1
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Diensthuber RP, Hartmann FK, Kathmann D, Franz P, Tsiavaliaris G. Switch-2 determines Mg 2+ADP-release kinetics and fine-tunes the duty ratio of Dictyostelium class-1 myosins. Front Physiol 2024; 15:1393952. [PMID: 38887318 PMCID: PMC11181000 DOI: 10.3389/fphys.2024.1393952] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2024] [Accepted: 05/02/2024] [Indexed: 06/20/2024] Open
Abstract
Though myosins share a structurally conserved motor domain, single amino acid variations of active site elements, including the P-loop, switch-1 and switch-2, which act as nucleotide sensors, can substantially determine the kinetic signature of a myosin, i.e., to either perform fast movement or enable long-range transport and tension generation. Switch-2 essentially contributes to the ATP hydrolysis reaction and determines product release. With few exceptions, class-1 myosin harbor a tyrosine in the switch-2 consensus sequence DIYGFE, at a position where class-2 myosins and a selection of myosins from other classes have a substitution. Here, we addressed the role of the tyrosine in switch-2 of class-1 myosins as potential determinant of the duty ratio. We generated constitutively active motor domain constructs of two class-1 myosins from the social amoeba Dictyostelium discoideum, namely, Myo1E, a high duty ratio myosin and Myo1B, a low duty ratio myosin. In Myo1E we introduced mutation Y388F and in Myo1B mutation F387Y. The detailed functional characterization by steady-state and transient kinetic experiments, combined with in vitro motility and landing assays revealed an almost reciprocal relationship of a number of critical kinetic parameters and equilibrium constants between wild-type and mutants that dictate the lifetime of the strongly actin-attached states of myosin. The Y-to-F mutation increased the duty ratio of Moy1B by almost one order of magnitude, while the introduction of the phenylalanine in switch-2 of Myo1E transformed the myosin into a low duty ratio motor. These data together with structural considerations propose a role of switch-2 in fine-tuning ADP release through a mechanism, where the class-specific tyrosine together with surrounding residues contributes to the coordination of Mg2+ and ADP. Our results highlight the importance of conserved switch-2 residues in class-1 myosins for efficient chemo-mechanical coupling, revealing that switch-2 is important to adjust the duty ratio of the amoeboid class-1 myosins for performing movement, transport or gating functions.
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Affiliation(s)
| | | | | | | | - Georgios Tsiavaliaris
- Institute for Biophysical Chemistry, OE 4350, Hannover Medical School, Hannover, Germany
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2
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Gaydar V, Zananiri R, Saied L, Dvir O, Kaplan A, Henn A. Communication between DNA and nucleotide binding sites facilitates stepping by the RecBCD helicase. Nucleic Acids Res 2024; 52:3911-3923. [PMID: 38364872 DOI: 10.1093/nar/gkae108] [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: 05/22/2023] [Revised: 01/30/2024] [Accepted: 02/05/2024] [Indexed: 02/18/2024] Open
Abstract
Double-strand DNA breaks are the severest type of genomic damage, requiring rapid response to ensure survival. RecBCD helicase in prokaryotes initiates processive and rapid DNA unzipping, essential for break repair. The energetics of RecBCD during translocation along the DNA track are quantitatively not defined. Specifically, it's essential to understand the mechanism by which RecBCD switches between its binding states to enable its translocation. Here, we determine, by systematic affinity measurements, the degree of coupling between DNA and nucleotide binding to RecBCD. In the presence of ADP, RecBCD binds weakly to DNA that harbors a double overhang mimicking an unwinding intermediate. Consistently, RecBCD binds weakly to ADP in the presence of the same DNA. We did not observe coupling between DNA and nucleotide binding for DNA molecules having only a single overhang, suggesting that RecBCD subunits must both bind DNA to 'sense' the nucleotide state. On the contrary, AMPpNp shows weak coupling as RecBCD remains strongly bound to DNA in its presence. Detailed thermodynamic analysis of the RecBCD reaction mechanism suggests an 'energetic compensation' between RecB and RecD, which may be essential for rapid unwinding. Our findings provide the basis for a plausible stepping mechanism' during the processive translocation of RecBCD.
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Affiliation(s)
- Vera Gaydar
- Faculty of Biology, Technion - Israel Institute of Technology, Haifa 3200003, Israel
| | - Rani Zananiri
- Faculty of Biology, Technion - Israel Institute of Technology, Haifa 3200003, Israel
| | - Layla Saied
- Faculty of Biology, Technion - Israel Institute of Technology, Haifa 3200003, Israel
| | - Or Dvir
- Faculty of Biology, Technion - Israel Institute of Technology, Haifa 3200003, Israel
| | - Ariel Kaplan
- Faculty of Biology, Technion - Israel Institute of Technology, Haifa 3200003, Israel
| | - Arnon Henn
- Faculty of Biology, Technion - Israel Institute of Technology, Haifa 3200003, Israel
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3
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Gray S, Cao W, Montpetit B, De La Cruz EM. OUP accepted manuscript. Nucleic Acids Res 2022; 50:3998-4011. [PMID: 35286399 PMCID: PMC9023272 DOI: 10.1093/nar/gkac164] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2021] [Revised: 02/02/2022] [Accepted: 02/25/2022] [Indexed: 11/14/2022] Open
Abstract
The DEAD-box protein Dbp5 is essential for RNA export, which involves regulation by the nucleoporins Gle1 and Nup159 at the cytoplasmic face of the nuclear pore complex (NPC). Mechanistic understanding of how these nucleoporins regulate RNA export requires analyses of the intrinsic and activated Dbp5 ATPase cycle. Here, kinetic and equilibrium analyses of the Saccharomyces cerevisiae Gle1-activated Dbp5 ATPase cycle are presented, indicating that Gle1 and ATP, but not ADP-Pi or ADP, binding to Dbp5 are thermodynamically coupled. As a result, Gle1 binds Dbp5-ATP > 100-fold more tightly than Dbp5 in other nucleotide states and Gle1 equilibrium binding of ATP to Dbp5 increases >150-fold via slowed ATP dissociation. Second, Gle1 accelerated Dbp5 ATPase activity by increasing the rate-limiting Pi release rate constant ∼20-fold, which remains rate limiting. These data show that Gle1 activates Dbp5 by modulating ATP binding and Pi release. These Gle1 activities are expected to facilitate ATPase cycling, ensuring a pool of ATP bound Dbp5 at NPCs to engage RNA during export. This work provides a mechanism of Gle1-activation of Dbp5 and a framework to understand the joint roles of Gle1, Nup159, and other nucleoporins in regulating Dbp5 to mediate RNA export and other Dbp5 functions in gene expression.
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Affiliation(s)
- Shawn Gray
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520-8114, USA
| | - Wenxiang Cao
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520-8114, USA
| | - Ben Montpetit
- Department of Viticulture and Enology, University of California, Davis, Davis, CA 95616, USA
- Department of Food Science and Technology, University of California, Davis, Davis, CA 95616, USA
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4
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Gargey A, Iragavarapu SB, Grdzelishvili AV, Nesmelov YE. Electrostatic interactions in the SH1-SH2 helix of human cardiac myosin modulate the time of strong actomyosin binding. J Muscle Res Cell Motil 2021; 42:137-147. [PMID: 32929610 PMCID: PMC7956043 DOI: 10.1007/s10974-020-09588-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2020] [Accepted: 09/02/2020] [Indexed: 10/23/2022]
Abstract
Two single mutations, R694N and E45Q, were introduced in the beta isoform of human cardiac myosin to remove permanent salt bridges E45:R694 and E98:R694 in the SH1-SH2 helix of the myosin head. Beta isoform-specific bridges E45:R694 and E98:R694 were discovered in the molecular dynamics simulations of the alpha and beta myosin isoforms. Alpha and beta isoforms exhibit different kinetics, ADP dissociates slower from actomyosin containing beta myosin isoform, therefore, beta myosin stays strongly bound to actin longer. We hypothesize that the electrostatic interactions in the SH1-SH2 helix modulate the affinity of ADP to actomyosin, and therefore, the time of the strong actomyosin binding. Wild type and the mutants of the myosin head construct (1-843 amino acid residues) were expressed in differentiated C2C12 cells, and the duration of the strongly bound state of actomyosin was characterized using transient kinetics spectrophotometry. All myosin constructs exhibited a fast rate of ATP binding to actomyosin and a slow rate of ADP dissociation, showing that ADP release limits the time of the strongly bound state of actomyosin. The mutant R694N showed a faster rate of ADP release from actomyosin, compared to the wild type and the E45Q mutant, thus indicating that electrostatic interactions within the SH1-SH2 helix region of human cardiac myosin modulate ADP release and thus, the duration of the strongly bound state of actomyosin.
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Affiliation(s)
- Akhil Gargey
- Department of Physics and Optical Science, University of North Carolina Charlotte, 9201 University City Blvd, Charlotte, NC, 28223, USA
- Department of Biological Science, University of North Carolina Charlotte, Charlotte, NC, 28223, USA
| | - Shiril Bhardwaj Iragavarapu
- Department of Physics and Optical Science, University of North Carolina Charlotte, 9201 University City Blvd, Charlotte, NC, 28223, USA
| | - Alexander V Grdzelishvili
- Department of Physics and Optical Science, University of North Carolina Charlotte, 9201 University City Blvd, Charlotte, NC, 28223, USA
| | - Yuri E Nesmelov
- Department of Physics and Optical Science, University of North Carolina Charlotte, 9201 University City Blvd, Charlotte, NC, 28223, USA.
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5
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Cardiomyopathy mutations impact the actin-activated power stroke of human cardiac myosin. Biophys J 2021; 120:2222-2236. [PMID: 33864791 DOI: 10.1016/j.bpj.2021.04.007] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2020] [Revised: 03/02/2021] [Accepted: 04/01/2021] [Indexed: 11/24/2022] Open
Abstract
Cardiac muscle contraction is driven by the molecular motor myosin, which uses the energy from ATP hydrolysis to generate a power stroke when interacting with actin filaments, although it is unclear how this mechanism is impaired by mutations in myosin that can lead to heart failure. We have applied a fluorescence resonance energy transfer (FRET) strategy to investigate structural changes in the lever arm domain of human β-cardiac myosin subfragment 1 (M2β-S1). We exchanged the human ventricular regulatory light chain labeled at a single cysteine (V105C) with Alexa 488 onto M2β-S1, which served as a donor for Cy3ATP bound to the active site. We monitored the FRET signal during the actin-activated product release steps using transient kinetic measurements. We propose that the fast phase measured with our FRET probes represents the macroscopic rate constant associated with actin-activated rotation of the lever arm during the power stroke in M2β-S1. Our results demonstrated M2β-S1 has a slower actin-activated power stroke compared with fast skeletal muscle myosin and myosin V. Measurements at different temperatures comparing the rate constants of the actin-activated power stroke and phosphate release are consistent with a model in which the power stroke occurs before phosphate release and the two steps are tightly coupled. We suggest that the actin-activated power stroke is highly reversible but followed by a highly irreversible phosphate release step in the absence of load and free phosphate. We demonstrated that hypertrophic cardiomyopathy (R723G)- and dilated cardiomyopathy (F764L)-associated mutations both reduced actin activation of the power stroke in M2β-S1. We also demonstrate that both mutations alter in vitro actin gliding in the presence and absence of load. Thus, examining the structural kinetics of the power stroke in M2β-S1 has revealed critical mutation-associated defects in the myosin ATPase pathway, suggesting these measurements will be extremely important for establishing structure-based mechanisms of contractile dysfunction.
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6
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Mugnai ML, Thirumalai D. Step-Wise Hydration of Magnesium by Four Water Molecules Precedes Phosphate Release in a Myosin Motor. J Phys Chem B 2021; 125:1107-1117. [PMID: 33481593 DOI: 10.1021/acs.jpcb.0c10004] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Molecular motors, such as myosin, kinesin, and dynein, convert the energy released by the hydrolysis of ATP into mechanical work, thus allowing them to undergo directional motion on cytoskeletal tracks. A pivotal step in the chemomechanical transduction in myosin motors occurs after they bind to the actin filament, which triggers the release of phosphate (Pi, product of ATP hydrolysis) and the rotation of the lever arm. Here, we investigate the mechanism of phosphate release in myosin VI using extensive molecular dynamics simulations involving multiple trajectories of several μs. Because the escape of phosphate is expected to occur on time-scales on the order of milliseconds or more in myosin VI, we observed Pi release only if the trajectories were initiated with a rotated phosphate inside the nucleotide binding pocket. We discovered that although Pi populates the traditional "back door" route, phosphate exits through various other gateways, thus establishing the heterogeneity in the escape routes. Remarkably, we observed that the release of phosphate is preceded by a stepwise hydration of the ADP-bound magnesium ion. The release of the anion occurred only after four water molecules hydrated the cation (Mg2+). By performing comparative structural analyses, we show that hydration of magnesium is the key step in the phosphate release in a number of ATPases and GTPases. Nature may have evolved hydration of Mg2+ as a general molecular switch for Pi release, which is a universal step in the catalytic cycle of many machines that share little sequence or structural similarity.
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Affiliation(s)
- Mauro Lorenzo Mugnai
- Department of Chemistry, The University of Texas at Austin, Austin, Texas 78712, United States
| | - D Thirumalai
- Department of Chemistry, The University of Texas at Austin, Austin, Texas 78712, United States
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7
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Jiang F, Takagi Y, Shams A, Heissler SM, Friedman TB, Sellers JR, Bird JE. The ATPase mechanism of myosin 15, the molecular motor mutated in DFNB3 human deafness. J Biol Chem 2021; 296:100243. [PMID: 33372036 PMCID: PMC7948958 DOI: 10.1074/jbc.ra120.014903] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2020] [Revised: 12/23/2020] [Accepted: 12/28/2020] [Indexed: 11/18/2022] Open
Abstract
Cochlear hair cells each possess an exquisite bundle of actin-based stereocilia that detect sound. Unconventional myosin 15 (MYO15) traffics and delivers critical molecules required for stereocilia development and thus is essential for building the mechanosensory hair bundle. Mutations in the human MYO15A gene interfere with stereocilia trafficking and cause hereditary hearing loss, DFNB3, but the impact of these mutations is not known, as MYO15 itself is poorly characterized. To learn more, we performed a kinetic study of the ATPase motor domain to characterize its mechanochemical cycle. Using the baculovirus-Sf9 system, we purified a recombinant minimal motor domain (S1) by coexpressing the mouse MYO15 ATPase, essential and regulatory light chains that bind its IQ domains, and UNC45 and HSP90A chaperones required for correct folding of the ATPase. MYO15 purified with either UNC45A or UNC45B coexpression had similar ATPase activities (kcat = ∼ 6 s-1 at 20 °C). Using stopped-flow and quenched-flow transient kinetic analyses, we measured the major rate constants describing the ATPase cycle, including ATP, ADP, and actin binding; hydrolysis; and phosphate release. Actin-attached ADP release was the slowest measured transition (∼12 s-1 at 20 °C), although this did not rate-limit the ATPase cycle. The kinetic analysis shows the MYO15 motor domain has a moderate duty ratio (∼0.5) and weak thermodynamic coupling between ADP and actin binding. These findings are consistent with MYO15 being kinetically adapted for processive motility when oligomerized. Our kinetic characterization enables future studies into how deafness-causing mutations affect MYO15 and disrupt stereocilia trafficking necessary for hearing.
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Affiliation(s)
- Fangfang Jiang
- Department of Pharmacology and Therapeutics, and the Myology Institute, University of Florida College of Medicine, Gainesville, Florida, USA
| | - Yasuharu Takagi
- Laboratory of Molecular Physiology, Cell and Developmental Biology Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
| | - Arik Shams
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland, USA
| | - Sarah M Heissler
- Department of Physiology and Cell Biology, The Ohio State University Wexner Medical Center, Columbus, Ohio, USA
| | - Thomas B Friedman
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland, USA
| | - James R Sellers
- Laboratory of Molecular Physiology, Cell and Developmental Biology Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
| | - Jonathan E Bird
- Department of Pharmacology and Therapeutics, and the Myology Institute, University of Florida College of Medicine, Gainesville, Florida, USA.
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8
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Franz P, Ewert W, Preller M, Tsiavaliaris G. Unraveling a Force-Generating Allosteric Pathway of Actomyosin Communication Associated with ADP and P i Release. Int J Mol Sci 2020; 22:ijms22010104. [PMID: 33374308 PMCID: PMC7795666 DOI: 10.3390/ijms22010104] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2020] [Revised: 12/20/2020] [Accepted: 12/21/2020] [Indexed: 11/16/2022] Open
Abstract
The actomyosin system generates mechanical work with the execution of the power stroke, an ATP-driven, two-step rotational swing of the myosin-neck that occurs post ATP hydrolysis during the transition from weakly to strongly actin-bound myosin states concomitant with Pi release and prior to ADP dissociation. The activating role of actin on product release and force generation is well documented; however, the communication paths associated with weak-to-strong transitions are poorly characterized. With the aid of mutant analyses based on kinetic investigations and simulations, we identified the W-helix as an important hub coupling the structural changes of switch elements during ATP hydrolysis to temporally controlled interactions with actin that are passed to the central transducer and converter. Disturbing the W-helix/transducer pathway increased actin-activated ATP turnover and reduced motor performance as a consequence of prolonged duration of the strongly actin-attached states. Actin-triggered Pi release was accelerated, while ADP release considerably decelerated, both limiting maximum ATPase, thus transforming myosin-2 into a high-duty-ratio motor. This kinetic signature of the mutant allowed us to define the fractional occupancies of intermediate states during the ATPase cycle providing evidence that myosin populates a cleft-closure state of strong actin interaction during the weak-to-strong transition with bound hydrolysis products before accomplishing the power stroke.
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Affiliation(s)
- Peter Franz
- Cellular Biophysics, Institute for Biophysical Chemistry, Hannover Medical School, 30625 Hannover, Germany;
| | - Wiebke Ewert
- Structural Bioinformatics and Chemical Biology, Institute for Biophysical Chemistry, Hannover Medical School, 30625 Hannover, Germany; (W.E.); (M.P.)
| | - Matthias Preller
- Structural Bioinformatics and Chemical Biology, Institute for Biophysical Chemistry, Hannover Medical School, 30625 Hannover, Germany; (W.E.); (M.P.)
- Department of Natural Sciences, University of Applied Sciences Bonn-Rhein-Sieg, 53757 Sankt Augustin, Germany
| | - Georgios Tsiavaliaris
- Cellular Biophysics, Institute for Biophysical Chemistry, Hannover Medical School, 30625 Hannover, Germany;
- Correspondence:
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9
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Force and phosphate release from Arp2/3 complex promote dissociation of actin filament branches. Proc Natl Acad Sci U S A 2020; 117:13519-13528. [PMID: 32461373 DOI: 10.1073/pnas.1911183117] [Citation(s) in RCA: 37] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Networks of branched actin filaments formed by Arp2/3 complex generate and experience mechanical forces during essential cellular functions, including cell motility and endocytosis. External forces regulate the assembly and architecture of branched actin networks both in vitro and in cells. Considerably less is known about how mechanical forces influence the disassembly of actin filament networks, specifically, the dissociation of branches. We used microfluidics to apply force to branches formed from purified muscle actin and fission yeast Arp2/3 complex and observed debranching events in real time with total internal reflection fluorescence microscopy. Low forces in the range of 0 pN to 2 pN on branches accelerated their dissociation from mother filaments more than two orders of magnitude, from hours to <1 min. Neither force on the mother filament nor thermal fluctuations in mother filament shape influenced debranching. Arp2/3 complex at branch junctions adopts two distinct mechanical states with different sensitivities to force, which we name "young/strong" and "old/weak." The "young/strong" state 1 has adenosine 5'-diphosphate (ADP)-P i bound to Arp2/3 complex. Phosphate release converts Arp2/3 complex into the "old/weak" state 2 with bound ADP, which is 20 times more sensitive to force than state 1. Branches with ADP-Arp2/3 complex are more sensitive to debranching by fission yeast GMF (glia maturation factor) than branches with ADP-P i -Arp2/3 complex. These findings suggest that aging of branch junctions by phosphate release from Arp2/3 complex and mechanical forces contribute to disassembling "old" actin filament branches in cells.
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10
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Kodera N, Ando T. High-Speed Atomic Force Microscopy to Study Myosin Motility. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2020; 1239:127-152. [PMID: 32451858 DOI: 10.1007/978-3-030-38062-5_7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
High-speed atomic force microscopy (HS-AFM) is a unique tool that enables imaging of protein molecules during their functional activity at sub-100 ms temporal and submolecular spatial resolution. HS-AFM is suited for the study of highly dynamic proteins, including myosin motors. HS-AFM images of myosin V walking on actin filaments provide irrefutable evidence for the swinging lever arm motion propelling the molecule forward. Moreover, molecular behaviors that have not been noticed before are also displayed on the AFM movies. This chapter describes the principle, underlying techniques and performance of HS-AFM, filmed images of myosin V, and mechanistic insights into myosin motility provided from the filmed images.
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Affiliation(s)
- Noriyuki Kodera
- Nano Life Science Institute (WPI NanoLSI), Kanazawa University, Kanazawa, Japan
| | - Toshio Ando
- Nano Life Science Institute (WPI NanoLSI), Kanazawa University, Kanazawa, Japan.
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11
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Processivity and Velocity for Motors Stepping on Periodic Tracks. Biophys J 2020; 118:1537-1551. [PMID: 32367805 DOI: 10.1016/j.bpj.2020.01.047] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2019] [Revised: 01/08/2020] [Accepted: 01/31/2020] [Indexed: 12/23/2022] Open
Abstract
Processive molecular motors enable cargo transportation by assembling into dimers capable of taking several consecutive steps along a cytoskeletal filament. In the well-accepted hand-over-hand stepping mechanism, the trailing motor detaches from the track and binds the filament again in the leading position. This requires fuel consumption in the form of ATP hydrolysis and coordination of the catalytic cycles between the leading and the trailing heads. Alternate stepping pathways also exist, including inchworm-like movements, backward steps, and foot stomps. Whether all the pathways are coupled to ATP hydrolysis remains to be determined. Here, to establish the principles governing the dynamics of processive movement, we present a theoretical framework that includes all of the alternative stepping mechanisms. Our theory bridges the gap between the elemental rates describing the biochemical and structural transitions in each head and the experimentally measurable quantities such as velocity, processivity, and probability of backward stepping. Our results, obtained under the assumption that the track is periodic and infinite, provide expressions that hold regardless of the topology of the network connecting the intermediate states, and are therefore capable of describing the function of any molecular motor. We apply the theory to myosin VI, a motor that takes frequent backward steps and moves forward with a combination of hand-over-hand and inchworm-like steps. Our model quantitatively reproduces various observables of myosin VI motility reported by four experimental groups. The theory is used to predict the gating mechanism, the pathway for backward stepping, and the energy consumption as a function of ATP concentration.
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12
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Tang W, Unrath WC, Desetty R, Yengo CM. Dilated cardiomyopathy mutation in the converter domain of human cardiac myosin alters motor activity and response to omecamtiv mecarbil. J Biol Chem 2019; 294:17314-17325. [PMID: 31578282 DOI: 10.1074/jbc.ra119.010217] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2019] [Revised: 09/27/2019] [Indexed: 12/14/2022] Open
Abstract
We investigated a dilated cardiomyopathy (DCM) mutation (F764L) in human β-cardiac myosin by determining its motor properties in the presence and absence of the heart failure drug omecamtive mecarbil (OM). The mutation is located in the converter domain, a key region of communication between the catalytic motor and lever arm in myosins, and is nearby but not directly in the OM-binding site. We expressed and purified human β-cardiac myosin subfragment 1 (M2β-S1) containing the F764L mutation, and compared it to WT with in vitro motility as well as steady-state and transient kinetics measurements. In the absence of OM we demonstrate that the F764L mutation does not significantly change maximum actin-activated ATPase activity but slows actin sliding velocity (15%) and the actomyosin ADP release rate constant (25%). The transient kinetic analysis without OM demonstrates that F764L has a similar duty ratio as WT in unloaded conditions. OM is known to enhance force generation in cardiac muscle while it inhibits the myosin power stroke and enhances actin-attachment duration. We found that OM has a reduced impact on F764L ATPase and sliding velocity compared with WT. Specifically, the EC50 for OM induced inhibition of in vitro motility was 3-fold weaker in F764L. Also, OM reduces maximum actin-activated ATPase 2-fold in F764L, compared with 4-fold with WT. Overall, our results suggest that F764L attenuates the impact of OM on actin-attachment duration and/or the power stroke. Our work highlights the importance of mutation-specific considerations when pursuing small molecule therapies for cardiomyopathies.
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Affiliation(s)
- Wanjian Tang
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033
| | - William C Unrath
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033
| | - Rohini Desetty
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033
| | - Christopher M Yengo
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033
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13
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Barber‐Zucker S, Hall J, Mangapuram SV, Kass I, Kolusheva S, MacMillan F, Zarivach R, Henn A. Metal binding to the dynamic cytoplasmic domain of the cation diffusion facilitator (CDF) protein MamM induces a ‘locked‐in’ configuration. FEBS J 2019; 286:2193-2215. [DOI: 10.1111/febs.14795] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2018] [Revised: 02/02/2019] [Accepted: 02/25/2019] [Indexed: 01/03/2023]
Affiliation(s)
- Shiran Barber‐Zucker
- Department of Life Sciences Ben‐Gurion University of the Negev Beer Sheva Israel
- The National Institute for Biotechnology in the Negev Ben‐Gurion University of the Negev Beer Sheva Israel
- Ilse Katz Institute for Nanoscale Science and Technology Ben‐Gurion University of the Negev Beer Sheva Israel
| | - Jenny Hall
- School of Chemistry University of East Anglia Norwich Research Park UK
| | | | - Itamar Kass
- The National Institute for Biotechnology in the Negev Ben‐Gurion University of the Negev Beer Sheva Israel
| | - Sofiya Kolusheva
- Ilse Katz Institute for Nanoscale Science and Technology Ben‐Gurion University of the Negev Beer Sheva Israel
| | - Fraser MacMillan
- School of Chemistry University of East Anglia Norwich Research Park UK
| | - Raz Zarivach
- Department of Life Sciences Ben‐Gurion University of the Negev Beer Sheva Israel
- The National Institute for Biotechnology in the Negev Ben‐Gurion University of the Negev Beer Sheva Israel
- Ilse Katz Institute for Nanoscale Science and Technology Ben‐Gurion University of the Negev Beer Sheva Israel
| | - Arnon Henn
- Faculty of Biology Technion‐ Israel Institute of Technology Haifa Israel
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14
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Kobayashi M, Ramirez BE, Warren CM. Interplay of actin, ADP and Mg 2+ interactions with striated muscle myosin: Implications of their roles in ATPase. Arch Biochem Biophys 2018; 662:101-110. [PMID: 30529103 DOI: 10.1016/j.abb.2018.12.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2018] [Revised: 11/25/2018] [Accepted: 12/03/2018] [Indexed: 12/15/2022]
Abstract
The effects of Mg2+ on the interaction between ADP, a product of the ATPase reaction, and striated muscle myosin-subfragment 1 (S1) were investigated with both functional and spectroscopic methods. Mg2+ inhibited striated muscle myosin ATPase in the presence of F-actin. Significant effects of Mg2+ were observed in both rate constants of NOE build-up and maximal intensities in WaterLOGSY NMR experiments as F-actin concentration increased. In the absence of F-actin, myosin S1 with Mg2+ bound to a fluorescent ADP analog about five-times tighter than without Mg2+. In the presence of F-actin, the affinity of myosin S1 toward the ADP analog significantly decreased both with and without Mg2+. The equilibrium titration of myosin-S1 into F-actin revealed that in the presence of ADP the apparent dissociation constant (Kd) without Mg2+ was more than five-fold smaller than with Mg2+. Further, we examined effects of F-actin, ADP and Mg2+ binding to myosin on the tertiary structure of myosin-S1 using near UV circular dichroism (CD) spectroscopy. Both in the presence and absence of ADP, there was a Mg2+-dependent difference in the near UV CD spectra of actomyosin. Our results show that Mg2+ affects myosin-ADP and actin-myosin interactions which may be reflected in myosin ATPase activity.
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Affiliation(s)
- Minae Kobayashi
- Department of Physiology and Biophysics, University of Illinois at Chicago, Chicago, IL, USA; Center for Cardiovascular Research, University of Illinois at Chicago, Chicago, IL, USA.
| | - Benjamin E Ramirez
- Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, Chicago, IL, USA
| | - Chad M Warren
- Department of Physiology and Biophysics, University of Illinois at Chicago, Chicago, IL, USA; Center for Cardiovascular Research, University of Illinois at Chicago, Chicago, IL, USA
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15
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Wong EV, Gray S, Cao W, Montpetit R, Montpetit B, De La Cruz EM. Nup159 Weakens Gle1 Binding to Dbp5 But Does Not Accelerate ADP Release. J Mol Biol 2018; 430:2080-2095. [PMID: 29782832 DOI: 10.1016/j.jmb.2018.05.025] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2018] [Revised: 05/03/2018] [Accepted: 05/15/2018] [Indexed: 12/17/2022]
Abstract
Dbp5, DDX19 in humans, is an essential DEAD-box protein involved in mRNA export, which has also been linked to other cellular processes, including rRNA export and translation. Dbp5 ATPase activity is regulated by several factors, including RNA, the nucleoporin proteins Nup159 and Gle1, and the endogenous small-molecule inositol hexakisphosphate (InsP6). To better understand how these factors modulate Dbp5 activity and how this modulation relates to in vivo RNA metabolism, a detailed characterization of the Dbp5 mechanochemical cycle in the presence of those regulators individually or together is necessary. In this study, we test the hypothesis that Nup159 controls the ADP-bound state of Dbp5. In addition, the contributions of Mg2+ to the kinetics and thermodynamics of ADP binding to Dbp5 were assessed. Using a solution based in vitro approach, Mg2+ was found to slow ADP and ATP release from Dbp5 and increased the overall ADP and ATP affinities, as observed with other NTPases. Furthermore, Nup159 did not accelerate ADP release, while Gle1 actually slowed ADP release independent of Mg2+. These findings are not consistent with Nup159 acting as a nucleotide exchange factor to promote ADP release and Dbp5 ATPase cycling. Instead, in the presence of Nup159, the interaction between Gle1 and ADP-bound Dbp5 was found to be reduced by ~18-fold, suggesting that Nup159 alters the Dbp5-Gle1 interaction to aid Gle1 release from Dbp5.
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Affiliation(s)
- Emily V Wong
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA
| | - Shawn Gray
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA
| | - Wenxiang Cao
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA
| | - Rachel Montpetit
- Department of Viticulture and Enology, University of California, Davis, Davis, CA 95616, USA; Department of Food Science and Technology, University of California, Davis, Davis, CA 95616, USA
| | - Ben Montpetit
- Department of Viticulture and Enology, University of California, Davis, Davis, CA 95616, USA; Department of Food Science and Technology, University of California, Davis, Davis, CA 95616, USA.
| | - Enrique M De La Cruz
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA.
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16
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Ušaj M, Henn A. Kinetic adaptation of human Myo19 for active mitochondrial transport to growing filopodia tips. Sci Rep 2017; 7:11596. [PMID: 28912602 PMCID: PMC5599584 DOI: 10.1038/s41598-017-11984-6] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2017] [Accepted: 08/29/2017] [Indexed: 11/09/2022] Open
Abstract
Myosins are actin-based molecular motors which are enzymatically adapted for their cellular functions such as transportation and membrane tethering. Human Myo19 affects mitochondrial motility, and promotes their localization to stress-induced filopodia. Therefore, studying Myo19 enzymology is essential to understand how this motor may facilitate mitochondrial motility. Towards this goal, we have purified Myo19 motor domain (Myo19-3IQ) from a human-cell expression system and utilized transient kinetics to study the Myo19-3IQ ATPase cycle. We found that Myo19-3IQ exhibits noticeable conformational changes (isomerization steps) preceding both ATP and ADP binding, which may contribute to nucleotide binding regulation. Notably, the ADP isomerization step and subsequent ADP release contribute significantly to the rate-limiting step of the Myo19-3IQ ATPase cycle. Both the slow ADP isomerization and ADP release prolong the time Myo19-3IQ spend in the strong actin binding state and hence contribute to its relatively high duty ratio. However, the predicted duty ratio is lower than required to support motility as a monomer. Therefore, it may be that several Myo19 motors are required to propel mitochondria movement on actin filaments efficiently. Finally, we provide a model explaining how Myo19 translocation may be regulated by the local ATP/ADP ratio, coupled to the mitochondria presence in the filopodia.
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Affiliation(s)
- Marko Ušaj
- Faculty of Biology, Technion- Israel Institute of Technology, Haifa, 3200003, Israel
| | - Arnon Henn
- Faculty of Biology, Technion- Israel Institute of Technology, Haifa, 3200003, Israel.
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17
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Geeves MA. Review: The ATPase mechanism of myosin and actomyosin. Biopolymers 2017; 105:483-91. [PMID: 27061920 DOI: 10.1002/bip.22853] [Citation(s) in RCA: 49] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2016] [Revised: 03/31/2016] [Accepted: 04/01/2016] [Indexed: 11/05/2022]
Abstract
Myosins are a large family of molecular motors that use the common P-loop, Switch 1 and Switch 2 nucleotide binding motifs to recognize ATP, to create a catalytic site than can efficiently hydrolyze ATP and to communicate the state of the nucleotide pocket to other allosteric binding sites on myosin. The energy of ATP hydrolysis is used to do work against an external load. In this short review I will outline current thinking on the mechanism of ATP hydrolysis and how the energy of ATP hydrolysis is coupled to a series of protein conformational changes that allow a myosin, with the cytoskeleton track actin, to operate as a molecular motor of distinct types; fast movers, processive motors or strain sensors. © 2016 Wiley Periodicals, Inc. Biopolymers 105: 483-491, 2016.
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18
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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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19
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Biological Nanomotors with a Revolution, Linear, or Rotation Motion Mechanism. Microbiol Mol Biol Rev 2016; 80:161-86. [PMID: 26819321 DOI: 10.1128/mmbr.00056-15] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The ubiquitous biological nanomotors were classified into two categories in the past: linear and rotation motors. In 2013, a third type of biomotor, revolution without rotation (http://rnanano.osu.edu/movie.html), was discovered and found to be widespread among bacteria, eukaryotic viruses, and double-stranded DNA (dsDNA) bacteriophages. This review focuses on recent findings about various aspects of motors, including chirality, stoichiometry, channel size, entropy, conformational change, and energy usage rate, in a variety of well-studied motors, including FoF1 ATPase, helicases, viral dsDNA-packaging motors, bacterial chromosome translocases, myosin, kinesin, and dynein. In particular, dsDNA translocases are used to illustrate how these features relate to the motion mechanism and how nature elegantly evolved a revolution mechanism to avoid coiling and tangling during lengthy dsDNA genome transportation in cell division. Motor chirality and channel size are two factors that distinguish rotation motors from revolution motors. Rotation motors use right-handed channels to drive the right-handed dsDNA, similar to the way a nut drives the bolt with threads in same orientation; revolution motors use left-handed motor channels to revolve the right-handed dsDNA. Rotation motors use small channels (<2 nm in diameter) for the close contact of the channel wall with single-stranded DNA (ssDNA) or the 2-nm dsDNA bolt; revolution motors use larger channels (>3 nm) with room for the bolt to revolve. Binding and hydrolysis of ATP are linked to different conformational entropy changes in the motor that lead to altered affinity for the substrate and allow work to be done, for example, helicase unwinding of DNA or translocase directional movement of DNA.
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20
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Direct measurements of the coordination of lever arm swing and the catalytic cycle in myosin V. Proc Natl Acad Sci U S A 2015; 112:14593-8. [PMID: 26553992 DOI: 10.1073/pnas.1517566112] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Myosins use a conserved structural mechanism to convert the energy from ATP hydrolysis into a large swing of the force-generating lever arm. The precise timing of the lever arm movement with respect to the steps in the actomyosin ATPase cycle has not been determined. We have developed a FRET system in myosin V that uses three donor-acceptor pairs to examine the kinetics of lever arm swing during the recovery and power stroke phases of the ATPase cycle. During the recovery stroke the lever arm swing is tightly coupled to priming the active site for ATP hydrolysis. The lever arm swing during the power stroke occurs in two steps, a fast step that occurs before phosphate release and a slow step that occurs before ADP release. Time-resolved FRET demonstrates a 20-Å change in distance between the pre- and postpower stroke states and shows that the lever arm is more dynamic in the postpower stroke state. Our results suggest myosin binding to actin in the ADP.Pi complex triggers a rapid power stroke that gates the release of phosphate, whereas a second slower power stroke may be important for mediating strain sensitivity.
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21
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Swenson AM, Trivedi DV, Rauscher AA, Wang Y, Takagi Y, Palmer BM, Málnási-Csizmadia A, Debold EP, Yengo CM. Magnesium modulates actin binding and ADP release in myosin motors. J Biol Chem 2014; 289:23977-91. [PMID: 25006251 DOI: 10.1074/jbc.m114.562231] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
We examined the magnesium dependence of five class II myosins, including fast skeletal muscle myosin, smooth muscle myosin, β-cardiac myosin (CMIIB), Dictyostelium myosin II (DdMII), and nonmuscle myosin IIA, as well as myosin V. We found that the myosins examined are inhibited in a Mg(2+)-dependent manner (0.3-9.0 mm free Mg(2+)) in both ATPase and motility assays, under conditions in which the ionic strength was held constant. We found that the ADP release rate constant is reduced by Mg(2+) in myosin V, smooth muscle myosin, nonmuscle myosin IIA, CMIIB, and DdMII, although the ADP affinity is fairly insensitive to Mg(2+) in fast skeletal muscle myosin, CMIIB, and DdMII. Single tryptophan probes in the switch I (Trp-239) and switch II (Trp-501) region of DdMII demonstrate these conserved regions of the active site are sensitive to Mg(2+) coordination. Cardiac muscle fiber mechanic studies demonstrate cross-bridge attachment time is increased at higher Mg(2+) concentrations, demonstrating that the ADP release rate constant is slowed by Mg(2+) in the context of an activated muscle fiber. Direct measurements of phosphate release in myosin V demonstrate that Mg(2+) reduces actin affinity in the M·ADP·Pi state, although it does not change the rate of phosphate release. Therefore, the Mg(2+) inhibition of the actin-activated ATPase activity observed in class II myosins is likely the result of Mg(2+)-dependent alterations in actin binding. Overall, our results suggest that Mg(2+) reduces the ADP release rate constant and rate of attachment to actin in both high and low duty ratio myosins.
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Affiliation(s)
- Anja M Swenson
- From the Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033
| | - Darshan V Trivedi
- From the Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033
| | - Anna A Rauscher
- the Department of Biochemistry, Eötvös Loránd University, H-1117 Budapest, Hungary
| | - Yuan Wang
- the Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vermont 05405
| | - Yasuharu Takagi
- the Laboratory of Molecular Physiology, NHLBI, National Institutes of Health, Bethesda, Maryland 20892
| | - Bradley M Palmer
- the Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vermont 05405
| | - András Málnási-Csizmadia
- the Department of Biochemistry, Eötvös Loránd University, H-1117 Budapest, Hungary, the Hungarian Academy of Sciences-Eötvös Loránd University Molecular Biophysics Research Group, H-1117 Budapest, Hungary
| | - Edward P Debold
- the Department of Kinesiology, University of Massachusetts, Amherst, Massachusetts 02210, and
| | - Christopher M Yengo
- From the Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033,
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22
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Kodera N, Ando T. The path to visualization of walking myosin V by high-speed atomic force microscopy. Biophys Rev 2014; 6:237-260. [PMID: 25505494 PMCID: PMC4256461 DOI: 10.1007/s12551-014-0141-7] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2013] [Accepted: 05/07/2014] [Indexed: 01/14/2023] Open
Abstract
The quest for understanding the mechanism of myosin-based motility started with studies on muscle contraction. From numerous studies, the basic frameworks for this mechanism were constructed and brilliant hypotheses were put forward. However, the argument about the most crucial issue of how the actin-myosin interaction generates contractile force and shortening has not been definitive. To increase the "directness of measurement", in vitro motility assays and single-molecule optical techniques were created and used. Consequently, detailed knowledge of the motility of muscle myosin evolved, which resulted in provoking more arguments to a higher level. In parallel with technical progress, advances in cell biology led to the discovery of many classes of myosins. Myosin V was discovered to be a processive motor, unlike myosin II. The processivity reduced experimental difficulties because it allowed continuous tracing of the motor action of single myosin V molecules. Extensive studies of myosin V were expected to resolve arguments and build a consensus but did not necessarily do so. The directness of measurement was further enhanced by the recent advent of high-speed atomic force microscopy capable of directly visualizing biological molecules in action at high spatiotemporal resolution. This microscopy clearly visualized myosin V molecules walking on actin filaments and at last provided irrefutable evidence for the swinging lever-arm motion propelling the molecules. However, a peculiar foot stomp behavior also appeared in the AFM movie, raising new questions of the chemo-mechanical coupling in this motor and myosin motors in general. This article reviews these changes in the research of myosin motility and proposes new ideas to resolve the newly raised questions.
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Affiliation(s)
- Noriyuki Kodera
- Bio-AFM Frontier Research Center, Kanazawa University, Kanazawa, 920-1192 Japan
- PREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, 332-0012 Japan
| | - Toshio Ando
- Bio-AFM Frontier Research Center, Kanazawa University, Kanazawa, 920-1192 Japan
- Department of Physics, College of Science and Engineering, Kanazawa University, Kakuma-machi, Kanazawa, 920-1192 Japan
- CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, 332-0012 Japan
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23
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Haraguchi T, Tominaga M, Matsumoto R, Sato K, Nakano A, Yamamoto K, Ito K. Molecular characterization and subcellular localization of Arabidopsis class VIII myosin, ATM1. J Biol Chem 2014; 289:12343-55. [PMID: 24637024 PMCID: PMC4007431 DOI: 10.1074/jbc.m113.521716] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2013] [Revised: 03/12/2014] [Indexed: 02/02/2023] Open
Abstract
Land plants possess myosin classes VIII and XI. Although some information is available on the molecular properties of class XI myosins, class VIII myosins are not characterized. Here, we report the first analysis of the enzymatic properties of class VIII myosin. The motor domain of Arabidopsis class VIII myosin, ATM1 (ATM1-MD), and the motor domain plus one IQ motif (ATM1-1IQ) were expressed in a baculovirus system and characterized. ATM1-MD and ATM1-1IQ had low actin-activated Mg(2+)-ATPase activity (Vmax = 4 s(-1)), although their affinities for actin were high (Kactin = 4 μM). The actin-sliding velocities of ATM1-MD and ATM1-1IQ were 0.02 and 0.089 μm/s, respectively, from which the value for full-length ATM1 is calculated to be ∼0.2 μm/s. The results of actin co-sedimentation assay showed that the duty ratio of ATM1 was ∼90%. ADP dissociation from the actin·ATM1 complex (acto-ATM1) was extremely slow, which accounts for the low actin-sliding velocity, low actin-activated ATPase activity, and high duty ratio. The rate of ADP dissociation from acto-ATM1 was markedly biphasic with fast and slow phase rates (5.1 and 0.41 s(-1), respectively). Physiological concentrations of free Mg(2+) modulated actin-sliding velocity and actin-activated ATPase activity by changing the rate of ADP dissociation from acto-ATM1. GFP-fused full-length ATM1 expressed in Arabidopsis was localized to plasmodesmata, plastids, newly formed cell walls, and actin filaments at the cell cortex. Our results suggest that ATM1 functions as a tension sensor/generator at the cell cortex and other structures in Arabidopsis.
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Affiliation(s)
- Takeshi Haraguchi
- From the Department of Biology, Graduate School of Science, Chiba University, Inage-ku, Chiba 263-8522
| | - Motoki Tominaga
- the Live Cell Molecular Imaging Research Team, RIKEN Center for Advanced Photonics, Wako, Saitama 351-0198
- the Japan Science and Technology Agency, PRESTO, 4-1-8 Honcho Kawaguchi, Saitama 332-0012, and
| | - Rie Matsumoto
- From the Department of Biology, Graduate School of Science, Chiba University, Inage-ku, Chiba 263-8522
| | - Kei Sato
- the Department of Biological Sciences, Graduate School of Science, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
| | - Akihiko Nakano
- the Live Cell Molecular Imaging Research Team, RIKEN Center for Advanced Photonics, Wako, Saitama 351-0198
- the Department of Biological Sciences, Graduate School of Science, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
| | - Keiichi Yamamoto
- From the Department of Biology, Graduate School of Science, Chiba University, Inage-ku, Chiba 263-8522
| | - Kohji Ito
- From the Department of Biology, Graduate School of Science, Chiba University, Inage-ku, Chiba 263-8522
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24
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Cochran JC, Thompson ME, Kull FJ. Metal switch-controlled myosin II from Dictyostelium discoideum supports closure of nucleotide pocket during ATP binding coupled to detachment from actin filaments. J Biol Chem 2013; 288:28312-23. [PMID: 23960071 DOI: 10.1074/jbc.m113.466045] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
G-proteins, kinesins, and myosins are hydrolases that utilize a common protein fold and divalent metal cofactor (typically Mg(2+)) to coordinate purine nucleotide hydrolysis. The nucleoside triphosphorylase activities of these enzymes are activated through allosteric communication between the nucleotide-binding site and the activator/effector/polymer interface to convert the free energy of nucleotide hydrolysis into molecular switching (G-proteins) or force generation (kinesins and myosin). We have investigated the ATPase mechanisms of wild-type and the S237C mutant of non-muscle myosin II motor from Dictyostelium discoideum. The S237C substitution occurs in the conserved metal-interacting switch-1, and we show that this substitution modulates the actomyosin interaction based on the divalent metal present in solution. Surprisingly, S237C shows rapid basal steady-state Mg(2+)- or Mn(2+)-ATPase kinetics, but upon binding actin, its MgATPase is inhibited. This actin inhibition is relieved by Mn(2+), providing a direct and experimentally reversible linkage of switch-1 and the actin-binding cleft through the swapping of divalent metals in the reaction. Using pyrenyl-labeled F-actin, we demonstrate that acto·S237C undergoes slow and weak MgATP binding, which limits the rate of steady-state catalysis. Mn(2+) rescues this effect to near wild-type activity. 2'(3')-O-(N-Methylanthraniloyl)-ADP release experiments show the need for switch-1 interaction with the metal cofactor for tight ADP binding. Our results are consistent with strong reciprocal coupling of nucleoside triphosphate and F-actin binding and provide additional evidence for the allosteric communication pathway between the nucleotide-binding site and the filament-binding region.
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Affiliation(s)
- Jared C Cochran
- From the Department of Molecular and Cellular Biochemistry, Indiana University, Bloomington, Indiana 47405
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25
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Trivedi DV, Muretta JM, Swenson AM, Thomas DD, Yengo CM. Magnesium impacts myosin V motor activity by altering key conformational changes in the mechanochemical cycle. Biochemistry 2013; 52:4710-22. [PMID: 23725637 DOI: 10.1021/bi4004364] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We investigated how magnesium (Mg) impacts key conformational changes during the ADP binding/release steps in myosin V and how these alterations impact the actomyosin mechanochemical cycle. The conformation of the nucleotide binding pocket was examined with our established FRET system in which myosin V labeled with FlAsH in the upper 50 kDa domain participates in energy transfer with mant labeled nucleotides. We examined the maximum actin-activated ATPase activity of MV FlAsH at a range of free Mg concentrations (0.1-9 mM) and found that the highest activity occurs at low Mg (0.1-0.3 mM), while there is a 50-60% reduction in activity at high Mg (3-9 mM). The motor activity examined with the in vitro motility assay followed a similar Mg-dependence, and the trend was similar with dimeric myosin V. Transient kinetic FRET studies of mantdADP binding/release from actomyosin V FlAsH demonstrate that the transition between the weak and strong actomyosin.ADP states is coupled to movement of the upper 50 kDa domain and is dependent on Mg with the strong state stabilized by Mg. We find that the kinetics of the upper 50 kDa conformational change monitored by FRET correlates well with the ATPase and motility results over a wide range of Mg concentrations. Our results suggest the conformation of the upper 50 kDa domain is highly dynamic in the Mg free actomyosin.ADP state, which is in agreement with ADP binding being entropy driven in the absence of Mg. Overall, our results demonstrate that Mg is a key factor in coupling the nucleotide- and actin-binding regions. In addition, Mg concentrations in the physiological range can alter the structural transition that limits ADP dissociation from actomyosin V, which explains the impact of Mg on actin-activated ATPase activity and in vitro motility.
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Affiliation(s)
- Darshan V Trivedi
- Department of Cellular and Molecular Physiology, College of Medicine, Pennsylvania State University , Hershey, Pennsylvania 17033, United States
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26
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Chizhov I, Hartmann FK, Hundt N, Tsiavaliaris G. Global fit analysis of myosin-5b motility reveals thermodynamics of Mg2+-sensitive acto-myosin-ADP states. PLoS One 2013; 8:e64797. [PMID: 23738001 PMCID: PMC3662761 DOI: 10.1371/journal.pone.0064797] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2013] [Accepted: 04/18/2013] [Indexed: 01/27/2023] Open
Abstract
Kinetic and thermodynamic studies of the mechanochemical cycle of myosin motors are essential for understanding the mechanism of energy conversion. Here, we report our investigation of temperature and free Mg2+-ion dependencies of sliding velocities of a high duty ratio class-5 myosin motor, myosin-5b from D. discoideum using in vitro motility assays. Previous studies have shown that the sliding velocity of class-5 myosins obeys modulation by free Mg2+-ions. Free Mg2+-ions affect ADP release kinetics and the dwell time of actin-attached states. The latter determines the maximal velocity of actin translocation in the sliding filament assay. We measured the temperature dependence of sliding velocity in the range from 5 to 55°C at two limiting free Mg2+-ion concentrations. Arrhenius plots demonstrated non-linear behavior. Based on this observation we propose a kinetic model, which explains both sensitivity towards free Mg2+-ions and non-linearity of the temperature dependence of sliding velocity. According to this model, velocity is represented as a simple analytical function of temperature and free Mg2+-ion concentrations. This function has been applied to global non-linear fit analysis of three data sets including temperature and magnesium (at 20°C) dependence of sliding velocity. As a result we obtain thermodynamic parameters (ΔHMg and ΔSMg) of a fast equilibrium between magnesium free (AM·D) and magnesium bound acto-myosin-ADP (AM· Mg2+D) states and the corresponding enthalpic barriers associated with ADP release (ΔH1‡ and ΔH2‡). The herein presented integrative approach of data analysis based on global fitting can be applied to the remaining steps of the acto-myosin ATPase cycle facilitating the determination of energetic parameters and thermodynamics of acto-myosin interactions.
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Affiliation(s)
- Igor Chizhov
- Institute for Biophysical Chemistry, OE 4350, Hannover Medical School, Hannover, Germany
| | - Falk K. Hartmann
- Institute for Biophysical Chemistry, OE 4350, Hannover Medical School, Hannover, Germany
| | - Nikolas Hundt
- Institute for Biophysical Chemistry, OE 4350, Hannover Medical School, Hannover, Germany
| | - Georgios Tsiavaliaris
- Institute for Biophysical Chemistry, OE 4350, Hannover Medical School, Hannover, Germany
- * E-mail:
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27
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Elam WA, Kang H, De la Cruz EM. Biophysics of actin filament severing by cofilin. FEBS Lett 2013; 587:1215-9. [PMID: 23395798 DOI: 10.1016/j.febslet.2013.01.062] [Citation(s) in RCA: 78] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2012] [Revised: 01/25/2013] [Accepted: 01/28/2013] [Indexed: 11/16/2022]
Abstract
The continuous assembly and disassembly of actin filament networks is vital for cellular processes including division, growth, and motility. Network remodeling is facilitated by cofilins, a family of essential regulatory proteins that fragment actin filaments. Cofilin induces net structural changes in filaments that render them more compliant in bending and twisting. A model in which local stress accumulation at mechanical discontinuities, such as boundaries of bare and cofilin-decorated filament segments, accounts for the cofilin concentration dependence of severing, including maximal activity at sub-stoichiometric binding densities. Real-time imaging of cofilin-mediated filament severing supports the boundary-fracture model. The severing model predicts that fragmentation is promoted by factors modulating filament mechanics (e.g. tethering, cross-linking, or deformation), possibly explaining enhanced in vivo severing activities.
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Affiliation(s)
- W Austin Elam
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA
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28
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Temperature dependent measurements reveal similarities between muscle and non-muscle myosin motility. J Muscle Res Cell Motil 2012; 33:385-94. [PMID: 22930330 DOI: 10.1007/s10974-012-9316-7] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2012] [Accepted: 08/06/2012] [Indexed: 10/28/2022]
Abstract
We examined the temperature dependence of muscle and non-muscle myosin (heavy meromyosin, HMM) with in vitro motility and actin-activated ATPase assays. Our results indicate that myosin V (MV) has a temperature dependence that is similar in both ATPase and motility assays. We demonstrate that skeletal muscle myosin (SK), smooth muscle myosin (SM), and non-muscle myosin IIA (NM) have different temperature dependence in ATPase compared to in vitro motility assays. In the class II myosins we examined (SK, SM, and NM) the rate-limiting step in ATPase assays is thought to be attachment to actin or phosphate release, while for in vitro motility assays it is controversial. In MV the rate-limiting step for both in vitro motility and ATPase assays is known to be ADP release. Consequently, in MV the temperature dependence of the ADP release rate constant is similar to the temperature dependence of in vitro motility. Interestingly, the temperature dependence of the ADP release rate constant of SM and NM was shifted toward the in vitro motility temperature dependence. Our results suggest that the rate-limiting step in SK, SM, and NM may shift from attachment-limited in solution to detachment limited in the in vitro motility assay. Internal strain within the myosin molecule or by neighboring myosin motors may slow ADP release which becomes rate-limiting in the in vitro motility assay. Within this small subset of myosins examined, the in vitro sliding velocity correlates reasonably well with actin-activated ATPase activity, which was suggested by the original study by Barany (J Gen Physiol 50:197-218, 1967).
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29
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Switch II mutants reveal coupling between the nucleotide- and actin-binding regions in myosin V. Biophys J 2012; 102:2545-55. [PMID: 22713570 DOI: 10.1016/j.bpj.2012.04.025] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2011] [Revised: 04/11/2012] [Accepted: 04/17/2012] [Indexed: 11/21/2022] Open
Abstract
Conserved active-site elements in myosins and other P-loop NTPases play critical roles in nucleotide binding and hydrolysis; however, the mechanisms of allosteric communication among these mechanoenzymes remain unresolved. In this work we introduced the E442A mutation, which abrogates a salt-bridge between switch I and switch II, and the G440A mutation, which abolishes a main-chain hydrogen bond associated with the interaction of switch II with the γ phosphate of ATP, into myosin V. We used fluorescence resonance energy transfer between mant-labeled nucleotides or IAEDANS-labeled actin and FlAsH-labeled myosin V to examine the conformation of the nucleotide- and actin-binding regions, respectively. We demonstrate that in the absence of actin, both the G440A and E442A mutants bind ATP with similar affinity and result in only minor alterations in the conformation of the nucleotide-binding pocket (NBP). In the presence of ADP and actin, both switch II mutants disrupt the formation of a closed NBP actomyosin.ADP state. The G440A mutant also prevents ATP-induced opening of the actin-binding cleft. Our results indicate that the switch II region is critical for stabilizing the closed NBP conformation in the presence of actin, and is essential for communication between the active site and actin-binding region.
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30
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Heissler SM, Manstein DJ. Functional characterization of the human myosin-7a motor domain. Cell Mol Life Sci 2011; 69:299-311. [PMID: 21687988 PMCID: PMC3249170 DOI: 10.1007/s00018-011-0749-8] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2011] [Revised: 05/30/2011] [Accepted: 06/01/2011] [Indexed: 11/26/2022]
Abstract
Myosin-7a participates in auditory and visual processes. Defects in MYO7A, the gene encoding the myosin-7a heavy chain, are causative for Usher syndrome 1B, the most frequent cause of deaf-blindness in humans. In the present study, we performed a detailed kinetic and functional characterization of the isolated human myosin-7a motor domain to elucidate the details of chemomechanical coupling and the regulation of motor function. A rate-limiting, slow ADP release step causes long lifetimes of strong actin-binding intermediates and results in a high duty ratio. Moreover, our results reveal a Mg2+-sensitive regulatory mechanism tuning the kinetic and mechanical properties of the myosin-7a motor domain. We obtained direct evidence that changes in the concentration of free Mg2+ ions affect the motor properties of human myosin-7a using an in vitro motility assay system. Our results suggest that in a cellular environment, compartment-specific fluctuations in free Mg2+ ions can mediate the conditional switching of myosin-7a between cargo moving and tension bearing modes.
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Affiliation(s)
- Sarah M. Heissler
- Institut für Biophysikalische Chemie, Medizinische Hochschule Hannover, Carl-Neuberg-Str. 1, 30625 Hannover, Germany
| | - Dietmar J. Manstein
- Institut für Biophysikalische Chemie, Medizinische Hochschule Hannover, Carl-Neuberg-Str. 1, 30625 Hannover, Germany
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31
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Cao W, Coman MM, Ding S, Henn A, Middleton ER, Bradley MJ, Rhoades E, Hackney DD, Pyle AM, De La Cruz EM. Mechanism of Mss116 ATPase reveals functional diversity of DEAD-Box proteins. J Mol Biol 2011; 409:399-414. [PMID: 21501623 PMCID: PMC3125984 DOI: 10.1016/j.jmb.2011.04.004] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2011] [Revised: 03/31/2011] [Accepted: 04/01/2011] [Indexed: 10/18/2022]
Abstract
Mss116 is a Saccharomyces cerevisiae mitochondrial DEAD-box RNA helicase protein that is essential for efficient in vivo splicing of all group I and group II introns and for activation of mRNA translation. Catalysis of intron splicing by Mss116 is coupled to its ATPase activity. Knowledge of the kinetic pathway(s) and biochemical intermediates populated during RNA-stimulated Mss116 ATPase is fundamental for defining how Mss116 ATP utilization is linked to in vivo function. We therefore measured the rate and equilibrium constants underlying Mss116 ATP utilization and nucleotide-linked RNA binding. RNA accelerates the Mss116 steady-state ATPase ∼7-fold by promoting rate-limiting ATP hydrolysis such that inorganic phosphate (P(i)) release becomes (partially) rate-limiting. RNA binding displays strong thermodynamic coupling to the chemical states of the Mss116-bound nucleotide such that Mss116 with bound ADP-P(i) binds RNA more strongly than Mss116 with bound ADP or in the absence of nucleotide. The predominant biochemical intermediate populated during in vivo steady-state cycling is the strong RNA-binding Mss116-ADP-P(i) state. Strong RNA binding allows Mss116 to fulfill its biological role in the stabilization of group II intron folding intermediates. ATPase cycling allows for transient population of the weak RNA-binding ADP state of Mss116 and linked dissociation from RNA, which is required for the final stages of intron folding. In cases where Mss116 functions as a helicase, the data collectively favor a model in which ATP hydrolysis promotes a weak-to-strong RNA binding transition that disrupts stable RNA duplexes. The subsequent strong-to-weak RNA binding transition associated with P(i) release dissociates Mss116-RNA complexes, regenerating free Mss116.
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Affiliation(s)
- Wenxiang Cao
- Yale University, Department of Molecular Biophysics & Biochemistry, 260 Whitney Avenue, New Haven, CT 06520, USA
| | - Maria Magdalena Coman
- Yale University, Department of Molecular Biophysics & Biochemistry, 260 Whitney Avenue, New Haven, CT 06520, USA
| | - Steve Ding
- Yale University, Department of Molecular Biophysics & Biochemistry, 260 Whitney Avenue, New Haven, CT 06520, USA
| | - Arnon Henn
- Yale University, Department of Molecular Biophysics & Biochemistry, 260 Whitney Avenue, New Haven, CT 06520, USA
| | | | - Michael J. Bradley
- Yale University, Department of Molecular Biophysics & Biochemistry, 260 Whitney Avenue, New Haven, CT 06520, USA
| | - Elizabeth Rhoades
- Yale University, Department of Molecular Biophysics & Biochemistry, 260 Whitney Avenue, New Haven, CT 06520, USA
| | - David D. Hackney
- Department of Biological Sciences, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, PA 15213, USA
| | - Anna Marie Pyle
- Yale University, Department of Molecular Biophysics & Biochemistry, 260 Whitney Avenue, New Haven, CT 06520, USA
- The Howard Hughes Medical Institute
| | - Enrique M. De La Cruz
- Yale University, Department of Molecular Biophysics & Biochemistry, 260 Whitney Avenue, New Haven, CT 06520, USA
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32
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Zheng W. Coarse-grained modeling of conformational transitions underlying the processive stepping of myosin V dimer along filamentous actin. Proteins 2011; 79:2291-305. [PMID: 21590746 DOI: 10.1002/prot.23055] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2011] [Revised: 03/21/2011] [Accepted: 04/04/2011] [Indexed: 11/11/2022]
Abstract
To explore the structural basis of processive stepping of myosin V along filamentous actin, we have performed comprehensive modeling of its key conformational states and transitions with an unprecedented residue level of details. We have built structural models for a myosin V monomer complexed with filamentous actin at four biochemical states [adenosine diphosphate (ATP)-, adenosine diphosphate (ADP)-phosphate-, ADP-bound or nucleotide-free]. Then we have modeled a myosin V dimer (consisting of lead and rear head) at various two-head-bound states with nearly straight lever arms rotated by intramolecular strain. Next, we have performed transition pathway modeling to determine the most favorable sequence of transitions (namely, phosphate release at the lead head followed by ADP release at the rear head, while ADP release at the lead head is inhibited), which underlie the kinetic coordination between the two heads. Finally, we have used transition pathway modeling to reveal the order of structural changes during three key biochemical transitions (phosphate release at the lead head, ADP release and ATP binding at the rear head), which shed lights on the strain-dependence of the allosterically coupled motions at various stages of myosin V's work cycle. Our modeling results are in agreement with and offer structural insights to many results of kinetic, single-molecule and structural studies of myosin V.
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Affiliation(s)
- Wenjun Zheng
- Department of Physics, University at Buffalo, Buffalo, NY, USA.
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33
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Decarreau JA, James NG, Chrin LR, Berger CL. Switch I closure simultaneously promotes strong binding to actin and ADP in smooth muscle myosin. J Biol Chem 2011; 286:22300-7. [PMID: 21536675 DOI: 10.1074/jbc.m111.219014] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The motor protein myosin uses energy derived from ATP hydrolysis to produce force and motion. Important conserved components (P-loop, switch I, and switch II) help propagate small conformational changes at the active site into large scale conformational changes in distal regions of the protein. Structural and biochemical studies have indicated that switch I may be directly responsible for the reciprocal opening and closing of the actin and nucleotide-binding pockets during the ATPase cycle, thereby aiding in the coordination of these important substrate-binding sites. Smooth muscle myosin has displayed the ability to simultaneously bind tightly to both actin and ADP, although it is unclear how both substrate-binding clefts could be closed if they are rigidly coupled to switch I. Here we use single tryptophan mutants of smooth muscle myosin to determine how conformational changes in switch I are correlated with structural changes in the nucleotide and actin-binding clefts in the presence of actin and ADP. Our results suggest that a closed switch I conformation in the strongly bound actomyosin-ADP complex is responsible for maintaining tight nucleotide binding despite an open nucleotide-binding pocket. This unique state is likely to be crucial for prolonged tension maintenance in smooth muscle.
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Affiliation(s)
- Justin A Decarreau
- Department of Biochemistry, University of Vermont College of Medicine, Burlington, Vermont 05405, USA
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34
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Jacobs DJ, Trivedi D, David C, Yengo CM. Kinetics and thermodynamics of the rate-limiting conformational change in the actomyosin V mechanochemical cycle. J Mol Biol 2011; 407:716-30. [PMID: 21315083 DOI: 10.1016/j.jmb.2011.02.001] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2010] [Revised: 02/01/2011] [Accepted: 02/01/2011] [Indexed: 11/26/2022]
Abstract
We used FRET to examine the kinetics and thermodynamics of structural changes associated with ADP release in myosin V, which is thought to be a strain-sensitive step in many muscle and non-muscle myosins. We also explored essential dynamics using FIRST/FRODA starting with three different myosin V X-ray crystal structures to examine intrinsic flexibility and correlated motions. Our steady-state and time-resolved FRET analysis demonstrates a temperature-dependent reversible conformational change in the nucleotide-binding pocket (NBP). Our kinetic results demonstrate that the NBP goes from a closed to an open conformation prior to the release of ADP, while the actin-binding cleft remains closed. Interestingly, we find that the temperature dependence of the maximum actin-activated myosin V ATPase rate is similar to the pocket opening step, demonstrating that this is the rate-limiting structural transition in the ATPase cycle. Thermodynamic analysis demonstrates that the transition from the open to closed NBP conformation is unfavorable because of a decrease in entropy. The intrinsic flexibility analysis is consistent with conformational entropy playing a role in this transition as the MV.ADP structure is highly flexible compared to the MV.APO structure. Our experimental and modeling studies support the conclusion of a novel post-power-stroke actomyosin.ADP state in which the NBP and actin-binding cleft are closed. The novel state may be important for strain sensitivity as the transition from the closed to open NBP conformation may be altered by lever arm position.
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Affiliation(s)
- Donald J Jacobs
- Department of Physics and Optical Science, University of North Carolina at Charlotte, 9201 University City Blvd., Charlotte, NC 28223, USA
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35
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Islam K, Chin HF, Olivares AO, Saunders LP, De La Cruz EM, Kapoor TM. A myosin V inhibitor based on privileged chemical scaffolds. Angew Chem Int Ed Engl 2011; 49:8484-8. [PMID: 20878825 DOI: 10.1002/anie.201004026] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Affiliation(s)
- Kabirul Islam
- Laboratory of Chemistry and Cell Biology, Rockefeller University, 1230 York Avenue, New York, NY 10065, USA
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36
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Purcell TJ, Naber N, Franks-Skiba K, Dunn AR, Eldred CC, Berger CL, Málnási-Csizmadia A, Spudich JA, Swank DM, Pate E, Cooke R. Nucleotide pocket thermodynamics measured by EPR reveal how energy partitioning relates myosin speed to efficiency. J Mol Biol 2010; 407:79-91. [PMID: 21185304 DOI: 10.1016/j.jmb.2010.11.053] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2010] [Revised: 11/24/2010] [Accepted: 11/26/2010] [Indexed: 11/26/2022]
Abstract
We have used spin-labeled ADP to investigate the dynamics of the nucleotide-binding pocket in a series of myosins, which have a range of velocities. Electron paramagnetic resonance spectroscopy reveals that the pocket is in equilibrium between open and closed conformations. In the absence of actin, the closed conformation is favored. When myosin binds actin, the open conformation becomes more favored, facilitating nucleotide release. We found that faster myosins favor a more closed pocket in the actomyosin•ADP state, with smaller values of ΔH(0) and ΔS(0), even though these myosins release ADP at a faster rate. A model involving a partitioning of free energy between work-generating steps prior to rate-limiting ADP release explains both the unexpected correlation between velocity and opening of the pocket and the observation that fast myosins are less efficient than slow myosins.
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Affiliation(s)
- Thomas J Purcell
- Department of Biochemistry and Biophysics, UCSF MC 2240, Genentech Hall Room S416C, 600 16th Street, San Francisco, CA 94158-2517, USA.
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37
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Chuan P, Spudich JA, Dunn AR. Robust mechanosensing and tension generation by myosin VI. J Mol Biol 2010; 405:105-12. [PMID: 20970430 DOI: 10.1016/j.jmb.2010.10.010] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2010] [Revised: 09/29/2010] [Accepted: 10/08/2010] [Indexed: 10/18/2022]
Abstract
Myosin VI is a molecular motor that is thought to function both as a transporter and as a cytoskeletal anchor in vivo. Here we use optical tweezers to examine force generation by single molecules of myosin VI under physiological nucleotide concentrations. We find that myosin VI is an efficient transporter at loads of up to ∼2 pN but acts as a cytoskeletal anchor at higher loads. Our data and the resulting model are consistent with an indirect coupling of global structural motions to nucleotide binding and release. The model provides a mechanism by which load may regulate the dual functions of myosin VI in vivo. Our results suggest that myosin VI kinetics are tuned such that the motor maintains a consistent level of mechanical tension within the cell, a property potentially shared by other mechanosensitive proteins.
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Affiliation(s)
- Peiying Chuan
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305, USA
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38
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Islam K, Chin HF, Olivares AO, Saunders LP, De La Cruz EM, Kapoor TM. A Myosin V Inhibitor Based on Privileged Chemical Scaffolds. Angew Chem Int Ed Engl 2010. [DOI: 10.1002/ange.201004026] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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39
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Nagy NT, Sakamoto T, Takács B, Gyimesi M, Hazai E, Bikádi Z, Sellers JR, Kovács M. Functional adaptation of the switch-2 nucleotide sensor enables rapid processive translocation by myosin-5. FASEB J 2010; 24:4480-90. [PMID: 20631329 DOI: 10.1096/fj.10-163998] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Active site loops that are conserved across superfamilies of myosins, kinesins, and G proteins play key roles in allosteric coupling of NTP hydrolysis to interaction with track filaments or effector proteins. In this study, we investigated how the class-specific natural variation in the switch-2 active site loop contributes to the motor function of the intracellular transporter myosin-5. We used single-molecule, rapid kinetic and spectroscopic experiments and semiempirical quantum chemical simulations to show that the class-specific switch-2 structure including a tyrosine (Y439) in myosin-5 enables rapid processive translocation along actin filaments by facilitating Mg(2+)-dependent ADP release. Using wild-type control and Y439 point mutant myosin-5 proteins, we demonstrate that the translocation speed precisely correlates with the kinetics of nucleotide exchange. Switch-2 variants can thus be used to fine-tune translocation speed while maintaining high processivity. The class-specific variation of switch-2 in various NTPase superfamilies indicates its general role in the kinetic tuning of Mg(2+)-dependent nucleotide exchange.
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Affiliation(s)
- Nikolett T Nagy
- Department of Biochemistry, Eötvös University, Budapest, Hungary
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40
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Abstract
The general structural features of the motor region of myosin superfamily members are now well established, as is a subset of the structural and kinetic transitions of the actin-myosin catalytic cycle. Not yet visualized are the structural rearrangements triggered by actin binding that are coupled to force generation and product release. In this review we describe the recent progress in understanding these missing components of the mechanism of chemomechanical transduction by myosin motors. These insights come from a combination of kinetic and single-molecule studies on multiple classes of myosins, with additional insights from contracting muscle fibers. These recent studies have explored the effects of intermediate and high loads on the kinetics of the actin-bound myosin state transitions. We also describe studies that delineate how some classes of myosin motors are adapted for processive movement on actin.
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Affiliation(s)
- H Lee Sweeney
- Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6085, USA.
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41
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Direct observation of the myosin-Va power stroke and its reversal. Nat Struct Mol Biol 2010; 17:590-5. [PMID: 20418880 PMCID: PMC3487478 DOI: 10.1038/nsmb.1820] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2009] [Accepted: 02/25/2010] [Indexed: 11/13/2022]
Abstract
Complex forms of cellular motility, including cell division, organelle trafficking or signal amplification in the auditory system, require strong coordination of the myosin motors involved. The most basic mechanism of coordination is via direct mechanical interactions of individual motor heads leading to modification of their mechano-chemical cycles. Here we used an optical trap-based assay to investigate the reversibility of the force- generating conformational change (power stroke) of single myosin-V motor heads. By applying load to the head shortly after binding to actin, we found that at a certain load the power stroke could be reversed and the head fluctuated between an actin-bound pre- and a post-power stroke conformation. This load-dependent mechanical instability might be critical to coordinate the heads of processive, dimeric myosin-V. Non-linear response to load leading to coordination or oscillations amongst motors might be relevant for many cellular functions.
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42
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Xu Y, Wang Z. Comprehensive physical mechanism of two-headed biomotor myosin V. J Chem Phys 2010; 131:245104. [PMID: 20059116 DOI: 10.1063/1.3276283] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Two-headed biomotor myosin V autonomously coordinates its two identical heads in fuel consumption and mechanical stepping, so that the dimerized motor as a whole gains the capability of processive, unidirectional movement along cytoskeletal filament. How the dimer-level functions like sustained direction rectification and autonomous coordination emerge out of physical principles poses an outstanding question pertinent to motor protein biology as well as the nascent field of bioinspired nanomotors. Here the comprehensive physical mechanism for myosin V motor is identified by a dimer-level free-energy analysis that is methodologically calibrated against experimental data. A hallmark of the identified mechanism is a mechanically mediated symmetry breaking that occurs at the dimer level and prevails against ubiquitous thermal fluctuations. Another character is the onset of substantial free-energy gaps between major dimer-track binding configurations. The symmetry breaking is the basis for myosin V's directional rectification, and the energy gaps facilitate autonomous head-head coordination. The mechanism explains the experimental finding that myosin V makes ATP-independent consecutive steps under high opposing loads but not under pushing loads. Interestingly, myosin V and another major biomotor kinesin 1 are found to share essentially the same core mechanism but for distinctly different working regimes.
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Affiliation(s)
- Yuzhi Xu
- Institute of Modern Physics, Fudan University, Shanghai 200433, China
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43
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Pathway of ATP utilization and duplex rRNA unwinding by the DEAD-box helicase, DbpA. Proc Natl Acad Sci U S A 2010; 107:4046-50. [PMID: 20160110 DOI: 10.1073/pnas.0913081107] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
DEAD-box RNA helicase proteins use the energy of ATP hydrolysis to drive the unwinding of duplex RNA. However, the mechanism that couples ATP utilization to duplex RNA unwinding is unknown. We measured ATP utilization and duplex RNA unwinding by DbpA, a non-processive bacterial DEAD-box RNA helicase specifically activated by the peptidyl transferase center (PTC) of 23S rRNA. Consumption of a single ATP molecule is sufficient to unwind and displace an 8 base pair rRNA strand annealed to a 32 base pair PTC-RNA "mother strand" fragment. Strand displacement occurs after ATP binding and hydrolysis but before P(i) product release. P(i) release weakens binding to rRNA, thereby facilitating the release of the unwound rRNA mother strand and the recycling of DbpA for additional rounds of unwinding. This work explains how ATPase activity of DEAD-box helicases is linked to RNA unwinding.
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44
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Prochniewicz E, Chin HF, Henn A, Hannemann DE, Olivares AO, Thomas DD, De La Cruz EM. Myosin isoform determines the conformational dynamics and cooperativity of actin filaments in the strongly bound actomyosin complex. J Mol Biol 2009; 396:501-9. [PMID: 19962990 DOI: 10.1016/j.jmb.2009.11.063] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2009] [Revised: 10/06/2009] [Accepted: 11/27/2009] [Indexed: 10/20/2022]
Abstract
We used transient phosphorescence anisotropy to detect the microsecond rotational dynamics of erythrosin-iodoacetamide-labeled actin strongly bound to single-headed fragments of muscle myosin subfragment 1 (S1) and non-muscle myosin V (MV). The conformational dynamics of actin filaments in solution are markedly influenced by the isoform of bound myosin. Both myosins increase the final anisotropy of actin at substoichiometric binding densities, indicating long-range, non-nearest neighbor cooperative restriction of filament rotational dynamics amplitude, but the cooperative unit is larger with MV than with muscle S1. Both myosin isoforms also cooperatively affect the actin filament rotational correlation time, but with opposite effects: muscle S1 decreases rates of intrafilament torsional motion, while binding of MV increases the rates of motion. The cooperative effects on the rates of intrafilament motions correlate with the kinetics of myosin binding to actin filaments such that MV binds more rapidly and muscle myosin binds more slowly to partially decorated filaments than to bare filaments. The two isoforms also differ in their effects on the phosphorescence lifetime of the actin-bound erythrosin iodoacetamide: while muscle S1 increases the lifetime, suggesting decreased aqueous exposure of the probe, MV does not induce a significant change. We conclude that the dynamics and structure of actin in the strongly bound actomyosin complex are determined by the isoform of the bound myosin in a manner likely to accommodate the diverse functional roles of actomyosin in muscle and non-muscle cells.
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Affiliation(s)
- Ewa Prochniewicz
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN 55455, USA
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45
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De La Cruz EM, Olivares AO. Watching the walk: observing chemo-mechanical coupling in a processive myosin motor. HFSP JOURNAL 2009; 3:67-70. [PMID: 19794813 DOI: 10.2976/1.3095425] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/12/2009] [Accepted: 02/16/2009] [Indexed: 11/19/2022]
Abstract
Molecular motors are cellular nanomachines that convert the energy from nucleotide binding, hydrolysis, and product release into mechanical work. Because molecular motors contribute to fundamental processes in all living organisms, including genome replication, gene transcription, protein synthesis, organelle transport, and cell division, understanding how the chemical (ATP utilization) and mechanical (motility) cycles are linked is of fundamental importance. A recent study reports the direct visualization of simultaneous nucleotide binding and mechanical displacement of a single myosin 5a molecule, a processive molecular motor protein that takes successive approximately 36-nm steps along actin filaments of the cytoskeleton. This new work demonstrates an exciting advance in single-molecule enzymology and advances our understanding of the link between chemical catalysis and mechanical work in molecular motors, particularly those that operate under internal and external loads.
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Kinetic analysis of the guanine nucleotide exchange activity of TRAPP, a multimeric Ypt1p exchange factor. J Mol Biol 2009; 389:275-88. [PMID: 19361519 DOI: 10.1016/j.jmb.2009.03.068] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2009] [Revised: 03/24/2009] [Accepted: 03/30/2009] [Indexed: 11/22/2022]
Abstract
TRAPP complexes, which are large multimeric assemblies that function in membrane traffic, are guanine nucleotide exchange factors (GEFs) that activate the Rab GTPase Ypt1p. Here we measured rate and equilibrium constants that define the interaction of Ypt1p with guanine nucleotide (guanosine 5'-diphosphate and guanosine 5'-triphosphate/guanosine 5'-(beta,gamma-imido)triphosphate) and the core TRAPP subunits required for GEF activity. These parameters allowed us to identify the kinetic and thermodynamic bases by which TRAPP catalyzes nucleotide exchange from Ypt1p. Nucleotide dissociation from Ypt1p is slow (approximately 10(-4) s(-1)) and accelerated >1000-fold by TRAPP. Acceleration of nucleotide exchange by TRAPP occurs via a predominantly Mg(2+)-independent pathway. Thermodynamic linkage analysis indicates that TRAPP weakens nucleotide affinity by <80-fold and vice versa, in contrast to most other characterized GEF systems that weaken nucleotide binding affinities by 4-6 orders of magnitude. The overall net changes in nucleotide binding affinities are small because TRAPP accelerates both nucleotide binding and dissociation from Ypt1p. Weak thermodynamic coupling allows TRAPP, Ypt1p, and nucleotide to exist as a stable ternary complex, analogous to strain-sensing cytoskeleton motors. These results illustrate a novel strategy of guanine nucleotide exchange by TRAPP that is particularly suited for a multifunctional GEF involved in membrane traffic.
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Abstract
The myosin superfamily consists of more than 35 classes (each consisting of multiple isoforms) that have diverse cellular activities. The reaction pathway of the actin-activated myosin ATPase appears to be conserved for all myosin isoforms, but the rate and equilibrium constants that define the ATPase pathway vary significantly across the myosin superfamily, resulting in kinetic differences that that allow myosins to carry out diverse mechanical functions. Therefore, it is important to determine the lifetimes and relative populations of the key biochemical intermediates to obtain an understanding of a particular myosin's cellular function. This chapter provides procedures for determining the overall and individual rate and equilibrium constants of the actomyosin ATPase cycle, including actomyosin binding and dissociation, ATP binding, ATP hydrolysis, phosphate release, and ADP release and binding. Many of the methods described in the chapter are applicable to the characterization of other ATPase enzymes.
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Affiliation(s)
- Enrique M De La Cruz
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut, USA
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Cai Y, Chin HF, Lazarova D, Menon S, Fu C, Cai H, Sclafani A, Rodgers DW, De La Cruz EM, Ferro-Novick S, Reinisch KM. The structural basis for activation of the Rab Ypt1p by the TRAPP membrane-tethering complexes. Cell 2008; 133:1202-13. [PMID: 18585354 DOI: 10.1016/j.cell.2008.04.049] [Citation(s) in RCA: 149] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2007] [Revised: 04/07/2008] [Accepted: 04/25/2008] [Indexed: 11/30/2022]
Abstract
The multimeric membrane-tethering complexes TRAPPI and TRAPPII share seven subunits, of which four (Bet3p, Bet5p, Trs23p, and Trs31p) are minimally needed to activate the Rab GTPase Ypt1p in an event preceding membrane fusion. Here, we present the structure of a heteropentameric TRAPPI assembly complexed with Ypt1p. We propose that TRAPPI facilitates nucleotide exchange primarily by stabilizing the nucleotide-binding pocket of Ypt1p in an open, solvent-accessible form. Bet3p, Bet5p, and Trs23p interact directly with Ypt1p to stabilize this form, while the C terminus of Bet3p invades the pocket to participate in its remodeling. The Trs31p subunit does not interact directly with the GTPase but allosterically regulates the TRAPPI interface with Ypt1p. Our findings imply that TRAPPII activates Ypt1p by an identical mechanism. This view of a multimeric membrane-tethering assembly complexed with a Rab provides a framework for understanding events preceding membrane fusion at the molecular level.
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Affiliation(s)
- Yiying Cai
- Department of Cell Biology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA
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Hackney DD, Stock MF. Kinesin tail domains and Mg2+ directly inhibit release of ADP from head domains in the absence of microtubules. Biochemistry 2008; 47:7770-8. [PMID: 18578509 DOI: 10.1021/bi8006687] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Kinesin-1 is a vesicle motor that can fold into a compact inhibited conformation that is produced by interaction of the heavy chain C-terminal tail region with the N-terminal motor domains (heads). Binding of the tail domains to the heads inhibits net microtubule-stimulated ATPase activity by blocking the ability of the heads to bind to microtubules with coupled acceleration of ADP release. We now show that folding of kinesin-1 also directly inhibits ADP release even in the absence of microtubules. With long heavy chain constructs such as DKH960 that exhibit a high degree of regulation by folding, the basal rate of ADP release is inhibited up to 30-fold compared to that of truncated DKH894 which has lost the inhibitory tail domains and does not fold. Inhibition of ADP release is also observed when separate head and tail domain constructs are mixed at low salt concentrations. This inhibition of ADP release by tail domains is formally analogous to the action of nucleotide dissociation inhibitors (NDI or GDI) for regulatory GTPases. In contrast to their inhibition of ADP release, tail domains accelerate the rate of ADP binding to nucleotide-free kinesin-1. Inhibition of release of ADP by tail domains is reversed by Unc-76 (FEZ1) which is a potential regulator of kinesin-1. Tail domains only weakly inhibit the initial slow release of Mg (2+) from the kinesin-MgADP complex but strongly inhibit the fast release of Mg (2+)-free ADP.
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Affiliation(s)
- David D Hackney
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
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Characterization of the pre-force-generation state in the actomyosin cross-bridge cycle. Proc Natl Acad Sci U S A 2008; 105:8631-6. [PMID: 18552179 DOI: 10.1073/pnas.0710793105] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Myosin is an actin-based motor protein that generates force by cycling between actin-attached (strong binding: ADP or rigor) and actin-detached (weak binding: ATP or ADP.P(i)) states during its ATPase cycle. However, it remains unclear what specific conformational changes in the actin binding site take place on binding to actin, and how these structural changes lead to product release and the production of force and motion. We studied the dynamics of the actin binding region of myosin V by using fluorescence resonance energy transfer (FRET) to monitor conformational changes in the upper-50-kDa domain of the actin binding cleft in the weak and strong actin binding states. Steady-state and lifetime data monitoring the FRET signal suggest that the cleft is in a more open conformation in the weak actin binding states. Transient kinetic experiments suggest that a rapid conformational change occurs, which is consistent with cleft closure before actin-activated phosphate release. Our results have identified a pre-force-generation actomyosin ADP.P(i) state, and suggest force generation may occur from a state not yet seen by crystallography in which the actin binding cleft and the nucleotide binding pocket are closed. Computational modeling uncovers dramatic changes in the rigidity of the upper-50-kDa domain in different nucleotide states, which suggests that the intrinsic flexibility of this domain allows myosin motors to accomplish simultaneous tight nucleotide binding (closed nucleotide binding pocket) and high-affinity actin binding (closed actin binding cleft).
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