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首页> 外文期刊>Journal of Molecular Biology >X-ray diffraction evidence for the lack of stereospecific proteininteractions in highly activated actomyosin complex
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X-ray diffraction evidence for the lack of stereospecific proteininteractions in highly activated actomyosin complex

机译：X射线衍射证据表明高度活化的肌动球蛋白复合物缺乏立体定向蛋白相互作用

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摘要

The structure of actomyosin complex while hydrolyzing ATP was investigated by recording X-ray diffraction patterns from rabbit skeletal muscle fibers, in which exogenously introduced rabbit skeletal subfragment-l (S1) was covalently cross-linked to the endogenous actin filaments in rigor by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC). Approximately two-thirds of the introduced S1 was cross-linked. The cross-linking procedure did not affect the profile of the S1-induced enhancement of the actin-based layer line reflections in rigor, indicating that the acto-S1 interactions remained highly stereospecific. Ln the presence of ATP, the MgATPase of the S1 was highly activated regardless of calcium levels, presumably because the availability of the stereospecific binding sites for both proteins was maximized by the cross-linking. However, the diffraction pattern in the presence of ATP was striking in that the intensity profile of the strong 1/5.9 nm(-1) layer lines was indistinguishable from that from bare actin filaments, despite the fact that the majority of the S1 was still associated with actin. The change of the intensity profiles upon addition of ATP was completely reversible. Model calculations showed that this result can be explained if the S1 is not only swinging around its pivoting point, but the pivoting point itself is also moving on the actin surface in a range of a few nanometers. The results suggest that the stereospecific binding sites, which have been considered important for actomyosin cycling, are paradoxically left unoccupied for most of the time in this highly activated actomyosin complex.
机译：通过记录兔骨骼肌纤维的X射线衍射图谱来研究放线菌素复合物在水解ATP时的结构，其中外源导入的兔骨骼亚片段-l（S1）与内源性肌动蛋白丝共价交联，严格按照1-乙基-3-（3-二甲基氨基丙基）碳二亚胺（EDC）。引入的S1中大约三分之二是交联的。交联过程并未严格影响S1诱导的基于肌动蛋白的层线反射的增强，表明acto-S1相互作用仍然具有高度立体特异性。如果存在ATP，则无论钙水平如何，S1的MgATPase都被高度激活，这可能是因为两种蛋白质的立体特异性结合位点的可用性通过交联得以最大化。但是，在存在ATP的情况下，其衍射图谱非常引人注目，因为尽管大部分S1仍然存在，但强的1 / 5.9 nm（-1）层线的强度分布与裸肌动蛋白丝的强度分布没有区别。与肌动蛋白有关。加入ATP后强度分布的变化是完全可逆的。模型计算表明，如果S1不仅围绕其枢轴点摆动，而且枢轴点本身也在肌动蛋白表面上移动几纳米，则可以解释该结果。结果表明，立体特异性结合位点在放线菌素循环中被认为是重要的，但在这种高度活化的放线菌素复合体中，大部分时间却自相矛盾。

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