Genetics and Biochemistry Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
Genetics and Biochemistry Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
Mol Cell. 2021 May 6;81(9):2000-2012.e3. doi: 10.1016/j.molcel.2021.02.023. Epub 2021 Mar 10.
The β-barrel assembly machine (BAM) integrates β-barrel proteins into the outer membrane (OM) of Gram-negative bacteria. An essential BAM subunit (BamA) catalyzes integration by promoting the formation of a hybrid-barrel intermediate state between its own β-barrel domain and that of its client proteins. Here we show that in addition to catalyzing the integration of β-barrel proteins, BamA functions as a polypeptide export channel. In vivo structural mapping via intermolecular disulfide crosslinking showed that the extracellular "passenger" domain of a member of the "autotransporter" superfamily of virulence factors traverses the OM through the BamA β-barrel lumen. Furthermore, we demonstrate that a highly conserved residue within autotransporter β-barrels is required to position the passenger inside BamA to initiate translocation and that during translocation, the passenger stabilizes the hybrid-barrel state. Our results not only establish a new function for BamA but also unify the divergent functions of BamA and other "Omp85" superfamily transporters.
β-桶状装配机（BAM）将β-桶状蛋白整合到革兰氏阴性菌的外膜（OM）中。一个必需的 BAM 亚基（BamA）通过促进其自身β-桶状结构域与其客户蛋白之间的杂交桶状中间状态的形成来催化整合。在这里，我们表明 BamA 除了催化β-桶状蛋白的整合外，还作为一种多肽出口通道发挥作用。通过分子间二硫键交联的体内结构映射表明，毒力因子“自转运体”超家族成员的细胞外“乘客”结构域通过 BamA 的β-桶状腔穿过 OM。此外，我们证明自转运体β-桶中的一个高度保守残基需要将乘客定位在 BamA 内以启动易位，并且在易位过程中，乘客稳定杂交桶状状态。我们的结果不仅为 BamA 建立了一个新的功能，而且统一了 BamA 和其他“Omp85”超家族转运蛋白的不同功能。
