Rytkönen Anne, Poh John, Garmendia Junkal, Boyle Cliona, Thompson Arthur, Liu Mei, Freemont Paul, Hinton Jay C D, Holden David W
Department of Infectious Diseases, Centre for Molecular Microbiology and Infection and Division of Molecular Biosciences, Imperial College London, Flowers Building, Armstrong Road, London SW7 2AZ, United Kingdom.
Proc Natl Acad Sci U S A. 2007 Feb 27;104(9):3502-7. doi: 10.1073/pnas.0610095104. Epub 2007 Feb 20.
Expression of the Salmonella enterica serovar Typhimurium pathogenicity island 2 (SPI-2) type III secretion system is controlled by the two-component regulatory system SsrA-SsrB. We used a transcriptomic approach to help define the SsrA-SsrB regulon. We identified a gene encoding an uncharacterized effector (SseL) whose translocation into host cells depends on the SPI-2 secretion system. SseL has similarities to cysteine proteases with deubiquitinating activity. A GST-SseL fusion protein specifically hydrolyzed mono- and polyubiquitin substrates in vitro with a preference for K63-linked ubiquitin chains. Ubiquitin-modified proteins accumulated in macrophages infected with Salmonella sseL mutant strains but to a lesser extent when infected with bacteria expressing active protein, demonstrating that SseL functions as a deubiquitinase in vivo. Salmonella sseL mutant strains did not show a replication defect or induce altered levels of cytokine production upon infection of macrophages but were defective for a delayed cytotoxic effect and were attenuated for virulence in mice.
鼠伤寒沙门氏菌致病岛2（SPI-2）Ⅲ型分泌系统的表达受双组分调节系统SsrA-SsrB的控制。我们采用转录组学方法来帮助确定SsrA-SsrB调控子。我们鉴定出一个编码未表征效应蛋白（SseL）的基因，其转运到宿主细胞中依赖于SPI-2分泌系统。SseL与具有去泛素化活性的半胱氨酸蛋白酶相似。一种GST-SseL融合蛋白在体外特异性水解单泛素和多泛素底物，对K63连接的泛素链具有偏好性。泛素修饰的蛋白在感染沙门氏菌sseL突变株的巨噬细胞中积累，但在感染表达活性蛋白的细菌时积累程度较小，这表明SseL在体内作为一种去泛素酶发挥作用。沙门氏菌sseL突变株在感染巨噬细胞时未表现出复制缺陷或诱导细胞因子产生水平改变，但在延迟细胞毒性效应方面存在缺陷，并且在小鼠中的毒力减弱。
