contre le Cancer 2018
| | - Pauline Chanut
- Institut de Pharmacologie et Biologie Structurale (IPBS), Université de Toulouse, CNRS, Université Toulouse III - Paul Sabatier (UT3), Toulouse, France
- Equipe labélisée la Ligue contre le Cancer 2018
| | - Philippe Frit
- Institut de Pharmacologie et Biologie Structurale (IPBS), Université de Toulouse, CNRS, Université Toulouse III - Paul Sabatier (UT3), Toulouse, France
- Equipe labélisée la Ligue contre le Cancer 2018
| | - Patrick Calsou
- Institut de Pharmacologie et Biologie Structurale (IPBS), Université de Toulouse, CNRS, Université Toulouse III - Paul Sabatier (UT3), Toulouse, France
- Equipe labélisée la Ligue contre le Cancer 2018
| | - Joseph John Loparo
- Department of Biological Chemistry and Molecular Pharmacology, Blavatnik Institute, Harvard Medical School, Boston, Massachusetts 02115
| | - Sébastien Britton
- Institut de Pharmacologie et Biologie Structurale (IPBS), Université de Toulouse, CNRS, Université Toulouse III - Paul Sabatier (UT3), Toulouse, France
- Equipe labélisée la Ligue contre le Cancer 2018
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7
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Asada R, Dominguez A, Montpetit B. Single-molecule quantitation of RNA-binding protein occupancy and stoichiometry defines a role for Yra1 (Aly/REF) in nuclear mRNP organization. Cell Rep 2023; 42:113415. [PMID: 37963019 PMCID: PMC10841842 DOI: 10.1016/j.celrep.2023.113415] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2023] [Revised: 10/09/2023] [Accepted: 10/25/2023] [Indexed: 11/16/2023] Open
Abstract
RNA-binding proteins (RBPs) interact with mRNA to form supramolecular complexes called messenger ribonucleoprotein (mRNP) particles. These dynamic assemblies direct and regulate individual steps of gene expression; however, their composition and functional importance remain largely unknown. Here, we develop a total internal reflection fluorescence-based single-molecule imaging assay to investigate stoichiometry and co-occupancy of 15 RBPs within mRNPs from Saccharomyces cerevisiae. We show compositional heterogeneity of single mRNPs and plasticity across different growth conditions, with major co-occupants of mRNPs containing the nuclear cap-binding complex identified as Yra1 (1-10 copies), Nab2 (1-6 copies), and Npl3 (1-6 copies). Multicopy Yra1-bound mRNPs are specifically co-occupied by the THO complex and assembled on mRNAs biased by transcript length and RNA secondary structure. Yra1 depletion results in decreased compaction of nuclear mRNPs demonstrating a packaging function. Together, we provide a quantitative framework for gene- and condition-dependent RBP occupancy and stoichiometry in individual nuclear mRNPs.
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Affiliation(s)
- Ryuta Asada
- Department of Viticulture and Enology, University of California, Davis, Davis, CA 95616, USA
| | - Andrew Dominguez
- Department of Viticulture and Enology, University of California, Davis, Davis, CA 95616, USA; Biochemistry, Molecular, Cellular, and Developmental Biology Graduate Group, University of California, Davis, Davis, CA 95616, USA
| | - Ben Montpetit
- Department of Viticulture and Enology, University of California, Davis, Davis, CA 95616, USA; Biochemistry, Molecular, Cellular, and Developmental Biology Graduate Group, University of California, Davis, Davis, CA 95616, USA.
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8
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Deutz LN, Sarıkaya S, Dickinson DJ. Membrane extraction in native lipid nanodiscs reveals dynamic regulation of Cdc42 complexes during cell polarization. Biophys J 2023:S0006-3495(23)00721-X. [PMID: 38006206 DOI: 10.1016/j.bpj.2023.11.021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2023] [Revised: 10/13/2023] [Accepted: 11/21/2023] [Indexed: 11/26/2023] Open
Abstract
Embryonic development requires the establishment of cell polarity to enable cell fate segregation and tissue morphogenesis. This process is regulated by Par complex proteins, which partition into polarized membrane domains and direct downstream polarized cell behaviors. The kinase aPKC (along with its cofactor Par6) is a key member of this network and can be recruited to the plasma membrane by either the small GTPase Cdc42 or the scaffolding protein Par3. Although in vitro interactions among these proteins are well established, much is still unknown about the complexes they form during development. Here, to enable the study of membrane-associated complexes ex vivo, we used a maleic acid copolymer to rapidly isolate membrane proteins from single C. elegans zygotes into lipid nanodiscs. We show that native lipid nanodisc formation enables detection of endogenous complexes involving Cdc42, which are undetectable when cells are lysed in detergent. We found that Cdc42 interacts more strongly with aPKC/Par6 during polarity maintenance than polarity establishment, two developmental stages that are separated by only a few minutes. We further show that Cdc42 and Par3 do not bind aPKC/Par6 simultaneously, confirming recent in vitro findings in an ex vivo context. Our findings establish a new tool for studying membrane-associated signaling complexes and reveal an unexpected mode of polarity regulation via Cdc42.
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Affiliation(s)
- Lars N Deutz
- Department of Molecular Biosciences, The University of Texas at Austin, Austin, Texas
| | - Sena Sarıkaya
- Department of Molecular Biosciences, The University of Texas at Austin, Austin, Texas
| | - Daniel J Dickinson
- Department of Molecular Biosciences, The University of Texas at Austin, Austin, Texas.
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9
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Ernst M, Orabi EA, Stockbridge RB, Faraldo-Gómez JD, Robertson JL. Dimerization mechanism of an inverted-topology ion channel in membranes. Proc Natl Acad Sci U S A 2023; 120:e2308454120. [PMID: 37956279 PMCID: PMC10666096 DOI: 10.1073/pnas.2308454120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2023] [Accepted: 09/28/2023] [Indexed: 11/15/2023] Open
Abstract
Many ion channels are multisubunit complexes where oligomerization is an obligatory requirement for function as the binding axis forms the charged permeation pathway. However, the mechanisms of in-membrane assembly of thermodynamically stable channels are largely unknown. Here, we demonstrate a key advance by reporting the dimerization equilibrium reaction of an inverted-topology, homodimeric fluoride channel Fluc in lipid bilayers. While the wild-type channel is a long-lived dimer, we leverage a known mutation, N43S, that weakens Na+ binding in a buried site at the interface, thereby unlocking the complex for reversible association in lipid bilayers. Single-channel recordings show that Na+ binding is required for fluoride conduction while single-molecule microscopy experiments demonstrate that N43S Fluc exists in a dynamic monomer-dimer equilibrium in the membrane, even following removal of Na+. Quantifying the thermodynamic stability while titrating Na+ indicates that dimerization occurs first, providing a membrane-embedded binding site where Na+ binding weakly stabilizes the complex. To understand how these subunits form stable assemblies while presenting charged surfaces to the membrane, we carried out molecular dynamics simulations, which show the formation of a thinned membrane defect around the exposed dimerization interface. In simulations where subunits are permitted to encounter each other while preventing protein contacts, we observe spontaneous and selective association at the native interface, where stability is achieved by mitigation of the membrane defect. These results suggest a model wherein membrane-associated forces drive channel assembly in the native orientation while subsequent factors, such as Na+ binding, result in channel activation.
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Affiliation(s)
- Melanie Ernst
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO63110
| | - Esam A. Orabi
- Theoretical Molecular Biophysics Section, National Heart, Lung, and Blood Institute, NIH, Bethesda, MD20894
| | - Randy B. Stockbridge
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI48109
| | - José D. Faraldo-Gómez
- Theoretical Molecular Biophysics Section, National Heart, Lung, and Blood Institute, NIH, Bethesda, MD20894
| | - Janice L. Robertson
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO63110
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10
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Chadda R, Lee T, Mahoney-Kruszka R, Kelley EG, Bernhardt N, Sandal P, Robertson JL. A thermodynamic analysis of CLC transporter dimerization in lipid bilayers. Proc Natl Acad Sci U S A 2023; 120:e2305100120. [PMID: 37788312 PMCID: PMC10576108 DOI: 10.1073/pnas.2305100120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2023] [Accepted: 08/17/2023] [Indexed: 10/05/2023] Open
Abstract
The CLC-ec1 chloride/proton antiporter is a membrane-embedded homodimer with subunits that can dissociate and associate, but the thermodynamic driving forces favor the assembled dimer at biological densities. Yet, the physical reasons for this stability are confounding as dimerization occurs via the burial of hydrophobic interfaces away from the lipid solvent. For binding of nonpolar surfaces in aqueous solution, the driving force is often attributed to the hydrophobic effect, but this should not apply in the membrane since there is very little water. To investigate this further, we quantified the thermodynamic changes associated with CLC dimerization in membranes by carrying out a van 't Hoff analysis of the temperature dependency of the free energy of dimerization, ΔG°. To ensure that the reaction reached equilibrium at different temperatures, we utilized a Förster resonance energy transfer assay to report on relaxation kinetics of subunit exchange as a function of temperature. Equilibration times were then applied to measure CLC-ec1 dimerization isotherms at different temperatures using the single-molecule subunit-capture photobleaching analysis approach. The results demonstrate that the dimerization free energy of CLC in Escherichia coli-like membranes exhibits a nonlinear temperature dependency corresponding to a large, negative change in heat capacity, a signature of solvent ordering effects such as the hydrophobic effect. Consolidating this with our previous molecular analyses suggests that the nonbilayer defect required to solvate the monomeric state is one source of the observed change in heat capacity and indicates the existence of a generalizable driving force for protein association in membranes.
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Affiliation(s)
- Rahul Chadda
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO63110
| | - Taeho Lee
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO63110
- Department of Physics, Washington University, St. Louis, MO63130
| | - Robyn Mahoney-Kruszka
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO63110
| | - Elizabeth G. Kelley
- Center for Neutron Research, National Institute for Standards and Technology, Gaithersburg, MD20899
| | - Nathan Bernhardt
- Theoretical Molecular Biophysics Laboratory, National Heart, Lung and Blood Institute, NIH, Bethesda, MD20894
| | - Priyanka Sandal
- Department of Molecular Physiology and Biophysics, The University of Iowa, Iowa City, IA52242
| | - Janice L. Robertson
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO63110
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11
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Tenenbaum D, Inlow K, Friedman LJ, Cai A, Gelles J, Kondev J. RNA polymerase sliding on DNA can couple the transcription of nearby bacterial operons. Proc Natl Acad Sci U S A 2023; 120:e2301402120. [PMID: 37459525 PMCID: PMC10372574 DOI: 10.1073/pnas.2301402120] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2023] [Accepted: 05/19/2023] [Indexed: 07/20/2023] Open
Abstract
DNA transcription initiates after an RNA polymerase (RNAP) molecule binds to the promoter of a gene. In bacteria, the canonical picture is that RNAP comes from the cytoplasmic pool of freely diffusing RNAP molecules. Recent experiments suggest the possible existence of a separate pool of polymerases, competent for initiation, which freely slide on the DNA after having terminated one round of transcription. Promoter-dependent transcription reinitiation from this pool of posttermination RNAP may lead to coupled initiation at nearby operons, but it is unclear whether this can occur over the distance and timescales needed for it to function widely on a bacterial genome in vivo. Here, we mathematically model the hypothesized reinitiation mechanism as a diffusion-to-capture process and compute the distances over which significant interoperon coupling can occur and the time required. These quantities depend on molecular association and dissociation rate constants between DNA, RNAP, and the transcription initiation factor σ70; we measure these rate constants using single-molecule experiments in vitro. Our combined theory/experimental results demonstrate that efficient coupling can occur at physiologically relevant σ70 concentrations and on timescales appropriate for transcript synthesis. Coupling is efficient over terminator-promoter distances up to ∼1,000 bp, which includes the majority of terminator-promoter nearest neighbor pairs in the Escherichia coli genome. The results suggest a generalized mechanism that couples the transcription of nearby operons and breaks the paradigm that each binding of RNAP to DNA can produce at most one messenger RNA.
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Affiliation(s)
- Debora Tenenbaum
- Department of Biochemistry, Brandeis University, Waltham, MA02453
- Department of Physics, Brandeis University, Waltham, MA02453
- Simons Center for Quantitative Biology, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY11724
| | - Koe Inlow
- Department of Biochemistry, Brandeis University, Waltham, MA02453
| | | | - Anthony Cai
- Department of Biochemistry, Brandeis University, Waltham, MA02453
| | - Jeff Gelles
- Department of Biochemistry, Brandeis University, Waltham, MA02453
| | - Jane Kondev
- Department of Physics, Brandeis University, Waltham, MA02453
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12
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Amasino AL, Gupta S, Friedman LJ, Gelles J, Bell SP. Regulation of replication origin licensing by ORC phosphorylation reveals a two-step mechanism for Mcm2-7 ring closing. Proc Natl Acad Sci U S A 2023; 120:e2221484120. [PMID: 37428921 PMCID: PMC10629557 DOI: 10.1073/pnas.2221484120] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2022] [Accepted: 06/03/2023] [Indexed: 07/12/2023] Open
Abstract
Eukaryotic DNA replication must occur exactly once per cell cycle to maintain cell ploidy. This outcome is ensured by temporally separating replicative helicase loading (G1 phase) and activation (S phase). In budding yeast, helicase loading is prevented outside of G1 by cyclin-dependent kinase (CDK) phosphorylation of three helicase-loading proteins: Cdc6, the Mcm2-7 helicase, and the origin recognition complex (ORC). CDK inhibition of Cdc6 and Mcm2-7 is well understood. Here we use single-molecule assays for multiple events during origin licensing to determine how CDK phosphorylation of ORC suppresses helicase loading. We find that phosphorylated ORC recruits a first Mcm2-7 to origins but prevents second Mcm2-7 recruitment. The phosphorylation of the Orc6, but not of the Orc2 subunit, increases the fraction of first Mcm2-7 recruitment events that are unsuccessful due to the rapid and simultaneous release of the helicase and its associated Cdt1 helicase-loading protein. Real-time monitoring of first Mcm2-7 ring closing reveals that either Orc2 or Orc6 phosphorylation prevents Mcm2-7 from stably encircling origin DNA. Consequently, we assessed formation of the MO complex, an intermediate that requires the closed-ring form of Mcm2-7. We found that ORC phosphorylation fully inhibits MO complex formation and we provide evidence that this event is required for stable closing of the first Mcm2-7. Our studies show that multiple steps of helicase loading are impacted by ORC phosphorylation and reveal that closing of the first Mcm2-7 ring is a two-step process started by Cdt1 release and completed by MO complex formation.
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Affiliation(s)
- Audra L. Amasino
- HHMI, Massachusetts Institute of Technology, Cambridge, MA02139
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA02139
| | - Shalini Gupta
- HHMI, Massachusetts Institute of Technology, Cambridge, MA02139
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA02139
| | | | - Jeff Gelles
- Department of Biochemistry, Brandeis University, Waltham, MA02454
| | - Stephen P. Bell
- HHMI, Massachusetts Institute of Technology, Cambridge, MA02139
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA02139
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13
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Inlow K, Tenenbaum D, Friedman LJ, Kondev J, Gelles J. Recycling of bacterial RNA polymerase by the Swi2/Snf2 ATPase RapA. Proc Natl Acad Sci U S A 2023; 120:e2303849120. [PMID: 37406096 PMCID: PMC10334767 DOI: 10.1073/pnas.2303849120] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2023] [Accepted: 05/30/2023] [Indexed: 07/07/2023] Open
Abstract
Free-living bacteria have regulatory systems that can quickly reprogram gene transcription in response to changes in the cellular environment. The RapA ATPase, a prokaryotic homolog of the eukaryotic Swi2/Snf2 chromatin remodeling complex, may facilitate such reprogramming, but the mechanisms by which it does so are unclear. We used multiwavelength single-molecule fluorescence microscopy in vitro to examine RapA function in the Escherichia coli transcription cycle. In our experiments, RapA at <5 nM concentration did not appear to alter transcription initiation, elongation, or intrinsic termination. Instead, we directly observed a single RapA molecule bind specifically to the kinetically stable post termination complex (PTC)-consisting of core RNA polymerase (RNAP)-bound sequence nonspecifically to double-stranded DNA-and efficiently remove RNAP from DNA within seconds in an ATP-hydrolysis-dependent reaction. Kinetic analysis elucidates the process through which RapA locates the PTC and the key mechanistic intermediates that bind and hydrolyze ATP. This study defines how RapA participates in the transcription cycle between termination and initiation and suggests that RapA helps set the balance between global RNAP recycling and local transcription reinitiation in proteobacterial genomes.
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Affiliation(s)
- Koe Inlow
- Department of Biochemistry, Brandeis University, Waltham, MA02453
| | | | | | - Jane Kondev
- Department of Physics, Brandeis University, Waltham, MA02453
| | - Jeff Gelles
- Department of Biochemistry, Brandeis University, Waltham, MA02453
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14
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Zhang A, Friedman LJ, Gelles J, Bell SP. Changing protein-DNA interactions promote ORC binding site exchange during replication origin licensing. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.06.16.545300. [PMID: 37398123 PMCID: PMC10312730 DOI: 10.1101/2023.06.16.545300] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/04/2023]
Abstract
During origin licensing, the eukaryotic replicative helicase Mcm2-7 forms head-to-head double hexamers to prime origins for bidirectional replication. Recent single-molecule and structural studies revealed that one molecule of the helicase loader ORC can sequentially load two Mcm2-7 hexamers to ensure proper head-to-head helicase alignment. To perform this task, ORC must release from its initial high-affinity DNA binding site and "flip" to bind a weaker, inverted DNA site. However, the mechanism of this binding-site switch remains unclear. In this study, we used single-molecule Förster resonance energy transfer (sm-FRET) to study the changing interactions between DNA and ORC or Mcm2-7. We found that the loss of DNA bending that occurs during DNA deposition into the Mcm2-7 central channel increases the rate of ORC dissociation from DNA. Further studies revealed temporally-controlled DNA sliding of helicase-loading intermediates, and that the first sliding complex includes ORC, Mcm2-7, and Cdt1. We demonstrate that sequential events of DNA unbending, Cdc6 release, and sliding lead to a stepwise decrease in ORC stability on DNA, facilitating ORC dissociation from its strong binding site during site switching. In addition, the controlled sliding we observed provides insight into how ORC accesses secondary DNA binding sites at different locations relative to the initial binding site. Our study highlights the importance of dynamic protein-DNA interactions in the loading of two oppositely-oriented Mcm2-7 helicases to ensure bidirectional DNA replication. Significance Statement Bidirectional DNA replication, in which two replication forks travel in opposite directions from each origin of replication, is required for complete genome duplication. To prepare for this event, two copies of the Mcm2-7 replicative helicase are loaded at each origin in opposite orientations. Using single-molecule assays, we studied the sequence of changing protein-DNA interactions involved in this process. These stepwise changes gradually reduce the DNA-binding strength of ORC, the primary DNA binding protein involved in this event. This reduced affinity promotes ORC dissociation and rebinding in the opposite orientation on the DNA, facilitating the sequential assembly of two Mcm2-7 molecules in opposite orientations. Our findings identify a coordinated series of events that drive proper DNA replication initiation.
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Affiliation(s)
- Annie Zhang
- Howard Hughes Medical Institute, Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Larry J. Friedman
- Department of Biochemistry, Brandeis University, Waltham, MA 02454, USA
| | - Jeff Gelles
- Department of Biochemistry, Brandeis University, Waltham, MA 02454, USA
| | - Stephen P Bell
- Howard Hughes Medical Institute, Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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15
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Rodgers ML, Sun Y, Woodson SA. Ribosomal Protein S12 Hastens Nucleation of Co-Transcriptional Ribosome Assembly. Biomolecules 2023; 13:951. [PMID: 37371531 DOI: 10.3390/biom13060951] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2023] [Revised: 06/01/2023] [Accepted: 06/04/2023] [Indexed: 06/29/2023] Open
Abstract
Ribosomal subunits begin assembly during transcription of the ribosomal RNA (rRNA), when the rRNA begins to fold and associate with ribosomal proteins (RPs). In bacteria, the first steps of ribosome assembly depend upon recognition of the properly folded rRNA by primary assembly proteins such as S4, which nucleates assembly of the 16S 5' domain. Recent evidence, however, suggests that initial recognition by S4 is delayed due to variable folding of the rRNA during transcription. Here, using single-molecule colocalization co-transcriptional assembly (smCoCoA), we show that the late-binding RP S12 specifically promotes the association of S4 with the pre-16S rRNA during transcription, thereby accelerating nucleation of 30S ribosome assembly. Order of addition experiments suggest that S12 helps chaperone the rRNA during transcription, particularly near the S4 binding site. S12 interacts transiently with the rRNA during transcription and, consequently, a high concentration is required for its chaperone activity. These results support a model in which late-binding RPs moonlight as RNA chaperones during transcription in order to facilitate rapid assembly.
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Affiliation(s)
- Margaret L Rodgers
- Thomas C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, USA
- The Laboratory of Biochemistry and Genetics, The National Institute of Diabetes and Digestive and Kidney Diseases, The National Institutes of Health, Bethesda, MD 20892, USA
| | - Yunsheng Sun
- Thomas C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, USA
| | - Sarah A Woodson
- Thomas C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, USA
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16
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Rodgers ML, O'Brien B, Woodson SA. Small RNAs and Hfq capture unfolded RNA target sites during transcription. Mol Cell 2023; 83:1489-1501.e5. [PMID: 37116495 PMCID: PMC10176597 DOI: 10.1016/j.molcel.2023.04.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2022] [Revised: 02/11/2023] [Accepted: 03/31/2023] [Indexed: 04/30/2023]
Abstract
Small ribonucleoproteins (sRNPs) target nascent precursor RNAs to guide folding, modification, and splicing during transcription. Yet, rapid co-transcriptional folding of the RNA can mask sRNP sites, impeding target recognition and regulation. To examine how sRNPs target nascent RNAs, we monitored binding of bacterial Hfq⋅DsrA sRNPs to rpoS transcripts using single-molecule co-localization co-transcriptional assembly (smCoCoA). We show that Hfq⋅DsrA recursively samples the mRNA before transcription of the target site to poise it for base pairing with DsrA. We adapted smCoCoA to precisely measure when the target site is synthesized and revealed that Hfq⋅DsrA often binds the mRNA during target site synthesis close to RNA polymerase (RNAP). We suggest that targeting transcripts near RNAP allows an sRNP to capture a site before the transcript folds, providing a kinetic advantage over post-transcriptional targeting. We propose that other sRNPs may also use RNAP-proximal targeting to hasten recognition and regulation.
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Affiliation(s)
- Margaret L Rodgers
- T.C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, USA.
| | - Brett O'Brien
- Chemical Biology Interface Program, Johns Hopkins University, Baltimore, MD 21218, USA
| | - Sarah A Woodson
- T.C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, USA.
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17
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Harden TT, Vincent BJ, DePace AH. Transcriptional activators in the early Drosophila embryo perform different kinetic roles. Cell Syst 2023; 14:258-272.e4. [PMID: 37080162 PMCID: PMC10473017 DOI: 10.1016/j.cels.2023.03.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2021] [Revised: 06/26/2022] [Accepted: 03/21/2023] [Indexed: 04/22/2023]
Abstract
Combinatorial regulation of gene expression by transcription factors (TFs) may in part arise from kinetic synergy-wherein TFs regulate different steps in the transcription cycle. Kinetic synergy requires that TFs play distinguishable kinetic roles. Here, we used live imaging to determine the kinetic roles of three TFs that activate transcription in the Drosophila embryo-Zelda, Bicoid, and Stat92E-by introducing their binding sites into the even-skipped stripe 2 enhancer. These TFs influence different sets of kinetic parameters, and their influence can change over time. All three TFs increased the fraction of transcriptionally active nuclei; Zelda also shortened the first-passage time into transcription and regulated the interval between transcription events. Stat92E also increased the lifetimes of active transcription. Different TFs can therefore play distinct kinetic roles in activating the transcription. This has consequences for understanding the composition and flexibility of regulatory DNA sequences and the biochemical function of TFs. A record of this paper's transparent peer review process is included in the supplemental information.
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Affiliation(s)
- Timothy T Harden
- Department of Systems Biology, Harvard Medical School, Boston, MA 02115, USA
| | - Ben J Vincent
- Department of Systems Biology, Harvard Medical School, Boston, MA 02115, USA
| | - Angela H DePace
- Department of Systems Biology, Harvard Medical School, Boston, MA 02115, USA.
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18
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Inlow K, Tenenbaum D, Friedman LJ, Kondev J, Gelles J. Recycling of Bacterial RNA Polymerase by the Swi2/Snf2 ATPase RapA. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.03.22.533849. [PMID: 36993374 PMCID: PMC10055430 DOI: 10.1101/2023.03.22.533849] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/30/2023]
Abstract
Free-living bacteria have regulatory systems that can quickly reprogram gene transcription in response to changes in cellular environment. The RapA ATPase, a prokaryotic homolog of the eukaryote Swi2/Snf2 chromatin remodeling complex, may facilitate such reprogramming, but the mechanisms by which it does so is unclear. We used multi-wavelength single-molecule fluorescence microscopy in vitro to examine RapA function in the E. coli transcription cycle. In our experiments, RapA at < 5 nM concentration did not appear to alter transcription initiation, elongation, or intrinsic termination. Instead, we directly observed a single RapA molecule bind specifically to the kinetically stable post-termination complex (PTC) -- consisting of core RNA polymerase (RNAP) bound to dsDNA -- and efficiently remove RNAP from DNA within seconds in an ATP-hydrolysis-dependent reaction. Kinetic analysis elucidates the process through which RapA locates the PTC and the key mechanistic intermediates that bind and hydrolyze ATP. This study defines how RapA participates in the transcription cycle between termination and initiation and suggests that RapA helps set the balance between global RNAP recycling and local transcription re-initiation in proteobacterial genomes. SIGNIFICANCE RNA synthesis is an essential conduit of genetic information in all organisms. After transcribing an RNA, the bacterial RNA polymerase (RNAP) must be reused to make subsequent RNAs, but the steps that enable RNAP reuse are unclear. We directly observed the dynamics of individual molecules of fluorescently labeled RNAP and the enzyme RapA as they colocalized with DNA during and after RNA synthesis. Our studies show that RapA uses ATP hydrolysis to remove RNAP from DNA after the RNA is released from RNAP and reveal essential features of the mechanism by which this removal occurs. These studies fill in key missing pieces in our current understanding of the events that occur after RNA is released and that enable RNAP reuse.
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Affiliation(s)
- Koe Inlow
- Department of Biochemistry, Brandeis University, Waltham, MA 02453, USA
| | - Debora Tenenbaum
- Department of Physics, Brandeis University, Waltham, MA 02453, USA
| | - Larry J. Friedman
- Department of Biochemistry, Brandeis University, Waltham, MA 02453, USA
| | - Jane Kondev
- Department of Physics, Brandeis University, Waltham, MA 02453, USA
| | - Jeff Gelles
- Department of Biochemistry, Brandeis University, Waltham, MA 02453, USA
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Chadda R, Lee T, Sandal P, Mahoney-Kruszka R, Robertson JL. A thermodynamic analysis of CLC transporter dimerization in lipid bilayers. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.03.14.532678. [PMID: 36993257 PMCID: PMC10055089 DOI: 10.1101/2023.03.14.532678] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/19/2023]
Abstract
The CLC-ec1 chloride/proton antiporter is a membrane embedded homodimer where subunits can dissociate and associate, but the thermodynamic driving forces favor the assembled form at biological densities. Yet, the physical reasons for this stability are confounding since binding occurs via the burial of hydrophobic protein interfaces yet the hydrophobic effect should not apply since there is little water within the membrane. To investigate this further, we quantified the thermodynamic changes associated with CLC dimerization in membranes by carrying out a van 't Hoff analysis of the temperature dependency of the free energy of dimerization, ΔG° . To ensure that the reaction reached equilibrium under changing conditions, we utilized a Förster Resonance Energy Transfer based assay to report on the relaxation kinetics of subunit exchange as a function of temperature. These equilibration times were then applied to measure CLC-ec1 dimerization isotherms as a function of temperature using the single-molecule subunit-capture photobleaching analysis approach. The results demonstrate that the dimerization free energy of CLC in E. coli membranes exhibits a non-linear temperature dependency corresponding to a large, negative change in heat capacity, a signature of solvent ordering effects including the hydrophobic effect. Consolidating this with our previous molecular analyses suggests that the non-bilayer defect required to solvate the monomeric state is the molecular source of this large change in heat capacity and is a major and generalizable driving force for protein association in membranes.
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20
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Tenenbaum D, Inlow K, Friedman L, Cai A, Gelles J, Kondev J. RNA polymerase sliding on DNA can couple the transcription of nearby bacterial operons. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.02.10.528045. [PMID: 36798213 PMCID: PMC9934669 DOI: 10.1101/2023.02.10.528045] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 02/13/2023]
Abstract
DNA transcription initiates after an RNA polymerase (RNAP) molecule binds to the promoter of a gene. In bacteria, the canonical picture is that RNAP comes from the cytoplasmic pool of freely diffusing RNAP molecules. Recent experiments suggest the possible existence of a separate pool of polymerases, competent for initiation, which freely slide on the DNA after having terminated one round of transcription. Promoter-dependent transcription reinitiation from this pool of post-termination RNAP may lead to coupled initiation at nearby operons, but it is unclear whether this can occur over the distance- and time-scales needed for it to function widely on a bacterial genome in vivo. Here, we mathematically model the hypothesized reinitiation mechanism as a diffusion-to-capture process and compute the distances over which significant inter-operon coupling can occur and the time required. These quantities depend on previously uncharacterized molecular association and dissociation rate constants between DNA, RNAP and the transcription initiation factor σ 70 ; we measure these rate constants using single-molecule experiments in vitro. Our combined theory/experimental results demonstrate that efficient coupling can occur at physiologically relevant σ 70 concentrations and on timescales appropriate for transcript synthesis. Coupling is efficient over terminator-promoter distances up to ∼ 1, 000 bp, which includes the majority of terminator-promoter nearest neighbor pairs in the E. coli genome. The results suggest a generalized mechanism that couples the transcription of nearby operons and breaks the paradigm that each binding of RNAP to DNA can produce at most one messenger RNA. SIGNIFICANCE STATEMENT After transcribing an operon, a bacterial RNA polymerase can stay bound to DNA, slide along it, and reini-tiate transcription of the same or a different operon. Quantitative single-molecule biophysics experiments combined with mathematical theory demonstrate that this reinitiation process can be quick and efficient over gene spacings typical of a bacterial genome. Reinitiation may provide a mechanism to orchestrate the transcriptional activities of groups of nearby operons.
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Affiliation(s)
- Debora Tenenbaum
- Department of Biochemistry, Brandeis University, Waltham, MA, United States
- Department of Physics, Brandeis University, Waltham, MA, United States
- Simons Center for Quantitative Biology, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY, USA
| | - Koe Inlow
- Department of Biochemistry, Brandeis University, Waltham, MA, United States
| | - Larry Friedman
- Department of Biochemistry, Brandeis University, Waltham, MA, United States
| | - Anthony Cai
- Department of Biochemistry, Brandeis University, Waltham, MA, United States
| | - Jeff Gelles
- Department of Biochemistry, Brandeis University, Waltham, MA, United States
| | - Jane Kondev
- Department of Physics, Brandeis University, Waltham, MA, United States
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21
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Ernst M, Orabi EA, Stockbridge RB, Faraldo-Gómez JD, Robertson JL. Dimerization mechanism of an inverted-topology ion channel in membranes. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.01.27.525942. [PMID: 36789410 PMCID: PMC9928038 DOI: 10.1101/2023.01.27.525942] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Many ion channels are multi-subunit complexes with a polar permeation pathway at the oligomeric interface, but their mechanisms of assembly into functional, thermodynamically stable units within the membrane are largely unknown. Here we characterize the assembly of the inverted-topology, homodimeric fluoride channel Fluc, leveraging a known mutation, N43S, that weakens Na + binding to the dimer interface, thereby unlocking the complex. While single-channel recordings show Na + is required for activation, single-molecule photobleaching and bulk Förster Resonance Energy Transfer experiments in lipid bilayers demonstrate that N43S Fluc monomers and dimers exist in dynamic equilibrium, even without Na + . Molecular dynamics simulations indicate this equilibrium is dominated by a differential in the lipid-solvation energetics of monomer and dimer, which stems from hydrophobic exposure of the polar ion pathway in the monomer. These results suggest a model wherein membrane-associated forces induce channel assembly while subsequent factors, in this case Na + binding, result in channel activation. Teaser Membrane morphology energetics foster inverted-topology Fluc channels to form dimers, which then become active upon Na + binding.
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22
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Amasino A, Gupta S, Friedman LJ, Gelles J, Bell SP. Regulation of replication origin licensing by ORC phosphorylation reveals a two-step mechanism for Mcm2-7 ring closing. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.01.02.522488. [PMID: 36711604 PMCID: PMC9881882 DOI: 10.1101/2023.01.02.522488] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Eukaryotic DNA replication must occur exactly once per cell cycle to maintain cell ploidy. This outcome is ensured by temporally separating replicative helicase loading (G1 phase) and activation (S phase). In budding yeast, helicase loading is prevented outside of G1 by cyclin-dependent kinase (CDK) phosphorylation of three helicase-loading proteins: Cdc6, the Mcm2-7 helicase, and the origin recognition complex (ORC). CDK inhibition of Cdc6 and Mcm2-7 are well understood. Here we use single-molecule assays for multiple events during origin licensing to determine how CDK phosphorylation of ORC suppresses helicase loading. We find that phosphorylated ORC recruits a first Mcm2-7 to origins but prevents second Mcm2-7 recruitment. Phosphorylation of the Orc6, but not of the Orc2 subunit, increases the fraction of first Mcm2-7 recruitment events that are unsuccessful due to the rapid and simultaneous release of the helicase and its associated Cdt1 helicase-loading protein. Real-time monitoring of first Mcm2-7 ring closing reveals that either Orc2 or Orc6 phosphorylation prevents Mcm2-7 from stably encircling origin DNA. Consequently, we assessed formation of the MO complex, an intermediate that requires the closed-ring form of Mcm2-7. We found that ORC phosphorylation fully inhibits MO-complex formation and provide evidence that this event is required for stable closing of the first Mcm2-7. Our studies show that multiple steps of helicase loading are impacted by ORC phosphorylation and reveal that closing of the first Mcm2-7 ring is a two-step process started by Cdt1 release and completed by MO-complex formation. Significance Statement Each time a eukaryotic cell divides (by mitosis) it must duplicate its chromosomal DNA exactly once to ensure that one full copy is passed to each resulting cell. Both under-replication or over-replication result in genome instability and disease or cell death. A key mechanism to prevent over-replication is the temporal separation of loading of the replicative DNA helicase at origins of replication and activation of these same helicases during the cell division cycle. Here we define the mechanism by which phosphorylation of the primary DNA binding protein involved in these events inhibits helicase loading. Our studies identify multiple steps of inhibition and provide new insights into the mechanism of helicase loading in the uninhibited condition.
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Affiliation(s)
- Audra Amasino
- Howard Hughes Medical Institute, Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Shalini Gupta
- Howard Hughes Medical Institute, Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Larry J. Friedman
- Department of Biochemistry, Brandeis University, Waltham, MA 02454, USA
| | - Jeff Gelles
- Department of Biochemistry, Brandeis University, Waltham, MA 02454, USA,Co-corresponding authors: Stephen P. Bell, , Phone: 617-253-2054, Jeff Gelles, , Phone: 781-736-2377
| | - Stephen P Bell
- Howard Hughes Medical Institute, Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA,Co-corresponding authors: Stephen P. Bell, , Phone: 617-253-2054, Jeff Gelles, , Phone: 781-736-2377
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23
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Fu X, Kaur H, Rodgers ML, Montemayor EJ, Butcher SE, Hoskins AA. Identification of transient intermediates during spliceosome activation by single molecule fluorescence microscopy. Proc Natl Acad Sci U S A 2022; 119:e2206815119. [PMID: 36417433 PMCID: PMC9860250 DOI: 10.1073/pnas.2206815119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2022] [Accepted: 10/05/2022] [Indexed: 11/24/2022] Open
Abstract
Spliceosome activation is the process of creating the catalytic site for RNA splicing and occurs de novo on each intron following spliceosome assembly. Dozens of factors bind to or are released from the activating spliceosome including the Lsm2-8 heteroheptameric ring that binds the U6 small nuclear RNA 3'-end. Lsm2-8 must be released to permit active site stabilization by the Prp19-containing complex (NineTeen Complex, NTC); however, little is known about the temporal order of events and dynamic interactions that lead up to and follow Lsm2-8 release. We have used colocalization single molecule spectroscopy (CoSMoS) to visualize Lsm2-8 dynamics during activation of Saccharomyces cerevisiae spliceosomes in vitro. Lsm2-8 is recruited as a component of the tri-snRNP and is released after integration of the Prp19-containing complex (NTC). Despite Lsm2-8 and the NTC being mutually exclusive in existing cryo-EM structures of yeast B complex spliceosomes, we identify a transient intermediate containing both ([Formula: see text]) and provide a kinetic framework for its formation and transformation during activation. Prior to [Formula: see text] assembly, the NTC rapidly and reversibly samples the spliceosome suggesting a mechanism for preventing NTC sequestration by defective spliceosomes that fail to properly activate. In complementary ensemble assays, we show that a base-pairing-dependent ternary complex can form between Lsm2-8 and U2 and U6 helix II RNAs. We propose that this interaction may play a role in formation of transient spliceosome intermediates formed during activation.
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Affiliation(s)
- Xingyang Fu
- Department of Chemistry, University of Wisconsin-Madison, Madison, WI53706
| | - Harpreet Kaur
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI53706
| | - Margaret L. Rodgers
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI53706
| | - Eric J. Montemayor
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI53706
| | - Samuel E. Butcher
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI53706
| | - Aaron A. Hoskins
- Department of Chemistry, University of Wisconsin-Madison, Madison, WI53706
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI53706
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24
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Fan J, Moreno AT, Baier AS, Loparo JJ, Peterson CL. H2A.Z deposition by SWR1C involves multiple ATP-dependent steps. Nat Commun 2022; 13:7052. [PMID: 36396651 PMCID: PMC9672302 DOI: 10.1038/s41467-022-34861-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2022] [Accepted: 11/09/2022] [Indexed: 11/18/2022] Open
Abstract
Histone variant H2A.Z is a conserved feature of nucleosomes flanking protein-coding genes. Deposition of H2A.Z requires ATP-dependent replacement of nucleosomal H2A by a chromatin remodeler related to the multi-subunit enzyme, yeast SWR1C. How these enzymes use ATP to promote this nucleosome editing reaction remains unclear. Here we use single-molecule and ensemble methodologies to identify three ATP-dependent phases in the H2A.Z deposition reaction. Real-time analysis of single nucleosome remodeling events reveals an initial priming step that occurs after ATP addition that involves a combination of both transient DNA unwrapping from the nucleosome and histone octamer deformations. Priming is followed by rapid loss of histone H2A, which is subsequently released from the H2A.Z nucleosomal product. Surprisingly, rates of both priming and the release of the H2A/H2B dimer are sensitive to ATP concentration. This complex reaction pathway provides multiple opportunities to regulate timely and accurate deposition of H2A.Z at key genomic locations.
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Affiliation(s)
- Jiayi Fan
- grid.168645.80000 0001 0742 0364Program in Molecular Medicine, University of Massachusetts Chan Medical School, Worcester, MA 01605 USA ,grid.168645.80000 0001 0742 0364Interdisciplinary Graduate Program, University of Massachusetts Chan Medical School, Worcester, MA 01605 USA
| | - Andrew T. Moreno
- grid.38142.3c000000041936754XDepartment of Biological Chemistry and Molecular Pharmacology, Blavatnik Institute, Harvard Medical School, Boston, MA 02115 USA
| | - Alexander S. Baier
- grid.168645.80000 0001 0742 0364Program in Molecular Medicine, University of Massachusetts Chan Medical School, Worcester, MA 01605 USA ,grid.168645.80000 0001 0742 0364Medical Scientist Training Program, University of Massachusetts Chan Medical School, Worcester, MA 01605 USA
| | - Joseph J. Loparo
- grid.38142.3c000000041936754XDepartment of Biological Chemistry and Molecular Pharmacology, Blavatnik Institute, Harvard Medical School, Boston, MA 02115 USA
| | - Craig L. Peterson
- grid.168645.80000 0001 0742 0364Program in Molecular Medicine, University of Massachusetts Chan Medical School, Worcester, MA 01605 USA
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25
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Chang Y, Dickinson DJ. Non-invasive chimeric HaloTag labeling to study clustering and diffusion of membrane proteins. STAR Protoc 2022; 3:101857. [PMID: 36595905 PMCID: PMC9676207 DOI: 10.1016/j.xpro.2022.101857] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2022] [Revised: 10/03/2022] [Accepted: 10/25/2022] [Indexed: 11/18/2022] Open
Abstract
As live imaging plays an increasingly critical role in cell biology research, the desire to label and track individual protein molecules in vivo has been growing. To address this, in this protocol we describe steps for sparse labeling using two different HaloTag ligand dyes in C. elegans. This labeling approach is simple, is non-invasive, and preserves the view of the bulk protein population. We further describe how to carry out single-particle tracking experiments and extract information about particle diffusion behavior. For complete details on the use and execution of this protocol, please refer to Chang and Dickinson (2022).1.
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Affiliation(s)
- Yiran Chang
- Department of Molecular Biosciences, University of Texas at Austin, Austin, TX 78712, USA
| | - Daniel J. Dickinson
- Department of Molecular Biosciences, University of Texas at Austin, Austin, TX 78712, USA,Corresponding author
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26
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Ray KK, Verma AR, Gonzalez RL, Kinz-Thompson CD. Inferring the shape of data: a probabilistic framework for analysing experiments in the natural sciences. Proc Math Phys Eng Sci 2022; 478:20220177. [PMID: 37767180 PMCID: PMC10521765 DOI: 10.1098/rspa.2022.0177] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2022] [Accepted: 09/26/2022] [Indexed: 09/29/2023] Open
Abstract
A critical step in data analysis for many different types of experiments is the identification of features with theoretically defined shapes in N -dimensional datasets; examples of this process include finding peaks in multi-dimensional molecular spectra or emitters in fluorescence microscopy images. Identifying such features involves determining if the overall shape of the data is consistent with an expected shape; however, it is generally unclear how to quantitatively make this determination. In practice, many analysis methods employ subjective, heuristic approaches, which complicates the validation of any ensuing results-especially as the amount and dimensionality of the data increase. Here, we present a probabilistic solution to this problem by using Bayes' rule to calculate the probability that the data have any one of several potential shapes. This probabilistic approach may be used to objectively compare how well different theories describe a dataset, identify changes between datasets and detect features within data using a corollary method called Bayesian Inference-based Template Search; several proof-of-principle examples are provided. Altogether, this mathematical framework serves as an automated 'engine' capable of computationally executing analysis decisions currently made by visual inspection across the sciences.
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Affiliation(s)
- Korak Kumar Ray
- Department of Chemistry, Columbia University, New York, NY 10027, USA
| | - Anjali R. Verma
- Department of Chemistry, Columbia University, New York, NY 10027, USA
| | - Ruben L. Gonzalez
- Department of Chemistry, Columbia University, New York, NY 10027, USA
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27
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Hansen SR, White DS, Scalf M, Corrêa IR, Smith LM, Hoskins AA. Multi-step recognition of potential 5' splice sites by the Saccharomyces cerevisiae U1 snRNP. eLife 2022; 11:70534. [PMID: 35959885 PMCID: PMC9436412 DOI: 10.7554/elife.70534] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2021] [Accepted: 08/11/2022] [Indexed: 11/13/2022] Open
Abstract
In eukaryotes, splice sites define the introns of pre-mRNAs and must be recognized and excised with nucleotide precision by the spliceosome to make the correct mRNA product. In one of the earliest steps of spliceosome assembly, the U1 small nuclear ribonucleoprotein (snRNP) recognizes the 5' splice site (5' SS) through a combination of base pairing, protein-RNA contacts, and interactions with other splicing factors. Previous studies investigating the mechanisms of 5' SS recognition have largely been done in vivo or in cellular extracts where the U1/5' SS interaction is difficult to deconvolute from the effects of trans-acting factors or RNA structure. In this work we used colocalization single-molecule spectroscopy (CoSMoS) to elucidate the pathway of 5' SS selection by purified yeast U1 snRNP. We determined that U1 reversibly selects 5' SS in a sequence-dependent, two-step mechanism. A kinetic selection scheme enforces pairing at particular positions rather than overall duplex stability to achieve long-lived U1 binding. Our results provide a kinetic basis for how U1 may rapidly surveil nascent transcripts for 5' SS and preferentially accumulate at these sequences rather than on close cognates.
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Affiliation(s)
- Sarah R Hansen
- Department of Biochemistry, University of Wisconsin-Madison, Madison, United States
| | - David S White
- Department of Biochemistry, University of Wisconsin-Madison, Madison, United States
| | - Mark Scalf
- Department of Chemistry, University of Wisconsin-Madison, Madison, United States
| | | | - Lloyd M Smith
- Department of Chemistry, University of Wisconsin-Madison, Madison, United States
| | - Aaron A Hoskins
- Department of Biochemistry, University of Wisconsin-Madison, Madison, United States
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28
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Baek I, Le SN, Jeon J, Chun Y, Reed C, Buratowski S. A set of Saccharomyces cerevisiae integration vectors for fluorescent dye labeling of proteins. G3 (BETHESDA, MD.) 2022; 12:6659097. [PMID: 35944214 PMCID: PMC9526040 DOI: 10.1093/g3journal/jkac201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/20/2022] [Accepted: 08/01/2022] [Indexed: 01/05/2023]
Abstract
Protein fusions are frequently used for fluorescence imaging of individual molecules, both in vivo and in vitro. The SNAP, CLIP, HALO (aka HaloTag7), and DHFR protein tags can be linked to small molecule dyes that provide brightness and photo-stability superior to fluorescent proteins. To facilitate fluorescent dye tagging of proteins in the yeast Saccharomyces cerevisiae, we constructed a modular set of vectors with various combinations of labeling protein tags and selectable markers. These vectors can be used in combination to create strains where multiple proteins labeled with different colored dyes can be simultaneously observed.
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Affiliation(s)
- Inwha Baek
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
| | - Sarah N Le
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
| | - Jongcheol Jeon
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
| | - Yujin Chun
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
| | - Charlotte Reed
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
| | - Stephen Buratowski
- Corresponding author: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA.
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29
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Abstract
Total internal reflection fluorescence (TIRF) microscopy (TIRFM) is an elegant optical technique that provides for the excitation of fluorophores in an extremely thin axial region ("optical section"). The method is based on the principle that when excitation light is completely internally reflected in a transparent solid (e.g., coverglass) at its interface with liquid, an electromagnetic field, called the evanescent wave, is generated in the liquid at the solid-liquid interface and is the same frequency as the excitation light. Since the intensity of the evanescent wave exponentially decays with distance from the surface of the solid, only fluorescent molecules within a few hundred nanometers of the solid are efficiently excited. This overview will review the history, optical theory, and hardware configurations used in TIRFM. In addition, it will provide experimental details and methodological considerations for studying receptors at the plasma membrane in neurons. © 2022 Wiley Periodicals LLC.
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Affiliation(s)
- Kenneth N Fish
- Department of Psychiatry, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
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30
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Chung J, Goode BL, Gelles J. Single-molecule analysis of actin filament debranching by cofilin and GMF. Proc Natl Acad Sci U S A 2022; 119:e2115129119. [PMID: 35858314 PMCID: PMC9304009 DOI: 10.1073/pnas.2115129119] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2021] [Accepted: 05/31/2022] [Indexed: 01/13/2023] Open
Abstract
Eukaryotic cells contain branched actin networks that are essential for endocytosis, motility, and other key cellular processes. These networks, which are formed by filamentous actin and the Arp2/3 complex, must subsequently be debranched to allow network remodeling and to recycle the Arp2/3 complex. Debranching appears to be catalyzed by two different members of the actin depolymerizing factor homology protein family: cofilin and glial maturation factor (GMF). However, their mechanisms of debranching are only partially understood. Here, we used single-molecule fluorescence imaging of Arp2/3 complex and actin filaments under physiological ionic conditions to observe debranching by GMF and cofilin. We demonstrate that cofilin, like GMF, is an authentic debrancher independent of its filament-severing activity and that the debranching activities of the two proteins are additive. While GMF binds directly to the Arp2/3 complex, cofilin selectively accumulates on branch-junction daughter filaments in tropomyosin-decorated networks just prior to debranching events. Quantitative comparison of debranching rates with the known kinetics of cofilin-actin binding suggests that cofilin occupancy of a particular single actin site at the branch junction is sufficient to trigger debranching. In rare cases in which the order of departure could be resolved during GMF- or cofilin-induced debranching, the Arp2/3 complex left the branch junction bound to the pointed end of the daughter filament, suggesting that both GMF and cofilin can work by destabilizing the mother filament-Arp2/3 complex interface. Taken together, these observations suggest that GMF and cofilin promote debranching by distinct yet complementary mechanisms.
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Affiliation(s)
- Johnson Chung
- Department of Biochemistry, Brandeis University, Waltham, MA 02454
| | - Bruce L. Goode
- Department of Biology, Brandeis University, Waltham, MA 02454
| | - Jeff Gelles
- Department of Biochemistry, Brandeis University, Waltham, MA 02454
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31
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Roca J, Santiago-Frangos A, Woodson SA. Diversity of bacterial small RNAs drives competitive strategies for a mutual chaperone. Nat Commun 2022; 13:2449. [PMID: 35508531 PMCID: PMC9068810 DOI: 10.1038/s41467-022-30211-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2021] [Accepted: 04/06/2022] [Indexed: 12/17/2022] Open
Abstract
Hundreds of bacterial small RNAs (sRNAs) require the Hfq chaperone to regulate mRNA expression. Hfq is limiting, thus competition among sRNAs for binding to Hfq shapes the proteomes of individual cells. To understand how sRNAs compete for a common partner, we present a single-molecule fluorescence platform to simultaneously visualize binding and release of multiple sRNAs with Hfq. We show that RNA residents rarely dissociate on their own. Instead, clashes between residents and challengers on the same face of Hfq cause rapid exchange, whereas RNAs that recognize different surfaces may cohabit Hfq for several minutes before one RNA departs. The prevalence of these pathways depends on the structure of each RNA and how it interacts with Hfq. We propose that sRNA diversity creates many pairwise interactions with Hfq that allow for distinct biological outcomes: active exchange favors fast regulation whereas co-residence of dissimilar RNAs favors target co-recognition or target exclusion.
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Affiliation(s)
- Jorjethe Roca
- T. C. Jenkins Department of Biophysics, Johns Hopkins University, 3400 N. Charles St., Baltimore, MD, 21218, USA
| | - Andrew Santiago-Frangos
- CMDB Program, Johns Hopkins University, 3400 N. Charles St., Baltimore, MD, 21218, USA.,Department of Microbiology and Cell Biology, Montana State University, Bozeman, MT, 59717, USA
| | - Sarah A Woodson
- T. C. Jenkins Department of Biophysics, Johns Hopkins University, 3400 N. Charles St., Baltimore, MD, 21218, USA.
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32
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A particle size threshold governs diffusion and segregation of PAR-3 during cell polarization. Cell Rep 2022; 39:110652. [PMID: 35417695 PMCID: PMC9093022 DOI: 10.1016/j.celrep.2022.110652] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2021] [Revised: 12/14/2021] [Accepted: 03/17/2022] [Indexed: 11/23/2022] Open
Abstract
The actomyosin cortex regulates the localization and function of proteins at the plasma membrane. Here, we study how membrane binding, cortical movements, and diffusion determine membrane protein distribution. In Caenorhabditis elegans zygotes, actomyosin flows transport PAR polarity proteins to establish the anterior-posterior axis. Oligomerization of a key scaffold protein, PAR-3, is required for polarization. PAR-3 oligomers are a heterogeneous population of many different sizes, and it remains unclear how oligomer size affects PAR-3 segregation. To address this question, we engineered PAR-3 to defined sizes. We report that PAR-3 trimers are necessary and sufficient for PAR-3 function during polarization and later embryo development. Quantitative analysis of PAR-3 diffusion shows that a threshold size of three subunits allows PAR-3 clusters to stably bind the membrane, where they are corralled and transported by the actomyosin cortex. Our study provides a quantitative model for size-dependent protein transportation of peripheral membrane proteins by cortical flow. The actomyosin cytoskeleton is a major regulator of cellular organization. Chang and Dickinson develop protein-engineering and particle-tracking tools to study how clustered membrane-bound proteins are transported by actomyosin contractions in vivo. Data-driven modeling reveals how membrane binding, diffusion, and collisions with F-actin contribute to protein movement.
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33
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Małecka EM, Hua B, Woodson SA. Single-Molecule FRET Studies of RNA Structural Rearrangements and RNA-RNA Interactions. Methods Mol Biol 2022; 2518:271-289. [PMID: 35666451 PMCID: PMC10052914 DOI: 10.1007/978-1-0716-2421-0_16] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
RNA-guided regulation of gene expression is found in all cell types. In this mode of regulation, antisense interactions between the regulatory RNA and its target are typically facilitated by a protein partner. Single-molecule fluorescence microscopy is a powerful tool for dissecting the conformational states and intermediates that contribute to target recognition. This chapter describes protocols for studying target recognition by bacterial small RNAs and their chaperone Hfq on the single-molecule level, using a total internal reflection fluorescence microscope. The sections cover the design of suitable RNA substrates for sRNA-mRNA annealing reactions, preparation of internally labeled mRNA for detecting conformational changes in the target, and key steps of the data analysis. These protocols can be adapted to other RNA-binding proteins that chaperone RNA interactions.
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Affiliation(s)
- Ewelina M Małecka
- T.C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, MD, USA
| | - Boyang Hua
- Department of Molecular Biology and Genetics, Johns Hopkins Medical School, Baltimore, MD, USA
| | - Sarah A Woodson
- T.C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, MD, USA.
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34
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Ordabayev YA, Friedman LJ, Gelles J, Theobald DL. Bayesian machine learning analysis of single-molecule fluorescence colocalization images. eLife 2022; 11:73860. [PMID: 35319463 PMCID: PMC9183235 DOI: 10.7554/elife.73860] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2021] [Accepted: 03/19/2022] [Indexed: 01/07/2023] Open
Abstract
Multi-wavelength single-molecule fluorescence colocalization (CoSMoS) methods allow elucidation of complex biochemical reaction mechanisms. However, analysis of CoSMoS data is intrinsically challenging because of low image signal-to-noise ratios, non-specific surface binding of the fluorescent molecules, and analysis methods that require subjective inputs to achieve accurate results. Here, we use Bayesian probabilistic programming to implement Tapqir, an unsupervised machine learning method that incorporates a holistic, physics-based causal model of CoSMoS data. This method accounts for uncertainties in image analysis due to photon and camera noise, optical non-uniformities, non-specific binding, and spot detection. Rather than merely producing a binary 'spot/no spot' classification of unspecified reliability, Tapqir objectively assigns spot classification probabilities that allow accurate downstream analysis of molecular dynamics, thermodynamics, and kinetics. We both quantitatively validate Tapqir performance against simulated CoSMoS image data with known properties and also demonstrate that it implements fully objective, automated analysis of experiment-derived data sets with a wide range of signal, noise, and non-specific binding characteristics.
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Affiliation(s)
| | - Larry J Friedman
- Department of Biochemistry, Brandeis UniversityWalthamUnited States
| | - Jeff Gelles
- Department of Biochemistry, Brandeis UniversityWalthamUnited States
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35
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Gupta S, Friedman LJ, Gelles J, Bell SP. A helicase-tethered ORC flip enables bidirectional helicase loading. eLife 2021; 10:74282. [PMID: 34882090 PMCID: PMC8828053 DOI: 10.7554/elife.74282] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2021] [Accepted: 12/08/2021] [Indexed: 11/13/2022] Open
Abstract
Replication origins are licensed by loading two Mcm2‑7 helicases around DNA in a head-to-head conformation poised to initiate bidirectional replication. This process requires ORC, Cdc6, and Cdt1. Although different Cdc6 and Cdt1 molecules load each helicase, whether two ORC proteins are required is unclear. Using colocalization single-molecule spectroscopy combined with FRET, we investigated interactions between ORC and Mcm2‑7 during helicase loading. In the large majority of events, we observed a single ORC molecule recruiting both Mcm2‑7/Cdt1 complexes via similar interactions that end upon Cdt1 release. Between first and second helicase recruitment, a rapid change in interactions between ORC and the first Mcm2-7 occurs. Within seconds, ORC breaks the interactions mediating first Mcm2-7 recruitment, releases from its initial DNA-binding site, and forms a new interaction with the opposite face of the first Mcm2-7. This rearrangement requires release of the first Cdt1 and tethers ORC as it flips over the first Mcm2-7 to form an inverted Mcm2‑7-ORC-DNA complex required for second-helicase recruitment. To ensure correct licensing, this complex is maintained until head-to-head interactions between the two helicases are formed. Our findings reconcile previous observations and reveal a highly-coordinated series of events through which a single ORC molecule can load two oppositely-oriented helicases.
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Affiliation(s)
- Shalini Gupta
- Department of Biology, Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, United States
| | - Larry J Friedman
- Department of Biochemistry, Brandeis University, Waltham, United States
| | - Jeff Gelles
- Department of Biochemistry, Brandeis University, Waltham, United States
| | - Stephen P Bell
- Department of Biology, Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, United States
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36
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Sarıkaya S, Dickinson DJ. Rapid extraction and kinetic analysis of protein complexes from single cells. Biophys J 2021; 120:5018-5031. [PMID: 34653388 PMCID: PMC8633716 DOI: 10.1016/j.bpj.2021.10.011] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2021] [Revised: 09/22/2021] [Accepted: 10/08/2021] [Indexed: 11/22/2022] Open
Abstract
Proteins contribute to cell biology by forming dynamic, regulated interactions, and measuring these interactions is a foundational approach in biochemistry. We present a rapid, quantitative in vivo assay for protein-protein interactions, based on optical cell lysis followed by time-resolved single-molecule analysis of protein complex binding to an antibody-coated substrate. We show that our approach has better reproducibility, higher dynamic range, and lower background than previous single-molecule pull-down assays. Furthermore, we demonstrate that by monitoring cellular protein complexes over time after cell lysis, we can measure the dissociation rate constant of a cellular protein complex, providing information about binding affinity and kinetics. Our dynamic single-cell, single-molecule pull-down method thus approaches the biochemical precision that is often sought from in vitro assays while being applicable to native protein complexes isolated from single cells in vivo.
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Affiliation(s)
- Sena Sarıkaya
- Department of Molecular Biosciences, University of Texas at Austin, Austin, Texas
| | - Daniel J Dickinson
- Department of Molecular Biosciences, University of Texas at Austin, Austin, Texas.
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37
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Lei KH, Yang HL, Chang HY, Yeh HY, Nguyen DD, Lee TY, Lyu X, Chastain M, Chai W, Li HW, Chi P. Crosstalk between CST and RPA regulates RAD51 activity during replication stress. Nat Commun 2021; 12:6412. [PMID: 34741010 PMCID: PMC8571288 DOI: 10.1038/s41467-021-26624-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2021] [Accepted: 10/06/2021] [Indexed: 11/09/2022] Open
Abstract
Replication stress causes replication fork stalling, resulting in an accumulation of single-stranded DNA (ssDNA). Replication protein A (RPA) and CTC1-STN1-TEN1 (CST) complex bind ssDNA and are found at stalled forks, where they regulate RAD51 recruitment and foci formation in vivo. Here, we investigate crosstalk between RPA, CST, and RAD51. We show that CST and RPA localize in close proximity in cells. Although CST stably binds to ssDNA with a high affinity at low ionic strength, the interaction becomes more dynamic and enables facilitated dissociation at high ionic strength. CST can coexist with RPA on the same ssDNA and target RAD51 to RPA-coated ssDNA. Notably, whereas RPA-coated ssDNA inhibits RAD51 activity, RAD51 can assemble a functional filament and exhibit strand-exchange activity on CST-coated ssDNA at high ionic strength. Our findings provide mechanistic insights into how CST targets and tethers RAD51 to RPA-coated ssDNA in response to replication stress.
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Affiliation(s)
- Kai-Hang Lei
- Institute of Biochemical Sciences, National Taiwan University, Taipei, Taiwan
| | - Han-Lin Yang
- Department of Chemistry, National Taiwan University, Taipei, Taiwan
| | - Hao-Yen Chang
- Institute of Biochemical Sciences, National Taiwan University, Taipei, Taiwan
| | - Hsin-Yi Yeh
- Institute of Biochemical Sciences, National Taiwan University, Taipei, Taiwan
| | - Dinh Duc Nguyen
- Department of Cancer Biology, Cardinal Bernardin Cancer Center, Loyola University Chicago Stritch School of Medicine, Maywood, IL, USA
| | - Tzu-Yu Lee
- Department of Chemistry, National Taiwan University, Taipei, Taiwan
| | - Xinxing Lyu
- Department of Cancer Biology, Cardinal Bernardin Cancer Center, Loyola University Chicago Stritch School of Medicine, Maywood, IL, USA
| | - Megan Chastain
- Office of Research, Washington State University, Spokane, WA, USA
| | - Weihang Chai
- Department of Cancer Biology, Cardinal Bernardin Cancer Center, Loyola University Chicago Stritch School of Medicine, Maywood, IL, USA
| | - Hung-Wen Li
- Department of Chemistry, National Taiwan University, Taipei, Taiwan.
| | - Peter Chi
- Institute of Biochemical Sciences, National Taiwan University, Taipei, Taiwan. .,Institute of Biological Chemistry, Academia Sinica, Taipei, Taiwan.
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38
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Baek I, Friedman LJ, Gelles J, Buratowski S. Single-molecule studies reveal branched pathways for activator-dependent assembly of RNA polymerase II pre-initiation complexes. Mol Cell 2021; 81:3576-3588.e6. [PMID: 34384542 DOI: 10.1016/j.molcel.2021.07.025] [Citation(s) in RCA: 30] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2021] [Revised: 07/08/2021] [Accepted: 07/21/2021] [Indexed: 01/24/2023]
Abstract
RNA polymerase II (RNA Pol II) transcription reconstituted from purified factors suggests pre-initiation complexes (PICs) can assemble by sequential incorporation of factors at the TATA box. However, these basal transcription reactions are generally independent of activators and co-activators. To study PIC assembly under more realistic conditions, we used single-molecule microscopy to visualize factor dynamics during activator-dependent reactions in nuclear extracts. Surprisingly, RNA Pol II, TFIIF, and TFIIE can pre-assemble on enhancer-bound activators before loading into PICs, and multiple RNA Pol II complexes can bind simultaneously to create a localized cluster. Unlike TFIIF and TFIIE, TFIIH binding is singular and dependent on the basal promoter. Activator-tethered factors exhibit dwell times on the order of seconds. In contrast, PICs can persist on the order of minutes in the absence of nucleotide triphosphates, although TFIIE remains unexpectedly dynamic even after TFIIH incorporation. Our kinetic measurements lead to a new branched model for activator-dependent PIC assembly.
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Affiliation(s)
- Inwha Baek
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
| | - Larry J Friedman
- Department of Biochemistry, Brandeis University, Waltham, MA 02454, USA
| | - Jeff Gelles
- Department of Biochemistry, Brandeis University, Waltham, MA 02454, USA.
| | - Stephen Buratowski
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA.
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39
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Malecka EM, Bassani F, Dendooven T, Sonnleitner E, Rozner M, Albanese TG, Resch A, Luisi B, Woodson S, Bläsi U. Stabilization of Hfq-mediated translational repression by the co-repressor Crc in Pseudomonas aeruginosa. Nucleic Acids Res 2021; 49:7075-7087. [PMID: 34139006 PMCID: PMC8266614 DOI: 10.1093/nar/gkab510] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2021] [Revised: 05/26/2021] [Accepted: 06/15/2021] [Indexed: 01/02/2023] Open
Abstract
In Pseudomonas aeruginosa the RNA chaperone Hfq and the catabolite repression control protein (Crc) govern translation of numerous transcripts during carbon catabolite repression. Here, Crc was shown to enhance Hfq-mediated translational repression of several mRNAs. We have developed a single-molecule fluorescence assay to quantitatively assess the cooperation of Hfq and Crc to form a repressive complex on a RNA, encompassing the translation initiation region and the proximal coding sequence of the P. aeruginosa amiE gene. The presence of Crc did not change the amiE RNA-Hfq interaction lifetimes, whereas it changed the equilibrium towards more stable repressive complexes. This observation is in accord with Cryo-EM analyses, which showed an increased compactness of the repressive Hfq/Crc/RNA assemblies. These biophysical studies revealed how Crc protein kinetically stabilizes Hfq/RNA complexes, and how the two proteins together fold a large segment of the mRNA into a more compact translationally repressive structure. In fact, the presence of Crc resulted in stronger translational repression in vitro and in a significantly reduced half-life of the target amiE mRNA in vivo. Although Hfq is well-known to act with small regulatory RNAs, this study shows how Hfq can collaborate with another protein to down-regulate translation of mRNAs that become targets for the degradative machinery.
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Affiliation(s)
- Ewelina M Malecka
- Department of Biophysics, 3400 N. Charles Street, Johns Hopkins University, Baltimore, MD-21218, USA
| | - Flavia Bassani
- Department of Microbiology, Immunobiology and Genetics, Max Perutz Labs, University of Vienna, Vienna Biocenter (VBC), Dr. Bohrgasse 9/4, 1030 Vienna, Austria
| | - Tom Dendooven
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1GA, UK
| | - Elisabeth Sonnleitner
- Department of Microbiology, Immunobiology and Genetics, Max Perutz Labs, University of Vienna, Vienna Biocenter (VBC), Dr. Bohrgasse 9/4, 1030 Vienna, Austria
| | - Marlena Rozner
- Department of Microbiology, Immunobiology and Genetics, Max Perutz Labs, University of Vienna, Vienna Biocenter (VBC), Dr. Bohrgasse 9/4, 1030 Vienna, Austria
| | - Tanino G Albanese
- Department of Microbiology, Immunobiology and Genetics, Max Perutz Labs, University of Vienna, Vienna Biocenter (VBC), Dr. Bohrgasse 9/4, 1030 Vienna, Austria
| | - Armin Resch
- Department of Microbiology, Immunobiology and Genetics, Max Perutz Labs, University of Vienna, Vienna Biocenter (VBC), Dr. Bohrgasse 9/4, 1030 Vienna, Austria
| | - Ben Luisi
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1GA, UK
| | - Sarah Woodson
- Department of Biophysics, 3400 N. Charles Street, Johns Hopkins University, Baltimore, MD-21218, USA
| | - Udo Bläsi
- Department of Microbiology, Immunobiology and Genetics, Max Perutz Labs, University of Vienna, Vienna Biocenter (VBC), Dr. Bohrgasse 9/4, 1030 Vienna, Austria
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40
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Tibbs J, Ghoneim M, Caldwell CC, Buzynski T, Bowie W, Boehm EM, Washington MT, Tabei SMA, Spies M. KERA: analysis tool for multi-process, multi-state single-molecule data. Nucleic Acids Res 2021; 49:e53. [PMID: 33660771 PMCID: PMC8136784 DOI: 10.1093/nar/gkab087] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2020] [Revised: 01/17/2021] [Accepted: 02/24/2021] [Indexed: 12/16/2022] Open
Abstract
Molecular machines within cells dynamically assemble, disassemble and reorganize. Molecular interactions between their components can be observed at the single-molecule level and quantified using colocalization single-molecule spectroscopy, in which individual labeled molecules are seen transiently associating with a surface-tethered partner, or other total internal reflection fluorescence microscopy approaches in which the interactions elicit changes in fluorescence in the labeled surface-tethered partner. When multiple interacting partners can form ternary, quaternary and higher order complexes, the types of spatial and temporal organization of these complexes can be deduced from the order of appearance and reorganization of the components. Time evolution of complex architectures can be followed by changes in the fluorescence behavior in multiple channels. Here, we describe the kinetic event resolving algorithm (KERA), a software tool for organizing and sorting the discretized fluorescent trajectories from a range of single-molecule experiments. KERA organizes the data in groups by transition patterns, and displays exhaustive dwell time data for each interaction sequence. Enumerating and quantifying sequences of molecular interactions provides important information regarding the underlying mechanism of the assembly, dynamics and architecture of the macromolecular complexes. We demonstrate KERA's utility by analyzing conformational dynamics of two DNA binding proteins: replication protein A and xeroderma pigmentosum complementation group D helicase.
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Affiliation(s)
- Joseph Tibbs
- Department of Physics, University of Northern Iowa, Cedar Falls, IA 50614, USA
| | - Mohamed Ghoneim
- Department of Biochemistry and Molecular Genetics, School of Medicine, University of Colorado, Anschutz Medical Campus, Aurora, CO 80045, USA
| | - Colleen C Caldwell
- Department of Biochemistry, University of Iowa, Iowa City, IA 52242, USA
| | - Troy Buzynski
- Department of Physics, University of Northern Iowa, Cedar Falls, IA 50614, USA
| | - Wayne Bowie
- Department of Physics, University of Northern Iowa, Cedar Falls, IA 50614, USA
| | - Elizabeth M Boehm
- Department of Biochemistry, University of Iowa, Iowa City, IA 52242, USA
| | - M Todd Washington
- Department of Biochemistry, University of Iowa, Iowa City, IA 52242, USA
| | - S M Ali Tabei
- Department of Physics, University of Northern Iowa, Cedar Falls, IA 50614, USA
| | - Maria Spies
- Department of Biochemistry, University of Iowa, Iowa City, IA 52242, USA
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41
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Fairlamb MS, Whitaker AM, Bain FE, Spies M, Freudenthal BD. Construction of a Three-Color Prism-Based TIRF Microscope to Study the Interactions and Dynamics of Macromolecules. BIOLOGY 2021; 10:biology10070571. [PMID: 34201434 PMCID: PMC8301196 DOI: 10.3390/biology10070571] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/11/2021] [Revised: 06/08/2021] [Accepted: 06/15/2021] [Indexed: 02/05/2023]
Abstract
Simple Summary Prism-based single-molecule total internal reflection fluorescence (prismTIRF) microscopes are excellent tools for studying macromolecular dynamics and interactions. Here, we provide an easy-to-follow guide for the design, assembly, and operation of a three-color prismTIRF microscope using commercially available components with the hope of assisting those who aim to implement TIRF imaging techniques in their laboratory. Abstract Single-molecule total internal reflection fluorescence (TIRF) microscopy allows for the real-time visualization of macromolecular dynamics and complex assembly. Prism-based TIRF microscopes (prismTIRF) are relatively simple to operate and can be easily modulated to fit the needs of a wide variety of experimental applications. While building a prismTIRF microscope without expert assistance can pose a significant challenge, the components needed to build a prismTIRF microscope are relatively affordable and, with some guidance, the assembly can be completed by a determined novice. Here, we provide an easy-to-follow guide for the design, assembly, and operation of a three-color prismTIRF microscope which can be utilized for the study of macromolecular complexes, including the multi-component protein–DNA complexes responsible for DNA repair, replication, and transcription. Our hope is that this article can assist laboratories that aspire to implement single-molecule TIRF techniques, and consequently expand the application of this technology.
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Affiliation(s)
- Max S. Fairlamb
- Department of Biochemistry and Molecular Biology and Department of Cancer Biology, University of Kansas Medical Center, Kansas City, KS 66160, USA; (M.S.F.); (A.M.W.)
| | - Amy M. Whitaker
- Department of Biochemistry and Molecular Biology and Department of Cancer Biology, University of Kansas Medical Center, Kansas City, KS 66160, USA; (M.S.F.); (A.M.W.)
| | - Fletcher E. Bain
- Department of Biochemistry and Molecular Biology, University of Iowa Carver College of Medicine, 51 Newton Road, Iowa City, IA 52242, USA; (F.E.B.); (M.S.)
| | - Maria Spies
- Department of Biochemistry and Molecular Biology, University of Iowa Carver College of Medicine, 51 Newton Road, Iowa City, IA 52242, USA; (F.E.B.); (M.S.)
| | - Bret D. Freudenthal
- Department of Biochemistry and Molecular Biology and Department of Cancer Biology, University of Kansas Medical Center, Kansas City, KS 66160, USA; (M.S.F.); (A.M.W.)
- Correspondence:
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42
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Lee TY, Li YC, Lin MG, Hsiao CD, Li HW. Single-molecule binding characterization of primosomal protein PriA involved in replication restart. Phys Chem Chem Phys 2021; 23:13745-13751. [PMID: 34159970 DOI: 10.1039/d1cp00638j] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
DNA damage leads to stalled or collapsed replication forks. Replication restart primosomes re-initiate DNA synthesis at these stalled or collapsed DNA replication forks, which is important for bacterial survival. Primosomal protein PriA specifically recognizes the DNA fork structure and recruits other primosomal proteins to load the replicative helicase, in order to re-establish the replication fork. PriA binding on DNA is the first step to restart replication forks for proper DNA repair. Using a single-molecule fluorescence colocalization experiment, we measured the thermodynamic and real-time kinetic properties of fluorescence-labeled Gram-positive bacteria Geobacillus stearothermophilus PriA binding on DNA forks. We showed that PriA preferentially binds to a DNA fork structure with a fully duplexed leading strand at sub-nanomolar affinity (Kd = 268 ± 99 pM). PriA binds dynamically, and its association and dissociation rate constants can be determined using the appearance and disappearance of the fluorescence signal. In addition, we showed that PriA binds to DNA forks as a monomer using photobleaching step counting. This information offers a molecular basis essential for understanding the mechanism of replication restart.
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Affiliation(s)
- Tzu-Yu Lee
- Department of Chemistry, National Taiwan University, Taiwan.
| | - Yi-Ching Li
- Institute of Molecular Biology, Academia Sinica, Taiwan.
| | - Min-Guan Lin
- Institute of Molecular Biology, Academia Sinica, Taiwan.
| | | | - Hung-Wen Li
- Department of Chemistry, National Taiwan University, Taiwan.
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43
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Nicholson DA, Nesbitt DJ. Pushing Camera-Based Single-Molecule Kinetic Measurements to the Frame Acquisition Limit with Stroboscopic smFRET. J Phys Chem B 2021; 125:6080-6089. [PMID: 34097408 DOI: 10.1021/acs.jpcb.1c01036] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Single-molecule fluorescence resonance energy transfer (smFRET) experiments permit detailed examination of microscopic dynamics. However, kinetic rate constants determined by smFRET are susceptible to systematic underestimation when the rate constants are comparable to the data acquisition rate. We demonstrate how such systematic errors in camera-based total internal reflection fluorescence microscopy experiments can be greatly reduced by using stroboscopic illumination/detection, allowing accurate rate constant determination up to the data sampling rate and yielding an order of magnitude increase in the dynamic range. Implementation of these stroboscopic smFRET ideas is straightforward, and the stroboscopically obtained data are compatible with multiple trajectory analysis methods, including dwell-time analysis and hidden Markov modeling. Such stroboscopic methods therefore offer a remarkably simple yet valuable addition to the smFRET toolkit, requiring only relatively modest modification to the normal data collection and analysis procedures.
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Affiliation(s)
- David A Nicholson
- National Institute of Standards and Technology and University of Colorado, JILA, Boulder, Colorado 80309, United States.,Department of Chemistry, University of Colorado, Boulder, Colorado 80309, United States
| | - David J Nesbitt
- National Institute of Standards and Technology and University of Colorado, JILA, Boulder, Colorado 80309, United States.,Department of Chemistry, University of Colorado, Boulder, Colorado 80309, United States.,Department of Physics, University of Colorado, Boulder, Colorado 80309, United States
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44
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Małecka EM, Woodson SA. Stepwise sRNA targeting of structured bacterial mRNAs leads to abortive annealing. Mol Cell 2021; 81:1988-1999.e4. [PMID: 33705712 PMCID: PMC8106647 DOI: 10.1016/j.molcel.2021.02.019] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Revised: 01/08/2021] [Accepted: 02/16/2021] [Indexed: 12/13/2022]
Abstract
Bacterial small RNAs (sRNAs) regulate the expression of hundreds of transcripts via base pairing mediated by the Hfq chaperone protein. sRNAs and the mRNA sites they target are heterogeneous in sequence, length, and secondary structure. To understand how Hfq can flexibly match diverse sRNA and mRNA pairs, we developed a single-molecule Förster resonance energy transfer (smFRET) platform that visualizes the target search on timescales relevant in cells. Here we show that unfolding of target secondary structure on Hfq creates a kinetic energy barrier that determines whether target recognition succeeds or aborts before a stable anti-sense complex is achieved. Premature dissociation of the sRNA can be alleviated by strong RNA-Hfq interactions, explaining why sRNAs have different target recognition profiles. We propose that the diverse sequences and structures of Hfq substrates create an additional layer of information that tunes the efficiency and selectivity of non-coding RNA regulation in bacteria.
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Affiliation(s)
- Ewelina M Małecka
- T.C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, USA
| | - Sarah A Woodson
- T.C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, USA.
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45
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Chadda R, Bernhardt N, Kelley EG, Teixeira SC, Griffith K, Gil-Ley A, Öztürk TN, Hughes LE, Forsythe A, Krishnamani V, Faraldo-Gómez JD, Robertson JL. Membrane transporter dimerization driven by differential lipid solvation energetics of dissociated and associated states. eLife 2021; 10:63288. [PMID: 33825681 PMCID: PMC8116059 DOI: 10.7554/elife.63288] [Citation(s) in RCA: 26] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2020] [Accepted: 04/06/2021] [Indexed: 12/22/2022] Open
Abstract
Over two-thirds of integral membrane proteins of known structure assemble into oligomers. Yet, the forces that drive the association of these proteins remain to be delineated, as the lipid bilayer is a solvent environment that is both structurally and chemically complex. In this study, we reveal how the lipid solvent defines the dimerization equilibrium of the CLC-ec1 Cl-/H+ antiporter. Integrating experimental and computational approaches, we show that monomers associate to avoid a thinned-membrane defect formed by hydrophobic mismatch at their exposed dimerization interfaces. In this defect, lipids are strongly tilted and less densely packed than in the bulk, with a larger degree of entanglement between opposing leaflets and greater water penetration into the bilayer interior. Dimerization restores the membrane to a near-native state and therefore, appears to be driven by the larger free-energy cost of lipid solvation of the dissociated protomers. Supporting this theory, we demonstrate that addition of short-chain lipids strongly shifts the dimerization equilibrium toward the monomeric state, and show that the cause of this effect is that these lipids preferentially solvate the defect. Importantly, we show that this shift requires only minimal quantities of short-chain lipids, with no measurable impact on either the macroscopic physical state of the membrane or the protein's biological function. Based on these observations, we posit that free-energy differentials for local lipid solvation define membrane-protein association equilibria. With this, we argue that preferential lipid solvation is a plausible cellular mechanism for lipid regulation of oligomerization processes, as it can occur at low concentrations and does not require global changes in membrane properties. A cell’s outer membrane is made of molecules called lipids, which band together to form a flexible thin film, just two molecules thick. This membrane is dotted with proteins that transport materials in to and out of cells. Most of these membrane proteins join with other proteins to form structures known as oligomers. Except, how membrane-bound proteins assemble into oligomers – the physical forces driving these molecules to take shape – remains unclear. This is partly because the structural, physical and chemical properties of fat-like lipid membranes are radically different to the cell’s watery interior. Consequently, the conditions under which membrane oligomers form are distinct from those surrounding proteins inside cells. Membrane proteins are also more difficult to study and characterize than water-soluble proteins inside the cell, and yet many therapeutic drugs such as antibiotics specifically target membrane proteins. Overall, our understanding of how the unique properties of lipid membranes affect the formation of protein structures embedded within, is lacking and warrants further investigation. Now, Chadda, Bernhardt et al. focused on one membrane protein, known as CLC, which tends to exist in pairs – or dimers. To understand why these proteins form dimers (a process called dimerization) Chadda, Bernhardt et al. first used computer simulations, and then validated the findings in experimental tests. These complementary approaches demonstrated that the main reason CLC proteins ‘dimerize’ lies in their interaction with the lipid membrane, and not the attraction of one protein to its partner. When CLC proteins are on their own, they deform the surrounding membrane and create structural defects that put the membrane under strain. But when two CLC proteins join as a dimer, this membrane strain disappears – making dimerization the more stable and energetically favorable option. Chadda, Bernhardt et al. also showed that with the addition of a few certain lipids, specifically smaller lipids, cell membranes become more tolerant of protein-induced structural changes. This might explain how cells could use various lipids to fine-tune the activity of membrane proteins by controlling how oligomers form. However, the theory needs to be examined further. Altogether, this work has provided fundamental insights into the physical forces shaping membrane-bound proteins, relevant to researchers studying cell biology and pharmacology alike.
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Affiliation(s)
- Rahul Chadda
- Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, United States
| | - Nathan Bernhardt
- Theoretical Molecular Biophysics Laboratory, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, United States
| | - Elizabeth G Kelley
- NIST Center for Neutron Research, National Institute for Standards and Technology, Gaithersburg, United States
| | - Susana Cm Teixeira
- NIST Center for Neutron Research, National Institute for Standards and Technology, Gaithersburg, United States.,Center for Neutron Science, Chemical and Biomolecular Engineering, University of Delaware, Newark, United States
| | - Kacie Griffith
- Molecular Physiology and Biophysics, Carver College of Medicine, The University of Iowa, Iowa City, United States
| | - Alejandro Gil-Ley
- Theoretical Molecular Biophysics Laboratory, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, United States.,Molecular Physiology and Biophysics, Carver College of Medicine, The University of Iowa, Iowa City, United States
| | - Tuğba N Öztürk
- Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, United States
| | - Lauren E Hughes
- Molecular Physiology and Biophysics, Carver College of Medicine, The University of Iowa, Iowa City, United States
| | - Ana Forsythe
- Molecular Physiology and Biophysics, Carver College of Medicine, The University of Iowa, Iowa City, United States
| | - Venkatramanan Krishnamani
- Molecular Physiology and Biophysics, Carver College of Medicine, The University of Iowa, Iowa City, United States
| | - José D Faraldo-Gómez
- Theoretical Molecular Biophysics Laboratory, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, United States
| | - Janice L Robertson
- Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, United States
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46
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Jin Y, Kotler JLM, Wang S, Huang B, Halpin JC, Street TO. The ER Chaperones BiP and Grp94 Regulate the Formation of Insulin-Like Growth Factor 2 (IGF2) Oligomers. J Mol Biol 2021; 433:166963. [PMID: 33811917 DOI: 10.1016/j.jmb.2021.166963] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2020] [Revised: 03/07/2021] [Accepted: 03/22/2021] [Indexed: 01/05/2023]
Abstract
While cytosolic Hsp90 chaperones have been extensively studied, less is known about how the ER Hsp90 paralog Grp94 recognizes clients and influences client folding. Here, we examine how Grp94 and the ER Hsp70 paralog, BiP, influence the folding of insulin-like growth factor 2 (IGF2), an established client protein of Grp94. ProIGF2 is composed of a disulfide-bonded insulin-like hormone and a C-terminal E-peptide that has sequence characteristics of an intrinsically disordered region. BiP and Grp94 have a minimal influence on folding whereby both chaperones slow proIGF2 folding and do not substantially alter the disulfide-bonded folding intermediates, suggesting that BiP and Grp94 may have an additional influence unrelated to proIGF2 folding. Indeed, we made the unexpected discovery that the E-peptide region allows proIGF2 to form dynamic oligomers. ProIGF2 oligomers can transition from a dynamic state that is capable of exchanging monomers to an irreversibly aggregated state, providing a plausible role for BiP and Grp94 in regulating proIGF2 oligomerization. In contrast to the modest influence on folding, BiP and Grp94 have a stronger influence on proIGF2 oligomerization and these chaperones exert counteracting effects. BiP suppresses proIGF2 oligomerization while Grp94 can enhance proIGF2 oligomerization in a nucleotide-dependent manner. We propose that BiP and Grp94 regulate the assembly and dynamic behavior of proIGF2 oligomers, although the biological role of proIGF2 oligomerization is not yet known.
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Affiliation(s)
- Yi Jin
- Department of Biochemistry, Brandeis University, Waltham, MA 02454, USA
| | - Judy L M Kotler
- Department of Biochemistry, Brandeis University, Waltham, MA 02454, USA
| | - Shiyu Wang
- Department of Biology, Brandeis University, Waltham, MA 02454, USA
| | - Bin Huang
- Department of Biochemistry, Brandeis University, Waltham, MA 02454, USA
| | - Jackson C Halpin
- Department of Biochemistry, Brandeis University, Waltham, MA 02454, USA
| | - Timothy O Street
- Department of Biochemistry, Brandeis University, Waltham, MA 02454, USA.
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47
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Mersch K, Ozturk TN, Park K, Lim HH, Robertson JL. Altering CLC stoichiometry by reducing non-polar side-chains at the dimerization interface. J Mol Biol 2021; 433:166886. [PMID: 33617898 DOI: 10.1016/j.jmb.2021.166886] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2020] [Revised: 02/03/2021] [Accepted: 02/16/2021] [Indexed: 10/22/2022]
Abstract
CLC-ec1 is a Cl-/H+ antiporter that forms stable homodimers in lipid bilayers, with a free energy of -10.9 kcal/mol in 2:1 POPE/POPG lipid bilayers. The dimerization interface is formed by four transmembrane helices: H, I, P and Q, that are lined by non-polar side-chains that come in close contact, yet it is unclear as to whether their interactions drive dimerization. To investigate whether non-polar side-chains are required for dimer assembly, we designed a series of constructs where side-chain packing in the dimer state is significantly reduced by making 4-5 alanine substitutions along each helix (H-ala, I-ala, P-ala, Q-ala). All constructs are functional and three purify as stable dimers in detergent micelles despite the removal of significant side-chain interactions. On the other hand, H-ala shows the unique behavior of purifying as a mixture of monomers and dimers, followed by a rapid and complete conversion to monomers. In lipid bilayers, all four constructs are monomeric as examined by single-molecule photobleaching analysis. Further study of the H-helix shows that the single mutation L194A is sufficient to yield monomeric CLC-ec1 in detergent micelles and lipid bilayers. X-ray crystal structures of L194A reveal the protein re-assembles to form dimers, with a structure that is identical to wild-type. Altogether, these results demonstrate that non-polar membrane embedded side-chains play an important role in defining dimer stability, but the stoichiometry is highly contextual to the solvent environment. Furthermore, we discovered that L194 is a molecular hot-spot for defining dimerization of CLC-ec1.
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Affiliation(s)
- Kacey Mersch
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine in St. Louis, St. Louis, MO, USA; Department of Molecular Physiology and Biophysics, The University of Iowa, Iowa City, IA, USA
| | - Tugba N Ozturk
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine in St. Louis, St. Louis, MO, USA
| | - Kunwoong Park
- Department of Structure and Function of Neural Network, Korea Brain Research Institute, 41068 Daegu, Republic of Korea
| | - Hyun-Ho Lim
- Department of Structure and Function of Neural Network, Korea Brain Research Institute, 41068 Daegu, Republic of Korea; Department of Brain & Cognitive Sciences, Daegu Gyeongbuk Institute of Science & Technology, 42988 Daegu, Republic of Korea
| | - Janice L Robertson
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine in St. Louis, St. Louis, MO, USA.
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48
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De Jesús-Kim L, Friedman LJ, Lõoke M, Ramsoomair CK, Gelles J, Bell SP. DDK regulates replication initiation by controlling the multiplicity of Cdc45-GINS binding to Mcm2-7. eLife 2021; 10:65471. [PMID: 33616038 PMCID: PMC7954526 DOI: 10.7554/elife.65471] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2020] [Accepted: 02/21/2021] [Indexed: 01/07/2023] Open
Abstract
The committed step of eukaryotic DNA replication occurs when the pairs of Mcm2-7 replicative helicases that license each replication origin are activated. Helicase activation requires the recruitment of Cdc45 and GINS to Mcm2-7, forming Cdc45-Mcm2-7-GINS complexes (CMGs). Using single-molecule biochemical assays to monitor CMG formation, we found that Cdc45 and GINS are recruited to loaded Mcm2-7 in two stages. Initially, Cdc45, GINS, and likely additional proteins are recruited to unstructured Mcm2-7 N-terminal tails in a Dbf4-dependent kinase (DDK)-dependent manner, forming Cdc45-tail-GINS intermediates (CtGs). DDK phosphorylation of multiple phosphorylation sites on the Mcm2-7 tails modulates the number of CtGs formed per Mcm2-7. In a second, inefficient event, a subset of CtGs transfer their Cdc45 and GINS components to form CMGs. Importantly, higher CtG multiplicity increases the frequency of CMG formation. Our findings reveal the molecular mechanisms sensitizing helicase activation to DDK levels with implications for control of replication origin efficiency and timing.
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Affiliation(s)
- Lorraine De Jesús-Kim
- Howard Hughes Medical Institute, Department of Biology, Massachusetts Institute of TechnologyCambridgeUnited States
| | - Larry J Friedman
- Department of Biochemistry, Brandeis UniversityWalthamUnited States
| | - Marko Lõoke
- Howard Hughes Medical Institute, Department of Biology, Massachusetts Institute of TechnologyCambridgeUnited States
| | - Christian K Ramsoomair
- Howard Hughes Medical Institute, Department of Biology, Massachusetts Institute of TechnologyCambridgeUnited States
| | - Jeff Gelles
- Department of Biochemistry, Brandeis UniversityWalthamUnited States
| | - Stephen P Bell
- Howard Hughes Medical Institute, Department of Biology, Massachusetts Institute of TechnologyCambridgeUnited States
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Dynamics of RNA polymerase II and elongation factor Spt4/5 recruitment during activator-dependent transcription. Proc Natl Acad Sci U S A 2020; 117:32348-32357. [PMID: 33293419 DOI: 10.1073/pnas.2011224117] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
In eukaryotes, RNA polymerase II (RNApII) transcribes messenger RNA from template DNA. Decades of experiments have identified the proteins needed for transcription activation, initiation complex assembly, and productive elongation. However, the dynamics of recruitment of these proteins to transcription complexes, and of the transitions between these steps, are poorly understood. We used multiwavelength single-molecule fluorescence microscopy to directly image and quantitate these dynamics in a budding yeast nuclear extract that reconstitutes activator-dependent transcription in vitro. A strong activator (Gal4-VP16) greatly stimulated reversible binding of individual RNApII molecules to template DNA. Binding of labeled elongation factor Spt4/5 to DNA typically followed RNApII binding, was NTP dependent, and was correlated with association of mRNA binding protein Hek2, demonstrating specificity of Spt4/5 binding to elongation complexes. Quantitative kinetic modeling shows that only a fraction of RNApII binding events are productive and implies a rate-limiting step, probably associated with recruitment of general transcription factors, needed to assemble a transcription-competent preinitiation complex at the promoter. Spt4/5 association with transcription complexes was slowly reversible, with DNA-bound RNApII molecules sometimes binding and releasing Spt4/5 multiple times. The average Spt4/5 residence time was of similar magnitude to the time required to transcribe an average length yeast gene. These dynamics suggest that a single Spt4/5 molecule remains associated during a typical transcription event, yet can dissociate from RNApII to allow disassembly of abnormally long-lived (i.e., stalled) elongation complexes.
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50
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Beier DH, Carrocci TJ, van der Feltz C, Tretbar US, Paulson JC, Grabowski N, Hoskins AA. Dynamics of the DEAD-box ATPase Prp5 RecA-like domains provide a conformational switch during spliceosome assembly. Nucleic Acids Res 2020; 47:10842-10851. [PMID: 31712821 PMCID: PMC6846040 DOI: 10.1093/nar/gkz765] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2018] [Revised: 07/29/2019] [Accepted: 08/21/2019] [Indexed: 11/26/2022] Open
Abstract
The DEAD-box family of proteins are ATP-dependent, RNA-binding proteins implicated in many aspects of RNA metabolism. Pre-mRNA splicing in eukaryotes requires three DEAD-box ATPases (Prp5, Prp28 and Sub2), the molecular mechanisms of which are poorly understood. Here, we use single molecule FRET (smFRET) to study the conformational dynamics of yeast Prp5. Prp5 is essential for stable association of the U2 snRNP with the intron branch site (BS) sequence during spliceosome assembly. Our data show that the Prp5 RecA-like domains undergo a large conformational rearrangement only in response to binding of both ATP and RNA. Mutations in Prp5 impact the fidelity of BS recognition and change the conformational dynamics of the RecA-like domains. We propose that BS recognition during spliceosome assembly involves a set of coordinated conformational switches among U2 snRNP components. Spontaneous toggling of Prp5 into a stable, open conformation may be important for its release from U2 and to prevent competition between Prp5 re-binding and subsequent steps in spliceosome assembly.
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Affiliation(s)
- David H Beier
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Tucker J Carrocci
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53706, USA.,Integrated Program in Biochemistry, University of Wisconsin-Madison, Madison, WI 53706 USA
| | | | - U Sandy Tretbar
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Joshua C Paulson
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Nikolai Grabowski
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Aaron A Hoskins
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53706, USA.,Integrated Program in Biochemistry, University of Wisconsin-Madison, Madison, WI 53706 USA
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