Department of Chemistry, King's College London, London, United Kingdom.
Department of Chemistry, Imperial College London, London, United Kingdom.
Elife. 2019 Jul 10;8:e47402. doi: 10.7554/eLife.47402.
The bacterial Sec translocon is a multi-protein complex responsible for translocating diverse proteins across the plasma membrane. For post-translational protein translocation, the Sec-channel - SecYEG - associates with the motor protein SecA to mediate the ATP-dependent transport of pre-proteins across the membrane. Previously, a diffusional-based Brownian ratchet mechanism for protein secretion has been proposed; the structural dynamics required to facilitate this mechanism remain unknown. Here, we employ hydrogen-deuterium exchange mass spectrometry (HDX-MS) to reveal striking nucleotide-dependent conformational changes in the Sec protein-channel from . In addition to the ATP-dependent opening of SecY, reported previously, we observe a counteracting, and ATP-dependent, constriction of SecA around the pre-protein. ATP binding causes SecY to open and SecA to close; while, ADP produced by hydrolysis, has the opposite effect. This alternating behaviour could help impose the directionality of the Brownian ratchet for protein transport through the Sec machinery.
细菌 Sec 转运通道是一种负责将多种蛋白质穿过质膜转运的多蛋白复合物。对于翻译后蛋白质转运，Sec 通道 - SecYEG - 与马达蛋白 SecA 结合，介导前体蛋白在膜上的 ATP 依赖性运输。以前，已经提出了一种基于扩散的布朗棘轮机制用于蛋白质分泌；促进这种机制所需的结构动力学仍然未知。在这里，我们使用氘氢交换质谱 (HDX-MS) 来揭示. 中 Sec 蛋白通道的惊人的核苷酸依赖性构象变化。除了以前报道的 ATP 依赖性 SecY 打开之外，我们还观察到围绕前体蛋白的 SecA 的拮抗的、ATP 依赖性收缩。ATP 结合导致 SecY 打开和 SecA 关闭；而水解产生的 ADP 则产生相反的效果。这种交替的行为可以帮助为通过 Sec 机械的布朗棘轮施加蛋白质运输的方向性。
