Department of Molecular Microbiology and Immunology, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97239, USA.
Infect Immun. 2011 Jun;79(6):2182-92. doi: 10.1128/IAI.01277-10. Epub 2011 Apr 4.
Salmonella enterica serovar Typhimurium, an intracellular pathogen and leading cause of food-borne illness, encodes a plethora of virulence effectors. Salmonella virulence factors are translocated into host cells and manipulate host cellular activities, providing a more hospitable environment for bacterial proliferation. In this study, we report a new set of virulence factors that is translocated into the host cytoplasm via bacterial outer membrane vesicles (OMV). PagK (or PagK1), PagJ, and STM2585A (or PagK2) are small proteins composed of ∼70 amino acids and have high sequence homology to each other (>85% identity). Salmonella lacking all three homologues was attenuated for virulence in a mouse infection model, suggesting at least partial functional redundancy among the homologues. While each homologue was translocated into the macrophage cytoplasm, their translocation was independent of all three Salmonella gene-encoded type III secretion systems (T3SSs)-Salmonella pathogenicity island 1 (SPI-1) T3SS, SPI-2 T3SS, and the flagellar system. Selected methods, including direct microscopy, demonstrated that the PagK-homologous proteins were secreted through OMV, which were enriched with lipopolysaccharide (LPS) and outer membrane proteins. Vesicles produced by intracellular bacteria also contained lysosome-associated membrane protein 1 (LAMP1), suggesting the possibility of OMV convergence with host cellular components during intracellular trafficking. This study identified novel Salmonella virulence factors secreted via OMV and demonstrated that OMV can function as a vehicle to transfer virulence determinants to the cytoplasm of the infected host cell.
鼠伤寒沙门氏菌（Salmonella enterica serovar Typhimurium）是一种细胞内病原体，也是食源性疾病的主要致病菌，它编码了大量的毒力效应因子。沙门氏菌的毒力因子被转运到宿主细胞内，并操纵宿主细胞的活动，为细菌增殖提供了更适宜的环境。在本研究中，我们报告了一组新的毒力因子，它们通过细菌外膜囊泡（OMV）转运到宿主细胞质中。PagK（或 PagK1）、PagJ 和 STM2585A（或 PagK2）是由约 70 个氨基酸组成的小蛋白，彼此之间具有高度的序列同源性（>85%的同一性）。沙门氏菌缺失这三个同源物后，在小鼠感染模型中的毒力显著减弱，表明这些同源物之间至少存在部分功能冗余。虽然每个同源物都被转运到巨噬细胞质中，但它们的转运与三种沙门氏菌编码的 III 型分泌系统（T3SS）无关，包括沙门氏菌致病性岛 1（SPI-1）T3SS、SPI-2 T3SS 和鞭毛系统。包括直接显微镜观察在内的多种方法表明，PagK 同源蛋白是通过 OMV 分泌的，这些 OMV 富含脂多糖（LPS）和外膜蛋白。胞内细菌产生的囊泡还含有溶酶体相关膜蛋白 1（LAMP1），这表明在细胞内运输过程中，OMV 可能与宿主细胞成分融合。本研究鉴定了通过 OMV 分泌的新型沙门氏菌毒力因子，并证明 OMV 可以作为一种载体，将毒力决定因子转运到感染宿主细胞的细胞质中。
