Streptococcus gordonii and Streptococcus sanguinis are typically found among the normal oral microbiota but can also cause infective endocarditis. These organisms express cell surface serine-rich repeat adhesins containing "Siglec-like" binding regions (SLBRs) that mediate attachment to α2-3-linked sialic acids on human glycoproteins. Two known receptors for the Siglec-like adhesins are the salivary mucin MG2/MUC7 and platelet GPIbα, and the interaction of streptococci with these targets may contribute to oral colonization and endocarditis, respectively. The SLBRs display a surprising diversity of preferences for defined glycans, ranging from highly selective to broader specificity. In this report, we characterize the glycoproteins in human plasma recognized by four SLBRs that prefer different α2-3 sialoglycan structures. We found that the SLBRs recognize a surprisingly small subset of plasma proteins that are extensively O-glycosylated. The preferred plasma protein ligands for a sialyl-T antigen-selective SLBR are proteoglycan 4 (lubricin) and inter-alpha-trypsin inhibitor heavy chain H4. Conversely, the preferred ligand for a 3'sialyllactosamine-selective SLBR is glycocalicin (the extracellular portion of platelet GPIbα). All four SLBRs recognize C1 inhibitor but detect distinctly different glycoforms of this key regulator of the complement and kallikrein protease cascades. The four plasma ligands have potential roles in thrombosis and inflammation, and each has been cited as a biomarker for one or more vascular or other diseases. The combined results suggest that the interaction of Siglec-like adhesins with different subsets of plasma glycoproteins could have a significant impact on the propensity of streptococci to establish endocardial infections.

中文翻译：

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链球菌类Siglec粘附素识别人血浆糖蛋白的不同子集：对感染性心内膜炎的影响。

戈登链球菌和血红链球菌通常存在于正常口腔微生物群中，但也可引起感染性心内膜炎。这些生物体表达富含细胞表面丝氨酸的重复粘附素，该粘附素含有“ Siglec样”结合区（SLBR），介导人糖蛋白上与α2-3连接的唾液酸的附着。Siglec样粘附素的两个已知受体是唾液粘蛋白​​MG2 / MUC7和血小板GPIbα，而链球菌与这些靶标的相互作用可能分别导致口腔定植和心内膜炎。SLBR对定义的聚糖显示出令人惊讶的偏好多样性，范围从高度选择性到更广泛的特异性。在本报告中，我们表征了被优选具有不同α2-3唾液酸聚糖结构的四种SLBR识别的人血浆中的糖蛋白。我们发现SLBRs可以识别出被广泛O-糖基化的血浆蛋白的一小部分。唾液酸-T抗原选择性SLBR的优选血浆蛋白配体是蛋白聚糖4（lubricin）和α-胰蛋白酶抑制剂重链H4。相反，对于3'唾液酸神经酰胺胺选择性SLBR而言，优选的配体是糖钙调素（血小板GPIbα的细胞外部分）。所有四个SLBR均识别C1抑制剂，但检测到该补体和激肽释放酶蛋白酶级联反应的关键调节剂的明显不同的糖型。四种血浆配体在血栓形成和炎症中具有潜在作用，并且每种均被引用为一种或多种血管疾病或其他疾病的生物标记。