Bacterial secretory proteins are translocated post‐translationally by the SecA ATPase through the protein‐conducting SecY channel in the plasma membrane. During the ATP hydrolysis cycle, SecA undergoes large conformational changes of its two‐helix finger and clamp domains, but how these changes result in polypeptide movement is unclear. Here, we use a reconstituted purified system and protease protection assays to show that ATP binding to SecA results in a segment of the translocation substrate being pushed into the channel. This motion is prevented by mutation of conserved residues at the finger's tip. Mutation of SecA's clamp causes backsliding of the substrate in the ATP‐bound state. Together, these data support a power stroke model of translocation in which, upon ATP binding, the two‐helix finger pushes the substrate into the channel, where it is held by the clamp until nucleotide hydrolysis has occurred.

中文翻译：

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蛋白酶保护测定显示多肽通过 SecA ATPase 的功率冲击进入 SecY 通道。

细菌分泌蛋白由 SecA ATPase 通过质膜中的蛋白质传导 SecY 通道在翻译后易位。在 ATP 水解循环中，SecA 的双螺旋指和钳结构域发生了较大的构象变化，但这些变化如何导致多肽运动尚不清楚。在这里，我们使用重组纯化系统和蛋白酶保护测定来显示 ATP 与 SecA 结合导致易位底物的一部分被推入通道。这种运动是通过手指尖端保守残基的突变来阻止的。SecA 夹子的突变导致底物在 ATP 结合状态下向后滑动。总之，这些数据支持易位的动力冲程模型，其中，在 ATP 结合后，双螺旋指将底物推入通道，