Phosphorylation of cMyBP-C Affects Contractile Mechanisms in a Site-specific Manner Journal Article

Authors: Wang, L; Ji, X.; Barefield, D.; Sadayappan, S; Kawai, M.
Article 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 ( approximately 50%), stiffness, the fast apparent rate constant 2pic, and its magnitude C, as well as its magnitude H, but an increase in the medium rate constant 2pib, with respect to WT. The t/t fibers showed a smaller drop in stiffness and a significant decrease in 2pic 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 2pic and increased 2pib. 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.
Journal Title: Biophysical journal
Volume: 106
Issue: 5
ISSN: 1542-0086; 0006-3495
Publisher: Unknown  
Journal Place: United States
Date Published: 2014
Start Page: 1112
End Page: 1122
Language: eng
Notes: CI: Copyright (c) 2014; JID: 0370626; 2013/10/10 [received]; 2014/01/18 [revised]; 2014/01/23 [accepted]; ppublish