背景:B族链球菌(GBS)是健康成年人的共生菌,也是新生儿的重要病原体,老年人和免疫功能低下的人。GBS显示几种促进定植和宿主感染的毒力因子,包括ST-17菌株特异性粘附素Srr2,先前表征为其与纤维蛋白原的结合。细菌粘附素和宿主定植的另一个常见靶标是纤连蛋白,一种普遍存在于体液中的多域糖蛋白,在细胞外基质和细胞表面。
结果:在这项研究中,纤连蛋白被鉴定为GBS的Srr2粘附素的新型配体。过表达srr2基因的ST-17菌株BM110的衍生物显示出结合纤维蛋白原和纤连蛋白的能力增加,与等基因野生型菌株相比。相反,srr2的缺失损害了细菌对两种配体的粘附。使用Srr2的重组结合区(BR)形式的ELISA测定和表面等离子体共振研究证实了与纤连蛋白的直接相互作用,估计Kd为92nM。纤维蛋白原结合缺陷的Srr2-BR变体也没有表现出与纤连蛋白的相互作用,表明Srr2通过dock-lock-latch机制与这种配体结合,先前描述的纤维蛋白原结合。鉴定了负责重组Srr2-BR结合的纤连蛋白位点,并将其定位在蛋白质的中央细胞结合域中。最后,在纤连蛋白的存在下,Δsrr2突变体粘附于人宫颈阴道上皮细胞的能力显着低于野生型菌株。
结论:通过结合遗传和生化方法,我们证明了Srr2的新作用,即与纤连蛋白相互作用。我们表征了这种相互作用的分子机制,并证明了它在促进GBS与人宫颈阴道上皮细胞的粘附中起作用。进一步证实了Srr2作为GBSST-17菌株高毒力因子的作用。先前未描述的Srr2和纤连蛋白之间相互作用的发现确立了该粘附素作为宿主组织GBS定殖的关键因素。
BACKGROUND: Group B Streptococcus (GBS) is a commensal of healthy adults and an important pathogen in newborns, the elderly and immunocompromised individuals. GBS displays several virulence factors that promote colonisation and host infection, including the ST-17 strain-specific adhesin Srr2, previously characterised for its binding to fibrinogen. Another common target for bacterial adhesins and for host colonization is fibronectin, a multi-domain glycoprotein found ubiquitously in body fluids, in the extracellular matrix and on the surface of cells.
RESULTS: In this study, fibronectin was identified as a novel ligand for the Srr2 adhesin of GBS. A derivative of the ST-17 strain BM110 overexpressing the srr2 gene showed an increased ability to bind fibrinogen and fibronectin, compared to the isogenic wild-type strain. Conversely, the deletion of srr2 impaired bacterial adhesion to both ligands. ELISA assays and surface plasmon resonance studies using the recombinant binding region (BR) form of Srr2 confirmed a direct interaction with fibronectin with an estimated Kd of 92 nM. Srr2-BR variants defective in fibrinogen binding also exhibited no interaction with fibronectin, suggesting that Srr2 binds this ligand through the dock-lock-latch mechanism, previously described for fibrinogen binding. The fibronectin site responsible for recombinant Srr2-BR binding was identified and localised in the central cell-binding domain of the protein. Finally, in the presence of fibronectin, the ability of a Δsrr2 mutant to adhere to human cervico-vaginal epithelial cells was significantly lower than that of the wild-type strain.
CONCLUSIONS: By combining genetic and biochemical approaches, we demonstrate a new role for Srr2, namely interacting with fibronectin. We characterised the molecular mechanism of this interaction and demonstrated that it plays a role in promoting the adhesion of GBS to human cervico-vaginal epithelial cells, further substantiating the role of Srr2 as a factor responsible for the hypervirulence of GBS ST-17 strains. The discovery of the previously undescribed interaction between Srr2 and fibronectin establishes this adhesin as a key factor for GBS colonisation of host tissues.