Hsa, an adhesin of Streptococcus gordonii DL1, binds to alpha2-3-linked sialic acid on glycophorin A of the erythrocyte membrane.

Bacterial recognition of host sialic acid-containing receptors plays an important role in microbial colonization of the human oral cavity. The aggregation of human platelets by Streptococcus gordonii DL1 is implicated in the pathogenesis of infective endocarditis. In addition, we consider that hemagglutination of this organism may act as an additive factor to increase the severity of this disease. We previously reported that this interaction requires the bacterial expression of a 203-kDa protein (Hsa), which has sialic acid-binding activity. In the present study, we confirmed that erythrocyte surface sialoglycoproteins are the receptors for Hsa. We examined the effects of proteinase K, chymotrypsin, phospholipase C, and alpha(2-3) or alpha(2-3, 6, 8) neuraminidase on hemagglutination activity and found that the interaction occurs between Hsa and alpha2-3-linked sialic acid-containing proteins of erythrocytes. We expressed recombinant NR2, which is the putative binding domain of Hsa, fused with GST in Escherichia coli BL21. Dot-blot analysis demonstrated that GST-HsaNR2 binds both glycophorin A (GPA) and band 3. Moreover, GPA and a small amount of band 3 were detected by GST pull-down assays. These findings indicate that S. gordonii Hsa specifically binds to GPA and band 3, alpha2-3-linked sialic acid membrane glycoproteins.