Molecular mimic of group A streptococcal surface proteins

背景。化脓性链球菌的表面相关纤维连接蛋白（Fn）结合蛋白在细菌侵袭上皮细胞中起重要作用。我们检测了fn结合蛋白FbaA的功能域和保护性抗原性。方法。为了研究FbaA的功能域及其在s.s pyogenes上的定位，我们使用了一系列重组谷胱甘肽s -转移酶（GST）截短的FbaA蛋白进行免疫荧光显微镜、配体印迹和Biacore分析。用截断的蛋白免疫小鼠，以确定对化脓性葡萄球菌感染有保护作用的免疫原结构域。结果。配体blotting和Biacore分析显示，FbaA片段含有富含脯氨酸的重复结构域（RD），而不含N端和c端区域，具有fn结合活性。免疫荧光显微镜检查结果显示，N末端和RD暴露在外部区域，这表明RD在活的生物体上是一个与fn结合的元件。在N端和rd免疫小鼠体内有效地诱导出特异性抗体，并在体外对化脓性葡萄球菌显示出杀灭活性。FbaA免疫小鼠感染表达FbaA的M1和M49血清型菌株后，存活时间明显长于gst免疫小鼠。结论。FbaA结合fn的RD和N端是M1型化脓链球菌感染的潜在候选疫苗。

Background. Surface-associated fibronectin (Fn) binding proteins of Streptococcus pyogenes play an important role in the bacterial invasion of epithelial cells. We examined the functional domain and protective antigenicity of the Fn-binding protein FbaA. Methods. To investigate the functional domain of FbaA and its localization on S.pyogenes, a series of recombinant glutathione S-transferase (GST) truncated FbaA proteins was used for immunofluorescent microscopy, ligand blotting, and Biacore analyses. Mice were immunized with the truncated proteins for the determination of the immunogenic domains that contribute to protection against S.pyogenes infection. Results. Ligand-blotting and Biacore analyses revealed that the FbaA fragments harboring a proline-rich repeat domain (RD), but not the N- and C-terminal regions, possessed Fn-binding activity. Immunofluorescent microscopy findings showed that the N terminus and RD were exposed to external regions, which suggests that the RD serves as a Fn-binding element on live organisms. Specific antibodies were efficiently induced in N terminus and RD-immunized mice and demonstrated bactericidal activity against S. pyogenes in vitro. FbaA-immunized mice survived significantly longer than GST-immunized mice after infection with serotype M1 and M49 strains expressing FbaA. Conclusion. The Fn-binding RD and N terminus of FbaA are potential vaccine candidates for M1 strains of S.pyogenes infection.