Streptococcus suis is part of the pig commensal microbiome and a major pig pathogen causing pneumonia and meningitis, occasionally also in humans. The genomic analysis divides S. suis to asymptomatic carriage, respiratory and invasive systemic strains with distinct genomic signatures. The virulence factor S. suis adhesin P (SadP) recognizes the galabiose Galα1−4Gal-oligosaccharide. Based on the oligosaccharide fine specificity, SadP can be divided into subtypes P_N and P_O. We show that subtype P_N is distributed in the systemic strains. Both types of SadP are shown to predominantly bind to pig lung globotriaosylceramide (Gb3). SadP adhesin from virulent subtype P_N strain also binds to globotetraosylceramide (Gb4). Mutants of type P_N SadP adhesin were constructed into the galabiose-binding domain and analyzed to reveal the mechanism for Gb4 binding. Functional and structural analysis of type P_N SadP mutants showed that amino acid N285 of the galabiose-binding site was required for binding to Gb4 and strikingly was also required for interaction with the glycomimetic inhibitor phenylurea-galabiose. Molecular dynamics simulations provided further insight into the role of N285 for Gb4 and phenylurea-galabiose binding, suggesting additional hydrogen bonding to terminal GalNAc of Gb4 and urea-group. Importantly, type P_N SadP adhesin expressed by strains causing invasive systemic disease binds via a distinct amino acid N285 mediated mechanism to Gb4. Thus, this molecular mechanism of type P_N SadP binding is a candidate for selectively targeting S. suis meningitis without interfering with commensal strains, which opens up new venues for developing intervention strategies against this pathogen.

中文翻译：

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猪链球菌辅助毒力因子和粘附素S​​adP与球四糖神经酰胺的结合机制

猪链球菌是猪共生微生物组的一部分，是引起肺炎和脑膜炎的主要猪病原体，有时在人类中也是如此。基因组分析将猪链球菌分为无症状携带，呼吸道和侵入性系统菌株，具有独特的基因组特征。所述毒力因子的猪链球菌粘附素P（SADP）识别galabioseGalα1-4Gal寡糖。基于寡糖的优良特异性，SadP可分为P _N和P _O亚型。我们表明亚型P _ñ分布在全身的菌株。已显示两种类型的SadP主要结合猪肺球糖苷神经酰胺（Gb3）。来自强毒亚型P _N的SadP粘附素该菌株还与球四糖神经酰胺（Gb4）结合。将P _N SadP粘附素类型的突变体构建到半乳糖结合域中，并进行分析以揭示Gb4结合的机制。P _N SadP突变体的功能和结构分析表明，半乳糖结合位点的氨基酸N285是与Gb4结合所必需的，而与拟糖酶抑制剂苯基脲-半乳糖的相互作用也很重要。分子动力学模拟提供了对N285在Gb4和苯基脲-半乳糖结合中的作用的进一步了解，这表明在Gb4和脲基的末端GalNAc上存在额外的氢键。重要的是，键入P _N由引起侵袭性系统疾病的菌株表达的SadP粘附素通过独特的N285氨基酸介导的机制与Gb4结合。因此，P _N SadP结合的这种分子机制是选择性靶向猪链球菌脑膜炎而不干扰共生菌株的候选者，这为开发针对该病原体的干预策略开辟了新的场所。