CRYOELECTRON MICROSCOPY OF ACTOS1 ATPASE INTERMEDIATES

描述（改编自摘要）：肌肉力量的分子基础是 附着在肌动蛋白上时肌球蛋白头部的构型变化。这样一个 变化可能是头部本身的构象变化，或者是 可能是肌动蛋白结合角的改变。力的能量 已知生产来自 ATP 水解，但“倾斜” “跨桥”假设仍然很有吸引力，但尚未得到证实。而且， 最近的结构数据表明附着的肌球蛋白的构型 ATP 和 ADP-Pi 状态下的头可能相似。 检验倾斜桥假说的一个问题是困难 建立所谓的弱结合肌动球蛋白状态的结构 在 ATP 存在的情况下发生。人们对以下方面有相当多的了解 ADP 或无核苷酸中发生的强结合态的结构。 然而，其他束缚态也难以捉摸，因为它们在 中等分辨率显微镜所需的低蛋白质浓度 肌动球蛋白头 (S1) 复合物或它们仅短暂存在。的 申请人最近发现了可以观察瞬态和 弱束缚态并一直通过电子研究它们的结构 水合样本的冷冻显微镜。已经获得的显微照片显示 稳态 ATP 水解过程中各种附着的 S1 构型；这样的 因此，数据与倾斜桥假设兼容，但不兼容 证明它。

DESCRIPTION (Adapted from abstract): The molecular basis of muscle force is a configurational change in the myosin head while attached to actin. Such a change could either be a conformational change within the head itself, or it may be an alteration in the binding angle made with actin. The energy for force production is known to come from ATP hydrolysis, but while the "tilting cross-bridge" hypothesis remains attractive, it is still unproven. Moreover, recent structural data have suggested that the configuration of attached myosin heads may be similar in both the ATP and ADP-Pi states. One problem in testing the tilting bridge hypothesis has been the difficulty of establishing the structures of so-called weakly bound acto-myosin states that occur in the presence of ATP. A considerable amount is known about the structure of the strongly bound states that occur in ADP or no nucleotide. However, other bound states have been elusive either because they dissociate at the low protein concentrations required for moderate resolution microscopy of the acto-myosin head (S1) complex or they are present only transiently. The applicant recently found conditions that allow one to observe transient and weakly bound states and has been studying their structures by electron cryo-microscopy of hydrated specimens. The micrographs already obtained show a variety of attached S1 configurations during steady-state ATP hydrolysis; such data are therefore compatible with the tilting bridge hypothesis but do not prove it.