Load-dependent kinetics of myosin-V can explain its high processivity

Veigel, Claudia; Schmitz, Stephan; Wang, Fei; Sellers, James R.

doi:10.1038/ncb1287

Cited by 249 publications

(312 citation statements)

References 40 publications

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“…The resulting intramolecular load affects the ATPase cycle kinetics of at least one head (5,7,14) and is hypothesized to create the asymmetry responsible for effective, directional processive stepping (4,5,7,13,14). The hypothesis that the intramolecular load increases the efficiency of the processive movement by modulating biochemical kinetics is supported by mechanical measurements of individual singleheaded myosin V molecules (15,16). However, these studies yield partly conflicting conclusions regarding the kinetic basis of how the load-induced asymmetry between the two ADP-bound heads arises, and it remains unclear whether head-head communication through the intramolecular load results solely in inhibition of ADP dissociation from the leading head, or, additionally, acceleration of ADP dissociation from the trailing head.…”

mentioning

confidence: 70%

Load-dependent ADP binding to myosins V and VI: Implications for subunit coordination and function

Oguchi

Mikhailenko

Ohki

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

112

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mentioning

confidence: 70%

Load-dependent ADP binding to myosins V and VI: Implications for subunit coordination and function

Oguchi

Mikhailenko

Ohki

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

112

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“…The rate of movement of the 8IQ-HMM mutants in single-molecule TIRF assays at 2 mM ATP was slower than that of 6IQ-HMM despite the longer step-size in the former (8). This may reflect a loss of strain-dependent acceleration of the rate of ADP release from the trailing head in this mutant (26). If so, we provide further evidence that tampering with the wildtype neck alters the nucleotide binding and dissociation kinetics by disrupting the normal stereospecific attachment of myosin V to actin that has been finely tuned by nature.…”

Section: Discussionmentioning

confidence: 85%

Step-Size Is Determined by Neck Length in Myosin V

et al. 2005

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The highly processive motor, myosin V, has an extremely long neck containing six calmodulinbinding IQ motifs that allows it to take multiple 36 nm steps corresponding to the pseudo-repeat of actin. To further investigate how myosin V moves processively on actin filaments, we altered the length of the neck by adding or deleting IQ motifs in myosin constructs lacking the globular tail domain. These myosin V IQ mutants were fluorescently labeled by exchange of a single Cy3-labeled calmodulin into the neck region of one head. We measured the step-size of these individual IQ mutants with nanometer precision and subsecond resolution using FIONA. The step-size was proportional to neck length for constructs containing 2, 4, 6, and 8 IQ motifs, providing strong support for the swinging lever-arm model of myosin motility. In addition, the kinetics of stepping provided additional support for the hand-over-hand model whereby the two heads alternately assume the leading position. Interestingly, the 8IQ myosin V mutant gave a broad distribution of step-sizes with multiple peaks, suggesting that this mutant has many choices of binding sites on an actin filament. These data demonstrate that the step-size of myosin V is affected by the length of its neck and is not solely determined by the pseudo-repeat of the actin filament.Using biochemical assays, myosin V has been thoroughly characterized as a high duty ratio motor (1-3), spending a large fraction of its total enzymatic cycle time strongly bound to the actin filament. This kinetic property, along with the myosin V's unique long neck structure as a dimeric molecule, allows it to be highly processive. Therefore, the motor may undergo multiple enzymatic cycles while at least one head of the molecule is attached to the actin filament at anytime. This adaptation aids in the specific biological function of myosin V as a long-range vesicle transporter in cells (4, 5).The mouse myosin V heavy chain consists of an amino terminal motor domain joined to a long "neck" region containing six IQ motifs specific for calmodulin (CaM) 1 binding, followed by a carboxyl-terminal coiled-coil region and globular tail (6). The long neck region, which most likely functions as a lever-arm to amplify small nucleotidedependent structural changes in the motor domain, permits myosin V to take steps of an average distance of ∼36 nm, coinciding with the length of the half-pitch of an actin filament (2, 7). This step consists of a working stroke (defined as the distance myosin V translocates actin in a single movement of the lever-arm), followed by a diffusive search by the new lead head for a suitable binding site on actin. In studies with myosin II or myosin V mutants with different numbers of IQ motifs, the average working stroke taken by myosin in single interactions with actin was found to be proportional to neck length (8-13). In addition, one of these studies showed that the step-size of myosin V during processive runs in an optical trap was shorter for a construct containing four IQ motif...

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“…6 Using these values to solve for DDG ÀD = Dm mech = À4 kT, we obtain an interhead stiffness, k, of 0.14 pN nm À1 , consistent with experimental studies. 26 As discussed above, the work performed upon actin binding of the leading head (1/2k Â d 2 2 ) is limited by the actin-myosin binding energy. Here 44 pN nm E 11 kT of the actin-myosin binding energy is used to generate interhead strain, and roughly 36% of this energy is used to accelerate ADP release.…”

Section: Resultsmentioning

confidence: 99%

“…1b makes explicit a model-implied by numerous studies 11,22,25,26 -for the regulation of ADP release. Specifically, with one myosin head (the trailing head) bound to an actin filament (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…11,22,25,26 In these models, Dm mech has been described in terms of either a generalized potential or as a mean-force potential, F Â d, where upon ADP release myosin rotates a distance d against (or with) a mean interhead force, F. The problem with many of these models is that they do not explicitly describe the acceleration of ADP release as a dissipative mechanical process through which interhead forces are diminished, and thus they lack a proper description of the energetic origins, limits, and costs of the allosteric regulation of ADP release.…”

Section: Introductionmentioning

confidence: 99%

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Hysteresis in cross-bridge models of muscle

Walcott

Sun

2009

Phys. Chem. Chem. Phys.

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Myosin molecules are involved in a wide range of transport and contractile activities in cells. A single myosin head functions through its ATPase reaction as a force generator and as a mechanosensor, and when two or more myosin heads work together in moving along an actin filament, the interplay between these mechanisms contributes to collective myosin behaviors. For example, the interplay between force-generating and force-sensing mechanisms coordinates the two heads of a myosin V molecule in its hand-over-hand processive stepping along an actin filament. In muscle, it contributes to the Fenn effect and smooth muscle latch. In both examples, a key force-sensing mechanism is the regulation of ADP release via interhead forces that are generated upon actin-myosin binding. Here we present a model describing the mechanism of allosteric regulation of ADP release from myosin heads as a change, DDG ÀD , in the standard free energy for ADP release that results from the work, Dm mech , performed by that myosin head upon ADP release, or DDG ÀD = Dm mech . We show that this model is consistent with previous measurements for strain-dependent kinetics of ADP release in both myosin V and muscle myosin II. The model makes explicit the energetic cost of accelerating ADP release, showing that acceleration of ADP release during myosin V processivity requires B4 kT of energy whereas the energetic cost for accelerating ADP release in a myosin II-based actin motility assay is only B0.4 kT. The model also predicts that the acceleration of ADP release involves a dissipation of interhead forces. To test this prediction, we use an in vitro motility assay to show that the acceleration of ADP release from both smooth and skeletal muscle myosin II correlates with a decrease in interhead force. Our analyses provide clear energetic constraints for models of the allosteric regulation of ADP release and provide novel, testable insights into muscle and myosin V function.

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Load-dependent kinetics of myosin-V can explain its high processivity

Cited by 249 publications

References 40 publications

Load-dependent ADP binding to myosins V and VI: Implications for subunit coordination and function

Load-dependent ADP binding to myosins V and VI: Implications for subunit coordination and function

Step-Size Is Determined by Neck Length in Myosin V

Hysteresis in cross-bridge models of muscle

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