Flexibility Change in Actin Filaments Induced by Myosin Molecules at a Low ATP Concentration

Yuusuke Arii and Kuniyuki Hatori

Department of Bio-System Engineering, Yamagata University



Abstract
We examined flexibility of actin filaments under a fluorescence microscopy because the dynamic property of the filamental structure seems to be significant for transforming of forces exerted by myosin molecules into coordinating unidirectional movement of the actin filament. In this study, actin filaments labeled with rhodamine-phallodin were observed on myosin molecules fixed on a glass surface. Then both the contour length and the end-to-end distance of filaments were directly measured on the screen. The persistence length of the filament (as a parameter associated with flexural rigidity) was estimated by referring to the relation between the contour length and the end-to-end distance.
In the absence of ATP, the persistence length gradually increased up to 14 um as myosin concentration was increased in the range to 0.5 mg/ml. In contrast when a small amount of ATP (0.5 uM) was added, the persistence length decreased with an increase of myosin molecules. By further addition of ATP (1 uM), the persistence length declined until about 30 % compared with that in the absence of ATP. These results show that flexibility of an actin filament was modulated by contact with myosins even if ATP concentration was not sufficient for the activation of myosin-ATPase.