Unravelling lipid trafficking for the bacterial outer membrane

项目摘要 细菌外膜是一种脂双层，在对抗生素、洗涤剂和 其他外部压力。尽管对细菌包膜进行了数十年的研究，但尚不清楚它是如何 磷脂在细菌的内膜和外膜之间通过中间的 周质的亲水性空间。我们最近发现，哺乳动物细胞入口(MCE)的成员 蛋白质家族形成结构多样的六聚体环和桶，其中一些蛋白质可能形成 内膜和外膜之间的“桥梁”或“管道”，以促进脂质的运输(Ekiert等人)。单元格2017)。 在未来，我们将致力于了解MCE蛋白如何帮助创建跨越周质的运输 连接内膜和外膜的系统。我们将使用冷冻-EM和X射线结晶学来解开 单个成分的结构如何支持它们的生物学功能，以及这些成分如何 组装成更大的内膜、外膜，甚至跨膜复合体。我们还将 采用互补的遗传和生化方法来检验假说，并探索 初级保健教育系统的贩运情况，包括运输方向、运输活动如何受到管制、脂类如何 是从内膜和外膜中提取和插入的，以及脂类是如何被运输到 周质。这项工作将促进我们对一个基本但鲜为人知的方面的理解 细菌细胞生物学，并可能开辟新的途径，针对关键的抗生素 外膜生物发生过程。此外，在一些双核细胞中存在MCE蛋白。 膜细胞器，如叶绿体，表明了解大肠杆菌MCE系统也将有 对其他细菌衍生细胞器中的脂类运输的直接影响。

PROJECT ABSTRACT The bacterial outer membrane is a lipid bilayer that plays a key role in resistance to antibiotics, detergents, and other external stresses. Despite decades of research on the bacterial envelope, it is unknown how phospholipids are trafficked between the bacterial inner and outer membranes, through the intervening hydrophilic space of the periplasm. We recently discovered that members of the mammalian cell entry (MCE) protein family form structurally diverse hexameric rings and barrels, and that some of these proteins may form “bridges” or “pipes” between the inner and outer membrane to facilitate lipid transport (Ekiert, et al. Cell 2017). In the future, we will work to understand how MCE proteins help to create a periplasm-spanning transport system that links the inner and outer membranes. We will use cryo-EM and X-ray crystallography to unravel how the structure of the individual components supports their biological functions, and how these components assemble into larger inner membrane, outer membrane, and even transenvelope complexes. We will also employ complementary genetic and biochemical approaches to test hypotheses and probe the mechanism of trafficking by MCE systems, including the direction of transport, how transport activity is regulated, how lipids are are extracted from and inserted into the inner and outer membranes, and how lipids are transported across the periplasm. This work will advance our understanding of a fundamental yet poorly understood aspect of bacterial cell biology, and may open up avenues to the development of new antibiotics that target the essential process of outer membrane biogenesis. In addition, the presence of MCE proteins in some double- membraned organelles, such as chloroplasts, suggests that understanding E. coli MCE systems will also have direct implications for lipid trafficking in other bacterial-derived organelles.