Ronholm Jennifer, Zhang Cathy X Y, Cao Xudong, Lin Min
Canadian Food Inspection Agency, Ottawa Laboratory Fallowfield, Ottawa, Ontario, Canada; Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, Ontario, Canada.
J Basic Microbiol. 2014 Sep;54(9):1017-21. doi: 10.1002/jobm.201300007. Epub 2013 May 26.
Listeria monocytogenes is one of several Gram-positive bacteria known to contain an auxiliary ATPase (SecA2) involved in the Sec secretion of a subset of proteins important to bacterial pathogenesis, including autolysins. It is not known if IspC, a novel surface-associated autolysin essential for full virulence of L. monocytogenes serotype 4b, is SecA2-dependent for secretion. By creating a secA2 gene deletion (ΔsecA2) mutant from the wild type (WT) L. monocytogenes serotype 4b strain, in combination with the proteomic analysis of surface proteins and those secreted into the medium from both the mutant and the WT, we confirmed previous findings that two autolysins (p60 and NamA) are SecA2-dependent for secretion. However, this approach did not identify IspC as one of the surface proteins affected by the SecA2 deletion. Further experiments with immunofluorescence microscopy and Western blotting indicated that IspC was well displayed on the surface of both the ΔsecA2 mutant and WT cells, while p60 was not, clearly indicating that the secretion of IspC is not attributed to the SecA2 pathway. This finding sets IspC apart from other autolysins involved in virulence, such as p60 and NamA, in that SecA2 is not required for IspC secretion.
单核细胞增生李斯特菌是几种革兰氏阳性细菌之一，已知其含有一种辅助ATP酶（SecA2），该酶参与对细菌致病机制重要的一部分蛋白质（包括自溶素）的Sec分泌途径。目前尚不清楚IspC（一种对4b型单核细胞增生李斯特菌的完全毒力至关重要的新型表面相关自溶素）的分泌是否依赖于SecA2。通过从野生型（WT）4b型单核细胞增生李斯特菌菌株构建secA2基因缺失（ΔsecA2）突变体，并结合对突变体和野生型表面蛋白以及分泌到培养基中的蛋白进行蛋白质组学分析，我们证实了先前的发现，即两种自溶素（p60和NamA）的分泌依赖于SecA2。然而，这种方法并未将IspC鉴定为受SecA2缺失影响的表面蛋白之一。免疫荧光显微镜和蛋白质印迹的进一步实验表明，IspC在ΔsecA2突变体和野生型细胞表面均有良好展示，而p60则没有，这清楚地表明IspC的分泌不归因于SecA2途径。这一发现使IspC与其他参与毒力的自溶素（如p60和NamA）不同，因为IspC的分泌不需要SecA2。
