title: Myosin binding protein-C phosphorylation is the principal mediator of protein kinase A effects on thick filament structure in myocardium.
abstract: Phosphorylation of cardiac myosin binding protein-C (cMyBP-C) is a regulator of pump function in healthy hearts. However, the mechanisms of regulation by cAMP-dependent protein kinase (PKA)-mediated cMyBP-C phosphorylation have not been completely dissociated from other myofilament substrates for PKA, especially cardiac troponin I (cTnI). We have used synchrotron X-ray diffraction in skinned trabeculae to elucidate the roles of cMyBP-C and cTnI phosphorylation in myocardial inotropy and lusitropy. Myocardium in this study was isolated from four transgenic mouse lines in which the phosphorylation state of either cMyBP-C or cTnI was constitutively altered by site-specific mutagenesis. Analysis of peak intensities in X-ray diffraction patterns from trabeculae showed that cross-bridges are displaced similarly from the thick filament and toward actin (1) when both cMyBP-C and cTnI are phosphorylated, (2) when only cMyBP-C is phosphorylated, and (3) when cMyBP-C phosphorylation is mimicked by replacement with negative charge in its PKA sites. These findings suggest that phosphorylation of cMyBP-C relieves a constraint on cross-bridges, thereby increasing the proximity of myosin to binding sites on actin. Measurements of Ca(2+)-activated force in myocardium defined distinct molecular effects due to phosphorylation of cMyBP-C or co-phosphorylation with cTnI. Echocardiography revealed that mimicking the charge of cMyBP-C phosphorylation protects hearts from hypertrophy and systolic dysfunction that develops with constitutive dephosphorylation or genetic ablation, underscoring the importance of cMyBP-C phosphorylation for proper pump function.
authors: Department of Cell and Regenerative Biology, University of Wisconsin School of Medicine and Public Health, Madison, WI 53711, USA. bacolson@umn.edu
authors: Brett A
authors: BA
authors: Colson
authors: Jitandrakumar R
authors: JR
authors: Patel
authors: Peter P
authors: PP
authors: Chen
authors: Tanya
authors: T
authors: Bekyarova
authors: Mohamed I
authors: MI
authors: Abdalla
authors: Carl W
authors: CW
authors: Tong
authors: Daniel P
authors: DP
authors: Fitzsimons
authors: Thomas C
authors: TC
authors: Irving
authors: Richard L
authors: RL
authors: Moss
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism; D019943:Amino Acid Substitution; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology*; D006352:Heart Ventricles / Q000000981:diagnostic imaging; D051379:Mice; D008822:Mice, Transgenic; D009206:Myocardium / Q000201:enzymology* / Q000378:metabolism; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D013318:Stroke Volume; D019210:Troponin I / Q000235:genetics / Q000378:metabolism*; D014463:Ultrasonography; D016277:Ventricular Function, Left; D014961:X-Ray Diffraction; D000099163:Myosin Binding Protein C
chemical_list: D002352:Carrier Proteins; D017868:Cyclic AMP-Dependent Protein Kinases; D019210:Troponin I; D000099163:Myosin Binding Protein C