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首页> 外文期刊>Journal of Molecular Biology >Sites of Interaction of a Precursor Polypeptide on the Export Chaperone SecB Mapped by Site-directed Spin Labeling.
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Sites of Interaction of a Precursor Polypeptide on the Export Chaperone SecB Mapped by Site-directed Spin Labeling.

机译：前体多肽在出口伴侣蛋白SecB上的相互作用位点通过定点旋转标记进行映射。

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摘要

Export of protein into the periplasm of Escherichia coli via the general secretory system requires that the transported polypeptides be devoid of stably folded tertiary structure. Capture of the precursor polypeptides before they fold is achieved by the promiscuous binding to the chaperone SecB. SecB delivers its ligand to export sites through its specific binding to SecA, a peripheral component of the membrane translocon. At the translocon the ligand is passed from SecB to SecA and subsequently through the SecYEG channel. We have previously used site-directed spin labeling and electron paramagnetic resonance spectroscopy to establish a docking model between SecB and SecA. Here we report use of the same strategy to map the pathway of a physiologic ligand, the unfolded form of precursor galactose-binding protein, on SecB. Our set of SecB variants each containing a single cysteine, which was used in the previous study, has been expanded to 48 residues, which cover 49% of the surface of SecB. The residueson SecB involved in contacts were identified as those that, upon addition of the unfolded polypeptide ligand, showed changes in spectral line shape consistent with restricted motion of the nitroxide. We conclude that the bound precursor makes contact with a large portion of the surface of the small chaperone. The sites on SecB that interact with the ligand are compared with the previously identified sites that interact with SecA and a model for transfer of the ligand is discussed.
机译：通过一般的分泌系统将蛋白质输出到大肠杆菌的周质中，要求转运的多肽没有稳定折叠的三级结构。前体多肽在折叠之前的捕获是通过与伴侣SecB的混杂结合来实现的。 SecB通过与SecA特异性结合而将其配体递送至出口位点，SecA是膜转运蛋白的外围成分。在转运子上，配体从SecB传递到SecA，然后通过SecYEG通道。我们以前曾使用定点自旋标记和电子顺磁共振波谱建立SecB和SecA之间的对接模型。在这里，我们报告使用相同的策略在SecB上绘制生理配体的途径，即前体半乳糖结合蛋白的未折叠形式。我们在以前的研究中使用的一组SecB变体每个都包含一个半胱氨酸，现已扩展到48个残基，覆盖了SecB表面的49％。接触中涉及的残基SecB被鉴定为那些在添加未折叠的多肽配体后显示出谱线形状变化的硝酸根受限运动的残基。我们得出的结论是，结合的前体与小分子伴侣的大部分表面接触。将SecB上与配体相互作用的位点与先前确定的与SecA相互作用的位点进行比较，并讨论了配体转移的模型。

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