Cardiac Myosin Binding Protein C and Its Phosphorylation Regulate Multiple Steps in the Cross-Bridge Cycle of Muscle Contraction
Cardiac Myosin Binding Protein C and Its Phosphorylation Regulate Multiple Steps in the Cross-Bridge Cycle of Muscle Contraction
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DOI：
10.1021/bi300085x
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发表时间：
2012-04-17
期刊：
影响因子：
2.9
通讯作者：
Stelzer, Julian E.
中科院分区：
文献类型：
--
作者：
Coulton, Arthur T.;Stelzer, Julian E.
心肌肌球蛋白结合蛋白C （C - mybpc）是一种在心肌肌瘤中表达的粗丝蛋白，已知与肌球蛋白和肌动蛋白相互作用。虽然已经提出了c-MyBPC的结构和监管作用，但其真正的功能尚不清楚；然而，磷酸化已被证明是重要的。在这项研究中，我们利用快速反应动力学研究了c-MyBPC及其磷酸化对跨桥循环两个关键步骤的影响。我们发现未磷酸化的c-MyBPC与肌凝蛋白以1:1和3:1的比例络合：c-MyBPC化学计量学调节肌凝蛋白与肌动蛋白（K-D）的协同结合（Hill系数，h） (K-D = 16.44 +/- 0.33 μ M, h = 9.24 +/- 1.34；K- d = 11.48 +/- 0.75 μ M, h = 3.54 +/- 0.67)，显著减缓atp诱导的肌球蛋白与肌动蛋白的解离(K(1) K（+2）值分别为0.12 +/- 0.01和0.22 +/- 0.01 M-1 s(-1)，而单独肌球蛋白的K（1)值为0.42 +/- 0.01 M-1 s(-1)）。与未磷酸化的c-MyBPC存在时肌球蛋白与肌动蛋白的分离相比，c-MyBPC的磷酸化消除了关联期的调节(K(1) K（+2）值分别为0.32 +/- 0.02和0.33 +/- 0.01 M-1 s(-1)，当肌球蛋白与c-MyBPC的比值为1:1和3:1时，K(1) K（+2）值分别为0.23 +/- 0.01和0.29 +/- 0.01 M-1 s(-1))，加速了肌动蛋白与肌动蛋白的分离。这些结果表明，c-MyBPC对过桥动力学的直接影响与细丝无关，其磷酸化为微调过桥行为提供了一种机制，以满足心脏的收缩需求。
Cardiac myosin binding protein C (c-MyBPC) is a thick filament protein that is expressed in cardiac sarcomeres and is known to interact with myosin and actin. While both structural and regulatory roles have been proposed for c-MyBPC, its true function is unclear; however, phosphorylation has been shown to be important. In this study, we investigate the effect of c-MyBPC and its phosphorylation on two key steps of the cross-bridge cycle using fast reaction kinetics. We show that unphosphorylated c-MyBPC complexed with myosin in 1:1 and 3:1 myosin:c-MyBPC stoichiometries regulates the binding of myosin to actin (K-D) cooperatively (Hill coefficient, h) (K-D = 16.44 +/- 0.33 mu M, and h = 9.24 +/- 1.34; K-D = 11.48 +/- 0.75 mu M, and h = 3.54 +/- 0.67) and significantly decelerates the ATP-induced dissociation of myosin from actin (K(1)k(+2) values of 0.12 +/- 0.01 and 0.22 +/- 0.01 M-1 s(-1), respectively, compared with a value of 0.42 +/- 0.01 M-1 s(-1) for myosin alone). Phosphorylation of c-MyBPC abolished the regulation of the association phase (K(1)k(+2) values of 0.32 +/- 0.02 and 0.33 +/- 0.01 M-1 s(-1) at 1:1 and 3:1 myosin:c-MyBPC ratios, respectively) and also accelerated the dissociation of myosin from actin (K(1)k(+2) values of 0.23 +/- 0.01 and 0.29 +/- 0.01 M-1 s(-1) at a 1:1 and 3:1 myosin:c-MyBPC ratios, respectively) relative to the dissociation of myosin from actin in the presence of unphosphorylated c-MyBPC. These results indicate a direct effect of c-MyBPC on cross-bridge kinetics that is independent of the thin filament that together with its phosphorylation provides a mechanism for fine-tuning cross-bridge behavior to match the contractile requirements of the heart.