Characterization of surface proteins on cell invasion of streptococcus pyogenes

A组化脓性链球菌（GAS）具有位于表面的纤连蛋白（Fn）结合蛋白，已知其是粘附并侵入宿主细胞的主要毒力因子。我们提出了一种新的Fn结合蛋白的GAS血清型M3和M18株分离的患者中毒性休克样综合征（TSLS）。通过对1例TSLS患者的M3株全基因组序列的搜索，在推测的表面蛋白中发现了一个开放的阅读框架。它在C-末端区域具有LPXTG基序和Fn结合重复结构域，并被命名为Fba B（A组链球菌B型Fn结合蛋白）。fbaB基因被发现在所有的M3和M18菌株检查，但没有在其他M血清型。此外，FbaB蛋白表达在TSLS菌株的细胞表面，而不是在非TSLS的。ELISA和配体印迹分析表明，重组FbaB具有较强的Fn结合能力。FbaB缺陷型突变株对HEp-2细胞的粘附和侵袭效率比野生型低6倍。此外，与野生型相比，感染突变株的小鼠死亡率降低。这些数据表明，FbaB在病原学上参与了侵袭性链球菌疾病的发展。

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.