THE CONFORMATIONAL STATE OF THE ACTO-S-1 COMPLEX

跨桥模型提出肌肉的跨桥周期是 由肌球蛋白驱动的跨桥交替在两个主要 与肌动蛋白结合强度明显不同的构象 以及它们的整体结构。在构象中，它出现在 没有核苷酸或存在ADP时，肌球蛋白与 肌动蛋白呈45度角。在另一种构象中，它发生在 ATP或ADP与肌球蛋白结合，肌球蛋白与肌动蛋白结合很弱。 角度假定为90度。这两种构象还有不同之处 这种调节复合体，肌钙蛋白-原肌球蛋白，可以极大地削弱 Nyosin.S-1的强结合构象与肌动蛋白的结合，但有 对S-1弱结合构象的结合几乎没有影响。 我们之前发现，acto.S-1的结构在 ATP的存在和不存在，与我们的模型一致。该结构 用交联型放线菌素进行阴性染色检测acto.S-1， 这使得肌动蛋白能够在低浓度的情况下与S-1结合 电子显微镜所需的蛋白质。在目前的研究中，我们检查了 不同ATP存在下的交联型肌动蛋白S-1的结构 类似物来确定这些类似物是否导致 Acto.S-1与在ATP中获得的相似。我们发现，尽管 ATP类似物，AMP-PNP和PPI，以类似的程度解离acto.S-1， 令人惊讶的是，它们没有在acto.S-1中引起相同的结构变化。 在AMP-PNP存在下的交联型放线菌S-1看起来非常严谨， 而在PPI存在下，交联型Actin.S-1的结构是 就像是ATP一样。我们还考察了三元乙丙橡胶改性S-1的结构。 与肌动蛋白发生交叉连接。生化研究表明，聚丙二烯改性的 S-1与S-1相似。ATP与肌动蛋白的相互作用 肌钙蛋白-原肌球蛋白缺失。以支持这些生物化学 研究了交联型放线菌pPDM修饰的S-1的结构。 在没有ATP的情况下，类似于存在交联型肌动蛋白。 三磷酸腺苷。

The cross-bridge model proposes that the cross-bridge cycle of muscle is driven by the myosin cross-bridge alternating between two major conformations which differ markedly in their strength of binding to actin and in their overall structure. In the conformation, which occurs in the absence of nucleotide or the presence of ADP, myosin binds very tightly to actin at a 45 degrees angle. In the other conformation, which occurs when ATP or ADP.Pi is bound to myosin, myosin binds very weakly to actin at an angle postulated to be 90 degrees. These two conformations also differ in that the regulatory complex, troponin-tropomyosin, can greatly weaken the binding of the strong-binding conformation of nyosin.S-1 to actin, but has almost no effect on the binding of the weak-binding conformation of S-1. We previously found that the structure of acto.S-1 is very different in the presence and absence of of ATP, in agreement with our model. The structure of acto.S-1 was examined by negative staining using cross-linked actin.S-1, which enables actin to remain bound to S-1 at the low concentrations of protein needed for electron microscopy. In the present study, we examined the structure of cross-linked actin.S-1 in the presence of different ATP analogs to determine whether these analogs cause the conformation of acto.S-1 to resemble that obtained in ATP. We found that even though the ATP analogs, AMP-PNP and PPi, dissociate acto.S-1 to a similar extent, they, surprisingly, do not cause the same structural changes in acto.S-1. Cross-linked actin.S-1 in the presence of AMP-PNP appears quite rigor-like, whereas the structure of cross-linked actin.S-1 in the presence of PPi is ATP-like. We also examined the structure of pPDM modified S-1 when cross-linked to actin. Biochemical studies have shown that pPDM-modified S-1 resembles S-1.ATP in its interaction with actin both in the presence and absence of troponin-tropomyosin. In support of these biochemical studies, the structure of cross-linked actin.pPDM-modified S-1 in the absence of ATP resembles that of cross-linked actin.S-1 in the presence of ATP.