title: Phosphorylation of cMyBP-C affects contractile mechanisms in a site-specific manner.
abstract: Cardiac myosin binding protein-C (cMyBP-C) is a cardiac-specific, thick-filament regulatory protein that is differentially phosphorylated at Ser(273), Ser(282), and Ser(302) by various kinases and modulates contraction. In this study, phosphorylation-site-specific effects of cMyBP-C on myocardial contractility and cross-bridge kinetics were studied by sinusoidal analysis in papillary and trabecular muscle fibers isolated from t/t (cMyBP-C-null) mice and in their counterparts in which cMyBP-C contains the ADA (Ala(273)-Asp(282)-Ala(302)), DAD (Asp(273)-Ala(282)-Asp(302)), and SAS (Ser(273)-Ala(282)-Ser(302)) mutations; the results were compared to those from mice expressing the wild-type (WT) transgene on the t/t background. Under standard activating conditions, DAD fibers showed significant decreases in tension (~50%), stiffness, the fast apparent rate constant 2πc, and its magnitude C, as well as its magnitude H, but an increase in the medium rate constant 2πb, with respect to WT. The t/t fibers showed a smaller drop in stiffness and a significant decrease in 2πc that can be explained by isoform shift of myosin heavy chain. In the pCa-tension study using the 8 mM phosphate (Pi) solution, there was hardly any difference in Ca(2+) sensitivity (pCa50) and cooperativity (nH) between the mutant and WT samples. However, in the solutions without Pi, DAD showed increased nH and slightly decreased pCa50. We infer from these observations that the nonphosphorylatable residue 282 combined with phosphomimetic residues Asp(273) and/or Asp(302) (in DAD) is detrimental to cardiomyocytes by lowering isometric tension and altering cross-bridge kinetics with decreased 2πc and increased 2πb. In contrast, a single change of residue 282 to nonphosphorylatable Ala (SAS), or to phosphomimetic Asps together with the changes of residues 273 and 302 to nonphosphorylatable Ala (ADA) causes minute changes in fiber mechanics.
authors.affiliation: Department of Anatomy and Cell Biology, Carver College of Medicine, University of Iowa, Iowa City, Iowa; School of Nursing, Soochow University, Suzhou, Jiangsu, China.
authors.forename: Li
authors.initials: L
authors.lastname: Wang
authors.affiliation: Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, Illinois.
authors.forename: Xiang
authors.initials: X
authors.lastname: Ji
authors.affiliation: Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, Illinois.
authors.forename: David
authors.initials: D
authors.lastname: Barefield
authors.affiliation: Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, Illinois.
authors.forename: Sakthivel
authors.initials: S
authors.lastname: Sadayappan
authors.affiliation: Department of Anatomy and Cell Biology, Carver College of Medicine, University of Iowa, Iowa City, Iowa. Electronic address: masataka-kawai@uiowa.edu.
authors.forename: Masakata
authors.initials: M
authors.lastname: Kawai
mesh_terms: D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005260:Female; D005786:Gene Expression Regulation; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008297:Male; D051379:Mice; D009154:Mutation; D009200:Myocardial Contraction; D009218:Myosins / Q000378:metabolism; D010766:Phosphorylation; D020033:Protein Isoforms / Q000378:metabolism; D013314:Stress, Mechanical; D000099163:Myosin Binding Protein C
chemical_list: D002118:Calcium; D002352:Carrier Proteins; D009218:Myosins; D020033:Protein Isoforms; D000099163:Myosin Binding Protein C