National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, 20892, USA.
Mol Microbiol. 2014 Jun;92(6):1155-8. doi: 10.1111/mmi.12627. Epub 2014 May 19.
FhaC is an outer membrane transporter from Bordetella pertussis belonging to the two-partner secretion (TPS) pathway with its primary role being the secretion of the virulence factor filamentous haemagglutinin (FHA). FhaC serves as a model transporter of the TPS pathway and significant work has been done to characterize the role of FhaC in FHA secretion. Recent studies characterized interactions between FHA and the POTRA domains of FhaC, suggesting that secretion may involve a successive translocation mechanism mediated by β-augmentation and/or electrostatic interactions. Moreover, it was also shown that reconstituted FhaC is necessary and sufficient to transport FHA into proteoliposomes. While the crystal structure of FhaC clearly suggests a role in transport, the putative transport pore is plugged by an N-terminal α-helix (H1 helix) that occludes access by FHA. Therefore, it has been proposed that the H1 helix must be expelled from the pore in order for secretion of FHA to occur. However, this has yet to be shown experimentally. Guérin et al. (2014) report the first direct experimental evidence to show that the FhaC H1 helix is quite dynamic and exchanges between closed and open states upon interaction with FHA.
FhaC 是百日咳博德特氏菌的外膜转运蛋白，属于双组分分泌（TPS）途径，其主要作用是分泌毒力因子丝状血凝素（FHA）。FhaC 是 TPS 途径的模型转运蛋白，已经进行了大量工作来表征 FhaC 在 FHA 分泌中的作用。最近的研究描述了 FHA 与 FhaC 的 POTRA 结构域之间的相互作用，表明分泌可能涉及由β-增强和/或静电相互作用介导的连续易位机制。此外，还表明重建的 FhaC 足以将 FHA 转运到类脂体中。虽然 FhaC 的晶体结构清楚地表明其在运输中的作用，但假定的运输孔被 N 端α-螺旋（H1 螺旋）堵塞，阻止 FHA 进入。因此，有人提出，为了发生 FHA 的分泌，H1 螺旋必须从孔中排出。然而，这尚未在实验中得到证实。Guérin 等人（2014 年）报告了第一个直接的实验证据，表明 FhaC H1 螺旋相当动态，在与 FHA 相互作用时在关闭和打开状态之间交换。
