Myosin binding protein-C phosphorylation is the principal mediator of protein kinase A effects on thick filament structure in myocardium.
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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.
Colson, B. A., Patel, J. R., Chen, P. P., Bekyarova, T., Abdalla, M. I., Tong, C. W., ... Moss, R. L.
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Colson, Brett A||Patel, Jitandrakumar R||Chen, Peter P||Bekyarova, Tanya||Abdalla, Mohamed I||Tong, Carl W||Fitzsimons, Daniel P||Irving, Thomas C||Moss, Richard L
