Actomyosin interaction in striated muscle

The mechanics of the actomyosin interaction have been extensively studied using the organized filament array of striated muscle. However, the extrapolation of these data to the events occurring at the level of a single actomyosin interaction has not been simple. Problems arise in part because an active fiber has an ensemble of myosin heads that are spread out through the various steps of the active cycle, and it is likely that only a small fraction of the heads are generating tension at any given time. More recently, two new approaches have greatly extended our knowledge of the actomyosin interaction. First, the three-dimensional crystal structures of both the actin monomer and the myosin head have been determined, and these structures have been fit to lower resolution images to give atomic models of the actin filament and of the actin filament decorated by myosin heads. Second, the technology to measure picoNewton forces and nanometer distances has provided direct determinations of the force and step length generated by a single myosin molecule interacting with a single actin filament. This review synthesizes the existing mechanical data obtained from the more-organized array of the muscle filament with the results obtained by these two technologies.