Lalioui Lila, Pellegrini Elisabeth, Dramsi Shaynoor, Baptista Marina, Bourgeois Nadege, Doucet-Populaire Florence, Rusniok Christophe, Zouine Mohamed, Glaser Philippe, Kunst Frank, Poyart Claire, Trieu-Cuot Patrick
Unité de Biologie des Bactéries Pathogènes à Gram-Positif, Institut Pasteur, 25 rue du Dr. Roux, 75724 Paris, France.
Infect Immun. 2005 Jun;73(6):3342-50. doi: 10.1128/IAI.73.6.3342-3350.2005.
Streptococcus agalactiae (group B streptococcus [GBS]) is the leading cause of neonatal pneumonia, sepsis, and meningitis. An in silico genome analysis indicated that GBS strain NEM316 encodes 35 proteins containing an LPXTG motif which are thought to be covalently linked to the peptidoglycan by an enzyme called sortase. The role of these cell wall-anchored proteins in GBS pathogenesis was evaluated on a global level by inactivating the srtA gene. This gene encodes the major sortase SrtA that anchors most of the LPXTG-containing proteins. We chose the C5a peptidase (ScpB) and Alp2, an abundant immunogenic protein, as prototypical LPXTG-containing proteins. As expected, the SrtA knockout mutant was unable to anchor the C5a peptidase (ScpB) and Alp2 to the cell wall. Complementation with plasmid-borne srtA inserted into the chromosome restored the correct surface localization of both ScpB and Alp2. Interestingly, the SrtA mutant was impaired for binding to the major extracellular matrix components fibronectin and fibrinogen and displayed a significant reduction in adherence to human (A549, HeLa, and Caco-2) and murine (L2) epithelial cells compared to the parental wild-type strain. Surprisingly, the inactivation of srtA had no effect on the virulence of the type III strain of GBS in a neonatal rat model (measured by the 50% lethal dose and lung colonization) but strongly impaired the capacity of the strain to colonize the intestines of gnotobiotic mice in a competition assay. These results demonstrate that LPXTG-containing proteins are involved in cell adhesion and GBS persistence in vivo.
无乳链球菌（B族链球菌[GBS]）是新生儿肺炎、败血症和脑膜炎的主要病因。一项计算机基因组分析表明，GBS菌株NEM316编码35种含有LPXTG基序的蛋白质，这些蛋白质被认为通过一种名为分选酶的酶与肽聚糖共价连接。通过使srtA基因失活，在全球范围内评估了这些细胞壁锚定蛋白在GBS发病机制中的作用。该基因编码主要的分选酶SrtA，它锚定大多数含LPXTG的蛋白质。我们选择C5a肽酶（ScpB）和Alp（一种丰富的免疫原性蛋白）作为含LPXTG蛋白质的典型代表。正如预期的那样，SrtA基因敲除突变体无法将C5a肽酶（ScpB）和Alp2锚定到细胞壁上。用插入染色体的质粒携带的srtA进行互补，恢复了ScpB和Alp2的正确表面定位。有趣的是，与亲本野生型菌株相比，SrtA突变体与主要细胞外基质成分纤连蛋白和纤维蛋白原的结合受损，并且在与人（A549、HeLa和Caco-2）和鼠（L2）上皮细胞的黏附上显著降低。令人惊讶的是，srtA的失活对新生大鼠模型中GBS III型菌株的毒力没有影响（通过50%致死剂量和肺部定植来衡量），但在竞争试验中强烈损害了该菌株在无菌小鼠肠道中定植的能力。这些结果表明，含LPXTG的蛋白质参与细胞黏附以及GBS在体内的持续存在。
