A single myosin head moves along an actin filament with regular steps of 5.3 nanometres.

Abstract

Actomyosin, a complex of actin filaments and myosin motor proteins, is responsible for force generation during muscle contraction. To resolve the individual mechanical events of force generation by actomyosin, we have developed a new instrument with which we can capture and directly manipulate individual myosin subfragment-1 molecules using a scanning probe. Single subfragment-1 molecules can be visualized by using a fluorescent label. The data that we obtain using this technique are consistent with myosin moving along an actin filament with single mechanical steps of approximately 5.3 nanometres; groups of two to five rapid steps in succession often produce displacements of 11 to 30 nanometres. This multiple stepping is produced by a single myosin head during just one biochemical cycle of ATP hydrolysis.