Omecamtiv Mecarbil Modulates the Kinetic and Motile Properties of Porcine β-Cardiac Myosin
Omecamtiv Mecarbil Modulates the Kinetic and Motile Properties of Porcine β-Cardiac Myosin
复制标题
DOI：
10.1021/bi5015166
复制
发表时间：
2015-03-17
期刊：
影响因子：
2.9
通讯作者：
Forgacs, Eva
中科院分区：
文献类型：
--
作者：
Liu, Yingying;White, Howard D.;Forgacs, Eva
我们测定了心脏肌球蛋白的一种新型别构效应物——奥美卡替伐美卡比（Omecamtiv Mecarbil）对猪心室重酶解肌球蛋白（PV - HMM）的动力学和“体外”运动特性的影响。通过猝灭流动测定，奥美卡替伐美卡比使水解步骤（M - ATP⇌M - ADP - Pᵢ）的平衡常数从2.4增加到6，但该药物不改变水解步骤和色氨酸荧光增加的最大速率。奥美卡替伐美卡比还使与肌肉产生力相关的磷酸盐解离快速相的幅度（AM - ADP - Pᵢ→AM - ADP + Pᵢ）增加了4倍。这些结果表明一种机制，即M - ATP水解为M - ADP - Pᵢ在恢复冲程之前和之后都会发生，但肌动蛋白对磷酸盐解离的快速加速仅发生在恢复冲程后的A - M - ADP - Pᵢ上。奥美卡替伐美卡比对PV - HMM更显著的影响之一是通过体外运动测定法测量的无负荷缩短速度降低了14倍。该药物使通过磷酸盐解离的通量增加以及ADP解离速率（AM - ADP→AM + ADP）不变，从而产生了一种占空比更高的马达，其中更大比例的肌球蛋白头部与肌动蛋白丝紧密结合。更大比例的紧密附着的横桥产生的内部负荷增加，解释了在奥美卡替伐美卡比存在时体外运动速度降低的原因，并预测该药物将使心肌收缩更慢且更强。
We determined the effect of Omecamtiv Mecarbil, a novel allosteric effector of cardiac muscle myosin, on the kinetic and "in vitro" motility properties of the porcine ventricular heavy meromyosin (PV-HMM). Omecamtiv Mecarbil increases the equilibrium constant of the hydrolysis step (M-ATP reversible arrow M-ADP-P-i) from 2.4 to 6 as determined by quench flow, but the maximal rates of both the hydrolysis step and tryptophan fluorescence increase are unchanged by the drug. OM also increases the amplitude of the fast phase of phosphate dissociation (AM-ADP-P-i -> AM-ADP + P-i) that is associated with force production in muscle by 4-fold. These results suggest a mechanism in which hydrolysis of M-ATP to M-ADP-P-i occurs both before and after the recovery stroke, but rapid acceleration of phosphate dissociation by actin occurs only on post-recovery stroke A-M-ADP-P-i. One of the more dramatic effects of OM on PV-HMM is a 14-fold decrease in the unloaded shortening velocity measured by the in vitro motility assay. The increase in flux through phosphate dissociation and the unchanged rate of ADP dissociation (AM-ADP -> AM + ADP) by the drug produce a higher duty ratio motor in which a larger fraction of myosin heads are strongly bound to actin filaments. The increased internal load produced by a larger fraction of strongly attached crossbridges explains the reduced rate of in vitro motility velocity in the presence of OM and predicts that the drug will produce slower and stronger contraction of cardiac muscle.