Type III effector regulation of host GTPase signaling

描述（由申请人提供）：革兰氏阴性细菌病原体的III型分泌系统在病原体与其宿主之间形成最直接的界面之一。这些“针状”分子机器将细菌效应蛋白直接注射到宿主细胞中，目的是破坏先天免疫反应并促进细菌复制、传播和疾病进展。效应蛋白是独特的毒力因子，因为它们经常捕获或模拟宿主信号转导分子的特性。一个这样的靶标是GTP酶的进化上保守的Ras超家族。本研究的重点是最近确定的细菌III型效应家族。沙门氏菌、志贺氏菌和肠出血性大肠杆菌需要相关的III型效应子SifA、IpgB和Map。大肠杆菌的致病性，分别通过其共同的能力，激活Rho家族GT3信号级联。本文描述的研究试图通过检查1）Rho GTP酶的酶促活化，2）分子水平上GTP酶的III型效应子识别，以及3）效应子蛋白定位在宿主细胞内的影响，阐明该大型细菌毒力因子家族的宿主信号传导机制。通过揭示III型效应子家族成员的机制细节，这些研究将为几种感染因子的致病机制及其人类宿主的生物学提供新的见解。公共卫生相关性：人Rho家族GTP酶是细菌毒素和效应蛋白的主要靶点。病原体劫持这一关键信号通路，以促进细菌复制、传播和疾病进展。该提议研究了细菌III型效应蛋白大家族劫持人Rho GTP酶的能力。更深入地了解这些细菌效应子和人GTP酶之间的酶和生化界面，将导致对许多致病机制的更完整的了解，并可能揭示人类宿主细胞中信号转导的新方面。

DESCRIPTION (provided by applicant): The type III secretion system of Gram-negative bacterial pathogens creates one of the most direct interfaces between pathogens and their hosts. These 'needle-like' molecular machines inject bacterial effector proteins directly into host cells for the purpose of destroying an innate immune response and facilitating bacterial replication, dissemination, and disease progression. Effector proteins are unique virulence factors in that they often capture or mimic the properties of host signal transduction molecules. One such target is the evolutionarily conserved Ras-superfamily of GTPases. The present study focuses on a recently identified bacterial type III effector family. The related type III effectors SifA, IpgB, and Map are required for Salmonella, Shigella, and enterohaemorrhagic E. coli pathogenesis, respectively, through their common ability to activate Rho-family GTPase signaling cascades. The studies described here seek to elucidate the host signaling mechanisms of this large bacterial virulence factor family by examining 1) the enzymatic activation of Rho GTPases, 2) type III effector recognition of GTPases at the molecular level, and 3) the effects of effector protein localization within the host cell. By revealing mechanistic details of type III effector family members, these studies will provide new insights into the pathogenic mechanisms o several infectious agents and into the biology of their human host. PUBLIC HEALTH RELEVANCE: Human Rho-family GTPases are major targets of bacterial toxins and effector proteins. Pathogens hijack this critical signaling pathway to facilitate bacterial replication, dissemination, and disease progression. This proposal examines the ability of a large family of bacterial type III effector proteins to hijack human Rho GTPases. A deeper understanding of the enzymatic and biochemical interface between these bacterial effectors and human GTPases will lead to a more complete knowledge of numerous pathogenic mechanisms and may reveal new aspects of signal transduction in the human host cell.