C0 Domain of Cardiac Myosin Binding Protein-C Modulates Interaction of the Neighboring C1 Domain with Tropomyosin Through the Allosteric Interaction with F-Actin

Abstract

Mutations in cardiac myosin binding protein C (cMyBP-C) are the most common cause of hypertrophic cardiomyopathy affecting millions of people worldwide. Recent studies established that the N-terminal domains (NTDs) of cMyBP-C (e.g., C0, C1, M, and C2) can bind to and activate or inhibit the thin filament (TF). However, the molecular mechanism(s) by which NTDs modulate interaction of myosin with the TF remains unknown. Recently, we demonstrated that despite being structural homologs, C0 and C1 NTDs exhibit different patterns of binding on the surface of F-actin. Moreover, we showed that C1 but not C0 can activate the TF by means of shifting the tropomyosin (Tm) cable from the “closed” to the “open” structural state via direct interaction with Tm. Here we used cryo electron microscopy and image analysis to reveal how C0 and C1 Ig-domains connected by the Proline/Alanine-linker communicate with each other when interacting with the TF in tandem. Our results show that C0 binds to the front of actin subdomain-1 in two distinct modes, and that in these two modes C0 has different effect on the interaction of C1 domain with both actin filament and Tm cable. In one mode C0 enhances the activating effect of C1 domain so that the Tm cable is shifted towards the subdomain-4 of actin to an even larger extent than found in the “open” state of Tm. In the second mode C0 reverses the activation effect of C1 by means of disrupting the interaction of C1 with Tm. Importantly, we demonstrate that the two domains communicate with each other allosterically through the actin filament. Our data suggest that the internal dynamics of the actin molecule is essential for the regulation of the actomyosin interaction in cardiac muscle. We propose a mechanism by which cMyBP-C may modulate actomyosin interactions in cardiac muscle.