Direct measurement for elasticity of myosin head

During muscle contraction, chemical energy from ATP hydrolysis is converted to the relative sliding movement of actin and myosin filaments. In order to elucidate the molecular mechanism of sliding-force generation, it is a crucial clue to know an elastic modulus of myosin. Here, we report direct measurements of Young's modulus of myosin head (myosin subfragment-1) isolated from rabbit skeletal muscle, using a surface forces apparatus. Our results show that the elasticity of myosin subfragment-1 has direction and is about 0.3 GPa along the long axis during ATP hydrolysis. When the bow-shaped subfragment-1 is modelled as an elastic rod, the stiffness and the bending fluctuations of subfragment-1 are calculated to be 3-7 pN/nm and about 1 nm, respectively. These results strongly support a model of multiple power strokes rather than the conventional tilting-crossbridge model.