1
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Reddy KD, Rasool B, Akher FB, Kutlešić N, Pant S, Boudker O. Evolutionary analysis reveals the origin of sodium coupling in glutamate transporters. bioRxiv 2024:2023.12.03.569786. [PMID: 38106174 PMCID: PMC10723334 DOI: 10.1101/2023.12.03.569786] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2023]
Abstract
Secondary active membrane transporters harness the energy of ion gradients to concentrate their substrates. Homologous transporters evolved to couple transport to different ions in response to changing environments and needs. The bases of such diversification, and thus principles of ion coupling, are unexplored. Employing phylogenetics and ancestral protein reconstruction, we investigated sodium-coupled transport in prokaryotic glutamate transporters, a mechanism ubiquitous across life domains and critical to neurotransmitter recycling in humans. We found that the evolutionary transition from sodium-dependent to independent substrate binding to the transporter preceded changes in the coupling mechanism. Structural and functional experiments suggest that the transition entailed allosteric mutations, making sodium binding dispensable without affecting ion-binding sites. Allosteric tuning of transporters' energy landscapes might be a widespread route of their functional diversification.
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2
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Jiang Y, Miyagi A, Wang X, Qiu B, Boudker O, Scheuring S. HS-AFM single-molecule structural biology uncovers basis of transporter wanderlust kinetics. Nat Struct Mol Biol 2024:10.1038/s41594-024-01260-3. [PMID: 38632360 DOI: 10.1038/s41594-024-01260-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2023] [Accepted: 03/01/2024] [Indexed: 04/19/2024]
Abstract
The Pyrococcus horikoshii amino acid transporter GltPh revealed, like other channels and transporters, activity mode switching, previously termed wanderlust kinetics. Unfortunately, to date, the basis of these activity fluctuations is not understood, probably due to a lack of experimental tools that directly access the structural features of transporters related to their instantaneous activity. Here, we take advantage of high-speed atomic force microscopy, unique in providing simultaneous structural and temporal resolution, to uncover the basis of kinetic mode switching in proteins. We developed membrane extension membrane protein reconstitution that allows the analysis of isolated molecules. Together with localization atomic force microscopy, principal component analysis and hidden Markov modeling, we could associate structural states to a functional timeline, allowing six structures to be solved from a single molecule, and an inward-facing state, IFSopen-1, to be determined as a kinetic dead-end in the conformational landscape. The approaches presented on GltPh are generally applicable and open possibilities for time-resolved dynamic single-molecule structural biology.
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Affiliation(s)
- Yining Jiang
- Biochemistry and Structural Biology, Cell and Developmental Biology, and Molecular Biology Program, Weill Cornell Graduate School of Biomedical Sciences, New York, NY, USA
- Weill Cornell Medicine, Department of Anesthesiology, New York, NY, USA
| | - Atsushi Miyagi
- Weill Cornell Medicine, Department of Anesthesiology, New York, NY, USA
| | - Xiaoyu Wang
- Weill Cornell Medicine, Department of Physiology and Biophysics, New York, NY, USA
| | - Biao Qiu
- Howard Hughes Medical Institute, Chevy Chase, MD, USA
| | - Olga Boudker
- Weill Cornell Medicine, Department of Physiology and Biophysics, New York, NY, USA
- Howard Hughes Medical Institute, Chevy Chase, MD, USA
| | - Simon Scheuring
- Weill Cornell Medicine, Department of Anesthesiology, New York, NY, USA.
- Weill Cornell Medicine, Department of Physiology and Biophysics, New York, NY, USA.
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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 DOI: 10.1038/s41594-023-01210-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [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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Currie MJ, Davies JS, Scalise M, Gulati A, Wright JD, Newton-Vesty MC, Abeysekera GS, Subramanian R, Wahlgren WY, Friemann R, Allison JR, Mace PD, Griffin MDW, Demeler B, Wakatsuki S, Drew D, Indiveri C, Dobson RCJ, North RA. Structural and biophysical analysis of a Haemophilus influenzae tripartite ATP-independent periplasmic (TRAP) transporter. eLife 2024; 12:RP92307. [PMID: 38349818 PMCID: PMC10942642 DOI: 10.7554/elife.92307] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/15/2024] Open
Abstract
Tripartite ATP-independent periplasmic (TRAP) transporters are secondary-active transporters that receive their substrates via a soluble-binding protein to move bioorganic acids across bacterial or archaeal cell membranes. Recent cryo-electron microscopy (cryo-EM) structures of TRAP transporters provide a broad framework to understand how they work, but the mechanistic details of transport are not yet defined. Here we report the cryo-EM structure of the Haemophilus influenzae N-acetylneuraminate TRAP transporter (HiSiaQM) at 2.99 Å resolution (extending to 2.2 Å at the core), revealing new features. The improved resolution (the previous HiSiaQM structure is 4.7 Å resolution) permits accurate assignment of two Na+ sites and the architecture of the substrate-binding site, consistent with mutagenic and functional data. Moreover, rather than a monomer, the HiSiaQM structure is a homodimer. We observe lipids at the dimer interface, as well as a lipid trapped within the fusion that links the SiaQ and SiaM subunits. We show that the affinity (KD) for the complex between the soluble HiSiaP protein and HiSiaQM is in the micromolar range and that a related SiaP can bind HiSiaQM. This work provides key data that enhances our understanding of the 'elevator-with-an-operator' mechanism of TRAP transporters.
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Affiliation(s)
- Michael J Currie
- Biomolecular Interaction Centre, Maurice Wilkins Centre for Biodiscovery, MacDiarmid Institute for Advanced Materials and Nanotechnology, and School of Biological Sciences, University of CanterburyChristchurchNew Zealand
| | - James S Davies
- Biomolecular Interaction Centre, Maurice Wilkins Centre for Biodiscovery, MacDiarmid Institute for Advanced Materials and Nanotechnology, and School of Biological Sciences, University of CanterburyChristchurchNew Zealand
- Department of Biochemistry and Biophysics, Stockholm UniversityStockholmSweden
| | - Mariafrancesca Scalise
- Department DiBEST (Biologia, Ecologia, Scienze della Terra) Unit of Biochemistry and Molecular Biotechnology, University of CalabriaArcavacata di RendeItaly
| | - Ashutosh Gulati
- Department of Biochemistry and Biophysics, Stockholm UniversityStockholmSweden
| | - Joshua D Wright
- Biomolecular Interaction Centre, Maurice Wilkins Centre for Biodiscovery, MacDiarmid Institute for Advanced Materials and Nanotechnology, and School of Biological Sciences, University of CanterburyChristchurchNew Zealand
| | - Michael C Newton-Vesty
- Biomolecular Interaction Centre, Maurice Wilkins Centre for Biodiscovery, MacDiarmid Institute for Advanced Materials and Nanotechnology, and School of Biological Sciences, University of CanterburyChristchurchNew Zealand
| | - Gayan S Abeysekera
- Biomolecular Interaction Centre, Maurice Wilkins Centre for Biodiscovery, MacDiarmid Institute for Advanced Materials and Nanotechnology, and School of Biological Sciences, University of CanterburyChristchurchNew Zealand
| | - Ramaswamy Subramanian
- Biological Sciences and Biomedical Engineering, Bindley Bioscience Center, Purdue University West LafayetteWest LafayetteUnited States
| | - Weixiao Y Wahlgren
- Department of Chemistry and Molecular Biology, Biochemistry and Structural Biology, University of GothenburgGothenburgSweden
| | - Rosmarie Friemann
- Centre for Antibiotic Resistance Research (CARe) at University of GothenburgGothenburgSweden
| | - Jane R Allison
- Biomolecular Interaction Centre, Digital Life Institute, Maurice Wilkins Centre for Molecular Biodiscovery, and School of Biological Sciences, University of AucklandAucklandNew Zealand
| | - Peter D Mace
- Biochemistry Department, School of Biomedical Sciences, University of OtagoDunedinNew Zealand
| | - Michael DW Griffin
- ARC Centre for Cryo-electron Microscopy of Membrane Proteins, Bio Molecular Science and Biotechnology Institute, Department of Biochemistry and Pharmacology, University of MelbourneMelbourneAustralia
| | - Borries Demeler
- Department of Chemistry and Biochemistry, University of MontanaMissoulaUnited States
- Department of Chemistry and Biochemistry, University of LethbridgeLethbridgeCanada
| | - Soichi Wakatsuki
- Biological Sciences Division, SLAC National Accelerator LaboratoryMenlo ParkUnited States
- Department of Structural Biology, Stanford University School of MedicineStanfordUnited States
| | - David Drew
- Department of Biochemistry and Biophysics, Stockholm UniversityStockholmSweden
| | - Cesare Indiveri
- Department DiBEST (Biologia, Ecologia, Scienze della Terra) Unit of Biochemistry and Molecular Biotechnology, University of CalabriaArcavacata di RendeItaly
- CNR Institute of Biomembranes, Bioenergetics and Molecular Biotechnologies (IBIOM)BariItaly
| | - Renwick CJ Dobson
- Biomolecular Interaction Centre, Maurice Wilkins Centre for Biodiscovery, MacDiarmid Institute for Advanced Materials and Nanotechnology, and School of Biological Sciences, University of CanterburyChristchurchNew Zealand
- ARC Centre for Cryo-electron Microscopy of Membrane Proteins, Bio Molecular Science and Biotechnology Institute, Department of Biochemistry and Pharmacology, University of MelbourneMelbourneAustralia
| | - Rachel A North
- Department of Biochemistry and Biophysics, Stockholm UniversityStockholmSweden
- School of Medical Sciences, Faculty of Medicine and Health, University of SydneySydneyAustralia
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5
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Davies JS, Currie MJ, Dobson RCJ, Horne CR, North RA. TRAPs: the 'elevator-with-an-operator' mechanism. Trends Biochem Sci 2024; 49:134-144. [PMID: 38102017 DOI: 10.1016/j.tibs.2023.11.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2023] [Revised: 11/18/2023] [Accepted: 11/21/2023] [Indexed: 12/17/2023]
Abstract
Tripartite ATP-independent periplasmic (TRAP) transporters are nutrient-uptake systems found in bacteria and archaea. These evolutionary divergent transporter systems couple a substrate-binding protein (SBP) to an elevator-type secondary transporter, which is a first-of-its-kind mechanism of transport. Here, we highlight breakthrough TRAP transporter structures and recent functional data that probe the mechanism of transport. Furthermore, we discuss recent structural and biophysical studies of the ion transporter superfamily (ITS) members and highlight mechanistic principles that are relevant for further exploration of the TRAP transporter system.
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Affiliation(s)
- James S Davies
- Department of Biochemistry and Biophysics, Stockholm University, 106 91 Stockholm, Sweden
| | - Michael J Currie
- Biomolecular Interaction Centre, Maurice Wilkins Centre for Biodiscovery, MacDiarmid Institute for Advanced Materials and Nanotechnology, Christchurch 8140, New Zealand; School of Biological Sciences, University of Canterbury, Christchurch 8140, New Zealand
| | - Renwick C J Dobson
- Biomolecular Interaction Centre, Maurice Wilkins Centre for Biodiscovery, MacDiarmid Institute for Advanced Materials and Nanotechnology, Christchurch 8140, New Zealand; School of Biological Sciences, University of Canterbury, Christchurch 8140, New Zealand; Bio21 Molecular Science and Biotechnology Institute, Department of Biochemistry and Pharmacology, University of Melbourne, Parkville, VIC 3010, Australia
| | - Christopher R Horne
- Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, VIC 3052, Australia; Department of Medical Biology, University of Melbourne, Parkville, VIC 3052, Australia; Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Parkville, VIC 3052, Australia.
| | - Rachel A North
- Department of Biochemistry and Biophysics, Stockholm University, 106 91 Stockholm, Sweden; School of Medical Sciences, Faculty of Medicine and Health, University of Sydney, Sydney, NSW 2006, Australia.
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6
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Peter MF, Ruland JA, Kim Y, Hendricks P, Schneberger N, Siebrasse JP, Thomas GH, Kubitscheck U, Hagelueken G. Conformational coupling of the sialic acid TRAP transporter HiSiaQM with its substrate binding protein HiSiaP. Nat Commun 2024; 15:217. [PMID: 38191530 PMCID: PMC10774421 DOI: 10.1038/s41467-023-44327-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2023] [Accepted: 12/08/2023] [Indexed: 01/10/2024] Open
Abstract
The tripartite ATP-independent periplasmic (TRAP) transporters use an extra cytoplasmic substrate binding protein (SBP) to transport a wide variety of substrates in bacteria and archaea. The SBP can adopt an open- or closed state depending on the presence of substrate. The two transmembrane domains of TRAP transporters form a monomeric elevator whose function is strictly dependent on the presence of a sodium ion gradient. Insights from experimental structures, structural predictions and molecular modeling have suggested a conformational coupling between the membrane elevator and the substrate binding protein. Here, we use a disulfide engineering approach to lock the TRAP transporter HiSiaPQM from Haemophilus influenzae in different conformational states. The SBP, HiSiaP, is locked in its substrate-bound form and the transmembrane elevator, HiSiaQM, is locked in either its assumed inward- or outward-facing states. We characterize the disulfide-locked constructs and use single-molecule total internal reflection fluorescence (TIRF) microscopy to study their interactions. Our experiments demonstrate that the SBP and the transmembrane elevator are indeed conformationally coupled, meaning that the open and closed state of the SBP recognize specific conformational states of the transporter and vice versa.
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Affiliation(s)
- Martin F Peter
- Institute of Structural Biology, University of Bonn, Venusberg-Campus 1, 53127, Bonn, Germany
- Biochemistry Center, Heidelberg University, Im Neuenheimer Feld 328, 69120, Heidelberg, Germany
| | - Jan A Ruland
- Clausius Institute for Physical and Theoretical Chemistry, University of Bonn, Wegelerstr. 12, 53115, Bonn, Germany
| | - Yeojin Kim
- Institute of Structural Biology, University of Bonn, Venusberg-Campus 1, 53127, Bonn, Germany
| | - Philipp Hendricks
- Institute of Structural Biology, University of Bonn, Venusberg-Campus 1, 53127, Bonn, Germany
| | - Niels Schneberger
- Institute of Structural Biology, University of Bonn, Venusberg-Campus 1, 53127, Bonn, Germany
| | - Jan Peter Siebrasse
- Clausius Institute for Physical and Theoretical Chemistry, University of Bonn, Wegelerstr. 12, 53115, Bonn, Germany
| | - Gavin H Thomas
- Department of Biology (Area 10), University of York, York, YO10 5YW, UK
| | - Ulrich Kubitscheck
- Clausius Institute for Physical and Theoretical Chemistry, University of Bonn, Wegelerstr. 12, 53115, Bonn, Germany
| | - Gregor Hagelueken
- Institute of Structural Biology, University of Bonn, Venusberg-Campus 1, 53127, Bonn, Germany.
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7
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Zielewicz LJ, Wang J, Ndaru E, Maney B, Yu X, Albers T, Grewer C. Design and Characterization of Prodrug-like Inhibitors for Preventing Glutamate Efflux through Reverse Transport. ACS Chem Neurosci 2023; 14:4252-4263. [PMID: 37994790 DOI: 10.1021/acschemneuro.3c00651] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2023] Open
Abstract
Glutamate transporters are responsible for active transport of the major excitatory neurotransmitter glutamate across the cell membrane, regulating the extracellular glutamate concentration in the mammalian brain. Extracellular glutamate levels in the brain are usually in the submicromolar range but can increase by exocytosis, inhibition of cellular uptake, or through glutamate release by reverse transport, as well as other mechanisms, which can lead to neurodegeneration and neuronal cell death. Such conditions can be encountered upon energy deprivation during an ischemic stroke. Here, we developed acetoxymethyl (AM) ester prodrug-like derivatives of excitatory amino acid transporter (EAAT) inhibitors that permeate the cell membrane and are activated, most likely through hydrolysis by endogenous cellular esterases, to form the active EAAT inhibitor. Upon increase in external K+ concentration, the inhibitors block glutamate efflux by EAAT reverse transport. Using a novel high-affinity fluorescent prodrug-like inhibitor, dl-threo-9-anthracene-methoxy-aspartate (TAOA) AM ester, we demonstrate that the precursor rapidly accumulates inside cells. Electrophysiological methods and fluorescence assays utilizing the iGluSnFR external glutamate sensor were used to demonstrate the efficacy of AM ester-protected inhibitors in inhibiting K+-mediated glutamate release. Together, our results provide evidence for a novel method to potentially prevent glutamate release by reverse transport under pathophysiological conditions in a model cell system, as well as in human astrocytes, while leaving glutamate uptake under physiological conditions operational. This method could have wide-ranging applications in the prevention of glutamate-induced neuronal cell death.
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Affiliation(s)
- Laura J Zielewicz
- Department of Chemistry, Binghamton University, 4400 Vestal Parkway East, Binghamton, New York 13902, United States
| | - Jiali Wang
- Department of Chemistry, Binghamton University, 4400 Vestal Parkway East, Binghamton, New York 13902, United States
| | - Elias Ndaru
- Department of Chemistry, Binghamton University, 4400 Vestal Parkway East, Binghamton, New York 13902, United States
| | - Brien Maney
- Department of Chemistry, Binghamton University, 4400 Vestal Parkway East, Binghamton, New York 13902, United States
| | - Xiaozhen Yu
- Department of Chemistry, Binghamton University, 4400 Vestal Parkway East, Binghamton, New York 13902, United States
| | - Thomas Albers
- Department of Chemistry, Binghamton University, 4400 Vestal Parkway East, Binghamton, New York 13902, United States
| | - Christof Grewer
- Department of Chemistry, Binghamton University, 4400 Vestal Parkway East, Binghamton, New York 13902, United States
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8
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Boytsov D, Schicker K, Hellsberg E, Freissmuth M, Sandtner W. Allosteric modulators of solute carrier function: a theoretical framework. Front Physiol 2023; 14:1166450. [PMID: 37250134 PMCID: PMC10210158 DOI: 10.3389/fphys.2023.1166450] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2023] [Accepted: 04/24/2023] [Indexed: 05/31/2023] Open
Abstract
Large-scale drug screening is currently the basis for the identification of new chemical entities. This is a rather laborious approach, because a large number of compounds must be tested to cover the chemical space in an unbiased fashion. However, the structures of targetable proteins have become increasingly available. Thus, a new era has arguably been ushered in with the advent of methods, which allow for structure-based docking campaigns (i.e., virtual screens). Solute carriers (SLCs) are among the most promising drug targets. This claim is substantiated by the fact that a large fraction of the 400 solute carrier genes is associated with human diseases. The ability to dock large ligand libraries into selected structures of solute carriers has set the stage for rational drug design. In the present study, we show that these structure-based approaches can be refined by taking into account how solute carriers operate. We specifically address the feasibility of targeting solute carriers with allosteric modulators, because their actions differ fundamentally from those of ligands, which bind to the substrate binding site. For the pertinent analysis we used transition state theory in conjunction with the linear free energy relationship (LFER). These provide the theoretical framework to understand how allosteric modulators affect solute carrier function.
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Affiliation(s)
- D. Boytsov
- Center of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - K. Schicker
- Center of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - E. Hellsberg
- Computational Structural Biology Unit, National Institute of Neurological Disorders and Stroke (NINDS), National Institutes of Health (NIH), Bethesda, MD, United States
| | - M. Freissmuth
- Center of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - W. Sandtner
- Center of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
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9
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Abstract
Excitatory amino acid transporters (EAATs) uptake glutamate into glial cells and neurons. EAATs achieve million-fold transmitter gradients by symporting it with three sodium ions and a proton, and countertransporting a potassium ion via an elevator mechanism. Despite the availability of structures, the symport and antiport mechanisms still need to be clarified. We report high-resolution cryo-EM structures of human EAAT3 bound to the neurotransmitter glutamate with symported ions, potassium ions, sodium ions alone, or without ligands. We show that an evolutionarily conserved occluded translocation intermediate has a dramatically higher affinity for the neurotransmitter and the countertransported potassium ion than outward- or inward-facing transporters and plays a crucial role in ion coupling. We propose a comprehensive ion coupling mechanism involving a choreographed interplay between bound solutes, conformations of conserved amino acid motifs, and movements of the gating hairpin and the substrate-binding domain.
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Affiliation(s)
- Biao Qiu
- Department of Physiology & Biophysics, Weill Cornell Medicine, 1300 York Ave, New York, NY, 10021, USA.
| | - Olga Boudker
- Department of Physiology & Biophysics, Weill Cornell Medicine, 1300 York Ave, New York, NY, 10021, USA.
- Howard Hughes Medical Institute, Weill Cornell Medicine, 1300 York Ave, New York, NY, 10021, USA.
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10
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Huang Y, Reddy KD, Bracken C, Qiu B, Zhan W, Eliezer D, Boudker O. Environmentally Ultrasensitive Fluorine Probe to Resolve Protein Conformational Ensembles by 19F NMR and Cryo-EM. J Am Chem Soc 2023; 145:8583-8592. [PMID: 37023263 PMCID: PMC10119980 DOI: 10.1021/jacs.3c01003] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2023] [Indexed: 04/08/2023]
Abstract
Limited chemical shift dispersion represents a significant barrier to studying multistate equilibria of large membrane proteins by 19F NMR. We describe a novel monofluoroethyl 19F probe that dramatically increases the chemical shift dispersion. The improved conformational sensitivity and line shape enable the detection of previously unresolved states in one-dimensional (1D) 19F NMR spectra of a 134 kDa membrane transporter. Changes in the populations of these states in response to ligand binding, mutations, and temperature correlate with population changes of distinct conformations in structural ensembles determined by single-particle cryo-electron microscopy (cryo-EM). Thus, 19F NMR can guide sample preparation to discover and visualize novel conformational states and facilitate image analysis and three-dimensional (3D) classification.
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Affiliation(s)
- Yun Huang
- Department
of Physiology & Biophysics, Weill Cornell
Medicine, 1300 York Avenue, New York, New York 10021, United States
- Howard
Hughes Medical Institute, Chevy
Chase, Maryland 20815, United States
| | - Krishna D. Reddy
- Department
of Physiology & Biophysics, Weill Cornell
Medicine, 1300 York Avenue, New York, New York 10021, United States
- Howard
Hughes Medical Institute, Chevy
Chase, Maryland 20815, United States
| | - Clay Bracken
- Department
of Biochemistry, Weill Cornell Medicine, 1300 York Avenue, New York, New York 10021, United States
| | - Biao Qiu
- Department
of Physiology & Biophysics, Weill Cornell
Medicine, 1300 York Avenue, New York, New York 10021, United States
| | - Wenhu Zhan
- Department
of Microbiology & Immunology, Weill
Cornell Medicine, 1300 York Avenue, New York, New York 10021, United States
| | - David Eliezer
- Department
of Biochemistry, Weill Cornell Medicine, 1300 York Avenue, New York, New York 10021, United States
| | - Olga Boudker
- Department
of Physiology & Biophysics, Weill Cornell
Medicine, 1300 York Avenue, New York, New York 10021, United States
- Howard
Hughes Medical Institute, Chevy
Chase, Maryland 20815, United States
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11
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Reddy KD, Ciftci D, Scopelliti AJ, Boudker O. The archaeal glutamate transporter homologue GltPh shows heterogeneous substrate binding. J Gen Physiol 2022; 154:213177. [PMID: 35452090 PMCID: PMC9044058 DOI: 10.1085/jgp.202213131] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2022] [Accepted: 03/10/2022] [Indexed: 12/31/2022] Open
Abstract
Integral membrane glutamate transporters couple the concentrative substrate transport to ion gradients. There is a wealth of structural and mechanistic information about this protein family. Recent studies of an archaeal homologue, GltPh, revealed transport rate heterogeneity, which is inconsistent with simple kinetic models; however, its structural and mechanistic determinants remain undefined. Here, we demonstrate that in a mutant GltPh, which exclusively populates the outward-facing state, at least two substates coexist in slow equilibrium, binding the substrate with different apparent affinities. Wild type GltPh shows similar binding properties, and modulation of the substate equilibrium correlates with transport rates. The low-affinity substate of the mutant is transient following substrate binding. Consistently, cryo-EM on samples frozen within seconds after substrate addition reveals the presence of structural classes with perturbed helical packing of the extracellular half of the transport domain in regions adjacent to the binding site. By contrast, an equilibrated structure does not show such classes. The structure at 2.2-Å resolution details a pattern of waters in the intracellular half of the domain and resolves classes with subtle differences in the substrate-binding site. We hypothesize that the rigid cytoplasmic half of the domain mediates substrate and ion recognition and coupling, whereas the extracellular labile half sets the affinity and dynamic properties.
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Affiliation(s)
- Krishna D Reddy
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, NY
| | - Didar Ciftci
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, NY.,Tri-Institutional Training Program in Chemical Biology, New York, NY
| | - Amanda J Scopelliti
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, NY
| | - Olga Boudker
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, NY.,Howard Hughes Medical Institute, Weill Cornell Medicine, New York, NY
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12
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Beckstein O, Naughton F. General principles of secondary active transporter function. Biophys Rev (Melville) 2022; 3:011307. [PMID: 35434715 PMCID: PMC8984959 DOI: 10.1063/5.0047967] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/17/2021] [Accepted: 02/23/2022] [Indexed: 04/13/2023]
Abstract
Transport of ions and small molecules across the cell membrane against electrochemical gradients is catalyzed by integral membrane proteins that use a source of free energy to drive the energetically uphill flux of the transported substrate. Secondary active transporters couple the spontaneous influx of a "driving" ion such as Na+ or H+ to the flux of the substrate. The thermodynamics of such cyclical non-equilibrium systems are well understood, and recent work has focused on the molecular mechanism of secondary active transport. The fact that these transporters change their conformation between an inward-facing and outward-facing conformation in a cyclical fashion, called the alternating access model, is broadly recognized as the molecular framework in which to describe transporter function. However, only with the advent of high resolution crystal structures and detailed computer simulations, it has become possible to recognize common molecular-level principles between disparate transporter families. Inverted repeat symmetry in secondary active transporters has shed light onto how protein structures can encode a bi-stable two-state system. Based on structural data, three broad classes of alternating access transitions have been described as rocker-switch, rocking-bundle, and elevator mechanisms. More detailed analysis indicates that transporters can be understood as gated pores with at least two coupled gates. These gates are not just a convenient cartoon element to illustrate a putative mechanism but map to distinct parts of the transporter protein. Enumerating all distinct gate states naturally includes occluded states in the alternating access picture and also suggests what kind of protein conformations might be observable. By connecting the possible conformational states and ion/substrate bound states in a kinetic model, a unified picture emerges in which the symporter, antiporter, and uniporter functions are extremes in a continuum of functionality. As usual with biological systems, few principles and rules are absolute and exceptions are discussed as well as how biological complexity may be integrated in quantitative kinetic models that may provide a bridge from the structure to function.
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Affiliation(s)
- Oliver Beckstein
- Department of Physics, Arizona State University, Tempe, Arizona 85287, USA
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13
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Ciftci D, Martens C, Ghani VG, Blanchard SC, Politis A, Huysmans GHM, Boudker O. Linking function to global and local dynamics in an elevator-type transporter. Proc Natl Acad Sci U S A 2021; 118:e2025520118. [PMID: 34873050 PMCID: PMC8670510 DOI: 10.1073/pnas.2025520118] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/21/2021] [Indexed: 11/24/2022] Open
Abstract
Transporters cycle through large structural changes to translocate molecules across biological membranes. The temporal relationships between these changes and function, and the molecular properties setting their rates, determine transport efficiency-yet remain mostly unknown. Using single-molecule fluorescence microscopy, we compare the timing of conformational transitions and substrate uptake in the elevator-type transporter GltPh We show that the elevator-like movements of the substrate-loaded transport domain across membranes and substrate release are kinetically heterogeneous, with rates varying by orders of magnitude between individual molecules. Mutations increasing the frequency of elevator transitions and reducing substrate affinity diminish transport rate heterogeneities and boost transport efficiency. Hydrogen deuterium exchange coupled to mass spectrometry reveals destabilization of secondary structure around the substrate-binding site, suggesting that increased local dynamics leads to faster rates of global conformational changes and confers gain-of-function properties that set transport rates.
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Affiliation(s)
- Didar Ciftci
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, NY 10065
- Tri-Institutional Training Program in Chemical Biology, New York, NY 10065
| | - Chloe Martens
- Department of Chemistry, King's College London, London SE1 1DB, United Kingdom
| | - Vishnu G Ghani
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, NY 10065
| | - Scott C Blanchard
- Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN 38105
| | - Argyris Politis
- Department of Chemistry, King's College London, London SE1 1DB, United Kingdom
| | - Gerard H M Huysmans
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, NY 10065;
| | - Olga Boudker
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, NY 10065;
- Tri-Institutional Training Program in Chemical Biology, New York, NY 10065
- Howard Hughes Medical Institute, Weill Cornell Medicine, New York, NY 10065
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14
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Abstract
Uncovering the structure and function of biomolecules is a fundamental goal in structural biology. Membrane-embedded transport proteins are ubiquitous in all kingdoms of life. Despite structural flexibility, their mechanisms are typically studied by ensemble biochemical methods or by static high-resolution structures, which complicate a detailed understanding of their dynamics. Here, we review the recent progress of single molecule Förster Resonance Energy Transfer (smFRET) in determining mechanisms and timescales of substrate transport across membranes. These studies do not only demonstrate the versatility and suitability of state-of-the-art smFRET tools for studying membrane transport proteins but they also highlight the importance of membrane mimicking environments in preserving the function of these proteins. The current achievements advance our understanding of transport mechanisms and have the potential to facilitate future progress in drug design.
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Affiliation(s)
- Kim Bartels
- Centre for Structural Systems Biology (CSSB)DESY and European Molecular Biology Laboratory HamburgNotkestrasse 8522607HamburgGermany
| | - Tanya Lasitza‐Male
- Department of Structural BiologyWeizmann Institute of ScienceHerzl St. 2347610001RehovotIsrael
| | - Hagen Hofmann
- Department of Structural BiologyWeizmann Institute of ScienceHerzl St. 2347610001RehovotIsrael
| | - Christian Löw
- Centre for Structural Systems Biology (CSSB)DESY and European Molecular Biology Laboratory HamburgNotkestrasse 8522607HamburgGermany
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15
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Abstract
Elevator-type transporters are a group of proteins translocating nutrients and metabolites across cell membranes. Despite structural and functional differences, elevator-type transporters use a common mechanism of substrate translocation via reversible movements of a mobile core domain (the elevator), which includes the substrate binding site, along a rigid scaffold domain, stably anchored in the plasma membrane. How substrate specificity is determined in elevator transporters remains elusive. Here, I discuss how a recent report on the sliding elevator mechanism, seen under the context of genetic analysis of a prototype fungal transporter, sheds light on how specificity might be genetically modified. I propose that flexible specificity alterations might occur by 'loosening' of the sliding mechanism from tight coupling to substrate binding.
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Affiliation(s)
- George Diallinas
- Department of Biology, National and Kapodistrian University of Athens, Panepistimioupolis, 15784, Athens, Greece; Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology, Heraklion, Greece.
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Schmidt SG, Gether U, Loland CJ. Elucidating the Mechanism Behind Sodium-Coupled Neurotransmitter Transporters by Reconstitution. Neurochem Res 2021. [PMID: 34347265 DOI: 10.1007/s11064-021-03413-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2021] [Revised: 07/01/2021] [Accepted: 07/27/2021] [Indexed: 10/20/2022]
Abstract
Sodium-coupled neurotransmitter transporters play a fundamental role in the termination of synaptic neurotransmission, which makes them a major drug target. The reconstitution of these secondary active transporters into liposomes has shed light on their molecular transport mechanisms. From the earliest days of the reconstitution technique up to today's single-molecule studies, insights from live functioning transporters have been indispensable for our understanding of their physiological impact. The two classes of sodium-coupled neurotransmitter transporters, the neurotransmitter: sodium symporters and the excitatory amino acid transporters, have vastly different molecular structures, but complementary proteoliposome studies have sought to unravel their ion-dependence and transport kinetics. Furthermore, reconstitution experiments have been used on both protein classes to investigate the role of e.g. the lipid environment, of posttranslational modifications, and of specific amino acid residues in transport. Techniques that allow the detection of transport at a single-vesicle resolution have been developed, and single-molecule studies have started to reveal single transporter kinetics, which will expand our understanding of how transport across the membrane is facilitated at protein level. Here, we review a selection of the results and applications where the reconstitution of the two classes of neurotransmitter transporters has been instrumental.
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Wang X, Boudker O. Large domain movements through the lipid bilayer mediate substrate release and inhibition of glutamate transporters. eLife 2020; 9:58417. [PMID: 33155546 PMCID: PMC7682989 DOI: 10.7554/elife.58417] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2020] [Accepted: 11/05/2020] [Indexed: 01/21/2023] Open
Abstract
Glutamate transporters are essential players in glutamatergic neurotransmission in the brain, where they maintain extracellular glutamate below cytotoxic levels and allow for rounds of transmission. The structural bases of their function are well established, particularly within a model archaeal homolog, sodium, and aspartate symporter GltPh. However, the mechanism of gating on the cytoplasmic side of the membrane remains ambiguous. We report Cryo-EM structures of GltPh reconstituted into nanodiscs, including those structurally constrained in the cytoplasm-facing state and either apo, bound to sodium ions only, substrate, or blockers. The structures show that both substrate translocation and release involve movements of the bulky transport domain through the lipid bilayer. They further reveal a novel mode of inhibitor binding and show how solutes release is coupled to protein conformational changes. Finally, we describe how domain movements are associated with the displacement of bound lipids and significant membrane deformations, highlighting the potential regulatory role of the bilayer.
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Affiliation(s)
- Xiaoyu Wang
- Department of Physiology and Biophysics, Weill Cornell MedicineNew YorkUnited States
| | - Olga Boudker
- Department of Physiology and Biophysics, Weill Cornell MedicineNew YorkUnited States,Howard Hughes Medical InstituteChevy ChaseUnited States
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