Structural basis for mobilization of S. aureus pathogenicity islands

 描述(申请人提供)：金黄色葡萄球菌是一种条件致病菌，与人类和动物的一系列严重致病条件有关。对多种抗生素具有抗药性的社区获得的毒力金黄色葡萄球菌菌株的出现，已经成为一个重大的公共卫生问题。金黄色葡萄球菌中的许多毒力决定因素都携带在可移动的遗传元件上，包括携带编码超抗原毒素等毒力因子的基因的金黄色葡萄球菌致病岛(SaPI)。SAPI通常稳定地整合到宿主基因组中，但可以被特定的辅助噬菌体动员，如80A或fNM1，导致SAPI基因组包装成由辅助编码结构蛋白组成的噬菌体转导颗粒。SaPI已经进化出感知裂解噬菌体的存在、利用噬菌体功能和干扰噬菌体增殖的能力。这种干扰包括改变对噬菌体功能的依赖，特定选择SAPI DNA进行包装，以及形成太小而无法包装噬菌体基因组的衣壳。由此产生的颗粒可以高频率地将毒力因子转移到其他细胞，甚至跨属细胞。当前项目的总体目标是了解SAPI动员的结构基础、Helper-SAPI的特殊性以及它们的传播和建立所涉及的因素。这些过程是金黄色葡萄球菌进化和致病的重要因素。具体地说，我们的目标是：(1)确定80A支架蛋白在 (2)确定SAPI诱导衣壳大小重定向的机制；(3)确定gp44在DNA包装和稳定性中的作用；以及(4)了解辅助噬菌体dUTPase去抑制SAPI的过程。这些目标侧重于动员过程的不同方面，并将结合遗传、生化和结构方法进行研究。这些机制的阐明将对理解噬菌体、沙门氏菌和其他可移动的遗传元件在金黄色葡萄球菌中传播和建立毒力决定因素中的作用具有重要意义。此外，这项研究将有助于我们理解大分子组装过程和衣壳大小的一般确定。

 DESCRIPTION (provided by applicant): Staphylococcus aureus is an opportunistic pathogen that is associated with a range of serious pathogenic conditions in humans and animals. The emergence of virulent, community-acquired S. aureus strains that are resistant to many antibiotics has become a significant public health problem. Many virulence determinants in S. aureus are carried on mobile genetic elements, including S. aureus pathogenicity islands (SaPIs) that carry genes encoding virulence factors such as superantigen toxins. SaPIs are normally stably integrated into the host genome, but become mobilized by specific helper phages, such as 80a or fNM1, resulting in the packaging of the SaPI genome into phage-like transducing particles that are made from helper-encoded structural proteins. The SaPIs have evolved the ability to sense the presence of a lytic phage, exploit phage functions and interfere with phage multiplication. This interference includes altered dependency on phage functions, specific selection of SaPI DNA for packaging, and the formation of capsids that are too small to package phage genomes. The resulting particles can transfer virulence factors to other cells, even across genera, at high frequency. The overall aim of the current project is to understand the structural basis for SaPI mobilization, helper-SaPI specificity, and the factors involved in their spread and establishment. Such processes are important factors in S. aureus evolution and pathogenicity. Specifically, we aim to: (1) Define the roles of the 80a scaffolding protein in capsid assembly; (2) Determine the mechanism of SaPI-induced capsid size redirection; (3) Establish the role of gp44 in DNA packaging and stability; and (4) Understand the process of SaPI derepression by helper phage dUTPases. These aims focus on different aspects of the mobilization process and will be studied by a combination of genetic, biochemical and structural methods. Elucidation of these mechanisms will have significant implications for understanding the role of phages, SaPIs and other mobile genetic elements in the spread and establishment of virulence determinants in S. aureus. In addition, this research will aid our understanding of macromolecular assembly processes and capsid size determination in general.