May bind sialic acid residues of salivary agglutinin (SAG) in a calcium-dependent reaction. The interaction of SAG with its receptor in various oral streptococci modulate bacterial colonization of oral tissue and is associated with reduced levels of dental caries. Interacts with P.gingivalis fimbrial protein Mfa1. S.gordonii, a commensal oral cavity bacteria, is among the bacteria most frequently identified as being the primary etiological agents of subacute infective endocarditis (found in 13% of cases). Belongs to the antigen I/II family.