Comparison between actin decorated with wild-type smooth muscle myosin S1 and actin decorated with a R403Q smooth muscle myosin mutant.

A: Wild-type smooth muscle actomyosin in the presence of ADP. The top row shows a 4-nm thick central slice perpendicular to the filament axis. The second row shows a 4-nm thick central slice parallel to the filament axis (cutting plane indicated by the left line in top row). The pointed end is to the top of the figure in the two lower rows. The bottom row shows an adjacent 4-nm thick slice (cutting plane indicated by right line in top row). This slice goes primarily through the S1 molecules. B: R403Q mutant smooth muscle actomyosin in the presence of ADP. Organization of rows as in (A). C: Wild-type smooth muscle actomyosin in the absence of nucleotide (apo). The approximate location of the motor domain (MD) and the light chain (LC) regions are labeled in each view. Organization of rows as in A. The approximate outline of the actin portion of the filament is indicated. D: Apo R403Q mutant smooth muscle actomyosin. Organization of rows as in (A). Bar:10 nm.