革兰氏阴性菌中一种新的钙依赖性分泌途径的发现和机制研究

Gram-negative bacteria, of which Escherichia coli (E. coli) is a representative member, have evolved six types of secretion system (T1SS~T6SS) and outer membrane vesicle (OMV) to interact with the environment. Our preliminary data has unexpectedly found that protein aggregates generated within E. coli are secreted through a pathway distinct from T1SS~T6SS or OMV. This pathway critically depends on calcium, and can act on amyloid aggregates formed by various types of endogenous and exogenous proteins. This project thus aims to further depict the characteristics of the pathway, identify its components, and define the working mechanisms. The results may contribute to the establishment of a novel secretion pathway in gram-negative bacteria for coping with stresses.

革兰氏阴性菌与环境的互作依赖于6套分泌系统（types I～VI secretion system, T1SS～T6SS）和外膜囊泡（outer membrane vesicle, OMV）。大肠杆菌是一种典型的革兰氏阴性菌。我们在前期实验中意外发现，大肠杆菌中因错折叠而形成的蛋白聚集体会经由一条不同于T1SS～T6SS和OMV的途径分泌出胞。这条途径严格依赖于钙，可作用于多种不同类型的内源和外源蛋白，所处理的底物呈现淀粉样聚集特征。本项目将进一步刻画大肠杆菌中蛋白聚集体钙依赖性分泌途径的特征及构成，阐明其工作机制及可能的生物学功能，建立一种新的革兰氏阴性菌分泌模式，完善对细菌胁迫应对策略的理解。

本项目以大肠杆菌为模式细胞，发现了革兰氏阴性菌中的一条新分泌途径。此分泌途径独立于已知的分泌系统和外膜囊泡，选择性地将周质中发生错折叠的外源或内源蛋白输出胞外。PldA在该途径中同时发挥感受器和效应器的作用，其可通过N端周质基序感知并募集错折叠蛋白，从而诱导自身的富集和激发磷脂酶活性，并进一步削弱局部外膜屏障以介导错折叠蛋白的输出。PldA的敲除显著减少了细菌的蛋白分泌，严重影响了细菌在错折叠相关胁迫下的生存。这些结果建立了一种新的革兰氏阴性菌分泌模式，揭示了一种细菌应对胁迫的新策略。