Transport and Insertion of Outer Membrane Proteins

描述(申请人提供)：革兰氏阴性细菌的包膜由两层膜组成，由含有肽聚糖壁的周质隔间隔开。内膜(IM)接触胞浆，外膜(OM)接触细胞外环境。OM是一种独特的结构，对革兰氏阴性菌是必不可少的，由脂多糖(LPS)、磷脂和蛋白质组成。它是一种非常有选择性的渗透性屏障，允许细菌在恶劣的环境中生存，例如肠道，在肠道中，OM对胆盐的抵抗力使肠道细菌能够茁壮成长。OM的成分是感染后第一个与宿主接触的成分，并强烈调节共生细菌和病原菌与宿主的相互作用。清楚地了解OM的生物发生过程对于了解宿主-病原体的相互作用以及细菌生理学的一个基本方面是必不可少的。外膜蛋白(OMP)是嵌入在外膜蛋白中的具有桶状结构的完整膜蛋白。许多OMP具有免疫原性，其中一些作为粘附素介导宿主组织的黏附和定植。OMP是在胞浆中合成的，并通过SEC转位机制跨IM转位。然而，这些疏水蛋白是如何穿过周质并特异性地插入OM的，人们对此知之甚少。一些周质伴侣和OM中的BAM复合体参与了OMP的运输和插入。在这项提案中，我们将建立以BAM综合体为重点的OMP运输和组装机制。我们将(I)确定BAM复合体的结构；(Ii)检验由这些结构得出的机制假说；(Iii)建立OMP在外膜中运输、折叠和插入的综合模型。

DESCRIPTION (provided by applicant): The envelope of Gram-negative bacteria consists of two membranes separated by the periplasmic compartment that contains the peptidoglycan wall. The inner membrane (IM) is in contact with the cytosol while the outer membrane (OM) contacts the extracellular environment. The OM is a unique structure, essential for Gram-negative bacteria, composed of lipopolysaccharide (LPS), phospholipids and proteins. It is a very selective permeability barrier that allows the bacteria to survive in hostile environments such as the gut, where the OM resistance to bile salts allows enteric bacteria to thrive. The components of the OM are the first to come in contact with a host upon infection and strongly modulate the interaction of symbiotic and pathogenic bacteria with their host. A clear understanding of the OM biogenesis proces is esential to understand host- pathogen interactions as well as a fundamental aspect of bacterial physiology. Outer membrane proteins (OMPs) are integral membrane proteins with ?-barrel structures embedded in the OM. Many OMPs are immunogenic and some of them serve as adhesins mediating adhesion and colonization of host tissues. OMPs are synthesized in the cytosol and translocated across the IM by the Sec translocation machinery . However, how these hydrophobic proteins cross the periplasm and insert specifically into the OM is poorly understood. A number of periplasmic chaperones and the BAM complex in the OM have been implicated in the transport and insertion of OMPs. In this proposal we will establish the mechanisms of OMP transport and assembly focusing on the BAM complex. We will (i) determine the structure of the BAM complex; (ii) test mechanistic hypotheses derived from the structures and (iii) develop an integrated model of OMP transport folding and insertion in the outer membrane.