Talay S R, Zock A, Rohde M, Molinari G, Oggioni M, Pozzi G, Guzman C A, Chhatwal G S
Division of Microbiology, Technical University/GBF-National Research Centre for Biotechnology, Braunschweig, Germany.
Cell Microbiol. 2000 Dec;2(6):521-35. doi: 10.1046/j.1462-5822.2000.00076.x.
Streptococcal fibronectin binding protein I (SfbI) mediates adherence to and invasion of Streptococcus pyogenes into human epithelial cells. In this study, we analysed the binding activity of distinct domains of SfbI protein towards its ligand, the extracellular matrix component fibronectin, as well as the biological implication of the binding events during the infection process. By using purified recombinant SfbI derivatives as well as in vivo expressed SfbI domains on the surface of heterologous organism Streptococcus gordonii, we were able to dissociate the two major streptococcal target domains on the human fibronectin molecule. The SfbI repeat region exclusively bound to the 30 kDa N-terminal fragment of fibronectin, whereas the SfbI spacer region exclusively bound to the 45 kDa collagen-binding fragment of fibronectin. In the case of native surface-expressed SfbI protein, an induced fit mode of bacteria-fibronectin interaction was identified. We demonstrate that binding of the 30 kDa fibronectin fragment to the repeat region of SfbI protein co-operatively activates the adjacent SfbI spacer domain to bind the 45 kDa fibronectin fragment. The biological consequence arising from this novel mode of fibronectin targeting was analysed in eukaryotic cell invasion assays. The repeat region of SfbI protein is mediating adherence and constitutes a prerequisite for subsequent invasion, whereas the SfbI spacer domain efficiently triggers the invasion process of streptococci into the eukaryotic cell. Thus, we were able to dissect bacterial adhesion from invasion by manipulating one protein. SfbI protein therefore represents a highly evolved prokaryotic molecule that exploits the host factor fibronectin not only for extracellular targeting but also for its subsequent activation that leads to efficient cellular invasion.
链球菌纤连蛋白结合蛋白I（SfbI）介导化脓性链球菌对人上皮细胞的黏附和侵袭。在本研究中，我们分析了SfbI蛋白不同结构域与其配体——细胞外基质成分纤连蛋白的结合活性，以及感染过程中结合事件的生物学意义。通过使用纯化的重组SfbI衍生物以及在异源生物体戈登链球菌表面体内表达的SfbI结构域，我们能够分离人纤连蛋白分子上的两个主要链球菌靶结构域。SfbI重复区域仅与纤连蛋白的30 kDa N端片段结合，而SfbI间隔区域仅与纤连蛋白的45 kDa胶原结合片段结合。对于天然表面表达的SfbI蛋白，鉴定出一种细菌 - 纤连蛋白相互作用的诱导契合模式。我们证明，30 kDa纤连蛋白片段与SfbI蛋白重复区域的结合协同激活相邻的SfbI间隔结构域，以结合45 kDa纤连蛋白片段。在真核细胞侵袭试验中分析了这种新型纤连蛋白靶向模式产生的生物学后果。SfbI蛋白的重复区域介导黏附，并构成后续侵袭的先决条件，而SfbI间隔结构域有效地触发链球菌进入真核细胞的侵袭过程。因此，我们能够通过操纵一种蛋白质来区分细菌的黏附与侵袭。因此，SfbI蛋白代表了一种高度进化的原核分子，它不仅利用宿主因子纤连蛋白进行细胞外靶向，还利用其随后的激活来导致有效的细胞侵袭。
