BACKGROUND In Gram-negative bacteria, type Va and Vc autotransporters are proteins that contain both a secreted virulence factor (the "passenger" domain) and a β-barrel that aids its export. While it is known that the folding and insertion of the β-barrel domain utilize the β-barrel assembly machinery (BAM) complex, how the passenger domain is secreted and folded across the membrane remains to be determined. The hairpin model states that passenger domain secretion occurs independently through the fully-formed and membrane-inserted β-barrel domain via a hairpin folding intermediate. In contrast, the BamA-assisted model states that the passenger domain is secreted through a hybrid of BamA, the essential subunit of the BAM complex, and the β-barrel domain of the autotransporter. METHODS To ascertain the models' plausibility, we have used molecular dynamics to simulate passenger domain secretion for two autotransporters, EspP and YadA. RESULTS We observed that each protein's β-barrel is unable to accommodate the secreting passenger domain in a hairpin configuration without major structural distortions. Additionally, the force required for secretion through EspP's β-barrel is more than that through the BamA β-barrel. CONCLUSIONS Secretion of autotransporters most likely occurs through an incompletely formed β-barrel domain of the autotransporter in conjunction with BamA. GENERAL SIGNIFICANCE Secretion of virulence factors is a process used by practically all pathogenic Gram-negative bacteria. Understanding this process is a necessary step towards limiting their infectious capacity.

中文翻译：

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自动转运蛋白分泌需要BamA。

背景技术在革兰氏阴性细菌中，Va型和Vc型自转运蛋白是既包含分泌的毒力因子（“乘客”域）又包括有助于其输出的β-桶的蛋白质。尽管已知β-桶结构域的折叠和插入利用β-桶组装机械（BAM）复合物，但是仍然需要确定乘客结构域如何在膜上分泌和折叠。发夹模型指出，通过发夹折叠中间体，乘客结构域的分泌独立发生在完全形成且插入膜的β-桶结构域中。相比之下，BamA辅助模型指出，乘客区域是通过BamA，BAM复合体的基本亚基和自转运蛋白的β-桶结构域的混合物分泌的。方法为了确定模型的真实性，我们已经使用分子动力学模拟了两个自动转运蛋白EspP和YadA的乘客结构域分泌。结果我们观察到，在没有重大结构变形的情况下，每种蛋白质的β-桶都无法以发夹结构容纳分泌的乘客结构域。此外，通过EsP的β-桶进行分泌所需的力要大于通过BamA的β-桶进行分泌所需的力。结论自转运蛋白的分泌很可能通过与BamA结合的自转运蛋白的不完全形成的β-桶状结构域发生。一般意义毒力因子的分泌是几乎所有致病性革兰氏阴性细菌都使用的过程。了解此过程是限制其感染能力的必要步骤。