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Rasmussen DM, Semonis MM, Greene JT, Muretta JM, Thompson AR, Ramos ST, Thomas DD, Pomerantz WCK, Freedman TS, Levinson NM. Allosteric coupling asymmetry mediates paradoxical activation of BRAF by type II inhibitors. bioRxiv 2023:2023.04.18.536450. [PMID: 37131649 PMCID: PMC10153139 DOI: 10.1101/2023.04.18.536450] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
The type II class of RAF inhibitors currently in clinical trials paradoxically activate BRAF at subsaturating concentrations. Activation is mediated by induction of BRAF dimers, but why activation rather than inhibition occurs remains unclear. Using biophysical methods tracking BRAF dimerization and conformation we built an allosteric model of inhibitor-induced dimerization that resolves the allosteric contributions of inhibitor binding to the two active sites of the dimer, revealing key differences between type I and type II RAF inhibitors. For type II inhibitors the allosteric coupling between inhibitor binding and BRAF dimerization is distributed asymmetrically across the two dimer binding sites, with binding to the first site dominating the allostery. This asymmetry results in efficient and selective induction of dimers with one inhibited and one catalytically active subunit. Our allosteric models quantitatively account for paradoxical activation data measured for 11 RAF inhibitors. Unlike type II inhibitors, type I inhibitors lack allosteric asymmetry and do not activate BRAF homodimers. Finally, NMR data reveal that BRAF homodimers are dynamically asymmetric with only one of the subunits locked in the active αC-in state. This provides a structural mechanism for how binding of only a single αC-in inhibitor molecule can induce potent BRAF dimerization and activation.
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2
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Chen D, Wirth KM, Kizy S, Muretta JM, Markowski TW, Yong P, Sheka A, Abdelwahab H, Hertzel AV, Ikramuddin S, Yamamoto M, Bernlohr DA. Desmoglein 2 Functions as a Receptor for Fatty Acid Binding Protein 4 in Breast Cancer Epithelial Cells. Mol Cancer Res 2023; 21:836-848. [PMID: 37115197 PMCID: PMC10524127 DOI: 10.1158/1541-7786.mcr-22-0763] [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] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2022] [Revised: 01/19/2023] [Accepted: 04/26/2023] [Indexed: 04/29/2023]
Abstract
Fatty acid binding protein 4 (FABP4) is a secreted adipokine linked to obesity and progression of a variety of cancers. Obesity increases extracellular FABP4 (eFABP4) levels in animal models and in obese breast cancer patients compared with lean healthy controls. Using MCF-7 and T47D breast cancer epithelial cells, we show herein that eFABP4 stimulates cellular proliferation in a time and concentration dependent manner while the non-fatty acid-binding mutant, R126Q, failed to potentiate growth. When E0771 murine breast cancer cells were injected into mice, FABP4 null animals exhibited delayed tumor growth and enhanced survival compared with injections into control C57Bl/6J animals. eFABP4 treatment of MCF-7 cells resulted in a significant increase in phosphorylation of extracellular signal-regulated kinase 1/2 (pERK), transcriptional activation of nuclear factor E2-related factor 2 (NRF2) and corresponding gene targets ALDH1A1, CYP1A1, HMOX1, SOD1 and decreased oxidative stress, while R126Q treatment did not show any effects. Proximity-labeling employing an APEX2-FABP4 fusion protein revealed several proteins functioning in desmosomes as eFABP4 receptor candidates including desmoglein (DSG), desmocollin, junction plankoglobin, desomoplankin, and cytokeratins. AlphaFold modeling predicted an interaction between eFABP4, and the extracellular cadherin repeats of DSG2 and pull-down and immunoprecipitation assays confirmed complex formation that was potentiated by oleic acid. Silencing of DSG2 in MCF-7 cells attenuated eFABP4 effects on cellular proliferation, pERK levels, and ALDH1A1 expression compared with controls. IMPLICATIONS These results suggest desmosomal proteins, and in particular desmoglein 2, may function as receptors of eFABP4 and provide new insight into the development and progression of obesity-associated cancers.
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Affiliation(s)
- Dongmei Chen
- Department of Biochemistry, Molecular Biology and Biophysics, The University of Minnesota-Twin Cities, Minneapolis, MN USA
| | - Keith M. Wirth
- Department of Surgery, The University of Minnesota-Twin Cities, Minneapolis, MN USA
| | - Scott Kizy
- Department of Surgery, The University of Minnesota-Twin Cities, Minneapolis, MN USA
| | - Joseph M. Muretta
- Department of Biochemistry, Molecular Biology and Biophysics, The University of Minnesota-Twin Cities, Minneapolis, MN USA
| | - Todd W Markowski
- Department of Biochemistry, Molecular Biology and Biophysics, The University of Minnesota-Twin Cities, Minneapolis, MN USA
| | - Peter Yong
- Department of Biochemistry, Molecular Biology and Biophysics, The University of Minnesota-Twin Cities, Minneapolis, MN USA
| | - Adam Sheka
- Department of Surgery, The University of Minnesota-Twin Cities, Minneapolis, MN USA
| | - Hisham Abdelwahab
- Department of Surgery, The University of Minnesota-Twin Cities, Minneapolis, MN USA
| | - Ann V. Hertzel
- Department of Biochemistry, Molecular Biology and Biophysics, The University of Minnesota-Twin Cities, Minneapolis, MN USA
| | - Sayeed Ikramuddin
- Department of Surgery, The University of Minnesota-Twin Cities, Minneapolis, MN USA
| | - Masato Yamamoto
- Department of Surgery, The University of Minnesota-Twin Cities, Minneapolis, MN USA
- Department of Masonic Cancer Center, The University of Minnesota-Twin Cities, Minneapolis, MN USA
| | - David A Bernlohr
- Department of Biochemistry, Molecular Biology and Biophysics, The University of Minnesota-Twin Cities, Minneapolis, MN USA
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3
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Muretta JM, Rajasekaran D, Blat Y, Little S, Myers M, Nair C, Burdekin B, Yuen SL, Jimenez N, Guhathakurta P, Wilson A, Thompson AR, Surti N, Connors D, Chase P, Harden D, Barbieri CM, Adam L, Thomas DD. HTS driven by fluorescence lifetime detection of FRET identifies activators and inhibitors of cardiac myosin. SLAS Discov 2023; 28:223-232. [PMID: 37307989 PMCID: PMC10422832 DOI: 10.1016/j.slasd.2023.06.001] [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] [Subscribe] [Scholar Register] [Received: 11/03/2022] [Revised: 05/08/2023] [Accepted: 06/07/2023] [Indexed: 06/14/2023]
Abstract
Small molecules that bind to allosteric sites on target proteins to alter protein function are highly sought in drug discovery. High-throughput screening (HTS) assays are needed to facilitate the direct discovery of allosterically active compounds. We have developed technology for high-throughput time-resolved fluorescence lifetime detection of fluorescence resonance energy transfer (FRET), which enables the detection of allosteric modulators by monitoring changes in protein structure. We tested this approach at the industrial scale by adapting an allosteric FRET sensor of cardiac myosin to high-throughput screening (HTS), based on technology provided by Photonic Pharma and the University of Minnesota, and then used the sensor to screen 1.6 million compounds in the HTS facility at Bristol Myers Squibb. The results identified allosteric activators and inhibitors of cardiac myosin that do not compete with ATP binding, demonstrating high potential for FLT-based drug discovery.
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Affiliation(s)
- J M Muretta
- Photonic Pharma LLC and University of Minnesota, Minneapolis, MN, United States of America.
| | - D Rajasekaran
- Bristol Myers Squibb, Princeton, NJ, United States of America
| | - Y Blat
- Bristol Myers Squibb, Princeton, NJ, United States of America
| | - S Little
- Bristol Myers Squibb, Princeton, NJ, United States of America
| | - M Myers
- Bristol Myers Squibb, Princeton, NJ, United States of America
| | - C Nair
- Photonic Pharma LLC and University of Minnesota, Minneapolis, MN, United States of America
| | - B Burdekin
- Photonic Pharma LLC and University of Minnesota, Minneapolis, MN, United States of America
| | - S L Yuen
- Photonic Pharma LLC and University of Minnesota, Minneapolis, MN, United States of America
| | - N Jimenez
- Photonic Pharma LLC and University of Minnesota, Minneapolis, MN, United States of America
| | - P Guhathakurta
- Photonic Pharma LLC and University of Minnesota, Minneapolis, MN, United States of America
| | - A Wilson
- Photonic Pharma LLC and University of Minnesota, Minneapolis, MN, United States of America
| | - A R Thompson
- Photonic Pharma LLC and University of Minnesota, Minneapolis, MN, United States of America
| | - N Surti
- Bristol Myers Squibb, Princeton, NJ, United States of America
| | - D Connors
- Bristol Myers Squibb, Princeton, NJ, United States of America
| | - P Chase
- Bristol Myers Squibb, Princeton, NJ, United States of America
| | - D Harden
- Bristol Myers Squibb, Princeton, NJ, United States of America
| | - C M Barbieri
- Bristol Myers Squibb, Princeton, NJ, United States of America
| | - L Adam
- Bristol Myers Squibb, Princeton, NJ, United States of America
| | - D D Thomas
- Photonic Pharma LLC and University of Minnesota, Minneapolis, MN, United States of America.
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4
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Ramirez MP, Rajaganapathy S, Hagerty AR, Hua C, Baxter GC, Vavra J, Gordon WR, Muretta JM, Salapaka MV, Ervasti JM. Phosphorylation alters the mechanical stiffness of a model fragment of the dystrophin homologue utrophin. J Biol Chem 2023; 299:102847. [PMID: 36587764 PMCID: PMC9922815 DOI: 10.1016/j.jbc.2022.102847] [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] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2022] [Revised: 12/16/2022] [Accepted: 12/18/2022] [Indexed: 12/30/2022] Open
Abstract
Duchenne muscular dystrophy is a lethal muscle wasting disease caused by the absence of the protein dystrophin. Utrophin is a dystrophin homologue currently under investigation as a protein replacement therapy for Duchenne muscular dystrophy. Dystrophin is hypothesized to function as a molecular shock absorber that mechanically stabilizes the sarcolemma. While utrophin is homologous with dystrophin from a molecular and biochemical perspective, we have recently shown that full-length utrophin expressed in eukaryotic cells is stiffer than what has been reported for dystrophin fragments expressed in bacteria. In this study, we show that differences in expression system impact the mechanical stiffness of a model utrophin fragment encoding the N terminus through spectrin repeat 3 (UtrN-R3). We also demonstrate that UtrN-R3 expressed in eukaryotic cells was phosphorylated while bacterial UtrN-R3 was not detectably phosphorylated. Using atomic force microscopy, we show that phosphorylated UtrN-R3 exhibited significantly higher unfolding forces compared to unphosphorylated UtrN-R3 without altering its actin-binding activity. Consistent with the effect of phosphorylation on mechanical stiffness, mutating the phosphorylated serine residues on insect eukaryotic protein to alanine decreased its stiffness to levels not different from unphosphorylated bacterial protein. Taken together, our data suggest that the mechanical properties of utrophin may be tuned by phosphorylation, with the potential to improve its efficacy as a protein replacement therapy for dystrophinopathies.
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Affiliation(s)
- Maria Paz Ramirez
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota - Twin Cities, Minneapolis, MN, USA
| | - Sivaraman Rajaganapathy
- Department of Electrical and Computer Engineering, University of Minnesota - Twin Cities, Minneapolis, MN, USA
| | - Anthony R Hagerty
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota - Twin Cities, Minneapolis, MN, USA
| | - Cailong Hua
- Department of Electrical and Computer Engineering, University of Minnesota - Twin Cities, Minneapolis, MN, USA
| | - Gloria C Baxter
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota - Twin Cities, Minneapolis, MN, USA
| | - Joseph Vavra
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota - Twin Cities, Minneapolis, MN, USA
| | - Wendy R Gordon
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota - Twin Cities, Minneapolis, MN, USA
| | - Joseph M Muretta
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota - Twin Cities, Minneapolis, MN, USA
| | - Murti V Salapaka
- Department of Electrical and Computer Engineering, University of Minnesota - Twin Cities, Minneapolis, MN, USA
| | - James M Ervasti
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota - Twin Cities, Minneapolis, MN, USA.
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5
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Guhathakurta P, Carter AL, Thompson AR, Kurila D, LaFrence J, Zhang L, Trask JR, Vanderheyden B, Muretta JM, Ervasti JM, Thomas DD. Enhancing interaction of actin and actin-binding domain 1 of dystrophin with modulators: Toward improved gene therapy for Duchenne muscular dystrophy. J Biol Chem 2022; 298:102675. [PMID: 36372234 PMCID: PMC9731851 DOI: 10.1016/j.jbc.2022.102675] [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] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2022] [Revised: 10/27/2022] [Accepted: 10/31/2022] [Indexed: 11/13/2022] Open
Abstract
Duchenne muscular dystrophy is a lethal muscle disease, caused by mutations in the gene encoding dystrophin, an actin-binding cytoskeletal protein. Absence of functional dystrophin results in muscle weakness and degeneration, eventually leading to cardiac and respiratory failure. Strategies to replace the missing dystrophin via gene therapy have been intensively pursued. However, the dystrophin gene is too large for current gene therapy approaches. Currently available micro-dystrophin constructs lack the actin-binding domain 2 and show decreased actin-binding affinity in vitro compared to full-length dystrophin. Thus, increasing the actin-binding affinity of micro-dystrophin, using small molecules, could be a beneficial therapeutic approach. Here, we have developed and validated a novel high-throughput screening (HTS) assay to discover small molecules that increase the binding affinity of dystrophin's actin-binding domain 1 (ABD1). We engineered a novel FRET biosensor, consisting of the mClover3, fluorescent protein (donor) attached to the C-terminus of dystrophin ABD1, and Alexa Fluor 568 (acceptor) attached to the C-terminal cysteine of actin. We used this biosensor in small-molecule screening, using a unique high-precision, HTS fluorescence lifetime assay, identifying several compounds from an FDA-approved library that significantly increase the binding between actin and ABD1. This HTS assay establishes feasibility for the discovery of small-molecule modulators of the actin-dystrophin interaction, with the ultimate goal of developing therapies for muscular dystrophy.
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6
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Chu S, Muretta JM, Thomas DD. Direct detection of the myosin super-relaxed state and interacting-heads motif in solution. J Biol Chem 2021; 297:101157. [PMID: 34481842 PMCID: PMC8479475 DOI: 10.1016/j.jbc.2021.101157] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [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: 07/02/2021] [Revised: 08/31/2021] [Accepted: 08/31/2021] [Indexed: 11/30/2022] Open
Abstract
The interacting-heads motif (IHM) is a structure of myosin that has been proposed to modulate cardiac output by occluding myosin molecules from undergoing the force-generating cycle. It is hypothesized to be the structural basis for the super-relaxed state (SRX), a low-ATPase kinetic state thought to be cardioprotective. The goal of the present study was to test this hypothesis by determining directly and quantitatively the fractions of myosin in the IHM and SRX under the same conditions in solution. To detect the structural IHM, we used time-resolved fluorescence resonance energy transfer to quantitate two distinct populations. One population was observed at a center distance of 2.0 nm, whereas the other was not detectable by fluorescence resonance energy transfer, implying a distance greater than 4 nm. We confirmed the IHM assignment to the 2.0-nm population by applying the same cross-linking protocol used previously to image the IHM by electron microscopy. Under the same conditions, we also measured the fraction of myosin in the SRX using stopped-flow kinetics. Our results show that the populations of SRX and IHM myosin were similar, unless treated with mavacamten, a drug that recently completed phase III clinical trials to treat hypertrophic cardiomyopathy and is proposed to act by stabilizing both the SRX and IHM. However, we found that mavacamten had a much greater effect on the SRX (55% increase) than on the IHM (4% increase). We conclude that the IHM structure is sufficient but not necessary to produce the SRX kinetic state.
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Affiliation(s)
- Sami Chu
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota, USA
| | - Joseph M Muretta
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota, USA
| | - David D Thomas
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota, USA.
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7
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Muretta JM. The Myosin SRX Comes into Focus. Biophys J 2020; 119:1041-1042. [PMID: 32853563 DOI: 10.1016/j.bpj.2020.08.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2020] [Revised: 08/05/2020] [Accepted: 08/10/2020] [Indexed: 11/29/2022] Open
Affiliation(s)
- Joseph M Muretta
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota.
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8
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Olivieri C, Wang Y, Li GC, V S M, Kim J, Stultz BR, Neibergall M, Porcelli F, Muretta JM, Thomas DDT, Gao J, Blumenthal DK, Taylor SS, Veglia G. Multi-state recognition pathway of the intrinsically disordered protein kinase inhibitor by protein kinase A. eLife 2020; 9:e55607. [PMID: 32338601 PMCID: PMC7234811 DOI: 10.7554/elife.55607] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [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] [Received: 01/30/2020] [Accepted: 04/27/2020] [Indexed: 12/17/2022] Open
Abstract
In the nucleus, the spatiotemporal regulation of the catalytic subunit of cAMP-dependent protein kinase A (PKA-C) is orchestrated by an intrinsically disordered protein kinase inhibitor, PKI, which recruits the CRM1/RanGTP nuclear exporting complex. How the PKA-C/PKI complex assembles and recognizes CRM1/RanGTP is not well understood. Using NMR, SAXS, fluorescence, metadynamics, and Markov model analysis, we determined the multi-state recognition pathway for PKI. After a fast binding step in which PKA-C selects PKI's most competent conformations, PKI folds upon binding through a slow conformational rearrangement within the enzyme's binding pocket. The high-affinity and pseudo-substrate regions of PKI become more structured and the transient interactions with the kinase augment the helical content of the nuclear export sequence, which is then poised to recruit the CRM1/RanGTP complex for nuclear translocation. The multistate binding mechanism featured by PKA-C/PKI complex represents a paradigm on how disordered, ancillary proteins (or protein domains) are able to operate multiple functions such as inhibiting the kinase while recruiting other regulatory proteins for nuclear export.
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Affiliation(s)
- Cristina Olivieri
- Department of Biochemistry, Molecular Biology, and Biophysics, University of MinnesotaMinneapolisUnited States
| | - Yingjie Wang
- Department of Chemistry and Supercomputing Institute, University of MinnesotaMinneapolisUnited States
- Shenzhen Bay LaboratoryShenzhenChina
| | - Geoffrey C Li
- Department of Chemistry and Supercomputing Institute, University of MinnesotaMinneapolisUnited States
| | - Manu V S
- Department of Biochemistry, Molecular Biology, and Biophysics, University of MinnesotaMinneapolisUnited States
| | - Jonggul Kim
- Department of Chemistry and Supercomputing Institute, University of MinnesotaMinneapolisUnited States
| | | | | | | | - Joseph M Muretta
- Department of Biochemistry, Molecular Biology, and Biophysics, University of MinnesotaMinneapolisUnited States
| | - David DT Thomas
- Department of Biochemistry, Molecular Biology, and Biophysics, University of MinnesotaMinneapolisUnited States
| | - Jiali Gao
- Department of Chemistry and Supercomputing Institute, University of MinnesotaMinneapolisUnited States
- Laboratory of Computational Chemistry and Drug Design, Peking University Shenzhen Graduate SchoolShenzhenChina
| | - Donald K Blumenthal
- Department of Pharmacology and Toxicology, University of UtahSalt Lake CityUnited States
| | - Susan S Taylor
- Department of Chemistry and Biochemistry and Pharmacology, University of California, San DiegoLa JollaUnited States
| | - Gianluigi Veglia
- Department of Biochemistry, Molecular Biology, and Biophysics, University of MinnesotaMinneapolisUnited States
- Department of Chemistry and Supercomputing Institute, University of MinnesotaMinneapolisUnited States
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9
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Byrapuneni S, Chu S, Muretta JM, Thomas DD. Impact of Hypertrophic Cardiomyopathy Mutations on the Cardiac Myosin Super-Relaxed State. Biophys J 2019. [DOI: 10.1016/j.bpj.2018.11.663] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
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10
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Gunther LK, Rohde JA, Tang W, Walton SD, Unrath WC, Trivedi DV, Muretta JM, Thomas DD, Yengo CM. Converter domain mutations in myosin alter structural kinetics and motor function. J Biol Chem 2018; 294:1554-1567. [PMID: 30518549 DOI: 10.1074/jbc.ra118.006128] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2018] [Revised: 11/26/2018] [Indexed: 12/20/2022] Open
Abstract
Myosins are molecular motors that use a conserved ATPase cycle to generate force. We investigated two mutations in the converter domain of myosin V (R712G and F750L) to examine how altering specific structural transitions in the motor ATPase cycle can impair myosin mechanochemistry. The corresponding mutations in the human β-cardiac myosin gene are associated with hypertrophic and dilated cardiomyopathy, respectively. Despite similar steady-state actin-activated ATPase and unloaded in vitro motility-sliding velocities, both R712G and F750L were less able to overcome frictional loads measured in the loaded motility assay. Transient kinetic analysis and stopped-flow FRET demonstrated that the R712G mutation slowed the maximum ATP hydrolysis and recovery-stroke rate constants, whereas the F750L mutation enhanced these steps. In both mutants, the fast and slow power-stroke as well as actin-activated phosphate release rate constants were not significantly different from WT. Time-resolved FRET experiments revealed that R712G and F750L populate the pre- and post-power-stroke states with similar FRET distance and distance distribution profiles. The R712G mutant increased the mole fraction in the post-power-stroke conformation in the strong actin-binding states, whereas the F750L decreased this population in the actomyosin ADP state. We conclude that mutations in key allosteric pathways can shift the equilibrium and/or alter the activation energy associated with key structural transitions without altering the overall conformation of the pre- and post-power-stroke states. Thus, therapies designed to alter the transition between structural states may be able to rescue the impaired motor function induced by disease mutations.
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Affiliation(s)
- Laura K Gunther
- Department of Cellular and Molecular Physiology, College of Medicine, Pennsylvania State University, Hershey, Pennsylvania 17033
| | - John A Rohde
- Department of Biochemistry, Biophysics and Molecular Biology, University of Minnesota, Minneapolis, Minnesota 55455
| | - Wanjian Tang
- Department of Cellular and Molecular Physiology, College of Medicine, Pennsylvania State University, Hershey, Pennsylvania 17033
| | - Shane D Walton
- Department of Cellular and Molecular Physiology, College of Medicine, Pennsylvania State University, Hershey, Pennsylvania 17033
| | - William C Unrath
- Department of Cellular and Molecular Physiology, College of Medicine, Pennsylvania State University, Hershey, Pennsylvania 17033
| | - Darshan V Trivedi
- Department of Cellular and Molecular Physiology, College of Medicine, Pennsylvania State University, Hershey, Pennsylvania 17033
| | - Joseph M Muretta
- Department of Biochemistry, Biophysics and Molecular Biology, University of Minnesota, Minneapolis, Minnesota 55455
| | - David D Thomas
- Department of Biochemistry, Biophysics and Molecular Biology, University of Minnesota, Minneapolis, Minnesota 55455
| | - Christopher M Yengo
- Department of Cellular and Molecular Physiology, College of Medicine, Pennsylvania State University, Hershey, Pennsylvania 17033.
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11
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Abstract
We used transient biochemical and structural kinetics to elucidate the molecular mechanism of mavacamten, an allosteric cardiac myosin inhibitor and a prospective treatment for hypertrophic cardiomyopathy. We find that mavacamten stabilizes an autoinhibited state of two-headed cardiac myosin not found in the single-headed S1 myosin motor fragment. We determined this by measuring cardiac myosin actin-activated and actin-independent ATPase and single-ATP turnover kinetics. A two-headed myosin fragment exhibits distinct autoinhibited ATP turnover kinetics compared with a single-headed fragment. Mavacamten enhanced this autoinhibition. It also enhanced autoinhibition of ADP release. Furthermore, actin changes the structure of the autoinhibited state by forcing myosin lever-arm rotation. Mavacamten slows this rotation in two-headed myosin but does not prevent it. We conclude that cardiac myosin is regulated in solution by an interaction between its two heads and propose that mavacamten stabilizes this state.
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Affiliation(s)
- John A Rohde
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN 55455
| | - Osha Roopnarine
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN 55455
| | - David D Thomas
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN 55455
| | - Joseph M Muretta
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN 55455
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12
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Ruff EF, Muretta JM, Thompson AR, Lake EW, Cyphers S, Albanese SK, Hanson SM, Behr JM, Thomas DD, Chodera JD, Levinson NM. A dynamic mechanism for allosteric activation of Aurora kinase A by activation loop phosphorylation. eLife 2018; 7:32766. [PMID: 29465396 PMCID: PMC5849412 DOI: 10.7554/elife.32766] [Citation(s) in RCA: 48] [Impact Index Per Article: 8.0] [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: 10/13/2017] [Accepted: 02/19/2018] [Indexed: 12/12/2022] Open
Abstract
Many eukaryotic protein kinases are activated by phosphorylation on a specific conserved residue in the regulatory activation loop, a post-translational modification thought to stabilize the active DFG-In state of the catalytic domain. Here we use a battery of spectroscopic methods that track different catalytic elements of the kinase domain to show that the ~100 fold activation of the mitotic kinase Aurora A (AurA) by phosphorylation occurs without a population shift from the DFG-Out to the DFG-In state, and that the activation loop of the activated kinase remains highly dynamic. Instead, molecular dynamics simulations and electron paramagnetic resonance experiments show that phosphorylation triggers a switch within the DFG-In subpopulation from an autoinhibited DFG-In substate to an active DFG-In substate, leading to catalytic activation. This mechanism raises new questions about the functional role of the DFG-Out state in protein kinases. The transfer of phosphate groups onto proteins (protein phosphorylation) is one of the most important methods used to send signals inside cells. The enzymes that catalyze this process, called protein kinases, are themselves controlled by the phosphorylation of a flexible region called the activation loop. For many years it had been thought that the purpose of activation loop phosphorylation was to clamp the otherwise flexible activation loop in an active state that allows molecules that need to be phosphorylated to bind to the kinase. This assumption was based on static pictures of protein kinases obtained by X-ray crystallography, in which individual states are trapped and visualized in a crystal lattice. However, new methods and approaches now mean it is possible to visualize how the position of the activation loop changes as it moves in solution. By applying these techniques, Ruff et al. show that the static model is incorrect in a protein kinase called Aurora A. In this enzyme, the phosphorylated activation loop continues to switch back and forth between active and inactive states. Phosphorylation instead enhances the catalytic activity of the active state. Aurora A regulates several important steps in cell division, and plays important roles in several kinds of cancer. The discovery that activated forms of Aurora A can have different dynamic properties raises the possibility that inhibitor molecules could be designed to exploit these differences and block specific activities of Aurora A in cancer cells. To realize this goal we need to better understand how a kinase switching between active and inactive states affects the ability of inhibitors to interact with it.
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Affiliation(s)
- Emily F Ruff
- Department of Pharmacology, University of Minnesota, Minneapolis, United States
| | - Joseph M Muretta
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, United States
| | - Andrew R Thompson
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, United States
| | - Eric W Lake
- Department of Pharmacology, University of Minnesota, Minneapolis, United States
| | - Soreen Cyphers
- Department of Pharmacology, University of Minnesota, Minneapolis, United States
| | - Steven K Albanese
- Computational and Systems Biology Program, Sloan Kettering Institute, Memorial Sloan Kettering Cancer Center, New York, United States.,Gerstner Sloan Kettering Graduate School, Memorial Sloan Kettering Cancer Center, New York, United States
| | - Sonya M Hanson
- Computational and Systems Biology Program, Sloan Kettering Institute, Memorial Sloan Kettering Cancer Center, New York, United States
| | - Julie M Behr
- Computational and Systems Biology Program, Sloan Kettering Institute, Memorial Sloan Kettering Cancer Center, New York, United States.,Tri-Institutional Program in Computational Biology and Medicine, Weill Cornell Medical College, New York, United States
| | - David D Thomas
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, United States
| | - John D Chodera
- Computational and Systems Biology Program, Sloan Kettering Institute, Memorial Sloan Kettering Cancer Center, New York, United States
| | - Nicholas M Levinson
- Department of Pharmacology, University of Minnesota, Minneapolis, United States
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Rohde JA, Phung L, Thomas DD, Muretta JM. Detection of the Super-Relaxed State in Cardiac Heavy Meromyosin. Biophys J 2018. [DOI: 10.1016/j.bpj.2017.11.784] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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14
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Chu S, Phung LA, Muretta JM, Thomas DD. Time-Resolved FRET Detection of the Myosin Super-Relaxed off State in Cardiac Thick Filament. Biophys J 2018. [DOI: 10.1016/j.bpj.2017.11.2746] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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15
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Rohde J, Thomas DD, Muretta JM. Cardiac Myosin Strutural Kinetics are Modulated by Myk461. Biophys J 2018. [DOI: 10.1016/j.bpj.2017.11.2738] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022] Open
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16
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Atherton J, Yu IM, Cook A, Muretta JM, Joseph A, Major J, Sourigues Y, Clause J, Topf M, Rosenfeld SS, Houdusse A, Moores CA. The divergent mitotic kinesin MKLP2 exhibits atypical structure and mechanochemistry. eLife 2017; 6:27793. [PMID: 28826477 PMCID: PMC5602324 DOI: 10.7554/elife.27793] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2017] [Accepted: 08/07/2017] [Indexed: 01/17/2023] Open
Abstract
MKLP2, a kinesin-6, has critical roles during the metaphase-anaphase transition and cytokinesis. Its motor domain contains conserved nucleotide binding motifs, but is divergent in sequence (~35% identity) and size (~40% larger) compared to other kinesins. Using cryo-electron microscopy and biophysical assays, we have undertaken a mechanochemical dissection of the microtubule-bound MKLP2 motor domain during its ATPase cycle, and show that many facets of its mechanism are distinct from other kinesins. While the MKLP2 neck-linker is directed towards the microtubule plus-end in an ATP-like state, it does not fully dock along the motor domain. Furthermore, the footprint of the MKLP2 motor domain on the MT surface is altered compared to motile kinesins, and enhanced by kinesin-6-specific sequences. The conformation of the highly extended loop6 insertion characteristic of kinesin-6s is nucleotide-independent and does not contact the MT surface. Our results emphasize the role of family-specific insertions in modulating kinesin motor function. Cells constantly replicate to provide new cells for growing tissues, and to replace ageing or defective cells around the body. Each new cell needs a copy of the genetic material, and a cellular structure called the mitotic spindle makes sure that this material is shared correctly when a cell divides in two. The spindle is built from protein filaments called microtubules, and the protein filaments grow and shrink as the mitotic spindle carries out its role. Many of these changes in the spindle are driven by proteins called molecular motors, which break down energy-rich molecules of ATP to power them as they walk along the filaments. Kinesins, for example, are molecular motors that can move along microtubules and there are over 40 different kinesins encoded in the human genome. More than half of the human kinesins are involved in cell division including one called MKLP2. Little is known about MKLP2 but some earlier findings had suggested that it would behave very differently compared to other kinesins. Understanding how a kinesin motor works requires studying it in complex with its microtubule tracks. Atherton, Yu et al. have now used a technique called cryo-electron microscopy – which is uniquely suited to looking at large and complicated samples in three dimensions – to observe how the motor in MKLP2 changes shape as it works. This revealed that, while MKLP2 works in a fundamentally similar way to other kinesins, many aspects of its molecular mechanism are highly unusual. These include how it binds to the microtubule, how it interacts with ATP and how it generates force. These findings show that there is much greater diversity in the molecular mechanisms of the kinesins involved in cell division than was previously thought. Several anticancer drugs target kinesins to stop cells dividing and so this diversity may make it easier to target only certain kinesins with drugs, which in turn would have fewer side effects. First, though, it will be important to find out how the unusual mechanism of MKLP2 coordinates and influences other components of the spindle to reveal a fuller picture of what happens when cells replicate.
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Affiliation(s)
- Joseph Atherton
- Institute of Structural and Molecular Biology, Birkbeck College, London, United Kingdom
| | - I-Mei Yu
- Structural Motility, Institut Curie, Centre National de la Recherche Scientifique, Unité Mixte de Recherche, Paris, France
| | - Alexander Cook
- Institute of Structural and Molecular Biology, Birkbeck College, London, United Kingdom
| | - Joseph M Muretta
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, United Sates
| | - Agnel Joseph
- Institute of Structural and Molecular Biology, Birkbeck College, London, United Kingdom
| | - Jennifer Major
- Department of Cancer Biology, Lerner Research Institute, Cleveland Clinic, Cleveland, United States
| | - Yannick Sourigues
- Structural Motility, Institut Curie, Centre National de la Recherche Scientifique, Unité Mixte de Recherche, Paris, France
| | - Jeffrey Clause
- Structural Motility, Institut Curie, Centre National de la Recherche Scientifique, Unité Mixte de Recherche, Paris, France
| | - Maya Topf
- Institute of Structural and Molecular Biology, Birkbeck College, London, United Kingdom
| | - Steven S Rosenfeld
- Department of Cancer Biology, Lerner Research Institute, Cleveland Clinic, Cleveland, United States
| | - Anne Houdusse
- Structural Motility, Institut Curie, Centre National de la Recherche Scientifique, Unité Mixte de Recherche, Paris, France
| | - Carolyn A Moores
- Institute of Structural and Molecular Biology, Birkbeck College, London, United Kingdom
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17
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Schaaf TM, Peterson KC, Grant BD, Bawaskar P, Yuen S, Li J, Muretta JM, Gillispie GD, Thomas DD. High-Throughput Spectral and Lifetime-Based FRET Screening in Living Cells to Identify Small-Molecule Effectors of SERCA. SLAS Discov 2017; 22:262-273. [PMID: 27899691 PMCID: PMC5323330 DOI: 10.1177/1087057116680151] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
A robust high-throughput screening (HTS) strategy has been developed to discover small-molecule effectors targeting the sarco/endoplasmic reticulum calcium ATPase (SERCA), based on a fluorescence microplate reader that records both the nanosecond decay waveform (lifetime mode) and the complete emission spectrum (spectral mode), with high precision and speed. This spectral unmixing plate reader (SUPR) was used to screen libraries of small molecules with a fluorescence resonance energy transfer (FRET) biosensor expressed in living cells. Ligand binding was detected by FRET associated with structural rearrangements of green fluorescent protein (GFP, donor) and red fluorescent protein (RFP, acceptor) fused to the cardiac-specific SERCA2a isoform. The results demonstrate accurate quantitation of FRET along with high precision of hit identification. Fluorescence lifetime analysis resolved SERCA's distinct structural states, providing a method to classify small-molecule chemotypes on the basis of their structural effect on the target. The spectral analysis was also applied to flag interference by fluorescent compounds. FRET hits were further evaluated for functional effects on SERCA's ATPase activity via both a coupled-enzyme assay and a FRET-based calcium sensor. Concentration-response curves indicated excellent correlation between FRET and function. These complementary spectral and lifetime FRET detection methods offer an attractive combination of precision, speed, and resolution for HTS.
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Affiliation(s)
- Tory M. Schaaf
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455
| | | | | | - Prachi Bawaskar
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455
| | - Samantha Yuen
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455
| | - Ji Li
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455
| | - Joseph M. Muretta
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455
| | | | - David D. Thomas
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455
- Photonic Pharma LLC, Minneapolis, MN 55410
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18
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Phung LA, Muretta JM, Petersen KJ, Rohde JA, Mader TL, Lowe DA, Thomas DD. Probing Estradiol Effects on Super-Relaxed Myosin in Muscle Fibers with Fluorescence. Biophys J 2017. [DOI: 10.1016/j.bpj.2016.11.1299] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022] Open
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19
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Rohde JA, Cho H, Phung L, Thomas DD, Muretta JM. Cardiac Myosin Strutural Kinetics Modulated by Small Molecules. Biophys J 2017. [DOI: 10.1016/j.bpj.2016.11.670] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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20
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Rohde JA, Thomas DD, Muretta JM. Structural and Biochemical Kinetics of Cardiac Myosin and its Perturbation by a Known Heart Failure Drug Investigated with Transient Time-Resolved FRET. Biophys J 2016. [DOI: 10.1016/j.bpj.2015.11.1598] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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21
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Rohde J, Johnsrud DO, Cornea S, Peterson KC, Gillispie GD, Thomas DD, Muretta JM. Structural Thermodynamics and Kinetics of the Cardiac Myosin/Omecamtiv Mecarbil Complex Revealed by Time-Resolved FRET. Biophys J 2015. [DOI: 10.1016/j.bpj.2014.11.2429] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
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22
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Matzke JG, Thomas DD, Petersen KJ, Muretta JM, Titus MA. A Myosin II FRET-Based Biosensor Expressed in Dictyostelium. Biophys J 2015. [DOI: 10.1016/j.bpj.2014.11.1638] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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23
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Gruber SJ, Goldblum R, Zhong J, Peterson K, Schaaf TM, Autry JM, Gillispie GD, Thomas DD, Muretta JM. Direct Detection of the Thermodynamics and Structural Kinetics of a 2-Color SERCA Biosensor by Transient Time-Resolved FRET. Biophys J 2015. [DOI: 10.1016/j.bpj.2014.11.1985] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
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24
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Muretta JM, Major J, Thomas DD, Steven RS. Structural-Kinetics of the Switch-1 Loop and Neck-Linker Elements Explains the Distinct Molecular Physiologies of Kinesin-1 and Kinesin-5. Biophys J 2015. [DOI: 10.1016/j.bpj.2014.11.763] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
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25
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Petersen KJ, Peterson KC, Muretta JM, Higgins SE, Gillispie GD, Thomas DD. Fluorescence lifetime plate reader: resolution and precision meet high-throughput. Rev Sci Instrum 2014; 85:113101. [PMID: 25430092 PMCID: PMC4242087 DOI: 10.1063/1.4900727] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
We describe a nanosecond time-resolved fluorescence spectrometer that acquires fluorescence decay waveforms from each well of a 384-well microplate in 3 min with signal-to-noise exceeding 400 using direct waveform recording. The instrument combines high-energy pulsed laser sources (5-10 kHz repetition rate) with a photomultiplier and high-speed digitizer (1 GHz) to record a fluorescence decay waveform after each pulse. Waveforms acquired from rhodamine or 5-((2-aminoethyl)amino) naphthalene-1-sulfonic acid dyes in a 384-well plate gave lifetime measurements 5- to 25-fold more precise than the simultaneous intensity measurements. Lifetimes as short as 0.04 ns were acquired by interleaving with an effective sample rate of 5 GHz. Lifetime measurements resolved mixtures of single-exponential dyes with better than 1% accuracy. The fluorescence lifetime plate reader enables multiple-well fluorescence lifetime measurements with an acquisition time of 0.5 s per well, suitable for high-throughput fluorescence lifetime screening applications.
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Affiliation(s)
- Karl J Petersen
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | - Kurt C Peterson
- Fluorescence Innovations, Inc., Minneapolis, Minnesota 55455, USA
| | - Joseph M Muretta
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | - Sutton E Higgins
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | - Gregory D Gillispie
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | - David D Thomas
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA
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26
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Petersen KJ, Muretta JM, Higgins SE, Peterson KC, Gillispie GD, Thomas DD. High throughput Time Resolved Fluorescence in a Microplate Reader. Biophys J 2014. [DOI: 10.1016/j.bpj.2013.11.1207] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
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27
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Muretta JM, Prochniewicz E, Thomas DD. Biophysical Analysis of the Putative Heart Failure Drug Omecamtiv Mecarbil. Biophys J 2014. [DOI: 10.1016/j.bpj.2013.11.3124] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
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28
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Muretta JM, Behnke-Parks WM, Major J, Petersen KJ, Goulet A, Moores CA, Thomas DD, Rosenfeld SS. Loop L5 assumes three distinct orientations during the ATPase cycle of the mitotic kinesin Eg5: a transient and time-resolved fluorescence study. J Biol Chem 2013; 288:34839-49. [PMID: 24145034 DOI: 10.1074/jbc.m113.518845] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Members of the kinesin superfamily of molecular motors differ in several key structural domains, which probably allows these molecular motors to serve the different physiologies required of them. One of the most variable of these is a stem-loop motif referred to as L5. This loop is longest in the mitotic kinesin Eg5, and previous structural studies have shown that it can assume different conformations in different nucleotide states. However, enzymatic domains often consist of a mixture of conformations whose distribution shifts in response to substrate binding or product release, and this information is not available from the "static" images that structural studies provide. We have addressed this issue in the case of Eg5 by attaching a fluorescent probe to L5 and examining its fluorescence, using both steady state and time-resolved methods. This reveals that L5 assumes an equilibrium mixture of three orientations that differ in their local environment and segmental mobility. Combining these studies with transient state kinetics demonstrates that there is a major shift in this distribution during transitions that interconvert weak and strong microtubule binding states. Finally, in conjunction with previous cryo-EM reconstructions of Eg5·microtubule complexes, these fluorescence studies suggest a model in which L5 regulates both nucleotide and microtubule binding through a set of reversible interactions with helix α3. We propose that these features facilitate the production of sustained opposing force by Eg5, which underlies its role in supporting formation of a bipolar spindle in mitosis.
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Affiliation(s)
- Joseph M Muretta
- From the Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455
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Trivedi DV, Muretta JM, Swenson AM, Thomas DD, Yengo CM. Magnesium impacts myosin V motor activity by altering key conformational changes in the mechanochemical cycle. Biochemistry 2013; 52:4710-22. [PMID: 23725637 DOI: 10.1021/bi4004364] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We investigated how magnesium (Mg) impacts key conformational changes during the ADP binding/release steps in myosin V and how these alterations impact the actomyosin mechanochemical cycle. The conformation of the nucleotide binding pocket was examined with our established FRET system in which myosin V labeled with FlAsH in the upper 50 kDa domain participates in energy transfer with mant labeled nucleotides. We examined the maximum actin-activated ATPase activity of MV FlAsH at a range of free Mg concentrations (0.1-9 mM) and found that the highest activity occurs at low Mg (0.1-0.3 mM), while there is a 50-60% reduction in activity at high Mg (3-9 mM). The motor activity examined with the in vitro motility assay followed a similar Mg-dependence, and the trend was similar with dimeric myosin V. Transient kinetic FRET studies of mantdADP binding/release from actomyosin V FlAsH demonstrate that the transition between the weak and strong actomyosin.ADP states is coupled to movement of the upper 50 kDa domain and is dependent on Mg with the strong state stabilized by Mg. We find that the kinetics of the upper 50 kDa conformational change monitored by FRET correlates well with the ATPase and motility results over a wide range of Mg concentrations. Our results suggest the conformation of the upper 50 kDa domain is highly dynamic in the Mg free actomyosin.ADP state, which is in agreement with ADP binding being entropy driven in the absence of Mg. Overall, our results demonstrate that Mg is a key factor in coupling the nucleotide- and actin-binding regions. In addition, Mg concentrations in the physiological range can alter the structural transition that limits ADP dissociation from actomyosin V, which explains the impact of Mg on actin-activated ATPase activity and in vitro motility.
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Affiliation(s)
- Darshan V Trivedi
- Department of Cellular and Molecular Physiology, College of Medicine, Pennsylvania State University , Hershey, Pennsylvania 17033, United States
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30
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Li J, Langer H, Peterson KC, Muretta JM, Gillispie GD, Cornea RL, Thomas DD. Screening for SERCA Activators using a High-throughput Time-Resolved FRET Assay. Biophys J 2013. [DOI: 10.1016/j.bpj.2012.11.1664] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
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31
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Cornea RL, Gruber SJ, Lockamy EL, Muretta JM, Jin D, Chen J, Dahl R, Bartfai T, Zsebo KM, Gillispie GD, Thomas DD. High-throughput FRET assay yields allosteric SERCA activators. ACTA ACUST UNITED AC 2012; 18:97-107. [PMID: 22923787 DOI: 10.1177/1087057112456878] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Using fluorescence resonance energy transfer (FRET), we performed a high-throughput screen (HTS) in a reconstituted membrane system, seeking compounds that reverse inhibition of sarcoplasmic reticulum Ca-ATPase (SERCA) by its cardiac regulator, phospholamban (PLB). Such compounds have long been sought to correct aberrant Ca(2+) regulation in heart failure. Donor-SERCA was reconstituted in phospholipid membranes with or without acceptor-PLB, and FRET was measured in a steady-state fluorescence microplate reader. A 20 000-compound library was tested in duplicate. Compounds that decreased FRET by more than three standard deviations were considered hits. From 43 hits (0.2%), 31 (72%) were found to be false-positives upon more thorough FRET testing. The remaining 12 hits were tested in assays of Ca-ATPase activity, and six of these activated SERCA significantly, by as much as 60%, and several also enhanced cardiomyocyte contractility. These compounds directly activated SERCA from heart and other tissues. These results validate our FRET approach and set the stage for medicinal chemistry and preclinical testing. We were concerned about the high rate of false-positives, resulting from the low precision of steady-state fluorescence. Preliminary studies with a novel fluorescence lifetime plate reader show 20-fold higher precision. This instrument can dramatically increase the quality of future HTS.
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Affiliation(s)
- Razvan L Cornea
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, MN 55455, USA
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32
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Guhathakurta P, Prochniewicz E, Muretta JM, Titus MA, Thomas DD. Allosteric communication in Dictyostelium myosin II. J Muscle Res Cell Motil 2012; 33:305-12. [PMID: 22752265 DOI: 10.1007/s10974-012-9304-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2012] [Accepted: 05/22/2012] [Indexed: 12/14/2022]
Abstract
Myosin's affinities for nucleotides and actin are reciprocal. Actin-binding substantially reduces the affinity of ATP for myosin, but the effect of actin on myosin's ADP affinity is quite variable among myosin isoforms, serving as the principal mechanism for tuning the actomyosin system to specific physiological purposes. To understand the structural basis of this variable relationship between actin and ADP binding, we studied several constructs of the catalytic domain of Dictyostelium myosin II, varying their length (from the N-terminal origin) and cysteine content. The constructs varied considerably in their actin-activated ATPase activity and in the effect of actin on ADP affinity. Actin had no significant effect on ADP affinity for a single-cysteine catalytic domain construct, a double-cysteine construct partially restored the actin-dependence of ADP binding, and restoration of all native Cys restored it further, but full restoration of function (similar to that of skeletal muscle myosin II) was obtained only by adding all native Cys and an artificial lever arm extension. Pyrene-actin fluorescence confirmed these effects on ADP binding to actomyosin. We conclude that myosin's Cys content and lever arm both allosterically modulate the reciprocal affinities of myosin for ADP and actin, a key determinant of the biological functions of myosin isoforms.
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Affiliation(s)
- Piyali Guhathakurta
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, 6-155 Jackson Hall, 321 Church St. SE, Minneapolis, MN 55455, USA
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33
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Guhathakurta P, Prochniewicz E, Muretta JM, Thomas DD. Allosteric Effects within the Catalytic Domain of Dictyostelium Myosin on Interaction with Actin and Nucleotide. Biophys J 2011. [DOI: 10.1016/j.bpj.2010.12.3424] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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34
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Muretta JM, Kyrychenko A, Ladokhin AS, Kast DJ, Gillispie GD, Thomas DD. High-performance time-resolved fluorescence by direct waveform recording. Rev Sci Instrum 2010; 81:103101. [PMID: 21034069 PMCID: PMC2980540 DOI: 10.1063/1.3480647] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/20/2010] [Accepted: 07/26/2010] [Indexed: 05/25/2023]
Abstract
We describe a high-performance time-resolved fluorescence (HPTRF) spectrometer that dramatically increases the rate at which precise and accurate subnanosecond-resolved fluorescence emission waveforms can be acquired in response to pulsed excitation. The key features of this instrument are an intense (1 μJ/pulse), high-repetition rate (10 kHz), and short (1 ns full width at half maximum) laser excitation source and a transient digitizer (0.125 ns per time point) that records a complete and accurate fluorescence decay curve for every laser pulse. For a typical fluorescent sample containing a few nanomoles of dye, a waveform with a signal/noise of about 100 can be acquired in response to a single laser pulse every 0.1 ms, at least 10(5) times faster than the conventional method of time-correlated single photon counting, with equal accuracy and precision in lifetime determination for lifetimes as short as 100 ps. Using standard single-lifetime samples, the detected signals are extremely reproducible, with waveform precision and linearity to within 1% error for single-pulse experiments. Waveforms acquired in 0.1 s (1000 pulses) with the HPTRF instrument were of sufficient precision to analyze two samples having different lifetimes, resolving minor components with high accuracy with respect to both lifetime and mole fraction. The instrument makes possible a new class of high-throughput time-resolved fluorescence experiments that should be especially powerful for biological applications, including transient kinetics, multidimensional fluorescence, and microplate formats.
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Affiliation(s)
- Joseph M Muretta
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA
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35
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Abstract
Insulin stimulates glucose storage and metabolism by the tissues of the body, predominantly liver, muscle and fat. Storage in muscle and fat is controlled to a large extent by the rate of facilitative glucose transport across the plasma membrane of the muscle and fat cells. Insulin controls this transport. Exactly how remains debated. Work presented in this review focuses on the pathways responsible for the regulation of glucose transport by insulin. We present some historical work to show how the prevailing model for regulation of glucose transport by insulin was originally developed, then some more recent data challenging this model. We finish describing a unifying model for the control of glucose transport, and some very recent data illustrating potential molecular machinery underlying this regulation. This review is meant to give an overview of our current understanding of the regulation of glucose transport through the regulation of the trafficking of Glut4, highlighting important questions that remain to be answered. A more detailed treatment of specific aspects of this pathway can be found in several excellent recent reviews (Brozinick et al., 2007 Hou and Pessin, 2007; Huang and Czech, 2007;Larance et al., 2008 Sakamoto and Holman, 2008; Watson and Pessin, 2007; Zaid et al., 2008)One of the main objectives of this review is to discuss the results of the experiments measuring the kinetics of Glut4 movement between subcellular compartments in the context of our emerging model of the Glut4 trafficking pathway.
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Affiliation(s)
- Joseph M Muretta
- Department of Biochemistry, University of Minnesota, Minneapolis, Minnesota 55455, USA
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Muretta JM, Romenskaia I, Mastick CC. Insulin releases Glut4 from static storage compartments into cycling endosomes and increases the rate constant for Glut4 exocytosis. J Biol Chem 2007; 283:311-323. [PMID: 17967900 DOI: 10.1074/jbc.m705756200] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
In adipocytes, insulin triggers the redistribution of Glut4 from intracellular compartments to the plasma membrane. Two models have been proposed to explain the effect of insulin on Glut4 localization. In the first, termed dynamic exchange, Glut4 continually cycles between the plasma membrane and intracellular compartments in basal cells, and the major effect of insulin is through changes in the exocytic and endocytic rate constants, k(ex) and k(en). In the second model, termed static retention, Glut4 is packaged in specialized storage vesicles (GSVs) in basal cells and does not traffic through the plasma membrane or endosomes. Insulin triggers GSV exocytosis, increasing the amount of Glut4 in the actively cycling pool. Using a flow cytometry-based assay, we found that Glut4 is regulated by both static and dynamic retention mechanisms. In basal cells, 75-80% of the Glut4 is packaged in noncycling GSVs. Insulin increased the amount of Glut4 in the actively cycling pool 4-5-fold. Insulin also increased k(ex) in the cycling pool 3-fold. After insulin withdrawal, Glut4 is rapidly cleared from the plasma membrane (t((1/2)) of 20 min) by rapid adjustments in k(ex) and k(en) and recycled into static compartments. Complete recovery of the static pool required more than 3 h, however. We conclude that in fully differentiated confluent adipocytes, both the dynamic and static retention mechanisms are important for the regulation of plasma membrane Glut4 content. However, cell culture conditions affect Glut4 trafficking. For example, replating after differentiation inhibited the static retention of Glut4, which may explain differences in previous reports.
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Affiliation(s)
- Joseph M Muretta
- Department of Biochemistry and Molecular Biology, University of Nevada, Reno, Nevada 89557
| | - Irina Romenskaia
- Department of Biochemistry and Molecular Biology, University of Nevada, Reno, Nevada 89557
| | - Cynthia Corley Mastick
- Department of Biochemistry and Molecular Biology, University of Nevada, Reno, Nevada 89557.
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Muretta JM, Romenskaia I, Cassiday PA, Mastick CC. Expression of a synapsin IIb site 1 phosphorylation mutant in 3T3-L1 adipocytes inhibits basal intracellular retention of Glut4. J Cell Sci 2007; 120:1168-77. [PMID: 17341582 DOI: 10.1242/jcs.03413] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [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] [Indexed: 11/20/2022] Open
Abstract
Glut4 exocytosis in adipocytes uses protein machinery that is shared with other regulated secretory processes. Synapsins are phosphoproteins that regulate a ;reserve pool' of vesicles clustered behind the active zone in neurons. We found that adipocytes (primary cells and the 3T3-L1 cell line) express synapsin IIb mRNA and protein. Synapsin IIb co-localizes with Glut4 in perinuclear vesicle clusters. To test whether synapsin plays a role in Glut4 traffic, a site 1 phosphorylation mutant (S10A synapsin) was expressed in 3T3-L1 adipocytes. Interestingly, expression of S10A synapsin increased basal cell surface Glut4 almost fourfold (50% maximal insulin effect). Insulin caused a further twofold translocation of Glut4 in these cells. Expression of the N-terminus of S10A synapsin (amino acids 1-118) was sufficient to inhibit basal Glut4 retention. Neither wild-type nor S10D synapsin redistributed Glut4. S10A synapsin did not elevate surface levels of the transferrin receptor in adipocytes or Glut4 in fibroblasts. Therefore, S10A synapsin is inhibiting the specialized process of basal intracellular retention of Glut4 in adipocytes, without affecting general endocytic cycling. While mutant forms of many proteins inhibit Glut4 exocytosis in response to insulin, S10A synapsin is one of only a few that specifically inhibits Glut4 retention in basal adipocytes. These data indicate that the synapsins are important regulators of membrane traffic in many cell types.
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Affiliation(s)
- Joseph M Muretta
- Department of Biochemistry and Molecular Biology, Mailstop 330, University of Nevada, Reno, NV 89557, USA
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