Structure and strength of human cardiac myosin S1-S2 interaction

Abstract

The super-relaxed (SRX) state was recently discovered in cardiac muscle fibers as an OFF state of myosin where the myosin S1 heads have reduced ATPase activity. The SRX state is thought to be a regulatory state of myosin heads that modulates the availability of functionally accessible myosin heads. A hypothesis is that the protein-protein interactions which form the SRX state are related to the interacting-head motif (IHM) state of myosin in which the S1 heads are folded back onto their coiled-coil S2 tails due to head-to-head interactions.