Characterization of surface proteins on cell invasion of streptococcus pyogenes

A组化脓性链球菌(GAS)具有表面定位的纤维连接蛋白(FN)结合蛋白，是一种主要的毒力因子，可黏附和侵袭宿主细胞。我们从中毒性休克样综合征(TSLS)患者中分离到一种新的GAS血清型M3和M18毒株的Fn结合蛋白。通过搜索一例TSLS患者的M3株全基因组序列，在推测的表面蛋白中发现了一个开放阅读框架。它在C-末端含有一个LPXTG基序和Fn结合重复序列，命名为FbaB(A组B型链球菌Fn结合蛋白)。在检测的所有M3和M18菌株中均发现fbaB基因，但在其他M血清型中未发现该基因。此外，FbaB蛋白在TSLS株的细胞表面有表达，而在非TSLS株的细胞表面不表达。酶联免疫吸附试验和配体印迹分析表明，重组FbaB具有较强的Fn结合能力。FbaB缺陷突变株对Hep-2细胞的黏附和侵袭效率比野生型低6倍。此外，与野生型相比，感染突变株的小鼠的死亡率降低。这些数据表明，FbaB在病原学上与侵袭性链球菌疾病的发展有关。

Group A Streptococcus pyogenes (GAS) has surface-located fibronectin (Fn)-binding proteins known to be a major virulence factor, which adhere to and invade host cells. We present a novel Fn-binding protein of GAS serotype M3 and M18 strains isolated from patients with toxic shock-like syndrome (TSLS). By searching the whole genome sequence of an M3 strain from a TSLS patient, an open reading frame was found among the putative surface proteins. It possessed an LPXTG motif and Fn-binding repeat domains in the C-terminal region, and was designated as FbaB (Fn-binding protein of group A streptococci type B). The fbaB gene was found in all M3 and M18 strains examined, though not in other M serotypes. Furthermore, FbaB protein was expressed on the cell surface of TSLS strains but not on non-TSLS ones. ELISA and ligand blotting revealed that recombinant FbaB exhibits a strong Fn-binding ability. An FbaB-deficient mutant strain showed 6-fold lower adhesion and invasion efficiencies to HEp-2 cells than the wild type. Moreover, mortality was decreased in mice infected with the mutant strain in comparison to the wild type. These data suggest that FbaB is etiologically involved in the development of invasive streptococcal diseases.