Abstract 18037: Cardiac Myosin Binding Protein-C Phosphorylation Decreases the Super-Relaxed State of Myosin
Introduction: Cardiac myosin exists in three populations: the active, the disordered relaxed (DRX) and the super-relaxed (SRX) states. The latter represents an economical reserve that is not immediately available for contraction. We have previously shown that absence of the trans-filament protein, cardiac myosin binding protein-C (cMyBP-C), decreases the number of myosin heads in this inhibited SRX state. Herein, we investigate the role of cMyBP-C phosphorylation on the SRX state.
Hypothesis: cMyBP-C phosphorylation is sufficient to shift myosin heads from the SRX state into the DRX state.
Methods and Results: Phospho-mimetic (DDD) and Phospho-null (AAA) mouse models were generated by mutation of the PKA sites of cMyBP-C (S273, S282 and S302). These serines were mutated to either alanine to mimic dephosphorylation, or aspartic acid to mimic phosphorylation. Single nucleotide turnover by myosin was measured using fluorescent labelled ATP and the population of myosin heads in the SRX state was determined from this. Four hearts each from DDD, AAA and non-transgenic mice were studied. We found that the population of myosin heads in the SRX state was significantly decreased in DDD mice compared to non-transgenic and AAA mice (8.3±0.9% vs. 15±1% vs. 14.3±0.7%, respectively). No changes in the lifetime of ATP turnover were detected between groups. The reduced population of SRX myosin heads in the DDD mice is comparable to mice that lack cMyBP-C altogether. This loss of myosin in the SRX state is consistent with the model that cMyBP-C phosphorylation reduces its affinity for myosin.
Conclusion: Phosphorylation of cMyBP-C decreases the population of the SRX state. Therefore, in healthy hearts cMyBP-C phosphorylation would increase the fraction of myosin heads available for contraction. In end-stage failing hearts, the phosphorylation of cMyBP-C is diminished, and this may contribute to contractile dysfunction through its regulation of the SRX state.
Author Disclosures: J.W. McNamara: None. M. Kumar: None. R. Cooke: None. S. Sadayappan: None.
- © 2016 by American Heart Association, Inc.