Lenz Laurel L, Mohammadi Sina, Geissler Aimee, Portnoy Daniel A
Department of Molecular and Cell Biology, University of California, 401 Barker Hall, Berkeley, CA 94720-3202, USA.
Proc Natl Acad Sci U S A. 2003 Oct 14;100(21):12432-7. doi: 10.1073/pnas.2133653100. Epub 2003 Oct 3.
Pathogenic bacteria secrete proteins that promote invasion of host tissues and resistance to immune responses. However, secretion mechanisms that contribute to the enormous morbidity and mortality of Gram-positive bacteria are largely undefined. An auxiliary protein secretion system (SecA2) has recently emerged in Listeria monocytogenes and eight other Gram-positive pathogens. Here, a proteomics approach identified seventeen SecA2-dependent secreted and surface proteins of L. monocytogenes, the two most abundant of which [the p60 and N-acetylmuramidase (NamA) autolysins] hydrolyze bacterial peptidoglycan (PGN) and contribute to host colonization. SecA2-deficient (DeltaSecA2) bacteria were rapidly cleared after systemic infection of murine hosts, and in cultured cells showed reduced cell-cell spread. p60 or NamA deficiencies (Deltap60 and DeltaNamA) caused intermediate reductions in bacterial virulence in vivo, yet showed no defect for infection of cultured cells. Restoration of virulence in Deltap60 bacteria required full-length p60 with an intact catalytic domain, suggesting that PGN hydrolysis by p60 is crucial for L. monocytogenes virulence. Coordinated PGN hydrolysis by p60 and NamA activities is predicted to generate a muramyl glycopeptide, glucosaminylmuramyl dipeptide (GMDP), which is known to modify host inflammatory responses. Thus, SecA2-dependent secretion may promote release of muramyl peptides that subvert host pattern recognition.
致病细菌分泌促进宿主组织侵袭和免疫反应抗性的蛋白质。然而，导致革兰氏阳性菌极高发病率和死亡率的分泌机制在很大程度上尚不清楚。一种辅助蛋白分泌系统（SecA2）最近在单核细胞增生李斯特菌和其他八种革兰氏阳性病原体中出现。在这里，一种蛋白质组学方法鉴定出了单核细胞增生李斯特菌的17种SecA2依赖性分泌蛋白和表面蛋白，其中两种含量最高的蛋白（p60和N-乙酰胞壁酰胺酶（NamA）自溶素）可水解细菌肽聚糖（PGN）并有助于在宿主中定殖。SecA2缺陷型（DeltaSecA2）细菌在对小鼠宿主进行全身感染后迅速被清除，并且在培养细胞中显示出细胞间传播减少。p60或NamA缺陷（Deltap60和DeltaNamA）导致体内细菌毒力出现中度降低，但在感染培养细胞时未显示出缺陷。Deltap60细菌中毒力的恢复需要具有完整催化结构域的全长p60，这表明p60对PGN的水解对于单核细胞增生李斯特菌的毒力至关重要。预计p60和NamA活性协同进行的PGN水解会产生一种胞壁酰糖肽，即氨基葡萄糖胞壁酰二肽（GMDP），已知它可改变宿主的炎症反应。因此，SecA2依赖性分泌可能会促进胞壁酰肽的释放，从而颠覆宿主的模式识别。
