The molecular mechanism of muscle contraction has been investigated by X-ray diffraction and scattering. Intense synchrotron X-rays and a novel area detector enabled us to detect a tiny but significant intensity and spacing changes of the weaker actin-based reflections during muscle contraction with high accuracy. Our analyses have shown that the structural changes and extensibility of the actin filament play an important role in force-generation of muscle, necessitating quite significant reevaluation of the current models of crossbridge mechanism. Although the structural changes within crossbridges which produce force in muscle remain to be clarified, our recent X-ray solution scattering has showed distinct alterations of the structure of myosin heads during hydrolysis of ATP. For a real understanding of the force transduction in muscle, we need explicit structural models that explain the coupling between the structural changes in actin and myosin. This special report makes a survey of our recent progress in the X-ray structural reseach of muscle, on occasion for a Japan Crytallographic Society award.
