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Crystal structure of a substrate-engaged SecY protein-translocation channel

机译：底物结合的SecY蛋白易位通道的晶体结构

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摘要

Hydrophobic signal sequences target secretory polypeptides to a protein-conducting channel formed by a heterotrimeric membrane protein complex, the prokaryotic SecY or eukaryotic Sec61 complex. How signal sequences are recognized is poorly understood, particularly because they are diverse in sequence and length. Structures of the inactive channel show that the largest subunit, SecY or Sec61 alpha, consists of two halves that form an hourglass-shaped pore with a constriction in the middle of the membrane and a lateral gate that faces lipid(1-10). The cytoplasmic funnel is empty, while the extracellular funnel is filled with a plug domain. In bacteria, the SecY channel associates with the translating ribosome in co-translational translocation, and with the SecA ATPase in post-translational translocation(11). How a translocating polypeptide inserts into the channel is uncertain, as cryo-electron microscopy structures of the active channel have a relatively low resolution (similar to 10 angstrom) or are of insufficient quality(6-8). Here we report a crystal structure of the active channel, assembled from SecY complex, the SecA ATPase, and a segment of a secretory protein fused into SecA. The translocating protein segment inserts into the channel as a loop, displacing the plug domain. The hydrophobic core of the signal sequence forms a helix that sits in a groove outside the lateral gate, while the following polypeptide segment intercalates into the gate. The carboxy (C)-terminal section of the polypeptide loop is located in the channel, surrounded by residues of the pore ring. Thus, during translocation, the hydrophobic segments of signal sequences, and probably bilayer-spanning domains of nascent membrane proteins, exit the lateral gate and dock at a specific site that faces the lipid phase.
机译：疏水信号序列将分泌性多肽靶向由异源三聚体膜蛋白复合物，原核SecY或真核Sec61复合物形成的蛋白质传导通道。信号序列的识别方法知之甚少，特别是因为它们的序列和长度各不相同。无效通道的结构表明，最大的亚基SecY或Sec61 alpha由两半组成，它们形成一个沙漏形的孔，在膜的中间有一个狭窄的部分，而一个面向脂质的侧门（1-10）。细胞质漏斗是空的，而胞外漏斗充满了塞结构域。在细菌中，SecY通道在共翻译易位中与翻译的核糖体相关，在翻译后易位中与SecA ATPase相关（11）。易位多肽如何插入通道尚不确定，因为活性通道的低温电子显微镜结构分辨率较低（类似于10埃）或质量不足（6-8）。在这里，我们报告了由SecY复合物，SecA ATPase和融合到SecA中的分泌蛋白片段组装而成的主动通道的晶体结构。易位蛋白片段以环的形式插入通道，从而取代了插入域。信号序列的疏水核心形成一个螺旋，该螺旋位于侧向门外的凹槽中，而随后的多肽片段插入该门中。多肽环的羧基（C）末端部分位于通道中，被孔环的残基包围。因此，在易位过程中，信号序列的疏水性片段以及新生膜蛋白的可能跨过双层的结构域离开侧向门并停靠在面对脂质相的特定位点。

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  • 来源
    《Nature》 |2016年第7594期|395-399|共5页
  • 作者

    Li Long; Park Eunyong; Ling JingJing; Ingram Jessica; Ploegh Hidde; Rapoport Tom A.;

  • 作者单位

    Howard Hughes Med Inst, 240 Longwood Ave, Boston, MA 02115 USA|Harvard Univ, Sch Med, Dept Cell Biol, 240 Longwood Ave, Boston, MA 02115 USA;

    Howard Hughes Med Inst, 240 Longwood Ave, Boston, MA 02115 USA|Harvard Univ, Sch Med, Dept Cell Biol, 240 Longwood Ave, Boston, MA 02115 USA|Rockefeller Univ, 1230 York Ave, New York, NY 10065 USA|Howard Hughes Med Inst, 1230 York Ave, New York, NY 10065 USA;

    Whitehead Inst Biomed Res, 9 Cambridge Ctr, Cambridge, MA 02142 USA;

    Whitehead Inst Biomed Res, 9 Cambridge Ctr, Cambridge, MA 02142 USA;

    Whitehead Inst Biomed Res, 9 Cambridge Ctr, Cambridge, MA 02142 USA;

    Howard Hughes Med Inst, 240 Longwood Ave, Boston, MA 02115 USA|Harvard Univ, Sch Med, Dept Cell Biol, 240 Longwood Ave, Boston, MA 02115 USA;

  • 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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