Structure-Function Relationships in the Spirochetal Flagellar Motor

摘要 螺旋体是一类在系统发育上截然不同的细菌，对人类健康具有重要意义 因为它们会引起梅毒(梅毒螺旋体)、莱姆病(伯氏疏螺旋体)、 钩端螺旋体病(问号钩端螺旋体)和牙周炎(密螺旋体)。在…中感染和传播 在哺乳动物宿主中，螺旋体进化出一种独特的形态和运动性，对 通过粘性介质和组织屏障进行转移。螺旋体运动所必需的细胞器 是周质鞭毛，它们驻留在细菌的周质空间，与外部的 大肠杆菌和肠沙门氏菌模型系统中的鞭毛。鉴于鞭毛驱动的运动性是 对致病螺旋体和许多其他细菌的毒力至关重要，我们的长期目标是了解 鞭毛组装和功能的分子机制。在上一个资助期内，我们有 证明莱姆病螺旋体伯氏杆菌(Bb)是一个很好的模式系统 周质鞭毛以前所未有的分辨率原位显示。与MD Motaleb博士和Chunho博士合作 Li，我们已经建立并鉴定了一个包含60种不同鞭毛和趋化性的大型BB文库 变种人。在理解周质鞭毛及其显著特征方面取得了重大进展。 有能力驱动独特的螺旋索运动和形态。本应用程序的目标是阐明 周质鞭毛的三个基本但具有挑战性的方面：1)鞭毛的结构和功能 III型分泌器；2)质子驱动力驱动鞭毛旋转的机制 以及3)鞭毛转换旋转方向以控制运动的机制 和趋化性。与遗传和生化方法一起，冷冻-ET将被用于确定 纳米级自然细胞环境中螺旋体鞭毛马达的结构/功能关系 决议。

ABSTRACT Spirochetes are a phylogenetically distinct group of bacteria that are of significant importance in human health as they cause major diseases such as syphilis (Treponema pallidum), Lyme disease (Borrelia burgdorferi), leptospirosis (Leptospira interrogans), and periodontitis (Treponema spp.). To infect and disseminate in mammalian hosts, spirochetes have evolved a unique morphology and motility that is highly effective at translocating through viscous media and tissue barriers. The organelles essential for spirochetal motility are periplasmic flagella, which reside in the bacterial periplasmic space and are distinct from the external flagella in the model systems Escherichia coli and Salmonella enterica. Given that flagella-driven motility is crucial for virulence of pathogenic spirochetes and many other bacteria, our long-term goal is to understand molecular mechanisms underlying flagellar assembly and function. During the previous funding period, we have demonstrated that the Lyme disease spirochete B. burgdorferi (Bb) is a great model system for characterizing periplasmic flagella in situ at an unprecedented resolution. In collaboration with Drs. Md Motaleb and Chunhao Li, we have generated and characterized a large Bb library including 60 different flagellar and chemotaxis mutants. Significant progress has been made in understanding the periplasmic flagella and their remarkable capacity in driving the unique spirochetal motility and morphology. The objective of this application is to illuminate three fundamental but challenging aspects of the periplasmic flagella: 1) the structure and function of the flagellar type III secretion apparatus; 2) the mechanism underlying the flagellar rotation driven by proton motive force across membrane; and 3) the mechanisms by which flagella switch rotational directions to control the motility and chemotaxis. Together with genetic and biochemical approaches, cryo-ET will be utilized to determine the structure/function relationship of the spirochetal flagellar motor in a native cellular environment at nanometer resolution.