Smooth muscle contractility is modulated by myosin tail-S2-LMM hinge region interaction

The functional significance of two major smooth muscle myosin isoforms, which differ in the nonenzymic COOH-terminal tail region, is not known. We report here that a 13-amino acid peptide, which mimics a region of the tail unique to the SM1 myosin isoform, inhibits contraction velocity in permeabilized smooth muscle. This peptide is shown to bind to the S2-light meromyosin (LMM) hinge region of myosin using sodium dodecyl sulfate-polyacrylamide gel electrophoresis, photoaffinity labeling, and immunoelectron microscopy. Our results suggest that novel intermolecular contacts between the tail and S2-LMM hinge regions of adjacent myosin molecules in the thick filament may modulate contractility and provide a basis for distinct isoform function.