title: Modulation of thin filament activation of myosin ATP hydrolysis by N-terminal domains of cardiac myosin binding protein-C.
abstract: We have used enzyme kinetics to investigate the molecular mechanism by which the N-terminal domains of human and mouse cardiac MyBP-C (C0C1, C1C2, and C0C2) affect the activation of myosin ATP hydrolysis by F-actin and by native porcine thin filaments. N-Terminal domains of cMyBP-C inhibit the activation of myosin-S1 ATPase by F-actin. However, mouse and human C1C2 and C0C2 produce biphasic activating and inhibitory effects on the activation of myosin ATP hydrolysis by native cardiac thin filaments. Low ratios of MyBP-C N-terminal domains to thin filaments activate myosin-S1 ATP hydrolysis, but higher ratios inhibit ATP hydrolysis, as is observed with F-actin alone. These data suggest that low concentrations of C1C2 and C0C2 activate thin filaments by a mechanism similar to that of rigor myosin-S1, whereas higher concentrations inhibit the ATPase rate by competing with myosin-S1-ADP-Pi for binding to actin and thin filaments. In contrast to C0C2 and C1C2, the activating effects of the C0C1 domain are species-dependent: human C0C1 activates actomyosin-S1 ATPase rates, but mouse C0C1 does not produce significant activation or inhibition. Phosphorylation of serine residues in the m-linker between the C1 and C2 domains by protein kinase-A decreases the activation of thin filaments by huC0C2 at pCa > 8 but has little effect on the activation mechanism at pCa = 4. In sarcomeres, the low ratio of cMyBP-C to actin is expected to favor the activating effects of cMyBP-C while minimizing inhibition produced by competition with myosin heads.
authors.affiliation: Department of Physiological Sciences, Eastern Virginia Medical School , Norfolk, Virginia 23507, United States.
authors.forename: Betty
authors.initials: B
authors.lastname: Belknap
authors.forename: Samantha P
authors.initials: SP
authors.lastname: Harris
authors.forename: Howard D
authors.initials: HD
authors.lastname: White
mesh_terms: D008841:Actin Cytoskeleton / Q000737:chemistry*; D000199:Actins / Q000737:chemistry; D000255:Adenosine Triphosphate / Q000737:chemistry*; D000818:Animals; D002118:Calcium / Q000737:chemistry; D024722:Cardiac Myosins / Q000737:chemistry; D002352:Carrier Proteins / Q000737:chemistry*; D006801:Humans; D006868:Hydrolysis; D007700:Kinetics; D051379:Mice; D009206:Myocardium / Q000737:chemistry*; D009218:Myosins / Q000737:chemistry*; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D011817:Rabbits; D011994:Recombinant Proteins / Q000737:chemistry; D013045:Species Specificity; D013552:Swine; D000099163:Myosin Binding Protein C
chemical_list: D000199:Actins; D000255:Adenosine Triphosphate; D002118:Calcium; D024722:Cardiac Myosins; D002352:Carrier Proteins; D009218:Myosins; D011994:Recombinant Proteins; D000099163:Myosin Binding Protein C