Orientation dependence of displacements by a single one-headed myosin relative to the actin filament.

Displacements of single one-headed myosin molecules in a sparse myosin-rod cofilament were measured from bead displacements at various angles relative to an actin filament by dual optical trapping nanometry. The sparse myosin-rod cofilaments, 5-8 micron long, were synthesized by slowly mixing one-headed myosin prepared by papain digestion with myosin rods at molar ratios of 1:400 to 1:1500, so that one to four one-headed myosin molecules were on average scattered along the cofilament. The bead displacement was approximately 10 nm at low loads ( approximately 0.5 pN) and at angles of 5-10 degrees between the actin and myosin filaments (near physiologically correct orientation). The bead displacement decreased with an increase in the angle. The bead displacement at nearly 90 degrees was approximately 0 nm. When the angle was increased to approximately 150 degrees-170 degrees, the bead displacements increased to 5 nm. A native two-headed myosin showed similar size and orientation dependence of bead displacements as a one-headed myosin.