A nano-scale theoretical model of the myosin head mechanics

The conformational changes of the myosin head due to the ATP hydrolysis determine the tilting of the head and the consequent sliding of the actin filament. A mathematical model of the myosin head tilting mechanism is performed here. In particular the myosin head mechanics has been explored starting from recent findings about the myosin ultrastructure, morphology and energetics in order to calculate the working stroke and the force transmitted to the actin filament during muscle contraction. Two different working stroke mechanisms have been investigated, assuming that the tilting of the myosin head occurs in one step or in two steps. Our results show that force and working stroke values vary markedly between the two models. The maximum force generated is about 10 pN for the one step tilting model and 27 pN for the two step model, and the working stroke is about 13 nm and 5 nm respectively. The model results are in agreement with experimental measurements. A sensitivity analysis has also been performed. This research project is part of an overall model of sarcomere mechanics recently developed in our Laboratory (Redaelli et al., J. Biomech, 2001).