(3) Single molecule capture, manipulation and force
measurement of protein molecules

Kazuo KITAMURA1, Atsuko IWANE1, Toshio YANAGIDA1 and Makio TOKUNAGA (1Department of Physiology I, Osaka University Medical School)

A single myosin head molecule (myosin subfragment-1, S1) was captured onto the tip of a scanning microprobe, using a flexibleglass microneedle, and manipulated with subnanometer resolution. Single molecules were confirmed by examining it in the fluorescence glass microneedle at the same time using objective-type TIRFM. Movements and forces resulting from the interaction of a captured single S1 molecule with actin filaments were measured. Mean displacement amplitudes of individual S1 molecules ranged from 4 to 30 nm, certainly depending upon conditions for interactions of individual molecules. Moreover, it was found that a myosin head processively moves along the actin filament(s) with 5.3 nm steps, and undergoes 〜5 steps to produce a maximum displacement of 〜30 nm for each ATP hydrolysis. The results proves the loose coupling mechanism.