National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA.
Nature. 2013 Sep 19;501(7467):385-90. doi: 10.1038/nature12521. Epub 2013 Sep 1.
β-barrel membrane proteins are essential for nutrient import, signalling, motility and survival. In Gram-negative bacteria, the β-barrel assembly machinery (BAM) complex is responsible for the biogenesis of β-barrel membrane proteins, with homologous complexes found in mitochondria and chloroplasts. Here we describe the structure of BamA, the central and essential component of the BAM complex, from two species of bacteria: Neisseria gonorrhoeae and Haemophilus ducreyi. BamA consists of a large periplasmic domain attached to a 16-strand transmembrane β-barrel domain. Three structural features shed light on the mechanism by which BamA catalyses β-barrel assembly. First, the interior cavity is accessible in one BamA structure and conformationally closed in the other. Second, an exterior rim of the β-barrel has a distinctly narrowed hydrophobic surface, locally destabilizing the outer membrane. And third, the β-barrel can undergo lateral opening, suggesting a route from the interior cavity in BamA into the outer membrane.
β-桶膜蛋白对于营养物质的输入、信号转导、运动和存活至关重要。在革兰氏阴性菌中，β-桶组装机器（BAM）复合物负责β-桶膜蛋白的生物发生，在线粒体和叶绿体中也发现了同源复合物。在这里，我们描述了淋病奈瑟菌和杜克雷嗜血杆菌两种细菌中 BAM 复合物的核心和必需成分 BamA 的结构。BamA 由一个大的周质域和一个 16 链跨膜β-桶域组成。三个结构特征揭示了 BamA 催化β-桶组装的机制。首先，在一个 BamA 结构中，内部腔是可及的，而在另一个结构中则是构象封闭的。其次，β-桶的外部边缘有一个明显变窄的疏水面，局部破坏外膜的稳定性。第三，β-桶可以进行侧向开口，这表明了 BamA 内部腔进入外膜的途径。
