STRUCTURAL DYNAMICS OF F-ACTIN .1. CHANGES IN THE C-TERMINUS
STRUCTURAL DYNAMICS OF F-ACTIN .1. CHANGES IN THE C-TERMINUS
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DOI：
10.1006/jmbi.1994.0048
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发表时间：
1995-02-03
影响因子：
5.6
通讯作者：
EGELMAN, EH
中科院分区：
文献类型：
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作者：
ORLOVA, A;EGELMAN, EH
G-肌动蛋白的生物化学性质以及G-肌动蛋白聚合成F-肌动蛋白的动力学取决于Mg 2+或Ca 2+是否结合在肌动蛋白中的高亲和力金属结合位点。从电子显微照片的三维重建表明，密度的桥梁，我们解释为产生的C端的主要移位，存在于两股之间的细丝在Ca 2 +-肌动蛋白，是不存在的Mg 2 +-肌动蛋白。在由G-Ca 2 +-肌动蛋白的原子结构构建的F-肌动蛋白模型中也不存在这种桥。肌动蛋白中的DNA酶I结合环在残基42和43之间的切割，以及42个切割残基与肌动蛋白其余部分的非共价缔合，诱导了两条链之间更大的密度桥。当桥不存在时，F-肌动蛋白中的两个C-末端残基很容易被胰蛋白酶切割，而随着桥变得更加突出，这些残基对胰蛋白酶切割的抗性越来越强。相反，两个C-末端残基的切割导致DNA酶I结合环的构象变化。由于DNA酶I结合环和金属结合位点都离C末端很远，因此F-肌动蛋白中一定存在较大的变构效应。由这座桥的形成而导致的F-肌动蛋白的构象变化可能是由肌球蛋白结合引起的，因为这种运动产生了肌动蛋白衍射的变化，这与激活过程中肌肉X射线图案的变化非常相似，这些变化与肌球蛋白与细丝的结合有关。
The biochemical properties of G-actin, and the kinetics of polymerization of G-actin into F-actin, are dependent upon whether Mg2+ or Ca2+ is bound at the high-affinity metal-binding site in actin. Three-dimensional reconstructions from electron micrographs show that a bridge of density, that we interpret as arising from a major shift of the C terminus, exists between the two strands of the filament in Ca2+-actin that is absent in Mg2+-actin. This bridge is also absent in models of F-actin built from an atomic structure of G-Ca2+-actin. The cleavage of the DNase I-binding loop in actin between residues 42 and 43, with the non-covalent association of the 42 cleaved residues with the remainder of the actin, induces an even larger bridge of density between the two strands. When the bridge is absent, the two C-terminal residues in F-actin are easily cleaved by trypsin, while these residues become increasingly resistant to tryptic cleavage as the bridge becomes more prominent. Conversely, cleavage of the two C-terminal residues leads to a conformational change in the DNase I-binding loop. Since both the DNase I-binding loop and the metal-binding site are quite distant from the C terminus, large allosteric effects must exist in F-actin. The conformational change in F-actin that results from the creation of this bridge may be induced by myosin binding, since this movement generates changes in actin's diffraction that are very similar to the changes in the muscle X-ray pattern during activation that are associated with the binding of myosin to the thin filament.