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Structure of a nascent membrane protein as it folds on the BAM complex

机译：在BAM络合物上折叠时，膜蛋白的结构

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摘要

Mitochondria, chloroplasts and Gram-negative bacteria are encased in a double layer of membranes. The outer membrane contains proteins with a β-barrel structure~(1,2). β-Barrels are sheets of β-strands wrapped into a cylinder, in which the first strand is hydrogen-bonded to the final strand. Conserved multi-subunit molecular machines fold and insert these proteins into the outer membrane~(3-5). One subunit of the machines is itself a β-barrel protein that has a central role in folding other β-barrels. In Gram-negative bacteria, the β-barrel assembly machine (BAM) consists of the β-barrel protein BamA, and four lipoproteins~(5-8). To understand how the BAM complex accelerates folding without using exogenous energy (for example, ATP)~(9), we trapped folding intermediates on this machine. Here we report the structure of the BAM complex of Escherichia coli folding BamA itself. The BamA catalyst forms an asymmetric hybrid β-barrel with the BamA substrate. The N-terminal edge of the BamA catalyst has an antiparallel hydrogen-bonded interface with the C-terminal edge of the BamA substrate, consistent with previous crosslinking studies~(10-12); the other edges of the BamA catalyst and substrate are close to each other, but curl inward and do not pair. Six hydrogen bonds in a membrane environment make the interface between the two proteins very stable. This stability allows folding, but creates a high kinetic barrier to substrate release after folding has finished. Features at each end of the substrate overcome this barrier and promote release by stepwise exchange of hydrogen bonds. This mechanism of substrate-assisted product release explains how the BAM complex can stably associate with the substrate during folding and then turn over rapidly when folding is complete.
机译：线粒体，叶绿体和革兰氏阴性细菌被包裹在双层膜中。外膜含有β-镜筒结构的蛋白质〜（1,2）。 β-桶是包裹在圆柱体中的β-股的片材，其中第一链氢键合到最终股线。保守的多亚基分子机折叠并将这些蛋白质插入外膜〜（3-5）。机器的一个亚基本身是一种β-桶蛋白，其在折叠其他β-桶中具有核心作用。在革兰氏阴性细菌中，β-桶组装机（BAM）由β-桶蛋白BAMA和四个脂蛋白组成〜（5-8）。为了了解BAM复合物如何加速折叠而不使用外源性能量（例如，ATP）〜（9），我们在这台机器上捕获折叠中间体。在这里，我们报告了大肠杆菌折叠巴马本身的BAM综合体的结构。 BAMA催化剂与BAMA底物形成不对称杂交β-筒。 BAMA催化剂的N末端边缘具有反平行的氢键界面与BAMA底物的C末端边缘，与先前的交联研究一致〜（10-12）; BAMA催化剂和衬底的其他边缘彼此靠近，但向内卷曲并且不配对。膜环境中的六个氢键使两个蛋白质之间的界面非常稳定。这种稳定性允许折叠，但在折叠完成后，为衬底释放产生高动力学屏障。底物的每个端部的特征克服了该屏障并通过逐步交换氢键促进释放。该基板辅助产品释放的这种机制解释了BAM复合物在折叠期间如何与基板稳定相关，然后在折叠完成时迅速转动。

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  • 来源
    《Nature》 |2020年第7816期|473-478|共6页
  • 作者

    David Tomasek; Shaun Rawson; James Lee; Joseph S Wzorek; Stephen C Harrison; Zongli Li; Daniel Kahne;

  • 作者单位

    Department of Molecular and Cellular Biology Harvard University|Department of Chemistry and Chemical Biology Harvard University;

    Department of Biological Chemistry and Molecular Pharmacology Harvard Medical School;

    Department of Molecular and Cellular Biology Harvard University|Department of Chemistry and Chemical Biology Harvard University|Laboratory of Membrane Biophysics and Biology The Rockefeller University;

    Department of Chemistry and Chemical Biology Harvard University|Novartis Institutes for BioMedical Research;

    Department of Biological Chemistry and Molecular Pharmacology Harvard Medical School|Howard Hughes Medical Institute;

    Department of Biological Chemistry and Molecular Pharmacology Harvard Medical School|Howard Hughes Medical Institute;

    Department of Molecular and Cellular Biology Harvard University|Department of Chemistry and Chemical Biology Harvard University|Department of Biological Chemistry and Molecular Pharmacology Harvard Medical School;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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  • 正文语种 eng
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