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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Repriming the actomyosin crossbridge cycle.
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Repriming the actomyosin crossbridge cycle.

机译：重新启动放线菌素跨桥循环。

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摘要

The central features of the mechanical cycle that drives the contraction of muscle are two translational steps: the working stroke, whereby an attached myosin crossbridge moves relative to the actin filament, and the repriming step, in which the crossbridge returns to its original orientation. Although the mechanism of the first of these is understood in some detail, that of the second has received less attention. Here, we show that repriming occurs after detachment of the crossbridge from the actin, rather than intervening between two actomyosin states with ATP bound [Eisenberg, E. & Greene, L. E. (1980) Annu. Rev. Physiol. 42, 293-309]. To discriminate between these two models we investigated the single-molecule mechanics of the myosin-actin interaction in the presence of ATP analogues such as GTP, for which the hydrolytic step itself limits the actomyosin GTPase rate to a much lower rate than for ATP. The lifetimes of bound states was proportional to 1/[GTP], indicating that during the bound period myosin was in the actomyosin rigor configuration. Moreover, despite the very low actomyosin GTPase, the rate of actin binding and formation of the rigor state was higher than with ATP; it follows that most interactions with actin result in the release of GTP and not of the products, GDP and phosphate. There was no significant movement of the actin during this interaction, so repriming must occur while myosin is dissociated, as in the original Lymn-Taylor scheme [Lymn, R. W. & Taylor, E. W. (1971) Biochemistry 10, 4617-4624].
机译：驱动肌肉收缩的机械循环的主要特征是两个平移步骤：工作冲程，其中附着的肌球蛋白横桥相对于肌动蛋白丝运动，以及重新启动步骤，其中横桥返回其原始方向。尽管对第一种的机制有较详细的了解，但第二种的机制却很少受到关注。在这里，我们显示了在从肌动蛋白上分离过桥之后发生重新引发，而不是在两个ATP结合的肌动蛋白状态之间进行干预[Eisenberg，E.＆Greene，L. E.（1980）Annu。生理学家。 42，293-309]。为了区分这两种模型，我们研究了在存在ATP类似物（例如GTP）的情况下肌球蛋白与肌动蛋白相互作用的单分子机理，因为水解步骤本身将肌动球蛋白GTP酶的速率限制为比ATP低得多的速率。结合状态的寿命与1 / [GTP]成正比，表明在结合期间肌球蛋白处于放线菌素的严格构型。此外，尽管放线菌素GTP酶非常低，但肌动蛋白的结合速率和严格状态的形成要高于ATP。因此，大多数与肌动蛋白的相互作用都会导致GTP的释放，而不是产品，GDP和磷酸盐的释放。肌动蛋白在这种相互作用中没有明显的运动，因此肌球蛋白解离时必须进行重新引发，如最初的Lymn-Taylor方案[Lymn，R. W.＆Taylor，E. W.（1971）Biochemistry 10，4617-4624]。

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