Secretion of a bacterial virulence factor is driven by the folding of a C-terminal segment
Secretion of a bacterial virulence factor is driven by the folding of a C-terminal segment
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DOI：
10.1073/pnas.1009491107
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发表时间：
2010-10-12
影响因子：
11.1
通讯作者：
Bernstein, Harris D.
中科院分区：
文献类型：
--
作者：
Peterson, Janine H.;Tian, Pu;Bernstein, Harris D.
自转运蛋白是细菌毒力因子，由 C 端到 N 端方向分泌的 N 端“过客结构域”和驻留在外膜 (OM) 中的 C 端“β 结构域”组成。尽管过客结构域的分泌似乎不使用 ATP，但该反应的能量来源尚不清楚。在这里，我们表明，大肠杆菌 O157:H7 自转运蛋白 EspP 的过客结构域的有效分泌需要 C 端大约 17 kDa 过客结构域片段的稳定折叠。我们发现扰乱该片段折叠的突变不会影响其跨 OM 的易位，但会损害过客结构域其余部分的分泌。有趣的是，对动力学折叠突变体的检查强烈表明，大约 17 kDa 的片段在细胞外空间折叠。通过诱变大约 17 kDa 的片段，我们还偶然分离出了一个独特的易位中间体。对该中间体的分析表明，促进 OM 蛋白（Bam 复合物）膜整合的异寡聚体也促进了大约 17-kDa 片段的表面暴露。我们的结果提供了蛋白质折叠可以驱动易位的直接证据，并有助于阐明自转运蛋白的分泌机制。
Autotransporters are bacterial virulence factors consisting of an N-terminal "passenger domain" that is secreted in a C-to-N-terminal direction and a C-terminal "beta domain" that resides in the outer membrane (OM). Although passenger domain secretion does not appear to use ATP, the energy source for this reaction is unknown. Here, we show that efficient secretion of the passenger domain of the Escherichia coli O157:H7 autotransporter EspP requires the stable folding of a C-terminal approximate to 17-kDa passenger domain segment. We found that mutations that perturb the folding of this segment do not affect its translocation across the OM but impair the secretion of the remainder of the passenger domain. Interestingly, an examination of kinetic folding mutants strongly suggested that the approximate to 17-kDa segment folds in the extracellular space. By mutagenizing the approximate to 17-kDa segment, we also fortuitously isolated a unique translocation intermediate. Analysis of this intermediate suggests that a heterooligomer that facilitates the membrane integration of OM proteins (the Bam complex) also promotes the surface exposure of the approximate to 17-kDa segment. Our results provide direct evidence that protein folding can drive translocation and help to clarify the mechanism of autotransporter secretion.