Bierne Hélène, Garandeau Caroline, Pucciarelli M Graciela, Sabet Christophe, Newton Salete, Garcia-del Portillo Francisco, Cossart Pascale, Charbit Alain
Unité des Interactions Bactéries-Cellules, Institut Pasteur, 75724 Paris Cedex 15, France.
J Bacteriol. 2004 Apr;186(7):1972-82. doi: 10.1128/JB.186.7.1972-1982.2004.
Sortases are transamidases that covalently link proteins to the peptidoglycan of gram-positive bacteria. The genome of the pathogenic bacterium Listeria monocytogenes encodes two sortases genes, srtA and srtB. The srtA gene product anchors internalin and some other LPXTG-containing proteins to the listerial surface. Here, we focus on the role of the second sortase, SrtB. Whereas SrtA acts on most of the proteins in the peptidoglycan fraction, SrtB appears to target minor amounts of surface polypeptides. We identified one of the SrtB-anchored proteins as the virulence factor SvpA, a surface-exposed protein which does not contain the LPXTG motif. Therefore, as in Staphylococcus aureus, the listerial SrtB represents a second class of sortase in L. monocytogenes, involved in the attachment of a subset of proteins to the cell wall, most likely by recognizing an NXZTN sorting motif. The DeltasrtB mutant strain does not have defects in bacterial entry, growth, or motility in tissue-cultured cells and does not show attenuated virulence in mice. SrtB-mediated anchoring could therefore be required to anchor surface proteins involved in the adaptation of this microorganism to different environmental conditions.
分选酶是一种转酰胺酶，可将蛋白质与革兰氏阳性菌的肽聚糖共价连接。致病性细菌单核细胞增生李斯特菌的基因组编码两个分选酶基因，即srtA和srtB。srtA基因产物将内化素和其他一些含LPXTG的蛋白质锚定在李斯特菌表面。在此，我们聚焦于第二种分选酶SrtB的作用。虽然SrtA作用于肽聚糖组分中的大多数蛋白质，但SrtB似乎靶向少量的表面多肽。我们鉴定出一种由SrtB锚定的蛋白为毒力因子SvpA，这是一种表面暴露蛋白，不含LPXTG基序。因此，与金黄色葡萄球菌一样，李斯特菌的SrtB代表单核细胞增生李斯特菌中的第二类分选酶，参与将一部分蛋白质附着到细胞壁，很可能是通过识别NXZTN分选基序。缺失srtB的突变菌株在组织培养细胞中的细菌侵入、生长或运动方面没有缺陷，在小鼠中也没有表现出毒力减弱。因此，SrtB介导的锚定可能是将参与该微生物适应不同环境条件的表面蛋白进行锚定所必需的。
