Key result
The thermal ratchet model correctly predicts empirical force-velocity characteristics for motor molecules, whereas the conformational change model yields velocities larger than observed.
A thermally driven ratchet model accurately predicts the force-velocity characteristics of single-motor molecules like myosin, whereas a conformational change model overestimates velocity and duty cycle.
Favors thermal ratchet over conformational models for myosin mechanics; leaves open relevance to human cardiac contractility.
We present a model for single-motor molecules--myosin, dynein, or kinesin--that is powered either by thermal fluctuations or by conformational change. In the thermally driven model, the cross-bridge fluctuates about its equilibrium position against an elastic restoring force. The attachment and detachment of the cross-bridge are determined by modeling the electrostatic attraction between the cross-bridge and the fiber binding sites, so that binding depends on the strain in the cross-bridge and its velocity with respect to the fiber. The model correctly predicts the empirical force-velocity characteristics for populations of motor molecules. For a single motor, the apparent cross-bridge step size per ATP hydrolysis depends nonlinearly on the load. When the elastic energy driving the cross-bridge is generated by a conformational change, the velocity and duty cycle are much larger than is observed experimentally for myosin.
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Cordova et al. (1992) studied this question. Thermal ratchet model vs. Conformational change model was evaluated on Force-velocity characteristics and apparent step size. The thermal ratchet model correctly predicts empirical force-velocity characteristics for motor molecules, whereas the conformational change model yields velocities larger than observed.
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