Streptococcus suis, a major emerging pathogen in swine and humans, expresses immunoglobulin G (IgG)-binding proteins (IBPs), which contribute to the ability of organism to evasion of host immune system. The objective of this study was to identify novel pig IgG (pIgG) and human IgG (hIgG)-binding proteins and characterize the binding regions of enolase from Streptococcus suis serotype 2 (S. suis 2). Here, four pIgG-binding proteins (pIBPs) and five hIgG-binding proteins (hIBPs) were identified from S. suis 2 surface proteins by 2D-Far-western blot assays. All the newly captured proteins were expressed and further confirmed their binding activity to pIgG or hIgG by Far-western blot and dot blot. In addition to previously identified factor H, fibronectin, collagen, fibrinogen, plasminogen and laminin, we also found that both pIgG and hIgG can specifically interact with enolase. Binding assays indicated that interactions of S. suis 2 enolase with pIgG and hIgG is primarily mediated by the enolase C-terminal portion (Enolase-C, a.a. 142–432). We found that hIgG exhibited stronger binding ability to Enolase-C than pIgG. Further analysis of the C-terminal regions of enolase (Enolase-C1 and Enolase-C2) suggested that the C-terminus possessed two different binding domains with distinct host IgG proteins. Strikingly, we confirmed that pIgG interacted with the Enolase-C1 (a.a. 142–271) and hIgG interacted with the Enolase-C2 (a.a. 271–432). These observations of enolase provide interesting insights in the pathogenesis of S. suis infection.

猪链球菌是猪和人的主要新兴病原体，它表达免疫球蛋白G（IgG）结合蛋白（IBP），这些蛋白有助于生物体逃避宿主免疫系统的能力。这项研究的目的是鉴定新型猪IgG（pIgG）和人IgG（hIgG）结合蛋白，并表征猪链球菌血清型2（猪链球菌2）的烯醇酶的结合区。在这里，从猪链球菌中鉴定出四个pIgG结合蛋白（pIBPs）和五个hIgG结合蛋白（hIBPs）。通过2D-Far-western印迹检测2种表面蛋白。表达所有新捕获的蛋白，并通过Far-western印迹和点印迹进一步证实它们与pIgG或hIgG的结合活性。除了先前确定的因子H，纤连蛋白，胶原蛋白，纤维蛋白原，纤溶酶原和层粘连蛋白外，我们还发现pIgG和hIgG均可与烯醇酶特异性相互作用。结合测定表明猪链球菌的相互作用2带pIgG和hIgG的烯醇酶主要由烯醇酶C末端部分介导（Enolase-C，aa 142–432）。我们发现，hIgG对烯醇酶C的结合能力强于pIgG。对烯醇化酶（Enolase-C1和Enolase-C2）C端区域的进一步分析表明，C端具有两个不同的结合域，具有不同的宿主IgG蛋白。令人惊讶的是，我们证实pIgG与Enolase-C1（aa 142-271）相互作用，而hIgG与Enolase-C2（aa 271-432）相互作用。烯醇化酶的这些观察结果为猪链球菌感染的发病机理提供了有趣的见解。