Myosin Binding Protein C, a Phosphorylation-Dependent Force Regulator in Muscle That Controls the Attachment of Myosin Heads by Its Interaction With Myosin S2

• Published in: Circulation research Vol. 86; no. 1; p. 51
• Main Authors: Kunst, Gudrun, Kress, Kai R, Gruen, Mathias, Uttenweiler, Dietmar, Gautel, Mathias, Fink, Rainer H. A
• Format: Journal Article
• Language: English
• Published: Hagerstown, MD American Heart Association, Inc 07.01.2000; Lippincott; Lippincott Williams & Wilkins Ovid Technologies
• Subjects: Biological and medical sciences; Calcium - physiology; Cardiology. Vascular system; Carrier Proteins - metabolism; Carrier Proteins - physiology; Elasticity; Heart; Histological Techniques; Isometric Contraction - physiology; Kinetics; Medical sciences; Muscle Fibers, Skeletal - physiology; Muscle, Skeletal - metabolism; Myocardial Contraction - physiology; Myocarditis. Cardiomyopathies; Myosins - physiology; Peptide Fragments - physiology; Phosphorylation; Recombinant Proteins - metabolism; Sarcomeres - metabolism; Solubility; Human; Phosphorylation; Pathophysiology; Cardiovascular disease; Molecular interaction; Protein C; Myocardial disease; Muscle contraction; Binding protein; Regulation(control); Heart disease; Myosin; Hypertrophic cardiomyopathy; Myocardium; Familial relation; Circulatory system
• ISSN: 0009-7330; 1524-4571
• DOI: 10.1161/01.RES.86.1.51

Myosin binding protein C (MyBP-C) is one of the major sarcomeric proteins involved in the pathophysiology of familial hypertrophic cardiomyopathy (FHC). The cardiac isoform is tris-phosphorylated by cAMP-dependent protein kinase (cAPK) on β-adrenergic stimulation at a conserved N-terminal domain (MyBP-C motif), suggesting a role in regulating positive inotropy mediated by cAPK. Recent data show that the MyBP-C motif binds to a conserved segment of sarcomeric myosin S2 in a phosphorylation-regulated way. Given that most MyBP-C mutations that cause FHC are predicted to result in N-terminal fragments of the protein, we investigated the specific effects of the MyBP-C motif on contractility and its modulation by cAPK phosphorylation. The diffusion of proteins into skinned fibers allows the investigation of effects of defined molecular regions of MyBP-C, because the endogenous MyBP-C is associated with few myosin heads. Furthermore, the effect of phosphorylation of cardiac MyBP-C can be studied in a defined unphosphorylated background in skeletal muscle fibers only. Triton skinned fibers were tested for maximal isometric force, Ca/force relation, rigor force, and stiffness in the absence and presence of the recombinant cardiac MyBP-C motif. The presence of unphosphorylated MyBP-C motif resulted in a significant (1) depression of Ca-activated maximal force with no effect on dynamic stiffness, (2) increase of the Ca sensitivity of active force (leftward shift of the Ca/force relation), (3) increase of maximal rigor force, and (4) an acceleration of rigor force and rigor stiffness development. Tris-phosphorylation of the MyBP-C motif by cAPK abolished these effects. This is the first demonstration that the S2 binding domain of MyBP-C is a modulator of contractility. The anchorage of the MyBP-C motif to the myosin filament is not needed for the observed effects, arguing that the mechanism of MyBP-C regulation is at least partly independent of a “tether,” in agreement with a modulation of the head-tail mobility. Soluble fragments occurring in FHC, lacking the spatial specificity, might therefore lead to altered contraction regulation without affecting sarcomere structure directly.