[ODP-099] Diversity of the binding region in Hsa adhesin and its homologs among oral streptococcal strains
Dental plaque formation is initiated by the adhesion of early colonizers, such as mitis group streptococci, to acquired pellicle on the tooth surface. Hsa adhesin has been identified as a fibrillar antigen associated with the hemagglutinating (HA) activity of Streptococcus gordonii DL1. Hsa binds to the terminal sialic acid of host receptors, such as salivary mucin, via its NR2 (non-repetitive region 2). In this study, we analyzed the NR2-like region of 30 antigenically NR2-positive mitis group streptococcal strains. Nucleotide sequences encoding the NR2-like region were determined, resulting that the deduced amino acid sequences are similar but not identical to the NR2 sequence of DL1, and were classified into four groups according to their sequences. Almost all the NR2-positive S. gordonii strains showed relatively high or medium HA activity, that was inhibited by 3’-sialyllactose indicating that the HA activity is α2-3-linked sialic acid-dependent. In contrast, strains other than S. gordonii showed only low or medium HA activity, some of the latter was inhibited only when using relatively high concentrations of 3’-sialyllactose, implying the relatively low specificity, or the existence of other adhesins associated with HA activity. These results suggested that some of the mitis group streptococci possessed the HA activity via diversified NR2-like region of the Hsa homologs.