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Wu K, Patel H, Wu H, Quintanilla MA, Bennett MA, Sala S, Beach JR. Non-muscle myosin 2 can incorporate into established filaments in cells without an assembly competence domain. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.07.07.602405. [PMID: 39026829 PMCID: PMC11257479 DOI: 10.1101/2024.07.07.602405] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/20/2024]
Abstract
Myosin 2 dynamically assembles into filaments that exert force on the actin cytoskeleton. To form filaments, myosin 2 monomers transition between folded and unfolded states. Monomer unfolding exposes an extended coiled-coil that interacts with other monomers in parallel and antiparallel fashions, enabling bipolar filament formation. A C-terminal domain of the coiled-coil, termed assembly competence domain (ACD), has been repeatedly identified as necessary for filament assembly. Here, we revisit ACD contribution when full-length filaments are present. Non-muscle myosin 2A lacking the ACD (ΔACD) initially appears diffuse, but triton extraction of cytosolic fraction reveals cytoskeletal association. Disruption of the folded monomer enhances the cytoskeletal fraction, while inhibition of endogenous filament assembly appears to reduce it. Finally, high resolution imaging of endogenous and exogenous bipolar filamentous structures reveals highly coincident signal, suggesting ΔACD constructs co-assemble with endogenous myosin 2A filaments. Our data demonstrate that while the ACD is required for de novo filament assembly, it is not required for monomers to recognize and associate with established filaments in cells. More broadly, this highlights the existence of distinct mechanisms governing myosin 2 monomer assembly into nascent filaments, and monomer recognition and association with established filaments to maintain steady-state contractile networks.
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Affiliation(s)
- Kehan Wu
- Department of Cell and Molecular Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, IL
| | - Hiral Patel
- Department of Cell and Molecular Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, IL
| | - Huini Wu
- Department of Cell and Molecular Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, IL
| | - Melissa A Quintanilla
- Department of Cell and Molecular Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, IL
| | - Margaret A Bennett
- Department of Cell and Molecular Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, IL
| | - Stefano Sala
- Department of Cell and Molecular Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, IL
| | - Jordan R Beach
- Department of Cell and Molecular Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, IL
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2
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Duno-Miranda S, Nelson SR, Rasicci DV, Bodt SM, Cirilo JA, Vang D, Sivaramakrishnan S, Yengo CM, Warshaw DM. Tail length and E525K dilated cardiomyopathy mutant alter human β-cardiac myosin super-relaxed state. J Gen Physiol 2024; 156:e202313522. [PMID: 38709176 PMCID: PMC11074782 DOI: 10.1085/jgp.202313522] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2023] [Revised: 03/18/2024] [Accepted: 04/17/2024] [Indexed: 05/07/2024] Open
Abstract
Dilated cardiomyopathy (DCM) is a condition characterized by impaired cardiac function, due to myocardial hypo-contractility, and is associated with point mutations in β-cardiac myosin, the molecular motor that powers cardiac contraction. Myocardial function can be modulated through sequestration of myosin motors into an auto-inhibited "super-relaxed" state (SRX), which may be further stabilized by a structural state known as the "interacting heads motif" (IHM). Here, we sought to determine whether hypo-contractility of DCM myocardium results from reduced function of individual myosin molecules or from decreased myosin availability to interact with actin due to increased IHM/SRX stabilization. We used an established DCM myosin mutation, E525K, and characterized the biochemical and mechanical activity of wild-type and mutant human β-cardiac myosin constructs that differed in the length of their coiled-coil tail, which dictates their ability to form the IHM/SRX state. We found that short-tailed myosin constructs exhibited low IHM/SRX content, elevated actin-activated ATPase activity, and fast velocities in unloaded motility assays. Conversely, longer-tailed constructs exhibited higher IHM/SRX content and reduced actomyosin ATPase and velocity. Our modeling suggests that reduced velocities may be attributed to IHM/SRX-dependent sequestration of myosin heads. Interestingly, longer-tailed E525K mutants showed no apparent impact on velocity or actomyosin ATPase at low ionic strength but stabilized IHM/SRX state at higher ionic strength. Therefore, the hypo-contractility observed in DCM may be attributable to reduced myosin head availability caused by enhanced IHM/SRX stability in E525K mutants.
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Affiliation(s)
- Sebastian Duno-Miranda
- Department of Molecular Physiology and Biophysics, Cardiovascular Research Institute, University of Vermont, Burlington, VT, USA
| | - Shane R. Nelson
- Department of Molecular Physiology and Biophysics, Cardiovascular Research Institute, University of Vermont, Burlington, VT, USA
| | - David V. Rasicci
- Department of Cellular and Molecular Physiology, Penn State College of Medicine, Hershey, PA, USA
| | - Skylar M.L. Bodt
- Department of Cellular and Molecular Physiology, Penn State College of Medicine, Hershey, PA, USA
| | - Joseph A. Cirilo
- Department of Cellular and Molecular Physiology, Penn State College of Medicine, Hershey, PA, USA
| | - Duha Vang
- Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, MN, USA
| | - Sivaraj Sivaramakrishnan
- Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, MN, USA
| | - Christopher M. Yengo
- Department of Cellular and Molecular Physiology, Penn State College of Medicine, Hershey, PA, USA
| | - David M. Warshaw
- Department of Molecular Physiology and Biophysics, Cardiovascular Research Institute, University of Vermont, Burlington, VT, USA
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3
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Duno-Miranda S, Nelson SR, Rasicci DV, Bodt SL, Cirilo JA, Vang D, Sivaramakrishnan S, Yengo CM, Warshaw DM. Tail Length and E525K Dilated Cardiomyopathy Mutant Alter Human β-Cardiac Myosin Super-Relaxed State. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.12.07.570656. [PMID: 38105932 PMCID: PMC10723396 DOI: 10.1101/2023.12.07.570656] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2023]
Abstract
Dilated cardiomyopathy (DCM) is characterized by impaired cardiac function due to myocardial hypo-contractility and is associated with point mutations in β-cardiac myosin, the molecular motor that powers cardiac contraction. Myocardial function can be modulated through sequestration of myosin motors into an auto-inhibited "super relaxed" state (SRX), which is further stabilized by a structural state known as the "Interacting Heads Motif" (IHM). Therefore, hypo-contractility of DCM myocardium may result from: 1) reduced function of individual myosin, and/or; 2) decreased myosin availability due to increased IHM/SRX stabilization. To define the molecular impact of an established DCM myosin mutation, E525K, we characterized the biochemical and mechanical activity of wild-type (WT) and E525K human β-cardiac myosin constructs that differed in the length of their coiled-coil tail, which dictates their ability to form the IHM/SRX state. Single-headed (S1) and a short-tailed, double-headed (2HEP) myosin constructs exhibited low (~10%) IHM/SRX content, actin-activated ATPase activity of ~5s-1 and fast velocities in unloaded motility assays (~2000nm/s). Double-headed, longer-tailed (15HEP, 25HEP) constructs exhibited higher IHM/SRX content (~90%), and reduced actomyosin ATPase (<1s-1) and velocity (~800nm/s). A simple analytical model suggests that reduced velocities may be attributed to IHM/SRXdependent sequestration of myosin heads. Interestingly, the E525K 15HEP and 25HEP mutants showed no apparent impact on velocity or actomyosin ATPase at low ionic strength. However, at higher ionic strength, the E525K mutation stabilized the IHM/SRX state. Therefore, the E525K-associated DCM human cardiac hypo-contractility may be attributable to reduced myosin head availability caused by enhanced IHM/SRX stability.
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Affiliation(s)
- Sebastian Duno-Miranda
- Department of Molecular Physiology and Biophysics, Cardiovascular Research Institute, University of Vermont, Burlington, Vermont
| | - Shane R. Nelson
- Department of Molecular Physiology and Biophysics, Cardiovascular Research Institute, University of Vermont, Burlington, Vermont
| | - David V. Rasicci
- Department of Cellular and Molecular Physiology, Penn State College of Medicine, Hershey, Pennsylvania
| | - Skylar L.M. Bodt
- Department of Cellular and Molecular Physiology, Penn State College of Medicine, Hershey, Pennsylvania
| | - Joseph A. Cirilo
- Department of Cellular and Molecular Physiology, Penn State College of Medicine, Hershey, Pennsylvania
| | - Duha Vang
- Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, Minnesota
| | - Sivaraj Sivaramakrishnan
- Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, Minnesota
| | - Christopher M. Yengo
- Department of Cellular and Molecular Physiology, Penn State College of Medicine, Hershey, Pennsylvania
| | - David M. Warshaw
- Department of Molecular Physiology and Biophysics, Cardiovascular Research Institute, University of Vermont, Burlington, Vermont
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4
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Hojjatian A, Taylor DW, Daneshparvar N, Fagnant PM, Trybus KM, Taylor KA. Double-headed binding of myosin II to F-actin shows the effect of strain on head structure. J Struct Biol 2023; 215:107995. [PMID: 37414375 PMCID: PMC10544818 DOI: 10.1016/j.jsb.2023.107995] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2022] [Revised: 06/25/2023] [Accepted: 07/03/2023] [Indexed: 07/08/2023]
Abstract
Force production in muscle is achieved through the interaction of myosin and actin. Strong binding states in active muscle are associated with Mg·ADP bound to the active site; release of Mg·ADP allows rebinding of ATP and dissociation from actin. Thus, Mg·ADP binding is positioned for adaptation as a force sensor. Mechanical loads on the lever arm can affect the ability of myosin to release Mg·ADP but exactly how this is done is poorly defined. Here we use F-actin decorated with double-headed smooth muscle myosin fragments in the presence of Mg·ADP to visualize the effect of internally supplied tension on the paired lever arms using cryoEM. The interaction of the paired heads with two adjacent actin subunits is predicted to place one lever arm under positive and the other under negative strain. The converter domain is believed to be the most flexible domain within myosin head. Our results, instead, point to the segment of heavy chain between the essential and regulatory light chains as the location of the largest structural change. Moreover, our results suggest no large changes in the myosin coiled coil tail as the locus of strain relief when both heads bind F-actin. The method would be adaptable to double-headed members of the myosin family. We anticipate that the study of actin-myosin interaction using double-headed fragments enables visualization of domains that are typically noisy in decoration with single-headed fragments.
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Affiliation(s)
- Alimohammad Hojjatian
- Inst. of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, United States
| | - Dianne W Taylor
- Inst. of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, United States
| | - Nadia Daneshparvar
- Inst. of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, United States
| | - Patricia M Fagnant
- Dept of Molecular Physiology & Biophysics, University of Vermont College of Medicine, Burlington, VT 05405, United States
| | - Kathleen M Trybus
- Dept of Molecular Physiology & Biophysics, University of Vermont College of Medicine, Burlington, VT 05405, United States
| | - Kenneth A Taylor
- Inst. of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, United States.
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5
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Nag S, Gollapudi SK, Del Rio CL, Spudich JA, McDowell R. Mavacamten, a precision medicine for hypertrophic cardiomyopathy: From a motor protein to patients. SCIENCE ADVANCES 2023; 9:eabo7622. [PMID: 37506209 DOI: 10.1126/sciadv.abo7622] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/23/2022] [Accepted: 06/23/2023] [Indexed: 07/30/2023]
Abstract
Hypertrophic cardiomyopathy (HCM) is a primary myocardial disorder characterized by left ventricular hypertrophy, hyperdynamic contraction, and impaired relaxation of the heart. These functional derangements arise directly from altered sarcomeric function due to either mutations in genes encoding sarcomere proteins, or other defects such as abnormal energetics. Current treatment options do not directly address this causal biology but focus on surgical and extra-sarcomeric (sarcolemmal) pharmacological symptomatic relief. Mavacamten (formerly known as MYK-461), is a small molecule designed to regulate cardiac function at the sarcomere level by selectively but reversibly inhibiting the enzymatic activity of myosin, the fundamental motor of the sarcomere. This review summarizes the mechanism and translational progress of mavacamten from proteins to patients, describing how the mechanism of action and pharmacological characteristics, involving both systolic and diastolic effects, can directly target pathophysiological derangements within the cardiac sarcomere to improve cardiac structure and function in HCM. Mavacamten was approved by the Food and Drug Administration in April 2022 for the treatment of obstructive HCM and now goes by the commercial name of Camzyos. Full information about the risks, limitations, and side effects can be found at www.accessdata.fda.gov/drugsatfda_docs/label/2022/214998s000lbl.pdf.
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Affiliation(s)
- Suman Nag
- MyoKardia Inc., a wholly owned subsidiary of Bristol Myers Squibb, Brisbane, CA 94005, USA
| | - Sampath K Gollapudi
- MyoKardia Inc., a wholly owned subsidiary of Bristol Myers Squibb, Brisbane, CA 94005, USA
| | - Carlos L Del Rio
- MyoKardia Inc., a wholly owned subsidiary of Bristol Myers Squibb, Brisbane, CA 94005, USA
- Cardiac Consulting, 1630 S Delaware St. #56426, San Mateo, CA 94403, USA
| | | | - Robert McDowell
- MyoKardia Inc., a wholly owned subsidiary of Bristol Myers Squibb, Brisbane, CA 94005, USA
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6
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Abstract
Non-muscle myosin 2 (NM2) motors are the major contractile machines in most cell types. Unsurprisingly, these ubiquitously expressed actin-based motors power a plethora of subcellular, cellular and multicellular processes. In this Cell Science at a Glance article and the accompanying poster, we review the biochemical properties and mechanisms of regulation of this myosin. We highlight the central role of NM2 in multiple fundamental cellular processes, which include cell migration, cytokinesis, epithelial barrier function and tissue morphogenesis. In addition, we highlight recent studies using advanced imaging technologies that have revealed aspects of NM2 assembly hitherto inaccessible. This article will hopefully appeal to both cytoskeletal enthusiasts and investigators from outside the cytoskeleton field who have interests in one of the many basic cellular processes requiring actomyosin force production.
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Affiliation(s)
- Melissa A. Quintanilla
- Department of Cell and Molecular Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, IL 60525, USA
| | - John A. Hammer
- National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Jordan R. Beach
- Department of Cell and Molecular Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, IL 60525, USA
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7
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Rasicci DV, Tiwari P, Bodt SML, Desetty R, Sadler FR, Sivaramakrishnan S, Craig R, Yengo CM. Dilated cardiomyopathy mutation E525K in human beta-cardiac myosin stabilizes the interacting-heads motif and super-relaxed state of myosin. eLife 2022; 11:e77415. [PMID: 36422472 PMCID: PMC9691020 DOI: 10.7554/elife.77415] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2022] [Accepted: 11/08/2022] [Indexed: 11/25/2022] Open
Abstract
The auto-inhibited, super-relaxed (SRX) state of cardiac myosin is thought to be crucial for regulating contraction, relaxation, and energy conservation in the heart. We used single ATP turnover experiments to demonstrate that a dilated cardiomyopathy (DCM) mutation (E525K) in human beta-cardiac myosin increases the fraction of myosin heads in the SRX state (with slow ATP turnover), especially in physiological ionic strength conditions. We also utilized FRET between a C-terminal GFP tag on the myosin tail and Cy3ATP bound to the active site of the motor domain to estimate the fraction of heads in the closed, interacting-heads motif (IHM); we found a strong correlation between the IHM and SRX state. Negative stain electron microscopy and 2D class averaging of the construct demonstrated that the E525K mutation increased the fraction of molecules adopting the IHM. Overall, our results demonstrate that the E525K DCM mutation may reduce muscle force and power by stabilizing the auto-inhibited SRX state. Our studies also provide direct evidence for a correlation between the SRX biochemical state and the IHM structural state in cardiac muscle myosin. Furthermore, the E525 residue may be implicated in crucial electrostatic interactions that modulate this conserved, auto-inhibited conformation of myosin.
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Affiliation(s)
- David V Rasicci
- Department of Cellular and Molecular Physiology, Penn State College of MedicineHersheyUnited States
| | - Prince Tiwari
- Department of Radiology, Division of Cell Biology and Imaging, UMass Chan Medical SchoolWorcesterUnited States
| | - Skylar ML Bodt
- Department of Cellular and Molecular Physiology, Penn State College of MedicineHersheyUnited States
| | - Rohini Desetty
- Department of Cellular and Molecular Physiology, Penn State College of MedicineHersheyUnited States
| | - Fredrik R Sadler
- Department of Genetics, Cell Biology, and Development, University of Minnesota Twin CitiesMinneapolisUnited States
| | - Sivaraj Sivaramakrishnan
- Department of Genetics, Cell Biology, and Development, University of Minnesota Twin CitiesMinneapolisUnited States
| | - Roger Craig
- Department of Radiology, Division of Cell Biology and Imaging, UMass Chan Medical SchoolWorcesterUnited States
| | - Christopher M Yengo
- Department of Cellular and Molecular Physiology, Penn State College of MedicineHersheyUnited States
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8
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Kawana M, Spudich JA, Ruppel KM. Hypertrophic cardiomyopathy: Mutations to mechanisms to therapies. Front Physiol 2022; 13:975076. [PMID: 36225299 PMCID: PMC9548533 DOI: 10.3389/fphys.2022.975076] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2022] [Accepted: 08/22/2022] [Indexed: 01/10/2023] Open
Abstract
Hypertrophic cardiomyopathy (HCM) affects more than 1 in 500 people in the general population with an extensive burden of morbidity in the form of arrhythmia, heart failure, and sudden death. More than 25 years since the discovery of the genetic underpinnings of HCM, the field has unveiled significant insights into the primary effects of these genetic mutations, especially for the myosin heavy chain gene, which is one of the most commonly mutated genes. Our group has studied the molecular effects of HCM mutations on human β-cardiac myosin heavy chain using state-of-the-art biochemical and biophysical tools for the past 10 years, combining insights from clinical genetics and structural analyses of cardiac myosin. The overarching hypothesis is that HCM-causing mutations in sarcomere proteins cause hypercontractility at the sarcomere level, and we have shown that an increase in the number of myosin molecules available for interaction with actin is a primary driver. Recently, two pharmaceutical companies have developed small molecule inhibitors of human cardiac myosin to counteract the molecular consequences of HCM pathogenesis. One of these inhibitors (mavacamten) has recently been approved by the FDA after completing a successful phase III trial in HCM patients, and the other (aficamten) is currently being evaluated in a phase III trial. Myosin inhibitors will be the first class of medication used to treat HCM that has both robust clinical trial evidence of efficacy and that targets the fundamental mechanism of HCM pathogenesis. The success of myosin inhibitors in HCM opens the door to finding other new drugs that target the sarcomere directly, as we learn more about the genetics and fundamental mechanisms of this disease.
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Affiliation(s)
- Masataka Kawana
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA, United States,Department of Medicine, Division of Cardiovascular Medicine, Stanford University School of Medicine, Stanford, CA, United States
| | - James A. Spudich
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA, United States
| | - Kathleen M. Ruppel
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA, United States,*Correspondence: Kathleen M. Ruppel,
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9
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Suay-Corredera C, Alegre-Cebollada J. The mechanics of the heart: zooming in on hypertrophic cardiomyopathy and cMyBP-C. FEBS Lett 2022; 596:703-746. [PMID: 35224729 DOI: 10.1002/1873-3468.14301] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2021] [Revised: 01/10/2022] [Accepted: 01/14/2022] [Indexed: 11/10/2022]
Abstract
Hypertrophic cardiomyopathy (HCM), a disease characterized by cardiac muscle hypertrophy and hypercontractility, is the most frequently inherited disorder of the heart. HCM is mainly caused by variants in genes encoding proteins of the sarcomere, the basic contractile unit of cardiomyocytes. The most frequently mutated among them is MYBPC3, which encodes cardiac myosin-binding protein C (cMyBP-C), a key regulator of sarcomere contraction. In this review, we summarize clinical and genetic aspects of HCM and provide updated information on the function of the healthy and HCM sarcomere, as well as on emerging therapeutic options targeting sarcomere mechanical activity. Building on what is known about cMyBP-C activity, we examine different pathogenicity drivers by which MYBPC3 variants can cause disease, focussing on protein haploinsufficiency as a common pathomechanism also in nontruncating variants. Finally, we discuss recent evidence correlating altered cMyBP-C mechanical properties with HCM development.
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10
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Heissler SM, Arora AS, Billington N, Sellers JR, Chinthalapudi K. Cryo-EM structure of the autoinhibited state of myosin-2. SCIENCE ADVANCES 2021; 7:eabk3273. [PMID: 34936462 PMCID: PMC8694606 DOI: 10.1126/sciadv.abk3273] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2021] [Accepted: 11/05/2021] [Indexed: 05/20/2023]
Abstract
We solved the near-atomic resolution structure of smooth muscle myosin-2 in the autoinhibited state (10S) using single-particle cryo–electron microscopy. The 3.4-Å structure reveals the precise molecular architecture of 10S and the structural basis for myosin-2 regulation. We reveal the position of the phosphorylation sites that control myosin autoinhibition and activation by phosphorylation of the regulatory light chain. Further, we present a previously unidentified conformational state in myosin-2 that traps ADP and Pi produced by the hydrolysis of ATP in the active site. This noncanonical state represents a branch of the myosin enzyme cycle and explains the autoinhibition of the enzyme function of 10S along with its reduced affinity for actin. Together, our structure defines the molecular mechanisms that drive 10S formation, stabilization, and relief by phosphorylation of the regulatory light chain.
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Affiliation(s)
- Sarah M. Heissler
- Department of Physiology and Cell Biology, Dorothy M. Davis Heart and Lung Research Institute, The Ohio State University College of Medicine, Columbus, OH, USA
| | - Amandeep S. Arora
- Department of Physiology and Cell Biology, Dorothy M. Davis Heart and Lung Research Institute, The Ohio State University College of Medicine, Columbus, OH, USA
| | - Neil Billington
- Laboratory of Molecular Physiology, National Heart, Lung, and Blood Institute, Bethesda, MD, USA
| | - James R. Sellers
- Laboratory of Molecular Physiology, National Heart, Lung, and Blood Institute, Bethesda, MD, USA
| | - Krishna Chinthalapudi
- Department of Physiology and Cell Biology, Dorothy M. Davis Heart and Lung Research Institute, The Ohio State University College of Medicine, Columbus, OH, USA
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11
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Two Classes of Myosin Inhibitors, Para-nitroblebbistatin and Mavacamten, Stabilize β-Cardiac Myosin in Different Structural and Functional States. J Mol Biol 2021; 433:167295. [PMID: 34627791 DOI: 10.1016/j.jmb.2021.167295] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2021] [Revised: 09/28/2021] [Accepted: 10/01/2021] [Indexed: 11/20/2022]
Abstract
In addition to a conventional relaxed state, a fraction of myosins in the cardiac muscle exists in a low-energy consuming super-relaxed (SRX) state, which is kept as a reserve pool that may be engaged under sustained increased cardiac demand. The conventional relaxed and the super-relaxed states are widely assumed to correspond to a structure where myosin heads are in an open configuration, free to interact with actin, and a closed configuration, inhibiting binding to actin, respectively. Disruption of the myosin SRX population is an emerging model in different heart diseases, such as hypertrophic cardiomyopathy, which results in excessive muscle contraction, and stabilizing them using myosin inhibitors is budding as an attractive therapeutic strategy. Here we examined the structure-function relationships of two myosin ATPase inhibitors, mavacamten and para-nitroblebbistatin, and found that binding of mavacamten at a site different than para-nitroblebbistatin populates myosin into the SRX state. Para-nitroblebbistatin, binding to a distal pocket to the myosin lever arm near the nucleotide-binding site, does not affect the usual myosin SRX state but instead appears to render myosin into a new, perhaps much more inhibited, 'ultra-relaxed' state. X-ray scattering-based rigid body modeling shows that both mavacamten and para-nitroblebbistatin induce novel conformations in human β-cardiac heavy meromyosin that diverge significantly from the hypothetical open and closed states, and furthermore, mavacamten treatment causes greater compaction than para-nitroblebbistatin. Taken together, we conclude that mavacamten and para-nitroblebbistatin stabilize myosin in different structural states, and such states may give rise to different functional energy-sparing states.
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12
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Barrick SK, Greenberg MJ. Cardiac myosin contraction and mechanotransduction in health and disease. J Biol Chem 2021; 297:101297. [PMID: 34634306 PMCID: PMC8559575 DOI: 10.1016/j.jbc.2021.101297] [Citation(s) in RCA: 38] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2021] [Revised: 10/06/2021] [Accepted: 10/07/2021] [Indexed: 12/17/2022] Open
Abstract
Cardiac myosin is the molecular motor that powers heart contraction by converting chemical energy from ATP hydrolysis into mechanical force. The power output of the heart is tightly regulated to meet the physiological needs of the body. Recent multiscale studies spanning from molecules to tissues have revealed complex regulatory mechanisms that fine-tune cardiac contraction, in which myosin not only generates power output but also plays an active role in its regulation. Thus, myosin is both shaped by and actively involved in shaping its mechanical environment. Moreover, these studies have shown that cardiac myosin-generated tension affects physiological processes beyond muscle contraction. Here, we review these novel regulatory mechanisms, as well as the roles that myosin-based force generation and mechanotransduction play in development and disease. We describe how key intra- and intermolecular interactions contribute to the regulation of myosin-based contractility and the role of mechanical forces in tuning myosin function. We also discuss the emergence of cardiac myosin as a drug target for diseases including heart failure, leading to the discovery of therapeutics that directly tune myosin contractility. Finally, we highlight some of the outstanding questions that must be addressed to better understand myosin's functions and regulation, and we discuss prospects for translating these discoveries into precision medicine therapeutics targeting contractility and mechanotransduction.
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Affiliation(s)
- Samantha K Barrick
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri, USA
| | - Michael J Greenberg
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri, USA.
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13
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Squire JM, Knupp C. Analysis methods and quality criteria for investigating muscle physiology using x-ray diffraction. J Gen Physiol 2021; 153:212538. [PMID: 34351359 PMCID: PMC8348228 DOI: 10.1085/jgp.202012778] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2020] [Revised: 12/23/2020] [Accepted: 07/12/2021] [Indexed: 12/20/2022] Open
Abstract
X-ray diffraction studies of muscle have been tremendously powerful in providing fundamental insights into the structures of, for example, the myosin and actin filaments in a variety of muscles and the physiology of the cross-bridge mechanism during the contractile cycle. However, interpretation of x-ray diffraction patterns is far from trivial, and if modeling of the observed diffraction intensities is required it needs to be performed carefully with full knowledge of the possible pitfalls. Here, we discuss (1) how x-ray diffraction can be used as a tool to monitor various specific muscle properties and (2) how to get the most out of the rest of the observed muscle x-ray diffraction patterns by modeling where the reliability of the modeling conclusions can be objectively tested. In other x-ray diffraction methods, such as protein crystallography, the reliability of every step of the process is estimated and quoted in published papers. In this way, the quality of the structure determination can be properly assessed. To be honest with ourselves in the muscle field, we need to do as near to the same as we can, within the limitations of the techniques that we are using. We discuss how this can be done. We also use test cases to reveal the dos and don’ts of using x-ray diffraction to study muscle physiology.
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Affiliation(s)
- John M Squire
- Muscle Contraction Group, School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, UK.,Faculty of Medicine, Imperial College, London, UK
| | - Carlo Knupp
- School of Optometry and Vision Sciences, Cardiff University, Cardiff, UK
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14
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Schmid M, Toepfer CN. Cardiac myosin super relaxation (SRX): a perspective on fundamental biology, human disease and therapeutics. Biol Open 2021; 10:bio057646. [PMID: 33589442 PMCID: PMC7904003 DOI: 10.1242/bio.057646] [Citation(s) in RCA: 42] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
The fundamental basis of muscle contraction 'the sliding filament model' (Huxley and Niedergerke, 1954; Huxley and Hanson, 1954) and the 'swinging, tilting crossbridge-sliding filament mechanism' (Huxley, 1969; Huxley and Brown, 1967) nucleated a field of research that has unearthed the complex and fascinating role of myosin structure in the regulation of contraction. A recently discovered energy conserving state of myosin termed the super relaxed state (SRX) has been observed in filamentous myosins and is central to modulating force production and energy use within the sarcomere. Modulation of myosin function through SRX is a rapidly developing theme in therapeutic development for both cardiovascular disease and infectious disease. Some 70 years after the first discoveries concerning muscular function, modulation of myosin SRX may bring the first myosin targeted small molecule to the clinic, for treating hypertrophic cardiomyopathy (Olivotto et al., 2020). An often monogenic disease HCM afflicts 1 in 500 individuals, and can cause heart failure and sudden cardiac death. Even as we near therapeutic translation, there remain many questions about the governance of muscle function in human health and disease. With this review, we provide a broad overview of contemporary understanding of myosin SRX, and explore the complexities of targeting this myosin state in human disease.This article has an associated Future Leaders to Watch interview with the authors of the paper.
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Affiliation(s)
- Manuel Schmid
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford OX3 9DU, UK
| | - Christopher N Toepfer
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford OX3 9DU, UK
- Department of Genetics, Harvard Medical School, Boston, MA 02115, USA
- Wellcome Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, UK
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15
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Abstract
Since the discovery of muscle in the 19th century, myosins as molecular motors have been extensively studied. However, in the last decade, a new functional super-relaxed (SRX) state of myosin has been discovered, which has a 10-fold slower ATP turnover rate than the already-known non-actin-bound, disordered relaxed (DRX) state. These two states are in dynamic equilibrium under resting muscle conditions and are thought to be significant contributors to adaptive thermogenesis in skeletal muscle and can act as a reserve pool that may be recruited when there is a sustained demand for increased cardiac muscle power. This report provides an evolutionary perspective of how striated muscle contraction is regulated by modulating this myosin DRX↔SRX state equilibrium. We further discuss this equilibrium with respect to different physiological and pathophysiological perturbations, including insults causing hypertrophic cardiomyopathy, and small-molecule effectors that modulate muscle contractility in diseased pathology.
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Affiliation(s)
- Suman Nag
- Department of Biology, MyoKardia IncBrisbaneUnited States
| | - Darshan V Trivedi
- Department of Biochemistry, Stanford University School of MedicineStanfordUnited States
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16
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Trivedi DV, Nag S, Spudich A, Ruppel KM, Spudich JA. The Myosin Family of Mechanoenzymes: From Mechanisms to Therapeutic Approaches. Annu Rev Biochem 2020; 89:667-693. [PMID: 32169021 DOI: 10.1146/annurev-biochem-011520-105234] [Citation(s) in RCA: 38] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Myosins are among the most fascinating enzymes in biology. As extremely allosteric chemomechanical molecular machines, myosins are involved in myriad pivotal cellular functions and are frequently sites of mutations leading to disease phenotypes. Human β-cardiac myosin has proved to be an excellent target for small-molecule therapeutics for heart muscle diseases, and, as we describe here, other myosin family members are likely to be potentially unique targets for treating other diseases as well. The first part of this review focuses on how myosins convert the chemical energy of ATP hydrolysis into mechanical movement, followed by a description of existing therapeutic approaches to target human β-cardiac myosin. The next section focuses on the possibility of targeting nonmuscle members of the human myosin family for several diseases. We end the review by describing the roles of myosin in parasites and the therapeutic potential of targeting them to block parasitic invasion of their hosts.
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Affiliation(s)
- Darshan V Trivedi
- Department of Biochemistry, Stanford University School of Medicine, Stanford, California 94305, USA; , , .,Stanford Cardiovascular Institute, Stanford University School of Medicine, Stanford, California 94305, USA
| | - Suman Nag
- MyoKardia Inc., Brisbane, California 94005, USA;
| | - Annamma Spudich
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560-097, India;
| | - Kathleen M Ruppel
- Department of Biochemistry, Stanford University School of Medicine, Stanford, California 94305, USA; , , .,Stanford Cardiovascular Institute, Stanford University School of Medicine, Stanford, California 94305, USA.,Division of Pediatric Cardiology, Department of Pediatrics, Stanford University School of Medicine, Stanford, California 94305, USA
| | - James A Spudich
- Department of Biochemistry, Stanford University School of Medicine, Stanford, California 94305, USA; , , .,Stanford Cardiovascular Institute, Stanford University School of Medicine, Stanford, California 94305, USA
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17
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Heling LWHJ, Geeves MA, Kad NM. MyBP-C: one protein to govern them all. J Muscle Res Cell Motil 2020; 41:91-101. [PMID: 31960266 PMCID: PMC7109175 DOI: 10.1007/s10974-019-09567-1] [Citation(s) in RCA: 45] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2019] [Accepted: 11/29/2019] [Indexed: 12/19/2022]
Abstract
The heart is an extraordinarily versatile pump, finely tuned to respond to a multitude of demands. Given the heart pumps without rest for decades its efficiency is particularly relevant. Although many proteins in the heart are essential for viability, the non-essential components can attract numerous mutations which can cause disease, possibly through alterations in pumping efficiency. Of these, myosin binding protein C is strongly over-represented with ~ 40% of all known mutations in hypertrophic cardiomyopathy. Therefore, a complete understanding of its molecular function in the cardiac sarcomere is warranted. In this review, we revisit contemporary and classical literature to clarify both the current standing of this fast-moving field and frame future unresolved questions. To date, much effort has been directed at understanding MyBP-C function on either thick or thin filaments. Here we aim to focus questions on how MyBP-C functions at a molecular level in the context of both the thick and thin filaments together. A concept that emerges is MyBP-C acts to govern interactions on two levels; controlling myosin access to the thin filament by sequestration on the thick filament, and controlling the activation state and access of myosin to its binding sites on the thin filament. Such affects are achieved through directed interactions mediated by phosphorylation (of MyBP-C and other sarcomeric components) and calcium.
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Affiliation(s)
- L W H J Heling
- School of Biosciences, University of Kent, Canterbury, CT2 7NH, UK
| | - M A Geeves
- School of Biosciences, University of Kent, Canterbury, CT2 7NH, UK
| | - N M Kad
- School of Biosciences, University of Kent, Canterbury, CT2 7NH, UK.
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18
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Caldwell JT, Mermelstein DJ, Walker RC, Bernstein SI, Huxford T. X-ray Crystallographic and Molecular Dynamic Analyses of Drosophila melanogaster Embryonic Muscle Myosin Define Domains Responsible for Isoform-Specific Properties. J Mol Biol 2020; 432:427-447. [PMID: 31786266 PMCID: PMC6995774 DOI: 10.1016/j.jmb.2019.11.013] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2019] [Revised: 11/19/2019] [Accepted: 11/19/2019] [Indexed: 01/19/2023]
Abstract
Drosophila melanogaster is a powerful system for characterizing alternative myosin isoforms and modeling muscle diseases, but high-resolution structures of fruit fly contractile proteins have not been determined. Here we report the first x-ray crystal structure of an insect myosin: the D melanogaster skeletal muscle myosin II embryonic isoform (EMB). Using our system for recombinant expression of myosin heavy chain (MHC) proteins in whole transgenic flies, we prepared and crystallized stable proteolytic S1-like fragments containing the entire EMB motor domain bound to an essential light chain. We solved the x-ray crystal structure by molecular replacement and refined the resulting model against diffraction data to 2.2 Å resolution. The protein is captured in two slightly different renditions of the rigor-like conformation with a citrate of crystallization at the nucleotide binding site and exhibits structural features common to myosins of diverse classes from all kingdoms of life. All atom molecular dynamics simulations on EMB in its nucleotide-free state and a derivative homology model containing 61 amino acid substitutions unique to the indirect flight muscle isoform (IFI) suggest that differences in the identity of residues within the relay and the converter that are encoded for by MHC alternative exons 9 and 11, respectively, directly contribute to increased mobility of these regions in IFI relative to EMB. This suggests the possibility that alternative folding or conformational stability within these regions contribute to the observed functional differences in Drosophila EMB and IFI myosins.
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Affiliation(s)
- James T Caldwell
- Structural Biochemistry Laboratory, Department of Chemistry & Biochemistry, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182-1030, USA; Department of Biology and Molecular Biology Institute, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182-4614, USA
| | - Daniel J Mermelstein
- San Diego Supercomputer Center and Department of Chemistry & Biochemistry, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0505, USA
| | - Ross C Walker
- San Diego Supercomputer Center and Department of Chemistry & Biochemistry, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0505, USA
| | - Sanford I Bernstein
- Department of Biology and Molecular Biology Institute, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182-4614, USA
| | - Tom Huxford
- Structural Biochemistry Laboratory, Department of Chemistry & Biochemistry, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182-1030, USA.
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19
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Special Issue: The Actin-Myosin Interaction in Muscle: Background and Overview. Int J Mol Sci 2019; 20:ijms20225715. [PMID: 31739584 PMCID: PMC6887992 DOI: 10.3390/ijms20225715] [Citation(s) in RCA: 38] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2019] [Accepted: 10/15/2019] [Indexed: 12/12/2022] Open
Abstract
Muscular contraction is a fundamental phenomenon in all animals; without it life as we know it would be impossible. The basic mechanism in muscle, including heart muscle, involves the interaction of the protein filaments myosin and actin. Motility in all cells is also partly based on similar interactions of actin filaments with non-muscle myosins. Early studies of muscle contraction have informed later studies of these cellular actin-myosin systems. In muscles, projections on the myosin filaments, the so-called myosin heads or cross-bridges, interact with the nearby actin filaments and, in a mechanism powered by ATP-hydrolysis, they move the actin filaments past them in a kind of cyclic rowing action to produce the macroscopic muscular movements of which we are all aware. In this special issue the papers and reviews address different aspects of the actin-myosin interaction in muscle as studied by a plethora of complementary techniques. The present overview provides a brief and elementary introduction to muscle structure and function and the techniques used to study it. It goes on to give more detailed descriptions of what is known about muscle components and the cross-bridge cycle using structural biology techniques, particularly protein crystallography, electron microscopy and X-ray diffraction. It then has a quick look at muscle mechanics and it summarises what can be learnt about how muscle works based on the other studies covered in the different papers in the special issue. A picture emerges of the main molecular steps involved in the force-producing process; steps that are also likely to be seen in non-muscle myosin interactions with cellular actin filaments. Finally, the remarkable advances made in studying the effects of mutations in the contractile assembly in causing specific muscle diseases, particularly those in heart muscle, are outlined and discussed.
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20
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Myosin Cross-Bridge Behaviour in Contracting Muscle-The T 1 Curve of Huxley and Simmons (1971) Revisited. Int J Mol Sci 2019; 20:ijms20194892. [PMID: 31581677 PMCID: PMC6801930 DOI: 10.3390/ijms20194892] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2019] [Revised: 09/26/2019] [Accepted: 09/29/2019] [Indexed: 12/19/2022] Open
Abstract
The stiffness of the myosin cross-bridges is a key factor in analysing possible scenarios to explain myosin head changes during force generation in active muscles. The seminal study of Huxley and Simmons (1971: Nature233: 533) suggested that most of the observed half-sarcomere instantaneous compliance (=1/stiffness) resides in the myosin heads. They showed with a so-called T1 plot that, after a very fast release, the half-sarcomere tension reduced to zero after a step size of about 60Å (later with improved experiments reduced to 40Å). However, later X-ray diffraction studies showed that myosin and actin filaments themselves stretch slightly under tension, which means that most (at least two-thirds) of the half sarcomere compliance comes from the filaments and not from cross-bridges. Here we have used a different approach, namely to model the compliances in a virtual half sarcomere structure in silico. We confirm that the T1 curve comes almost entirely from length changes in the myosin and actin filaments, because the calculated cross-bridge stiffness (probably greater than 0.4 pN/Å) is higher than previous studies have suggested. Our model demonstrates that the formulations produced by previous authors give very similar results to our model if the same starting parameters are used. However, we find that it is necessary to model the X-ray diffraction data as well as mechanics data to get a reliable estimate of the cross-bridge stiffness. In the light of the high cross-bridge stiffness found in the present study, we present a plausible modified scenario to describe aspects of the myosin cross-bridge cycle in active muscle. In particular, we suggest that, apart from the filament compliances, most of the cross-bridge contribution to the instantaneous T1 response may come from weakly-bound myosin heads, not myosin heads in strongly attached states. The strongly attached heads would still contribute to the T1 curve, but only in a very minor way, with a stiffness that we postulate could be around 0.1 pN/Å, a value which would generate a working stroke close to 100 Å from the hydrolysis of one ATP molecule. The new model can serve as a tool to calculate sarcomere elastic properties for any vertebrate striated muscle once various parameters have been determined (e.g., tension, T1 intercept, temperature, X-ray diffraction spacing results).
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21
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Knupp C, Morris E, Squire JM. The Interacting Head Motif Structure Does Not Explain the X-Ray Diffraction Patterns in Relaxed Vertebrate (Bony Fish) Skeletal Muscle and Insect ( Lethocerus) Flight Muscle. BIOLOGY 2019; 8:E67. [PMID: 31540109 PMCID: PMC6784062 DOI: 10.3390/biology8030067] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/18/2019] [Revised: 08/31/2019] [Accepted: 09/10/2019] [Indexed: 11/17/2022]
Abstract
Unlike electron microscopy, which can achieve very high resolution but to date can only be used to study static structures, time-resolved X-ray diffraction from contracting muscles can, in principle, be used to follow the molecular movements involved in force generation on a millisecond timescale, albeit at moderate resolution. However, previous X-ray diffraction studies of resting muscles have come up with structures for the head arrangements in resting myosin filaments that are different from the apparently ubiquitous interacting head motif (IHM) structures found by single particle analysis of electron micrographs of isolated myosin filaments from a variety of muscle types. This head organization is supposed to represent the super-relaxed state of the myosin filaments where adenosine triphosphate (ATP) usage is minimized. Here we have tested whether the interacting head motif structures will satisfactorily explain the observed low-angle X-ray diffraction patterns from resting vertebrate (bony fish) and invertebrate (insect flight) muscles. We find that the interacting head motif does not, in fact, explain what is observed. Previous X-ray models fit the observations much better. We conclude that the X-ray diffraction evidence has been well interpreted in the past and that there is more than one ordered myosin head state in resting muscle. There is, therefore, no reason to question some of the previous X-ray diffraction results on myosin filaments; time-resolved X-ray diffraction should be a reliable way to follow crossbridge action in active muscle and may be one of the few ways to visualise the molecular changes in myosin heads on a millisecond timescale as force is actually produced.
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Affiliation(s)
- Carlo Knupp
- School of Optometry and Vision Science, Cardiff University, Cardiff CF10 3NB, UK.
| | - Edward Morris
- Division of Structural Biology, Institute of Cancer Research, London SW7 3RP, UK.
| | - John M Squire
- Muscle Contraction Group, School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol BS8 1TD, UK.
- Computational and Systems Medicine, Faculty of Medicine, Imperial College, London SW7 2BZ, UK.
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22
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Spudich JA. Three perspectives on the molecular basis of hypercontractility caused by hypertrophic cardiomyopathy mutations. Pflugers Arch 2019; 471:701-717. [PMID: 30767072 PMCID: PMC6475635 DOI: 10.1007/s00424-019-02259-2] [Citation(s) in RCA: 104] [Impact Index Per Article: 20.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2018] [Revised: 01/11/2019] [Accepted: 01/20/2019] [Indexed: 01/10/2023]
Abstract
Several lines of evidence suggest that the primary effect of hypertrophic cardiomyopathy mutations in human β-cardiac myosin is hypercontractility of the heart, which leads to subsequent hypertrophy, fibrosis, and myofilament disarray. Here, I describe three perspectives on the molecular basis of this hypercontractility. The first is that hypercontractility results from changes in the fundamental parameters of the actin-activated β-cardiac myosin chemo-mechanical ATPase cycle. The second considers that hypercontractility results from an increase in the number of functionally accessible heads in the sarcomere for interaction with actin. The final and third perspective is that load dependence of contractility is affected by cardiomyopathy mutations and small-molecule effectors in a manner that changes the power output of cardiac contraction. Experimental approaches associated with each perspective are described along with concepts of therapeutic approaches that could prove valuable in treating hypertrophic cardiomyopathy.
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Affiliation(s)
- James A Spudich
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA, 94305, USA.
- Cardiovascular Institute, Stanford University School of Medicine, Stanford, CA, 94305, USA.
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23
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Bell KM, Kronert WA, Huang A, Bernstein SI, Swank DM. The R249Q hypertrophic cardiomyopathy myosin mutation decreases contractility in Drosophila by impeding force production. J Physiol 2019; 597:2403-2420. [PMID: 30950055 DOI: 10.1113/jp277333] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2018] [Accepted: 03/06/2019] [Indexed: 12/18/2022] Open
Abstract
KEY POINTS Hypertrophic cardiomyopathy (HCM) is a genetic disease that causes thickening of the heart's ventricular walls and is a leading cause of sudden cardiac death. HCM is caused by missense mutations in muscle proteins including myosin, but how these mutations alter muscle mechanical performance in largely unknown. We investigated the disease mechanism for HCM myosin mutation R249Q by expressing it in the indirect flight muscle of Drosophila melanogaster and measuring alterations to muscle and flight performance. Muscle mechanical analysis revealed R249Q decreased muscle power production due to slower muscle kinetics and decreased force production; force production was reduced because fewer mutant myosin cross-bridges were bound simultaneously to actin. This work does not support the commonly proposed hypothesis that myosin HCM mutations increase muscle contractility, or causes a gain in function; instead, it suggests that for some myosin HCM mutations, hypertrophy is a compensation for decreased contractility. ABSTRACT Hypertrophic cardiomyopathy (HCM) is an inherited disease that causes thickening of the heart's ventricular walls. A generally accepted hypothesis for this phenotype is that myosin heavy chain HCM mutations increase muscle contractility. To test this hypothesis, we expressed an HCM myosin mutation, R249Q, in Drosophila indirect flight muscle (IFM) and assessed myofibril structure, skinned fibre mechanical properties, and flight ability. Mechanics experiments were performed on fibres dissected from 2-h-old adult flies, prior to degradation of IFM myofilament structure, which started at 2 days old and increased with age. Homozygous and heterozygous R249Q fibres showed decreased maximum power generation by 67% and 44%, respectively. Decreases in force and work and slower overall muscle kinetics caused homozygous fibres to produce less power. While heterozygous fibres showed no overall slowing of muscle kinetics, active force and work production dropped by 68% and 47%, respectively, which hindered power production. The muscle apparent rate constant 2πb decreased 33% for homozygous but increased for heterozygous fibres. The apparent rate constant 2πc was greater for homozygous fibres. This indicates that R249Q myosin is slowing attachment while speeding up detachment from actin, resulting in less time bound. Decreased IFM power output caused 43% and 33% decreases in Drosophila flight ability and 19% and 6% drops in wing beat frequency for homozygous and heterozygous flies, respectively. Overall, our results do not support the increased contractility hypothesis. Instead, our results suggest the ventricular hypertrophy for human R249Q mutation is a compensatory response to decreases in heart muscle power output.
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Affiliation(s)
- Kaylyn M Bell
- Department of Biological Sciences & Biomedical Engineering, Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, NY, USA
| | - William A Kronert
- Department of Biology, Molecular Biology Institute and Heart Institute, San Diego State University, San Diego, CA, USA
| | - Alice Huang
- Department of Biological Sciences & Biomedical Engineering, Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, NY, USA
| | - Sanford I Bernstein
- Department of Biology, Molecular Biology Institute and Heart Institute, San Diego State University, San Diego, CA, USA
| | - Douglas M Swank
- Department of Biological Sciences & Biomedical Engineering, Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, NY, USA
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24
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Anderson RL, Trivedi DV, Sarkar SS, Henze M, Ma W, Gong H, Rogers CS, Gorham JM, Wong FL, Morck MM, Seidman JG, Ruppel KM, Irving TC, Cooke R, Green EM, Spudich JA. Deciphering the super relaxed state of human β-cardiac myosin and the mode of action of mavacamten from myosin molecules to muscle fibers. Proc Natl Acad Sci U S A 2018; 115:E8143-E8152. [PMID: 30104387 PMCID: PMC6126717 DOI: 10.1073/pnas.1809540115] [Citation(s) in RCA: 239] [Impact Index Per Article: 39.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Mutations in β-cardiac myosin, the predominant motor protein for human heart contraction, can alter power output and cause cardiomyopathy. However, measurements of the intrinsic force, velocity, and ATPase activity of myosin have not provided a consistent mechanism to link mutations to muscle pathology. An alternative model posits that mutations in myosin affect the stability of a sequestered, super relaxed state (SRX) of the protein with very slow ATP hydrolysis and thereby change the number of myosin heads accessible to actin. Here we show that purified human β-cardiac myosin exists partly in an SRX and may in part correspond to a folded-back conformation of myosin heads observed in muscle fibers around the thick filament backbone. Mutations that cause hypertrophic cardiomyopathy destabilize this state, while the small molecule mavacamten promotes it. These findings provide a biochemical and structural link between the genetics and physiology of cardiomyopathy with implications for therapeutic strategies.
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Affiliation(s)
| | - Darshan V Trivedi
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305
- Stanford Cardiovascular Institute, Stanford University School of Medicine, Stanford, CA 94305
| | - Saswata S Sarkar
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305
- Stanford Cardiovascular Institute, Stanford University School of Medicine, Stanford, CA 94305
| | | | - Weikang Ma
- BioCAT, Department of Biological Sciences, Illinois Institute of Technology, Chicago, IL 60616
| | - Henry Gong
- BioCAT, Department of Biological Sciences, Illinois Institute of Technology, Chicago, IL 60616
| | | | - Joshua M Gorham
- Department of Genetics, Harvard Medical School, Boston, MA 02115
| | | | - Makenna M Morck
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305
| | | | - Kathleen M Ruppel
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305
- Stanford Cardiovascular Institute, Stanford University School of Medicine, Stanford, CA 94305
- Department of Pediatrics (Cardiology), Stanford University School of Medicine, Stanford, CA 94305
| | - Thomas C Irving
- BioCAT, Department of Biological Sciences, Illinois Institute of Technology, Chicago, IL 60616
| | - Roger Cooke
- Department of Biochemistry, University of California, San Francisco, CA 94158
| | | | - James A Spudich
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305;
- Stanford Cardiovascular Institute, Stanford University School of Medicine, Stanford, CA 94305
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25
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Pecci A, Ma X, Savoia A, Adelstein RS. MYH9: Structure, functions and role of non-muscle myosin IIA in human disease. Gene 2018; 664:152-167. [PMID: 29679756 PMCID: PMC5970098 DOI: 10.1016/j.gene.2018.04.048] [Citation(s) in RCA: 169] [Impact Index Per Article: 28.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2018] [Revised: 04/13/2018] [Accepted: 04/16/2018] [Indexed: 12/16/2022]
Abstract
The MYH9 gene encodes the heavy chain of non-muscle myosin IIA, a widely expressed cytoplasmic myosin that participates in a variety of processes requiring the generation of intracellular chemomechanical force and translocation of the actin cytoskeleton. Non-muscle myosin IIA functions are regulated by phosphorylation of its 20 kDa light chain, of the heavy chain, and by interactions with other proteins. Variants of MYH9 cause an autosomal-dominant disorder, termed MYH9-related disease, and may be involved in other conditions, such as chronic kidney disease, non-syndromic deafness, and cancer. This review discusses the structure of the MYH9 gene and its protein, as well as the regulation and physiologic functions of non-muscle myosin IIA with particular reference to embryonic development. Moreover, the review focuses on current knowledge about the role of MYH9 variants in human disease.
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Affiliation(s)
- Alessandro Pecci
- Department of Internal Medicine, IRCCS Policlinico San Matteo Foundation, University of Pavia, Piazzale Golgi, 27100 Pavia, Italy.
| | - Xuefei Ma
- Laboratory of Molecular Cardiology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bldg. 10 Room 6C-103B, 10 Center Drive, Bethesda, MD 20892-1583, USA.
| | - Anna Savoia
- Department of Medical Sciences, University of Trieste, via Dell'Istria, 65/1, I-34137 Trieste, Italy; IRCCS Burlo Garofolo, via Dell'Istria, 65/1, I-34137 Trieste, Italy.
| | - Robert S Adelstein
- Laboratory of Molecular Cardiology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bldg. 10 Room 6C-103B, 10 Center Drive, Bethesda, MD 20892-1583, USA.
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Alamo L, Pinto A, Sulbarán G, Mavárez J, Padrón R. Lessons from a tarantula: new insights into myosin interacting-heads motif evolution and its implications on disease. Biophys Rev 2017; 10:1465-1477. [PMID: 28871552 DOI: 10.1007/s12551-017-0292-4] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2017] [Accepted: 07/27/2017] [Indexed: 12/18/2022] Open
Abstract
Tarantula's leg muscle thick filament is the ideal model for the study of the structure and function of skeletal muscle thick filaments. Its analysis has given rise to a series of structural and functional studies, leading, among other things, to the discovery of the myosin interacting-heads motif (IHM). Further electron microscopy (EM) studies have shown the presence of IHM in frozen-hydrated and negatively stained thick filaments of striated, cardiac, and smooth muscle of bilaterians, most showing the IHM parallel to the filament axis. EM studies on negatively stained heavy meromyosin of different species have shown the presence of IHM on sponges, animals that lack muscle, extending the presence of IHM to metazoans. The IHM evolved about 800 MY ago in the ancestor of Metazoa, and independently with functional differences in the lineage leading to the slime mold Dictyostelium discoideum (Mycetozoa). This motif conveys important functional advantages, such as Ca2+ regulation and ATP energy-saving mechanisms. Recent interest has focused on human IHM structure in order to understand the structural basis underlying various conditions and situations of scientific and medical interest: the hypertrophic and dilated cardiomyopathies, overfeeding control, aging and hormone deprival muscle weakness, drug design for schistosomiasis control, and conditioning exercise physiology for the training of power athletes.
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Affiliation(s)
- Lorenzo Alamo
- Centro de Biología Estructural "Humberto Fernández-Morán", Instituto Venezolano de Investigaciones Científicas (IVIC), Apdo. 20632, Caracas, 1020A, Venezuela
| | - Antonio Pinto
- Centro de Biología Estructural "Humberto Fernández-Morán", Instituto Venezolano de Investigaciones Científicas (IVIC), Apdo. 20632, Caracas, 1020A, Venezuela
| | - Guidenn Sulbarán
- Centro de Biología Estructural "Humberto Fernández-Morán", Instituto Venezolano de Investigaciones Científicas (IVIC), Apdo. 20632, Caracas, 1020A, Venezuela.,Institut de Biologie Structurale (IBS), CEA-CNRS Université Grenoble Alpes, Grenoble, France
| | - Jesús Mavárez
- Laboratoire d'Ecologie Alpine, UMR 5553 CNRS-Université Grenoble Alpes, 2233 Rue de la Piscine, 38041, Grenoble, France
| | - Raúl Padrón
- Centro de Biología Estructural "Humberto Fernández-Morán", Instituto Venezolano de Investigaciones Científicas (IVIC), Apdo. 20632, Caracas, 1020A, Venezuela.
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Alamo L, Koubassova N, Pinto A, Gillilan R, Tsaturyan A, Padrón R. Lessons from a tarantula: new insights into muscle thick filament and myosin interacting-heads motif structure and function. Biophys Rev 2017; 9:461-480. [PMID: 28871556 DOI: 10.1007/s12551-017-0295-1] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2017] [Accepted: 07/27/2017] [Indexed: 12/13/2022] Open
Abstract
The tarantula skeletal muscle X-ray diffraction pattern suggested that the myosin heads were helically arranged on the thick filaments. Electron microscopy (EM) of negatively stained relaxed tarantula thick filaments revealed four helices of heads allowing a helical 3D reconstruction. Due to its low resolution (5.0 nm), the unambiguous interpretation of densities of both heads was not possible. A resolution increase up to 2.5 nm, achieved by cryo-EM of frozen-hydrated relaxed thick filaments and an iterative helical real space reconstruction, allowed the resolving of both heads. The two heads, "free" and "blocked", formed an asymmetric structure named the "interacting-heads motif" (IHM) which explained relaxation by self-inhibition of both heads ATPases. This finding made tarantula an exemplar system for thick filament structure and function studies. Heads were shown to be released and disordered by Ca2+-activation through myosin regulatory light chain phosphorylation, leading to EM, small angle X-ray diffraction and scattering, and spectroscopic and biochemical studies of the IHM structure and function. The results from these studies have consequent implications for understanding and explaining myosin super-relaxed state and thick filament activation and regulation. A cooperative phosphorylation mechanism for activation in tarantula skeletal muscle, involving swaying constitutively Ser35 mono-phosphorylated free heads, explains super-relaxation, force potentiation and post-tetanic potentiation through Ser45 mono-phosphorylated blocked heads. Based on this mechanism, we propose a swaying-swinging, tilting crossbridge-sliding filament for tarantula muscle contraction.
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Affiliation(s)
- Lorenzo Alamo
- Centro de Biología Estructural "Humberto Fernández-Morán", Instituto Venezolano de Investigaciones Científicas (IVIC), Apdo. 20632, Caracas, 1020A, Venezuela
| | - Natalia Koubassova
- Institute of Mechanics, Moscow State University, Mitchurinsky prosp. 1, Moscow, 119992, Russia
| | - Antonio Pinto
- Centro de Biología Estructural "Humberto Fernández-Morán", Instituto Venezolano de Investigaciones Científicas (IVIC), Apdo. 20632, Caracas, 1020A, Venezuela
| | - Richard Gillilan
- Macromolecular Diffraction Facility, Cornell High Energy Synchrotron Source, Ithaca, NY, USA
| | - Andrey Tsaturyan
- Institute of Mechanics, Moscow State University, Mitchurinsky prosp. 1, Moscow, 119992, Russia
| | - Raúl Padrón
- Centro de Biología Estructural "Humberto Fernández-Morán", Instituto Venezolano de Investigaciones Científicas (IVIC), Apdo. 20632, Caracas, 1020A, Venezuela.
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28
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Gao N, Tsai MH, Chang AN, He W, Chen CP, Zhu M, Kamm KE, Stull JT. Physiological vs. pharmacological signalling to myosin phosphorylation in airway smooth muscle. J Physiol 2017; 595:6231-6247. [PMID: 28749013 PMCID: PMC5621497 DOI: 10.1113/jp274715] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2017] [Accepted: 07/25/2017] [Indexed: 01/05/2023] Open
Abstract
KEY POINTS Smooth muscle myosin regulatory light chain (RLC) is phosphorylated by Ca2+ /calmodulin-dependent myosin light chain kinase and dephosphorylated by myosin light chain phosphatase (MLCP). Tracheal smooth muscle contains significant amounts of myosin binding subunit 85 (MBS85), another myosin phosphatase targeting subunit (MYPT) family member, in addition to MLCP regulatory subunit MYPT1. Concentration/temporal responses to carbachol demonstrated similar sensitivities for bovine tracheal force development and phosphorylation of RLC, MYPT1, MBS85 and paxillin. Electrical field stimulation releases ACh from nerves to increase RLC phosphorylation but not MYPT1 or MBS85 phosphorylation. Thus, nerve-mediated muscarinic responses in signalling modules acting on RLC phosphorylation are different from pharmacological responses with bath added agonist. The conditional knockout of MYPT1 or the knock-in mutation T853A in mice had no effect on muscarinic force responses in isolated tracheal tissues. MLCP activity may arise from functionally shared roles between MYPT1 and MBS85, resulting in minimal effects of MYPT1 knockout on contraction. ABSTRACT Ca2+ /calmodulin activation of myosin light chain kinase (MLCK) initiates myosin regulatory light chain (RLC) phosphorylation for smooth muscle contraction with subsequent dephosphorylation for relaxation by myosin light chain phosphatase (MLCP) containing regulatory (MYPT1) and catalytic (PP1cδ) subunits. RLC phosphorylation-dependent force development is regulated by distinct signalling modules involving protein phosphorylations. We investigated responses to cholinergic agonist treatment vs. neurostimulation by electric field stimulation (EFS) in bovine tracheal smooth muscle. Concentration/temporal responses to carbachol demonstrated tight coupling between force development and RLC phosphorylation but sensitivity differences in MLCK, MYPT1 T853, MYPT1 T696, myosin binding subunit 85 (MBS85), paxillin and CPI-17 (PKC-potentiated protein phosphatase 1 inhibitor protein of 17 kDa) phosphorylations. EFS increased force and phosphorylation of RLC, CPI-17 and MLCK. In the presence of the cholinesterase inhibitor neostigmine, EFS led to an additional increase in phosphorylation of MYPT1 T853, MYPT1 T696, MBS85 and paxillin. Thus, there were distinct pharmacological vs. physiological responses in signalling modules acting on RLC phosphorylation and force responses, probably related to degenerate G protein signalling networks. Studies with genetically modified mice were performed. Expression of another MYPT1 family member, MBS85, was enriched in mouse, as well as bovine tracheal smooth muscle. Carbachol concentration/temporal-force responses were similar in trachea from MYPT1SM+/+ , MYPT1SM-/- and the knock-in mutant mice containing nonphosphorylatable MYPT1 T853A with no differences in RLC phosphorylation. Thus, MYPT1 T853 phosphorylation was not necessary for regulation of RLC phosphorylation in tonic airway smooth muscle. Furthermore, MLCP activity may arise from functionally shared roles between MYPT1 and MBS85, resulting in minimal effects of MYPT1 knockout on contraction.
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Affiliation(s)
- Ning Gao
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Ming-Ho Tsai
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX, USA.,Present address: Graduate Institute of Medicine, Kaohsiung Medical University, 100 Shih-Chuan 1st Rd, San Ming District, Kaohsiung, Taiwan
| | - Audrey N Chang
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Weiqi He
- Model Animal Research Center and MOE Key Laboratory of Model Animal for Disease Study, Nanjing University, Nanjing, China.,Present address: Cambridge-Suda (CAM-SU) Genomic Resource Center, Soochow University, Suzhou, China
| | - Cai-Ping Chen
- Model Animal Research Center and MOE Key Laboratory of Model Animal for Disease Study, Nanjing University, Nanjing, China.,Present address: Jiangsu Key Laboratory of Drug Discovery for Metabolic Disease, China Pharmaceutical University, Nanjing, PR China
| | - Minsheng Zhu
- Model Animal Research Center and MOE Key Laboratory of Model Animal for Disease Study, Nanjing University, Nanjing, China
| | - Kristine E Kamm
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - James T Stull
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX, USA
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Fission yeast myosin Myo2 is down-regulated in actin affinity by light chain phosphorylation. Proc Natl Acad Sci U S A 2017; 114:E7236-E7244. [PMID: 28808035 DOI: 10.1073/pnas.1703161114] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Studies in fission yeast Schizosaccharomyces pombe have provided the basis for the most advanced models of the dynamics of the cytokinetic contractile ring. Myo2, a class-II myosin, is the major source of tension in the contractile ring, but how Myo2 is anchored and regulated to produce force is poorly understood. To enable more detailed biochemical/biophysical studies, Myo2 was expressed in the baculovirus/Sf9 insect cell system with its two native light chains, Rlc1 and Cdc4. Milligram yields of soluble, unphosphorylated Myo2 were obtained that exhibited high actin-activated ATPase activity and in vitro actin filament motility. The fission yeast specific chaperone Rng3 was thus not required for expression or activity. In contrast to nonmuscle myosins from animal cells that require phosphorylation of the regulatory light chain for activation, phosphorylation of Rlc1 markedly reduced the affinity of Myo2 for actin. Another unusual feature of Myo2 was that, unlike class-II myosins, which generally form bipolar filamentous structures, Myo2 showed no inclination to self-assemble at approximately physiological salt concentrations, as analyzed by sedimentation velocity ultracentrifugation. This lack of assembly supports the hypothesis that clusters of Myo2 depend on interactions at the cell cortex in structural units called nodes for force production during cytokinesis.
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30
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Effect of ATP and regulatory light-chain phosphorylation on the polymerization of mammalian nonmuscle myosin II. Proc Natl Acad Sci U S A 2017; 114:E6516-E6525. [PMID: 28739905 DOI: 10.1073/pnas.1702375114] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Addition of 1 mM ATP substantially reduces the light scattering of solutions of polymerized unphosphorylated nonmuscle myosin IIs (NM2s), and this is reversed by phosphorylation of the regulatory light chain (RLC). It has been proposed that these changes result from substantial depolymerization of unphosphorylated NM2 filaments to monomers upon addition of ATP, and filament repolymerization upon RLC-phosphorylation. We now show that the differences in myosin monomer concentration of RLC-unphosphorylated and -phosphorylated recombinant mammalian NM2A, NM2B, and NM2C polymerized in the presence of ATP are much too small to explain their substantial differences in light scattering. Rather, we find that the decrease in light scattering upon addition of ATP to polymerized unphosphorylated NM2s correlates with the formation of dimers, tetramers, and hexamers, in addition to monomers, an increase in length, and decrease in width of the bare zones of RLC-unphosphorylated filaments. Both effects of ATP addition are reversed by phosphorylation of the RLC. Our data also suggest that, contrary to previous models, assembly of RLC-phosphorylated NM2s at physiological ionic strength proceeds from folded monomers to folded antiparallel dimers, tetramers, and hexamers that unfold and polymerize into antiparallel filaments. This model could explain the dynamic relocalization of NM2 filaments in vivo by dephosphorylation of RLC-phosphorylated filaments, disassembly of the dephosphorylated filaments to folded monomers, dimers, and small oligomers, followed by diffusion of these species, and reassembly of filaments at the new location following rephosphorylation of the RLC.
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31
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Trivedi DV, Adhikari AS, Sarkar SS, Ruppel KM, Spudich JA. Hypertrophic cardiomyopathy and the myosin mesa: viewing an old disease in a new light. Biophys Rev 2017; 10:27-48. [PMID: 28717924 PMCID: PMC5803174 DOI: 10.1007/s12551-017-0274-6] [Citation(s) in RCA: 105] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2017] [Accepted: 06/12/2017] [Indexed: 12/15/2022] Open
Abstract
The sarcomere is an exquisitely designed apparatus that is capable of generating force, which in the case of the heart results in the pumping of blood throughout the body. At the molecular level, an ATP-dependent interaction of myosin with actin drives the contraction and force generation of the sarcomere. Over the past six decades, work on muscle has yielded tremendous insights into the workings of the sarcomeric system. We now stand on the cusp where the acquired knowledge of how the sarcomere contracts and how that contraction is regulated can be extended to an understanding of the molecular mechanisms of sarcomeric diseases, such as hypertrophic cardiomyopathy (HCM). In this review we present a picture that combines current knowledge of the myosin mesa, the sequestered state of myosin heads on the thick filament, known as the interacting-heads motif (IHM), their possible interaction with myosin binding protein C (MyBP-C) and how these interactions can be abrogated leading to hyper-contractility, a key clinical manifestation of HCM. We discuss the structural and functional basis of the IHM state of the myosin heads and identify HCM-causing mutations that can directly impact the equilibrium between the 'on state' of the myosin heads (the open state) and the IHM 'off state'. We also hypothesize a role of MyBP-C in helping to maintain myosin heads in the IHM state on the thick filament, allowing release in a graded manner upon adrenergic stimulation. By viewing clinical hyper-contractility as the result of the destabilization of the IHM state, our aim is to view an old disease in a new light.
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Affiliation(s)
- Darshan V Trivedi
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA, 94305, USA
| | - Arjun S Adhikari
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA, 94305, USA
| | - Saswata S Sarkar
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA, 94305, USA
| | - Kathleen M Ruppel
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA, 94305, USA. .,Department of Pediatrics (Cardiology), Stanford University School of Medicine, Stanford, CA, 94305, USA.
| | - James A Spudich
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA, 94305, USA.
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32
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Fee L, Lin W, Qiu F, Edwards RJ. Myosin II sequences for Lethocerus indicus. J Muscle Res Cell Motil 2017; 38:193-200. [PMID: 28707142 PMCID: PMC5660136 DOI: 10.1007/s10974-017-9476-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2017] [Accepted: 07/10/2017] [Indexed: 11/14/2022]
Abstract
We present the genomic and expressed myosin II sequences from the giant waterbug, Lethocerus indicus. The intron rich gene appears relatively ancient and contains six regions of mutually exclusive exons that are alternatively spliced. Alternatively spliced regions may be involved in the asymmetric myosin dimer structure known as the interacting heads motif, as well as stabilizing the interacting heads motif within the thick filament. A lack of negative charge in the myosin S2 domain may explain why Lethocerus thick filaments display a perpendicular interacting heads motif, rather than one folded back to contact S2, as is seen in other thick filament types such as those from tarantula.
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Affiliation(s)
- Lanette Fee
- Department of Cell Biology, Duke University, Box 3011, Durham, NC, 27705, USA
| | - Weili Lin
- Shanghai Center for Bioinformation Technology, 1278 Keyuan Rd. Fl. 2, Shanghai, 201203, China
| | - Feng Qiu
- Shanghai Center for Bioinformation Technology, 1278 Keyuan Rd. Fl. 2, Shanghai, 201203, China
| | - Robert J Edwards
- Department of Cell Biology, Duke University, Box 3011, Durham, NC, 27705, USA.
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33
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Zhang W, Gunst SJ. Non-muscle (NM) myosin heavy chain phosphorylation regulates the formation of NM myosin filaments, adhesome assembly and smooth muscle contraction. J Physiol 2017; 595:4279-4300. [PMID: 28303576 DOI: 10.1113/jp273906] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2016] [Accepted: 03/14/2017] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Non-muscle (NM) and smooth muscle (SM) myosin II are both expressed in smooth muscle tissues, however the role of NM myosin in SM contraction is unknown. Contractile stimulation of tracheal smooth muscle tissues stimulates phosphorylation of the NM myosin heavy chain on Ser1943 and causes NM myosin filament assembly at the SM cell cortex. Expression of a non-phosphorylatable NM myosin mutant, NM myosin S1943A, in SM tissues inhibits ACh-induced NM myosin filament assembly and SM contraction, and also inhibits the assembly of membrane adhesome complexes during contractile stimulation. NM myosin regulatory light chain (RLC) phosphorylation but not SM myosin RLC phosphorylation is regulated by RhoA GTPase during ACh stimulation, and NM RLC phosphorylation is required for NM myosin filament assembly and SM contraction. NM myosin II plays a critical role in airway SM contraction that is independent and distinct from the function of SM myosin. ABSTRACT The molecular function of non-muscle (NM) isoforms of myosin II in smooth muscle (SM) tissues and their possible role in contraction are largely unknown. We evaluated the function of NM myosin during contractile stimulation of canine tracheal SM tissues. Stimulation with ACh caused NM myosin filament assembly, as assessed by a Triton solubility assay and a proximity ligation assay aiming to measure interactions between NM myosin monomers. ACh stimulated the phosphorylation of NM myosin heavy chain on Ser1943 in tracheal SM tissues, which can regulate NM myosin IIA filament assembly in vitro. Expression of the non-phosphorylatable mutant NM myosin S1943A in SM tissues inhibited ACh-induced endogenous NM myosin Ser1943 phosphorylation, NM myosin filament formation, the assembly of membrane adhesome complexes and tension development. The NM myosin cross-bridge cycling inhibitor blebbistatin suppressed adhesome complex assembly and SM contraction without inhibiting NM myosin Ser1943 phosphorylation or NM myosin filament assembly. RhoA inactivation selectively inhibited phosphorylation of the NM myosin regulatory light chain (RLC), NM myosin filament assembly and contraction, although it did not inhibit SM RLC phosphorylation. We conclude that the assembly and activation of NM myosin II is regulated during contractile stimulation of airway SM tissues by RhoA-mediated NM myosin RLC phosphorylation and by NM myosin heavy chain Ser1943 phosphorylation. NM myosin II actomyosin cross-bridge cycling regulates the assembly of membrane adhesome complexes that mediate the cytoskeletal processes required for tension generation. NM myosin II plays a critical role in airway SM contraction that is independent and distinct from the function of SM myosin.
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Affiliation(s)
- Wenwu Zhang
- Department of Cellular & Integrative Physiology, Indiana University School of Medicine, Indianapolis, IN, USA
| | - Susan J Gunst
- Department of Cellular & Integrative Physiology, Indiana University School of Medicine, Indianapolis, IN, USA
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34
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Milewicz DM, Trybus KM, Guo DC, Sweeney HL, Regalado E, Kamm K, Stull JT. Altered Smooth Muscle Cell Force Generation as a Driver of Thoracic Aortic Aneurysms and Dissections. Arterioscler Thromb Vasc Biol 2017; 37:26-34. [PMID: 27879251 PMCID: PMC5222685 DOI: 10.1161/atvbaha.116.303229] [Citation(s) in RCA: 158] [Impact Index Per Article: 22.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2016] [Accepted: 11/02/2016] [Indexed: 12/30/2022]
Abstract
The importance of maintaining contractile function in aortic smooth muscle cells (SMCs) is evident by the fact that heterozygous mutations in the major structural proteins or kinases controlling contraction lead to the formation of aneurysms of the ascending thoracic aorta that predispose to life-threatening aortic dissections. Force generation by SMC requires ATP-dependent cyclic interactions between filaments composed of SMC-specific isoforms of α-actin (encoded by ACTA2) and myosin heavy chain (MYH11). ACTA2 and MYH11 mutations are predicted or have been shown to disrupt this cyclic interaction predispose to thoracic aortic disease. Movement of the myosin motor domain is controlled by phosphorylation of the regulatory light chain on the myosin filament, and loss-of-function mutations in the dedicated kinase for this phosphorylation, myosin light chain kinase (MYLK) also predispose to thoracic aortic disease. Finally, a mutation in the cGMP-activated protein kinase (PRKG1) results in constitutive activation of the kinase in the absence of cGMP, thus driving SMC relaxation in part through increased dephosphorylation of the regulatory light chain and predisposes to thoracic aortic disease. Furthermore, SMCs cannot generate force without connections to the extracellular matrix through focal adhesions, and mutations in the major protein in the extracellular matrix, fibrillin-1, linking SMCs to the matrix also cause thoracic aortic disease in individuals with Marfan syndrome. Thus, disruption of the ability of the aortic SMC to generate force through the elastin-contractile units in response to pulsatile blood flow may be a primary driver for thoracic aortic aneurysms and dissections.
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MESH Headings
- Actins/genetics
- Actins/metabolism
- Aortic Dissection/genetics
- Aortic Dissection/metabolism
- Aortic Dissection/pathology
- Aortic Dissection/physiopathology
- Animals
- Aortic Aneurysm, Thoracic/genetics
- Aortic Aneurysm, Thoracic/metabolism
- Aortic Aneurysm, Thoracic/pathology
- Aortic Aneurysm, Thoracic/physiopathology
- Calcium-Binding Proteins/genetics
- Calcium-Binding Proteins/metabolism
- Cyclic GMP-Dependent Protein Kinase Type I/genetics
- Cyclic GMP-Dependent Protein Kinase Type I/metabolism
- Dilatation, Pathologic
- Elastin/metabolism
- Genetic Markers
- Genetic Testing
- Heredity
- Humans
- Mechanotransduction, Cellular
- Muscle, Smooth, Vascular/metabolism
- Muscle, Smooth, Vascular/pathology
- Muscle, Smooth, Vascular/physiopathology
- Mutation
- Myocytes, Smooth Muscle/metabolism
- Myocytes, Smooth Muscle/pathology
- Myosin Heavy Chains/genetics
- Myosin Heavy Chains/metabolism
- Myosin-Light-Chain Kinase/genetics
- Myosin-Light-Chain Kinase/metabolism
- Phenotype
- Pulsatile Flow
- Vasoconstriction/genetics
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Affiliation(s)
- Dianna M Milewicz
- From the Department of Internal Medicine, McGovern Medical School at The University of Texas Health Science Center at Houston (D.M.M., D.-c.G., E.R.); Department of Molecular Physiology and Biophysics, University of Vermont, Burlington (K.M.T.); Department of Pharmacology and Therapeutics, University of Florida College of Medicine, Gainesville (H.L.S.); and Department of Physiology, University of Texas Southwestern Medical Center, Dallas (K.K. J.T.S.).
| | - Kathleen M Trybus
- From the Department of Internal Medicine, McGovern Medical School at The University of Texas Health Science Center at Houston (D.M.M., D.-c.G., E.R.); Department of Molecular Physiology and Biophysics, University of Vermont, Burlington (K.M.T.); Department of Pharmacology and Therapeutics, University of Florida College of Medicine, Gainesville (H.L.S.); and Department of Physiology, University of Texas Southwestern Medical Center, Dallas (K.K. J.T.S.)
| | - Dong-Chuan Guo
- From the Department of Internal Medicine, McGovern Medical School at The University of Texas Health Science Center at Houston (D.M.M., D.-c.G., E.R.); Department of Molecular Physiology and Biophysics, University of Vermont, Burlington (K.M.T.); Department of Pharmacology and Therapeutics, University of Florida College of Medicine, Gainesville (H.L.S.); and Department of Physiology, University of Texas Southwestern Medical Center, Dallas (K.K. J.T.S.)
| | - H Lee Sweeney
- From the Department of Internal Medicine, McGovern Medical School at The University of Texas Health Science Center at Houston (D.M.M., D.-c.G., E.R.); Department of Molecular Physiology and Biophysics, University of Vermont, Burlington (K.M.T.); Department of Pharmacology and Therapeutics, University of Florida College of Medicine, Gainesville (H.L.S.); and Department of Physiology, University of Texas Southwestern Medical Center, Dallas (K.K. J.T.S.)
| | - Ellen Regalado
- From the Department of Internal Medicine, McGovern Medical School at The University of Texas Health Science Center at Houston (D.M.M., D.-c.G., E.R.); Department of Molecular Physiology and Biophysics, University of Vermont, Burlington (K.M.T.); Department of Pharmacology and Therapeutics, University of Florida College of Medicine, Gainesville (H.L.S.); and Department of Physiology, University of Texas Southwestern Medical Center, Dallas (K.K. J.T.S.)
| | - Kristine Kamm
- From the Department of Internal Medicine, McGovern Medical School at The University of Texas Health Science Center at Houston (D.M.M., D.-c.G., E.R.); Department of Molecular Physiology and Biophysics, University of Vermont, Burlington (K.M.T.); Department of Pharmacology and Therapeutics, University of Florida College of Medicine, Gainesville (H.L.S.); and Department of Physiology, University of Texas Southwestern Medical Center, Dallas (K.K. J.T.S.)
| | - James T Stull
- From the Department of Internal Medicine, McGovern Medical School at The University of Texas Health Science Center at Houston (D.M.M., D.-c.G., E.R.); Department of Molecular Physiology and Biophysics, University of Vermont, Burlington (K.M.T.); Department of Pharmacology and Therapeutics, University of Florida College of Medicine, Gainesville (H.L.S.); and Department of Physiology, University of Texas Southwestern Medical Center, Dallas (K.K. J.T.S.)
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35
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Nogara L, Naber N, Pate E, Canton M, Reggiani C, Cooke R. Spectroscopic Studies of the Super Relaxed State of Skeletal Muscle. PLoS One 2016; 11:e0160100. [PMID: 27479128 PMCID: PMC4968846 DOI: 10.1371/journal.pone.0160100] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2016] [Accepted: 07/13/2016] [Indexed: 11/18/2022] Open
Abstract
In the super-relaxed state of myosin, ATPase activity is strongly inhibited by binding of the myosin heads to the core of the thick filament in a structure known as the interacting-heads motif. In the disordered relaxed state myosin heads are not bound to the core of the thick filament and have an ATPase rate that is 10 fold greater. In the interacting-heads motif the two regulatory light chains appear to bind to each other. We have made single cysteine mutants of the regulatory light chain, placed both paramagnetic and fluorescent probes on them, and exchanged them into skinned skeletal muscle fibers. Many of the labeled light chains tended to disrupt the stability of the super-relaxed state, and showed spectral changes in the transition from the disordered relaxed state to the super-relaxed state. These data support the putative interface between the two regulatory light chains identified by cryo electron microscopy and show that both the divalent cation bound to the regulatory light chain and the N-terminus of the regulatory light chain play a role in the stability of the super-relaxed state. One probe showed a shift to shorter wavelengths in the super-relaxed state such that a ratio of intensities at 440nm to that at 520nm provided a measure of the population of the super-relaxed state amenable for high throughput screens for finding potential pharmaceuticals. The results provide a proof of concept that small molecules that bind to this region can destabilize the super-relaxed state and provide a method to search for small molecules that do so leading to a potentially effective treatment for Type 2 diabetes and obesity.
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Affiliation(s)
- Leonardo Nogara
- Dipartimento di Scienze Biomediche, University of Padua, Padua Italy
- * E-mail:
| | - Nariman Naber
- Department of Biochemistry/Biophysics, University of California San Francisco, San Francisco, California, United States of America
| | - Edward Pate
- Voiland School of Bioengineering, Washington State University, Pullman, Washington, United States of America
| | - Marcella Canton
- Dipartimento di Scienze Biomediche, University of Padua, Padua Italy
| | - Carlo Reggiani
- Dipartimento di Scienze Biomediche, University of Padua, Padua Italy
| | - Roger Cooke
- Department of Biochemistry/Biophysics, University of California San Francisco, San Francisco, California, United States of America
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36
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Hong F, Brizendine RK, Carter MS, Alcala DB, Brown AE, Chattin AM, Haldeman BD, Walsh MP, Facemyer KC, Baker JE, Cremo CR. Diffusion of myosin light chain kinase on actin: A mechanism to enhance myosin phosphorylation rates in smooth muscle. ACTA ACUST UNITED AC 2016; 146:267-80. [PMID: 26415568 PMCID: PMC4586593 DOI: 10.1085/jgp.201511483] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Smooth muscle myosin (SMM) light chain kinase (MLCK) phosphorylates SMM, thereby activating the ATPase activity required for muscle contraction. The abundance of active MLCK, which is tightly associated with the contractile apparatus, is low relative to that of SMM. SMM phosphorylation is rapid despite the low ratio of MLCK to SMM, raising the question of how one MLCK rapidly phosphorylates many SMM molecules. We used total internal reflection fluorescence microscopy to monitor single molecules of streptavidin-coated quantum dot-labeled MLCK interacting with purified actin, actin bundles, and stress fibers of smooth muscle cells. Surprisingly, MLCK and the N-terminal 75 residues of MLCK (N75) moved on actin bundles and stress fibers of smooth muscle cell cytoskeletons by a random one-dimensional (1-D) diffusion mechanism. Although diffusion of proteins along microtubules and oligonucleotides has been observed previously, this is the first characterization to our knowledge of a protein diffusing in a sustained manner along actin. By measuring the frequency of motion, we found that MLCK motion is permitted only if acto-myosin and MLCK-myosin interactions are weak. From these data, diffusion coefficients, and other kinetic and geometric considerations relating to the contractile apparatus, we suggest that 1-D diffusion of MLCK along actin (a) ensures that diffusion is not rate limiting for phosphorylation, (b) allows MLCK to locate to areas in which myosin is not yet phosphorylated, and (c) allows MLCK to avoid getting "stuck" on myosins that have already been phosphorylated. Diffusion of MLCK along actin filaments may be an important mechanism for enhancing the rate of SMM phosphorylation in smooth muscle.
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Affiliation(s)
- Feng Hong
- Department of Biochemistry and Molecular Biology, University of Nevada School of Medicine, Reno, NV 99557
| | - Richard K Brizendine
- Department of Biochemistry and Molecular Biology, University of Nevada School of Medicine, Reno, NV 99557
| | - Michael S Carter
- Department of Biochemistry and Molecular Biology, University of Nevada School of Medicine, Reno, NV 99557
| | - Diego B Alcala
- Department of Biochemistry and Molecular Biology, University of Nevada School of Medicine, Reno, NV 99557
| | - Avery E Brown
- Department of Biochemistry and Molecular Biology, University of Nevada School of Medicine, Reno, NV 99557
| | - Amy M Chattin
- Department of Biochemistry and Molecular Biology, University of Nevada School of Medicine, Reno, NV 99557
| | - Brian D Haldeman
- Department of Biochemistry and Molecular Biology, University of Nevada School of Medicine, Reno, NV 99557
| | - Michael P Walsh
- Department of Biochemistry and Molecular Biology, University of Calgary Faculty of Medicine, Calgary, Alberta T2N 4N1, Canada
| | - Kevin C Facemyer
- Department of Biochemistry and Molecular Biology, University of Nevada School of Medicine, Reno, NV 99557
| | - Josh E Baker
- Department of Biochemistry and Molecular Biology, University of Nevada School of Medicine, Reno, NV 99557
| | - Christine R Cremo
- Department of Biochemistry and Molecular Biology, University of Nevada School of Medicine, Reno, NV 99557
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Abstract
The myosin holoenzyme is a multimeric protein complex consisting of heavy chains and light chains. Myosin light chains are calmodulin family members which are crucially involved in the mechanoenzymatic function of the myosin holoenzyme. This review examines the diversity of light chains within the myosin superfamily, discusses interactions between the light chain and the myosin heavy chain as well as regulatory and structural functions of the light chain as a subunit of the myosin holoenzyme. It covers aspects of the myosin light chain in the localization of the myosin holoenzyme, protein-protein interactions and light chain binding to non-myosin binding partners. Finally, this review challenges the dogma that myosin regulatory and essential light chain exclusively associate with conventional myosin heavy chains while unconventional myosin heavy chains usually associate with calmodulin.
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Affiliation(s)
- Sarah M Heissler
- a Laboratory of Molecular Physiology; National Heart, Lung, and Blood Institute; National Institutes of Health ; Bethesda , MD USA
| | - James R Sellers
- a Laboratory of Molecular Physiology; National Heart, Lung, and Blood Institute; National Institutes of Health ; Bethesda , MD USA
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38
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Lai S, Collins BC, Colson BA, Kararigas G, Lowe DA. Estradiol modulates myosin regulatory light chain phosphorylation and contractility in skeletal muscle of female mice. Am J Physiol Endocrinol Metab 2016; 310:E724-33. [PMID: 26956186 PMCID: PMC4867308 DOI: 10.1152/ajpendo.00439.2015] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/07/2015] [Accepted: 03/02/2016] [Indexed: 11/22/2022]
Abstract
Impairment of skeletal muscle function has been associated with changes in ovarian hormones, especially estradiol. To elucidate mechanisms of estradiol on skeletal muscle strength, the hormone's effects on phosphorylation of the myosin regulatory light chain (pRLC) and muscle contractility were investigated, hypothesizing an estradiol-specific beneficial impact. In a skeletal muscle cell line, C2C12, pRLC was increased by 17β-estradiol (E2) in a concentration-dependent manner. In skeletal muscles of C57BL/6 mice that were E2 deficient via ovariectomy (OVX), pRLC was lower than that from ovary-intact, sham-operated mice (Sham). The reduced pRLC in OVX muscle was reversed by in vivo E2 treatment. Posttetanic potentiation (PTP) of muscle from OVX mice was low compared with that from Sham mice, and this decrement was reversed by acute E2 treatment, demonstrating physiological consequence. Western blot of those muscles revealed that low PTP corresponded with low pRLC and higher PTP with greater pRLC. We aimed to elucidate signaling pathways affecting E2-mediated pRLC using a kinase inhibitor library and C2C12 cells as well as a specific myosin light chain kinase inhibitor in muscles. PI3K/Akt, MAPK, and CamKII were identified as candidate kinases sensitive to E2 in terms of phosphorylating RLC. Applying siRNA strategy in C2C12 cells, pRLC triggered by E2 was found to be mediated by estrogen receptor-β and the G protein-coupled estrogen receptor. Together, these results provide evidence that E2 modulates myosin pRLC in skeletal muscle and is one mechanism by which this hormone can affect muscle contractility in females.
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Affiliation(s)
- Shaojuan Lai
- Programs in Rehabilitation Sciences and Physical Therapy, Department of Physical Medicine and Rehabilitation, Medical School, University of Minnesota, Minneapolis, Minnesota; College of Biological Engineering, Henan University of Technology, Zhengzhou, Henan, China; and
| | - Brittany C Collins
- Programs in Rehabilitation Sciences and Physical Therapy, Department of Physical Medicine and Rehabilitation, Medical School, University of Minnesota, Minneapolis, Minnesota
| | - Brett A Colson
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota
| | - Georgios Kararigas
- Institute of Gender in Medicine, Charite University Hospital, and German Centre for Cardiovascular Research (DZHK), Partner Site, Berlin, Germany
| | - Dawn A Lowe
- Programs in Rehabilitation Sciences and Physical Therapy, Department of Physical Medicine and Rehabilitation, Medical School, University of Minnesota, Minneapolis, Minnesota;
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39
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Espinoza-Fonseca LM, Alamo L, Pinto A, Thomas DD, Padrón R. Sequential myosin phosphorylation activates tarantula thick filament via a disorder-order transition. MOLECULAR BIOSYSTEMS 2016; 11:2167-79. [PMID: 26038232 DOI: 10.1039/c5mb00162e] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Phosphorylation of myosin regulatory light chain (RLC) N-terminal extension (NTE) activates myosin in thick filaments. RLC phosphorylation plays a primary regulatory role in smooth muscles and a secondary (modulatory) role in striated muscles, which is regulated by Ca(2+)via TnC/TM on the thin filament. Tarantula striated muscle exhibits both regulatory systems: one switches on/off contraction through thin filament regulation, and another through PKC constitutively Ser35 phosphorylated swaying free heads in the thick filaments that produces quick force on twitches regulated from 0 to 50% and modulation is accomplished recruiting additional force-potentiating free and blocked heads via Ca(2+)4-CaM-MLCK Ser45 phosphorylation. We have used microsecond molecular dynamics (MD) simulations of tarantula RLC NTE to understand the structural basis for phosphorylation-based regulation in tarantula thick filament activation. Trajectory analysis revealed that an inter-domain salt bridge network (R39/E58,E61) facilitates the formation of a stable helix-coil-helix (HCH) motif formed by helices P and A in the unphosphorylated NTE of both myosin heads. Phosphorylation of the blocked head on Ser45 does not induce any substantial structural changes. However, phosphorylation of the free head on Ser35 disrupts this salt bridge network and induces a partial extension of helix P along RLC helix A. While not directly participating in the HCH folding, phosphorylation of Ser35 unlocks a compact structure and allows the NTE to spontaneously undergo coil-helix transitions. The modest structural change induced by the subsequent Ser45 diphosphorylation monophosphorylated Ser35 free head facilitates full helix P extension into a single structurally stable α-helix through a network of intra-domain salt bridges (pS35/R38,R39,R42). We conclude that tarantula thick filament activation is controlled by sequential Ser35-Ser45 phosphorylation via a conserved disorder-to-order transition.
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Affiliation(s)
- L Michel Espinoza-Fonseca
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA
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40
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Heissler SM, Sellers JR. Kinetic Adaptations of Myosins for Their Diverse Cellular Functions. Traffic 2016; 17:839-59. [PMID: 26929436 DOI: 10.1111/tra.12388] [Citation(s) in RCA: 65] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2016] [Revised: 02/25/2016] [Accepted: 02/25/2016] [Indexed: 12/18/2022]
Abstract
Members of the myosin superfamily are involved in all aspects of eukaryotic life. Their function ranges from the transport of organelles and cargos to the generation of membrane tension, and the contraction of muscle. The diversity of physiological functions is remarkable, given that all enzymatically active myosins follow a conserved mechanoenzymatic cycle in which the hydrolysis of ATP to ADP and inorganic phosphate is coupled to either actin-based transport or tethering of actin to defined cellular compartments. Kinetic capacities and limitations of a myosin are determined by the extent to which actin can accelerate the hydrolysis of ATP and the release of the hydrolysis products and are indispensably linked to its physiological tasks. This review focuses on kinetic competencies that - together with structural adaptations - result in myosins with unique mechanoenzymatic properties targeted to their diverse cellular functions.
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Affiliation(s)
- Sarah M Heissler
- Laboratory of Molecular Physiology, National Heart, Lung, and Blood Institute, National Institutes of Health, 50 South Drive, B50/3523, Bethesda, MD 20892-8015, USA
| | - James R Sellers
- Laboratory of Molecular Physiology, National Heart, Lung, and Blood Institute, National Institutes of Health, 50 South Drive, B50/3523, Bethesda, MD 20892-8015, USA
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41
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Alamo L, Qi D, Wriggers W, Pinto A, Zhu J, Bilbao A, Gillilan RE, Hu S, Padrón R. Conserved Intramolecular Interactions Maintain Myosin Interacting-Heads Motifs Explaining Tarantula Muscle Super-Relaxed State Structural Basis. J Mol Biol 2016; 428:1142-1164. [PMID: 26851071 DOI: 10.1016/j.jmb.2016.01.027] [Citation(s) in RCA: 68] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2015] [Revised: 01/15/2016] [Accepted: 01/25/2016] [Indexed: 01/08/2023]
Abstract
Tarantula striated muscle is an outstanding system for understanding the molecular organization of myosin filaments. Three-dimensional reconstruction based on cryo-electron microscopy images and single-particle image processing revealed that, in a relaxed state, myosin molecules undergo intramolecular head-head interactions, explaining why head activity switches off. The filament model obtained by rigidly docking a chicken smooth muscle myosin structure to the reconstruction was improved by flexibly fitting an atomic model built by mixing structures from different species to a tilt-corrected 2-nm three-dimensional map of frozen-hydrated tarantula thick filament. We used heavy and light chain sequences from tarantula myosin to build a single-species homology model of two heavy meromyosin interacting-heads motifs (IHMs). The flexibly fitted model includes previously missing loops and shows five intramolecular and five intermolecular interactions that keep the IHM in a compact off structure, forming four helical tracks of IHMs around the backbone. The residues involved in these interactions are oppositely charged, and their sequence conservation suggests that IHM is present across animal species. The new model, PDB 3JBH, explains the structural origin of the ATP turnover rates detected in relaxed tarantula muscle by ascribing the very slow rate to docked unphosphorylated heads, the slow rate to phosphorylated docked heads, and the fast rate to phosphorylated undocked heads. The conservation of intramolecular interactions across animal species and the presence of IHM in bilaterians suggest that a super-relaxed state should be maintained, as it plays a role in saving ATP in skeletal, cardiac, and smooth muscles.
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Affiliation(s)
- Lorenzo Alamo
- Centro de Biología Estructural, Instituto Venezolano de Investigaciones Científicas, Apartado 20632, Caracas 1020A, Venezuela.
| | - Dan Qi
- Key Laboratory of Genome Sciences and Information, Beijing Institute of Genomics, 1 Beichen West Road, Chaoyang District, Beijing 100101, China.
| | - Willy Wriggers
- Department of Mechanical and Aerospace Engineering, Old Dominion University, 5115 Hampton Boulevard, Norfolk, VA 23529, USA.
| | - Antonio Pinto
- Centro de Biología Estructural, Instituto Venezolano de Investigaciones Científicas, Apartado 20632, Caracas 1020A, Venezuela.
| | - Jingui Zhu
- Key Laboratory of Genome Sciences and Information, Beijing Institute of Genomics, 1 Beichen West Road, Chaoyang District, Beijing 100101, China.
| | - Aivett Bilbao
- Centro de Biología Estructural, Instituto Venezolano de Investigaciones Científicas, Apartado 20632, Caracas 1020A, Venezuela.
| | - Richard E Gillilan
- Macromolecular Diffraction Facility, Cornell High Energy Synchrotron Source, 161 Wilson Laboratory, Synchrotron Drive, Ithaca, NY 14853, USA.
| | - Songnian Hu
- Key Laboratory of Genome Sciences and Information, Beijing Institute of Genomics, 1 Beichen West Road, Chaoyang District, Beijing 100101, China.
| | - Raúl Padrón
- Centro de Biología Estructural, Instituto Venezolano de Investigaciones Científicas, Apartado 20632, Caracas 1020A, Venezuela.
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42
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Heissler SM, Sellers JR. Various Themes of Myosin Regulation. J Mol Biol 2016; 428:1927-46. [PMID: 26827725 DOI: 10.1016/j.jmb.2016.01.022] [Citation(s) in RCA: 84] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2015] [Revised: 01/12/2016] [Accepted: 01/19/2016] [Indexed: 10/24/2022]
Abstract
Members of the myosin superfamily are actin-based molecular motors that are indispensable for cellular homeostasis. The vast functional and structural diversity of myosins accounts for the variety and complexity of the underlying allosteric regulatory mechanisms that determine the activation or inhibition of myosin motor activity and enable precise timing and spatial aspects of myosin function at the cellular level. This review focuses on the molecular basis of posttranslational regulation of eukaryotic myosins from different classes across species by allosteric intrinsic and extrinsic effectors. First, we highlight the impact of heavy and light chain phosphorylation. Second, we outline intramolecular regulatory mechanisms such as autoinhibition and subsequent activation. Third, we discuss diverse extramolecular allosteric mechanisms ranging from actin-linked regulatory mechanisms to myosin:cargo interactions. At last, we briefly outline the allosteric regulation of myosins with synthetic compounds.
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Affiliation(s)
- Sarah M Heissler
- Laboratory of Molecular Physiology, National Heart, Lung and Blood Institute, National Institutes of Health, 50 South Drive, B50/3529, Bethesda, MD 20892-8015, USA.
| | - James R Sellers
- Laboratory of Molecular Physiology, National Heart, Lung and Blood Institute, National Institutes of Health, 50 South Drive, B50/3529, Bethesda, MD 20892-8015, USA
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43
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Chantler PD. Scallop Adductor Muscles. ACTA ACUST UNITED AC 2016. [DOI: 10.1016/b978-0-444-62710-0.00004-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/07/2023]
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44
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Wilson C, Naber N, Pate E, Cooke R. The myosin inhibitor blebbistatin stabilizes the super-relaxed state in skeletal muscle. Biophys J 2015; 107:1637-46. [PMID: 25296316 DOI: 10.1016/j.bpj.2014.07.075] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2014] [Revised: 07/15/2014] [Accepted: 07/16/2014] [Indexed: 10/24/2022] Open
Abstract
The super-relaxed state of myosin (SRX), in which the myosin ATPase activity is strongly inhibited, has been observed in a variety of muscle types. It has been proposed that myosin heads in this state are inhibited by binding to the core of the thick filament in a structure known as the interacting-heads motif. The myosin inhibitor blebbistatin has been shown in structural studies to stabilize the binding of myosin heads to the thick filament, and here we have utilized measurements of single ATP turnovers to show that blebbistatin also stabilizes the SRX in both fast and slow skeletal muscle, providing further support for the proposal that myosin heads in the SRX are also in the interacting-heads motif. We find that the SRX is stabilized using blebbistatin even in conditions that normally destabilize it, e.g., rigor ADP. Using blebbistatin we show that spin-labeled nucleotides bound to myosin have an oriented spectrum in the SRX in both slow and fast skeletal muscle. This is to our knowledge the first observation of oriented spin probes on the myosin motor domain in relaxed skeletal muscle fibers. The spectra for skeletal muscle with blebbistatin are similar to those observed in relaxed tarantula fibers in the absence of blebbistatin, demonstrating that the structure of the SRX is similar in different muscle types and in the presence and absence of blebbistatin. The mobility of spin probes attached to nucleotides bound to myosin shows that the conformation of the nucleotide site is closed in the SRX.
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Affiliation(s)
- Clyde Wilson
- Department of Biochemistry and Biophysics, University of California, San Francisco, California
| | - Nariman Naber
- Department of Biochemistry and Biophysics, University of California, San Francisco, California
| | - Edward Pate
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, Washington
| | - Roger Cooke
- Department of Biochemistry and Biophysics, University of California, San Francisco, California; Cardiovascular Research Institute, University of California, San Francisco, California.
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45
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Chaperone-enhanced purification of unconventional myosin 15, a molecular motor specialized for stereocilia protein trafficking. Proc Natl Acad Sci U S A 2014; 111:12390-5. [PMID: 25114250 DOI: 10.1073/pnas.1409459111] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Unconventional myosin 15 is a molecular motor expressed in inner ear hair cells that transports protein cargos within developing mechanosensory stereocilia. Mutations of myosin 15 cause profound hearing loss in humans and mice; however, the properties of this motor and its regulation within the stereocilia organelle are unknown. To address these questions, we expressed a subfragment 1-like (S1) truncation of mouse myosin 15, comprising the predicted motor domain plus three light-chain binding sites. Following unsuccessful attempts to express functional myosin 15-S1 using the Spodoptera frugiperda (Sf9)-baculovirus system, we discovered that coexpression of the muscle-myosin-specific chaperone UNC45B, in addition to the chaperone heat-shock protein 90 (HSP90) significantly increased the yield of functional protein. Surprisingly, myosin 15-S1 did not bind calmodulin with high affinity. Instead, the IQ domains bound essential and regulatory light chains that are normally associated with class II myosins. We show that myosin 15-S1 is a barbed-end-directed motor that moves actin filaments in a gliding assay (∼ 430 nm · s(-1) at 30 °C), using a power stroke of 7.9 nm. The maximum ATPase rate (k(cat) ∼ 6 s(-1)) was similar to the actin-detachment rate (k(det) = 6.2 s(-1)) determined in single molecule optical trapping experiments, indicating that myosin 15-S1 was rate limited by transit through strongly actin-bound states, similar to other processive myosin motors. Our data further indicate that in addition to folding muscle myosin, UNC45B facilitates maturation of an unconventional myosin. We speculate that chaperone coexpression may be a simple method to optimize the purification of other myosin motors from Sf9 insect cells.
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46
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Márquez G, Pinto A, Alamo L, Baumann B, Ye F, Winkler H, Taylor K, Padrón R. A method for 3D-reconstruction of a muscle thick filament using the tilt series images of a single filament electron tomogram. J Struct Biol 2014; 186:265-72. [PMID: 24727133 DOI: 10.1016/j.jsb.2014.04.003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2013] [Revised: 03/19/2014] [Accepted: 04/04/2014] [Indexed: 10/25/2022]
Abstract
Myosin interacting-heads (MIH) motifs are visualized in 3D-reconstructions of thick filaments from striated muscle. These reconstructions are calculated by averaging methods using images from electron micrographs of grids prepared using numerous filament preparations. Here we propose an alternative method to calculate the 3D-reconstruction of a single thick filament using only a tilt series images recorded by electron tomography. Relaxed thick filaments, prepared from tarantula leg muscle homogenates, were negatively stained. Single-axis tilt series of single isolated thick filaments were obtained with the electron microscope at a low electron dose, and recorded on a CCD camera by electron tomography. An IHRSR 3D-recontruction was calculated from the tilt series images of a single thick filament. The reconstruction was enhanced by including in the search stage dual tilt image segments while only single tilt along the filament axis is usually used, as well as applying a band pass filter just before the back projection. The reconstruction from a single filament has a 40 Å resolution and clearly shows the presence of MIH motifs. In contrast, the electron tomogram 3D-reconstruction of the same thick filament - calculated without any image averaging and/or imposition of helical symmetry - only reveals MIH motifs infrequently. This is - to our knowledge - the first application of the IHRSR method to calculate a 3D reconstruction from tilt series images. This single filament IHRSR reconstruction method (SF-IHRSR) should provide a new tool to assess structural differences between well-ordered thick (or thin) filaments in a grid by recording separately their electron tomograms.
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Affiliation(s)
- G Márquez
- Centro de Biología Estructural, Instituto Venezolano de Investigaciones Científicas (IVIC), Apdo. 20632, Caracas 1020A, Venezuela.
| | - A Pinto
- Centro de Biología Estructural, Instituto Venezolano de Investigaciones Científicas (IVIC), Apdo. 20632, Caracas 1020A, Venezuela.
| | - L Alamo
- Centro de Biología Estructural, Instituto Venezolano de Investigaciones Científicas (IVIC), Apdo. 20632, Caracas 1020A, Venezuela.
| | - B Baumann
- Institute of Molecular Biophysics, Florida State University, 91 Chieftan way, Tallahassee, FL 32306-4380, USA.
| | - F Ye
- Institute of Molecular Biophysics, Florida State University, 91 Chieftan way, Tallahassee, FL 32306-4380, USA.
| | - H Winkler
- Institute of Molecular Biophysics, Florida State University, 91 Chieftan way, Tallahassee, FL 32306-4380, USA.
| | - K Taylor
- Institute of Molecular Biophysics, Florida State University, 91 Chieftan way, Tallahassee, FL 32306-4380, USA.
| | - R Padrón
- Centro de Biología Estructural, Instituto Venezolano de Investigaciones Científicas (IVIC), Apdo. 20632, Caracas 1020A, Venezuela.
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47
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Sulbarán G, Biasutto A, Alamo L, Riggs C, Pinto A, Méndez F, Craig R, Padrón R. Different head environments in tarantula thick filaments support a cooperative activation process. Biophys J 2013; 105:2114-22. [PMID: 24209856 PMCID: PMC3824520 DOI: 10.1016/j.bpj.2013.09.001] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2013] [Revised: 08/08/2013] [Accepted: 09/04/2013] [Indexed: 01/17/2023] Open
Abstract
Myosin filaments from many muscles are activated by phosphorylation of their regulatory light chains (RLCs). Structural analysis of relaxed tarantula thick filaments shows that the RLCs of the interacting free and blocked myosin heads are in different environments. This and other data suggested a phosphorylation mechanism in which Ser-35 of the free head is exposed and constitutively phosphorylated by protein kinase C, whereas the blocked head is hidden and unphosphorylated; on activation, myosin light chain kinase phosphorylates the monophosphorylated free head followed by the unphosphorylated blocked head, both at Ser-45. Our goal was to test this model of phosphorylation. Mass spectrometry of quickly frozen, intact muscles showed that only Ser-35 was phosphorylated in the relaxed state. The location of this constitutively phosphorylated Ser-35 was analyzed by immunofluorescence, using antibodies specific for unphosphorylated or phosphorylated Ser-35. In the relaxed state, myofibrils were labeled by anti-pSer-35 but not by anti-Ser-35, whereas in rigor, labeling was similar with both. This suggests that only pSer-35 is exposed in the relaxed state, while in rigor, Ser-35 is also exposed. In the interacting-head motif of relaxed filaments, only the free head RLCs are exposed, suggesting that the constitutive pSer-35 is on the free heads, consistent with the proposed mechanism.
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Affiliation(s)
- Guidenn Sulbarán
- Centro de Biología Estructural, Instituto Venezolano de Investigaciones Científicas (IVIC), Caracas, Venezuela
- Department of Cell Biology, University of Massachusetts Medical School, Worcester, Massachusetts
| | - Antonio Biasutto
- Centro de Biología Estructural, Instituto Venezolano de Investigaciones Científicas (IVIC), Caracas, Venezuela
| | - Lorenzo Alamo
- Centro de Biología Estructural, Instituto Venezolano de Investigaciones Científicas (IVIC), Caracas, Venezuela
| | - Claire Riggs
- Centro de Biología Estructural, Instituto Venezolano de Investigaciones Científicas (IVIC), Caracas, Venezuela
| | - Antonio Pinto
- Centro de Biología Estructural, Instituto Venezolano de Investigaciones Científicas (IVIC), Caracas, Venezuela
| | - Franklin Méndez
- Centro de Biología Estructural, Instituto Venezolano de Investigaciones Científicas (IVIC), Caracas, Venezuela
| | - Roger Craig
- Department of Cell Biology, University of Massachusetts Medical School, Worcester, Massachusetts
| | - Raúl Padrón
- Centro de Biología Estructural, Instituto Venezolano de Investigaciones Científicas (IVIC), Caracas, Venezuela
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48
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Billington N, Wang A, Mao J, Adelstein RS, Sellers JR. Characterization of three full-length human nonmuscle myosin II paralogs. J Biol Chem 2013; 288:33398-410. [PMID: 24072716 DOI: 10.1074/jbc.m113.499848] [Citation(s) in RCA: 140] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Nonmuscle myosin IIs (NM IIs) are a group of molecular motors involved in a wide variety of cellular processes including cytokinesis, migration, and control of cell morphology. There are three paralogs of the NM II heavy chain in humans (IIA, IIB, and IIC), each encoded by a separate gene. These paralogs are expressed at different levels according to cell type and have different roles and intracellular distributions in vivo. Most previous studies on NM II used tissue-purified protein or expressed fragments of the molecule, which presents potential drawbacks for characterizing individual paralogs of the intact protein in vitro. To circumvent current limitations and approach their native properties, we have successfully expressed and purified the three full-length human NM II proteins with their light chains, using the baculovirus/Sf9 system. The enzymatic and structural properties of the three paralogs were characterized. Although each NM II is capable of forming bipolar filaments, those formed by IIC tend to contain fewer constituent molecules than those of IIA and IIB. All paralogs adopt the compact conformation in the presence of ATP. Phosphorylation of the regulatory light chain leads to assembly into filaments, which bind to actin in the presence of ATP. The nature of interactions with actin filaments is shown with different paralogs exhibiting different actin binding behaviors under equivalent conditions. The data show that although NM IIA and IIB form filaments with similar properties, NM IIC forms filaments that are less well suited to roles such as tension maintenance within the cell.
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Guzik-Lendrum S, Heissler SM, Billington N, Takagi Y, Yang Y, Knight PJ, Homsher E, Sellers JR. Mammalian myosin-18A, a highly divergent myosin. J Biol Chem 2013; 288:9532-48. [PMID: 23382379 DOI: 10.1074/jbc.m112.441238] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The Mus musculus myosin-18A gene is expressed as two alternatively spliced isoforms, α and β, with reported roles in Golgi localization, in maintenance of cytoskeleton, and as receptors for immunological surfactant proteins. Both myosin-18A isoforms feature a myosin motor domain, a single predicted IQ motif, and a long coiled-coil reminiscent of myosin-2. The myosin-18Aα isoform, additionally, has an N-terminal PDZ domain. Recombinant heavy meromyosin- and subfragment-1 (S1)-like constructs for both myosin-18Aα and -18β species were purified from the baculovirus/Sf9 cell expression system. These constructs bound both essential and regulatory light chains, indicating an additional noncanonical light chain binding site in the neck. Myosin-18Aα-S1 and -18Aβ-S1 molecules bound actin weakly with Kd values of 4.9 and 54 μm, respectively. The actin binding data could be modeled by assuming an equilibrium between two myosin conformations, a competent and an incompetent form to bind actin. Actin binding was unchanged by presence of nucleotide. Both myosin-18A isoforms bound N-methylanthraniloyl-nucleotides, but the rate of ATP hydrolysis was very slow (<0.002 s(-1)) and not significantly enhanced by actin. Phosphorylation of the regulatory light chain had no effect on ATP hydrolysis, and neither did the addition of tropomyosin or of GOLPH3, a myosin-18A binding partner. Electron microscopy of myosin-18A-S1 showed that the lever is strongly angled with respect to the long axis of the motor domain, suggesting a pre-power stroke conformation regardless of the presence of ATP. These data lead us to conclude that myosin-18A does not operate as a traditional molecular motor in cells.
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Affiliation(s)
- Stephanie Guzik-Lendrum
- Laboratory of Molecular Physiology, NHLBI, National Institutes of Health, Bethesda, MD 20892-8015, USA
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Pinto A, Sánchez F, Alamo L, Padrón R. The myosin interacting-heads motif is present in the relaxed thick filament of the striated muscle of scorpion. J Struct Biol 2012; 180:469-78. [PMID: 22982253 DOI: 10.1016/j.jsb.2012.08.010] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2012] [Revised: 08/27/2012] [Accepted: 08/29/2012] [Indexed: 11/26/2022]
Abstract
Electron microscopy (EM) studies of 2D crystals of smooth muscle myosin molecules have shown that in the inactive state the two heads of a myosin molecule interact asymmetrically forming a myosin interacting-heads motif. This suggested that inactivation of the two heads occurs by blocking of the actin-binding site of one (free head) and the ATP hydrolysis site of the other (blocked head). This motif has been found by EM of isolated negatively stained myosin molecules of unregulated (vertebrate skeletal and cardiac muscle) and regulated (invertebrate striated and vertebrate smooth muscle) myosins, and nonmuscle myosin. The same motif has also been found in 3D-reconstructions of frozen-hydrated (tarantula, Limulus, scallop) and negatively stained (scallop, vertebrate cardiac) isolated thick filaments. We are carrying out studies of isolated thick filaments from other species to assess how general this myosin interacting-heads motif is. Here, using EM, we have visualized isolated, negatively stained thick filaments from scorpion striated muscle. We modified the iterative helical real space reconstruction (IHRSR) method to include filament tilt, and band-pass filtered the aligned segments before averaging, achieving a 3.3 nm resolution 3D-reconstruction. This reconstruction revealed the presence of the myosin interacting-heads motif (adding to evidence that is widely spread), together with 12 subfilaments in the filament backbone. This demonstrates that conventional negative staining and imaging can be used to detect the presence of the myosin interacting-heads motif in helically ordered thick filaments from different species and muscle types, thus avoiding the use of less accessible cryo-EM and low electron-dose procedures.
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Affiliation(s)
- Antonio Pinto
- Centro de Biología Estructural, Instituto Venezolano de Investigaciones Científicas-IVIC, Apdo. 20632, Caracas 1020A, Venezuela.
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