Force-generating domain of myosin motor.

To understand the underlying mechanism of force generation by myosin motor, it is crucial to know which part of the molecule is essential for the process. Recent structure determination of myosin motor domain at atomic resolution has revealed that the domain comprises two smaller domains, the "ATPase domain" consisting of only an N-terminal segment of the heavy chain and the "neck domain" consisting of a long alpha-helix of the heavy chain and two light chains. This atomic structure begs the question of whether both domains are required for force generation. To answer it, we genetically truncated the head to generate a recombinant fragment composed of the "ATPase domain" alone. The truncated head drove sliding movement of actin filaments and generated force in a novel in vitro assay system, which allows us to hold a specific site of the head on a glass surface. These results indicate that the compact ATPase domain functions as a force-generating machinery of the myosin motor.