Structure and function of MCE systems in bacteria

项目摘要 细菌外膜是一种脂双层，在抵抗抗生素、洗涤剂和抗生素的过程中起着关键作用。 其他外部压力。尽管对细菌包膜进行了数十年的研究， 磷脂在细菌内膜和外膜之间运输。此外，许多其他类型的 疏水分子必须从细胞中输入或输出，并且专用的运输系统 需要移动许多这些分子穿过水周质和外膜。研究 我的实验室致力于研究细菌细胞膜中的运输机制。我们已经证明， 哺乳动物细胞进入（MCE）蛋白家族的成员形成结构多样的六聚体环和桶， 这些蛋白质中的一些可以在内外膜之间形成隧道，以促进脂质 运输最近，我们的实验室和其他人发表了几项关于Mla途径的研究， 对这一途径如何将脂质转运穿过细胞包膜的机理性见解。其他几 MCE系统在很大程度上仍然没有特征，我们的初步工作表明，这些功能是由 相对于Mla途径而言，它们具有根本不同的机制。在未来，我们将努力了解 这些未开发的MCE运输系统驱动一系列疏水底物跨膜运输， 细胞膜我们将使用冷冻电镜和X射线晶体学来揭示个体的结构 组成部分支持它们的生物功能，以及这些组成部分如何组装成更大的内部 膜，外膜，和潜在的transenvelope复合物。我们还将使用辅助 遗传学和生物化学方法来检验假设和探索MCE贩运的机制 系统，包括转运蛋白底物的识别，转运活性如何调节， 脂质/底物是从内膜和外膜中提取并插入内膜和外膜的，以及如何 脂质/底物通过周质运输。这项工作将促进我们对 细菌细胞生物学的基本但知之甚少的方面，并可能开辟途径， 开发针对重要细胞过程的新抗生素。此外，MCE的存在 一些双膜细胞器，如叶绿体中的蛋白质，表明了解E。杆菌 MCE系统也将对其他细菌衍生细胞器中的脂质运输产生直接影响。

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 still unclear how phospholipids are trafficked between the bacterial inner and outer membranes. In addition, many other kinds of hydrophobic molecules must be imported or exported from the cell, and dedicated transport systems are required to move many of these molecules across the aqueous periplasm and outer membrane. Research in my lab focuses on studying transport mechanisms in the bacterial cell envelope. We have shown 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 tunnels between the inner and outer membrane to facilitate lipid transport. Very recently, several studies of the Mla pathway have been published by our lab and others, leading to mechanistic insights into how this pathway may transport lipids across the cell envelope. Several other MCE systems remain largely uncharacterized, and our initial work suggests that these function by fundamentally different mechanisms relative to the Mla pathway. In the future, we will work to understand how these unexplored MCE transport systems drive the transport of a range of hydrophobic substrates across the cell envelope. 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 potentially 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 identification of transporter substrates, how transport activity is regulated, how lipids/substrates are are extracted from and inserted into the inner and outer membranes, and how lipids/substrates 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 important cellular processes. 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.