Department of Chemistry, National University of Singapore, Singapore 117543, Singapore.
Microbiology (Reading). 2022 Apr;168(4). doi: 10.1099/mic.0.001177.
The outer membrane (OM) is a formidable permeability barrier that protects Gram-negative bacteria from detergents and antibiotics. It possesses exquisite lipid asymmetry, requiring the placement and retention of lipopolysaccharides (LPS) in the outer leaflet, and phospholipids (PLs) in the inner leaflet. To establish OM lipid asymmetry, LPS are transported from the inner membrane (IM) directly to the outer leaflet of the OM. In contrast, mechanisms for PL trafficking across the cell envelope are much less understood. In this review, we summarize and discuss recent advances in our understanding of PL transport, making parallel comparisons to well-established pathways for OM lipoprotein (Lol) and LPS (Lpt). Insights into putative PL transport systems highlight possible connections back to the 'Bayer bridges', adhesion zones between the IM and the OM that had been observed more than 50 years ago, and proposed as passages for export of OM components, including LPS and PLs.
外膜（OM）是一种强大的渗透屏障，可保护革兰氏阴性细菌免受清洁剂和抗生素的侵害。它具有精致的脂质不对称性，需要将脂多糖（LPS）放置并保留在外层，而将磷脂（PLs）保留在内层。为了建立 OM 脂质不对称性，LPS 从内膜（IM）直接运输到 OM 的外叶。相比之下，穿过细胞包膜的 PL 运输机制还不太清楚。在这篇综述中，我们总结和讨论了我们对 PL 运输的理解的最新进展，并与 OM 脂蛋白（Lol）和 LPS（Lpt）的既定途径进行了平行比较。对假定的 PL 运输系统的深入了解突出了与“拜耳桥”之间可能存在的联系，“拜耳桥”是 50 多年前观察到的位于内膜和外膜之间的粘附区，并被提议作为包括 LPS 和 PLs 在内的 OM 成分的出口通道。
