Structural basis for pathogenicity island mobilization in S. aureus

描述（由申请人提供）：金黄色葡萄球菌产生许多具有重要医学意义的毒素，包括中毒性休克综合征毒素（TSST-1）和肠毒素B和c。其中一些毒素携带在所谓的致病性岛（SaPIs）上，这些毒素是类似于噬菌体的遗传元件，但缺乏通常与噬菌体产生相关的大多数基因。这些元素通常是稳定的，但可以被某些噬菌体感染或通过诱导本地噬菌体调动，在这种情况下，SaPIs被切除并包装成噬菌体样颗粒，可以将毒素基因转移到新细胞中。SaPI1是SaPI家族的类型成员，可以被噬菌体80？并有效地包装成噬菌体样颗粒使用80？结构蛋白。然而，SaPI1衣壳只有正常80？衣壳，与其较小的基因组相称。随着耐药葡萄球菌菌株的出现以及噬菌体治疗这类感染的新兴趣，噬菌体诱导SaPI1的动员将是一个重要的考虑因素。本研究的总体目的是了解噬菌体诱导金黄色葡萄球菌致病岛的动员和传播的结构基础及其在细菌发病发展中的作用。在这个项目中，我们解决了与SaPI1动员有关的两个具体问题：SaPI1如何诱导80小衣壳的形成？编码的蛋白质?如何选择SaPI1 DNA包装到这些衣壳中？理解这些问题将对理解金黄色葡萄球菌致病性的进化产生影响。为此，我们将使用遗传，生化和结构方法的组合，包括低温电镜，x射线晶体学和质谱。本研究的具体目的是：(1)定义80？(2)确定SaPI1诱导衣壳大小决定的机制(3)确定SaPI1对DNA识别的决定因素。公共卫生相关性：金黄色葡萄球菌已成为医院的主要健康问题，特别是随着多种抗生素耐药菌株的出现。致病性金黄色葡萄球菌可以从细菌基因组中所谓的致病性岛屿上携带的基因中产生几种毒素，从而引起严重的全身性感染。本项目研究的噬菌体/致病性岛系统在人群中水平传播和长期建立致病性方面的作用特别令人感兴趣。

DESCRIPTION (provided by applicant): Staphylococcus aureus produces a number of toxins of great medical importance, including toxic shock syndrome toxin (TSST-1) and enterotoxins B and C. Several of these toxins are carried on so-called pathogenicity islands (SaPIs), genetic elements that resemble prophages, but lack most of the genes normally associated with phage production. These elements are normally stable, but can be mobilized by infection with certain phages or by the induction of indigenous prophages, upon which the SaPIs get excised and packaged into phage-like particles that can transfer the toxin genes to new cells. The type member of the SaPI family, SaPI1 can be mobilized by phage 80? and is efficiently packaged into phage-like particles using 80? structural proteins. However, the SaPI1 capsid is only 1/3 the size of the normal 80? capsid, commensurate with its smaller genome. With the emergence of antibiotic-resistant Staphylococcus strains and the renewed interest in therapeutic use of bacteriophages to treat such infections, the phage-induced mobilization of SaPI1 will be an important consideration. The overall objective of this study is to understand the structural basis for the phage-induced mobilization and spread of S. aureus pathogenicity islands and its role in the development of bacterial pathogenesis. In this project, we address two specific questions in relation to the SaPI1 mobilization: How does SaPI1 induce the formation of small capsids from 80?-encoded proteins? How is the SaPI1 DNA selected for packaging into these capsids? Understanding these questions will have a bearing on understanding the evolution of pathogenicity in S. aureus. To this end, we will use a combination of genetic, biochemical and structural approaches, including cryo-EM, X-ray crystallography and Mass Spectrometry. The specific aims of this study are: (1) Define the role of the 80? structural gene products in capsid formation (2) Determine the mechanism of SaPI1-induced capsid size determination (3) Identify the determinants for DNA discrimination by SaPI1. PUBLIC HEALTH RELEVANCE: Staphylococcus aureus has become a major health problem in hospitals, especially with the emergence of multiple antibiotic resistant strains. Pathogenic S. aureus may cause severe systemic infections by producing several toxins from genes carried on so-called pathogenicity islands in the bacterial genome. The bacteriophage/pathogenicity island system under study in this project is of special interest for its role in the horizontal spread and long-term establishment of pathogenicity in the population.