Thick filament-associated protein located in the crossbridge region of vertebrate striated muscle a bands. In vitro it binds MHC, F-actin and native thin filaments, and modifies the activity of actin-activated myosin ATPase. It may modulate muscle contraction or may play a more structural role. Substrate for phosphorylation by PKA and PKC. Reversible phosphorylation appears to modulate contraction (By similarity). Polyubiquitinated. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. MYBPC3 mutations may be involved in restrictive cardiomyopathy (RCM), a rare non-ischemic myocardial disease. RCM is characterized by restrictive ventricular-filling physiology in the presence of normal or reduced diastolic and/or systolic volumes (of 1 or both ventricles), biatrial enlargement, and normal ventricular wall thickness. The disease is caused by variants affecting the gene represented in this entry. Belongs to the immunoglobulin superfamily. MyBP family.