Mechanisms of the Type III Secretion

描述（由申请人提供）：许多革兰氏阴性致病菌使用称为III型分泌系统（T3SS）的复杂蛋白质分泌装置将细菌效应蛋白转运到真核宿主细胞质中。由T3SS传递的效应蛋白能够调节和干扰宿主细胞过程，从而导致鼠疫、伤寒和细菌性痢疾等疾病。超过20种结构蛋白、效应蛋白和伴侣蛋白参与了这个高度特化的分子装置的组装、功能和调节。易位子是T3SS的基本结构成分之一，是一种蛋白质复合物，被认为在宿主细胞膜上形成一个孔，用于效应蛋白的易位。T3SS易位的蛋白质易位的分子机制仍然知之甚少。福氏志贺氏菌是志贺氏菌病的病原，志贺氏菌病是一种全球性的健康问题，每年在全世界造成100万人死亡。IpaB和IpaC已被确定为flexneri易位的组成部分。这些蛋白质需要显著的构象可塑性，以适应其环境和功能。我们的长期目标是利用结构方法了解III型蛋白易位的分子机制。本研究将重点研究在脂质膜背景下IpaB:IpaC复合物的三维结构。转座子蛋白的结构细节及其与脂质膜的相互作用将有助于了解T3SS，并将为控制和预防这类病原微生物引起的感染和疾病开辟新的途径。具体目的是：(1)利用电子冷冻显微镜观察IpaB:IpaC复合物在膜整合形式和可溶性形式下的构象；(2)开展IpaB:IpgC配合物的晶体学研究。

DESCRIPTION (provided by applicant): Many Gram-negative pathogenic bacteria employ a complex protein secretion apparatus termed type III secretion system (T3SS) to transport bacterial effector proteins into eukaryotic host cytoplasm. The effector proteins delivered by T3SS are capable of modulating and interfering with host cellular processes, which then can cause diseases such as plague, typhoid fever and bacterial dysentery. More than 20 structural proteins, effector proteins, and chaperones are involved in assembly, function and regulation of this highly specialized molecular device. The translocon, one of the basic structural components of the T3SS, is a protein complex that is presumed to form a pore in the host cell membrane for translocation of effector proteins. The molecular mechanisms underlying protein translocation of the T3SS translocon remain poorly understood. Shigella flexneri is the etiologic agent of shigellosis, a global health problem that causes >1 million mortality worldwide annually. IpaB and IpaC have been identified as components of the translocon of S. flexneri. These proteins require significant conformational plasticity that is adaptive to their environments and functions. Our long-term goal is to understand the molecular mechanisms underlying the type III protein translocation using structural approaches. The proposed research will be focused on the three-dimensional structure of the IpaB:IpaC complex in the context of lipid membrane. The structural details about the translocon proteins and their interactions with the lipid membrane will be instrumental to understanding of T3SS, and will open avenues to new measures to control and prevent infection and diseases caused by this category of pathogenic microorganisms. Specific aims are to: (1) visualize the conformation of the IpaB:IpaC complex in the membrane-integrated form and the soluble form by means of electron cryo-microscopy; (2) initiate the crystallographic studies on the IpaB:IpgC complex.