Protein Expression Laboratory, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, United States.
Department of Microbiology and Immunology, Virginia Commonwealth University, Richmond, United States.
Elife. 2017 Oct 6;6:e30822. doi: 10.7554/eLife.30822.
pathogenicity islands (SaPIs), such as SaPI1, exploit specific helper bacteriophages, like 80α, for their high frequency mobilization, a process termed 'molecular piracy'. SaPI1 redirects the helper's assembly pathway to form small capsids that can only accommodate the smaller SaPI1 genome, but not a complete phage genome. SaPI1 encodes two proteins, CpmA and CpmB, that are responsible for this size redirection. We have determined the structures of the 80α and SaPI1 procapsids to near-atomic resolution by cryo-electron microscopy, and show that CpmB competes with the 80α scaffolding protein (SP) for a binding site on the capsid protein (CP), and works by altering the angle between capsomers. We probed these interactions genetically and identified second-site suppressors of lethal mutations in SP. Our structures show, for the first time, the detailed interactions between SP and CP in a bacteriophage, providing unique insights into macromolecular assembly processes.
致病岛 (SaPIs)，如 SaPI1，利用特定的辅助噬菌体，如 80α，进行高频转导，这个过程被称为“分子海盗”。SaPI1 改变了辅助噬菌体的装配途径，形成只能容纳较小 SaPI1 基因组的小衣壳，而不能容纳完整噬菌体基因组。SaPI1 编码两个蛋白，CpmA 和 CpmB，负责这种大小的重定向。我们通过低温电子显微镜确定了 80α 和 SaPI1 原衣壳的近原子分辨率结构，并表明 CpmB 与 80α 支架蛋白 (SP) 竞争衣壳蛋白 (CP) 上的结合位点，并通过改变衣壳蛋白之间的角度起作用。我们通过遗传方法探测了这些相互作用，并鉴定了 SP 中致死突变的第二位置抑制子。我们的结构首次展示了噬菌体中 SP 和 CP 之间的详细相互作用，为大分子组装过程提供了独特的见解。
