GSK3β Phosphorylates Newly Identified Site in the Proline-Alanine–Rich Region of Cardiac Myosin–Binding Protein C and Alters Cross-Bridge Cycling Kinetics in Human

Rationale: Cardiac myosin–binding protein C (cMyBP-C) regulates cross-bridge cycling kinetics and, thereby, fine-tunes the rate of cardiac muscle contraction and relaxation. Its effects on cardiac kinetics are modified by phosphorylation. Three phosphorylation sites (Ser275, Ser284, and Ser304) have been identified in vivo, all located in the cardiac-specific M-domain of cMyBP-C. However, recent work has shown that up to 4 phosphate groups are...