Support for a trimeric collar of myosin binding protein C in cardiac and fast skeletal muscle, but not in slow skeletal muscle.

Myosin-binding protein C (MyBPC) is proposed to take on a trimeric collar arrangement around the thick filament backbone in cardiac muscle, based on interactions between cardiac MyBPC domains C5 and C8. We have now determined, using yeast two-hybrid and in vitro binding assays, that the C5:C8 interaction is not dependent on the 28-residue cardiac-specific insert in C5. Furthermore, an interaction of similar affinity occurs between domains C5 and C8 of fast skeletal muscle MyBPC, but not between these domains of the slow skeletal muscle protein. These data have implications for the role and quaternary structure of MyBPC in skeletal muscle.