title: Affinity and specificity of the interactions between Streptococcus mutans antigen I/II and salivary components.
abstract: Adherence to salivary pellicle-coated tooth surfaces and aggregation by salivary components of Streptococcus mutans involves a major cell surface protein termed antigen (Ag) I/II. The objectives of this study were to evaluate the affinity and specificity of the interactions between AgI/II and human saliva in assays of 125I-AgI/II binding to saliva-coated hydroxyapatite (SHA) and of S. mutans aggregation by salivary agglutinin (SAG), monitored turbidimetrically. 125I-AgI/II binding to SHA followed saturation kinetics, and Scatchard plot analysis indicated two binding sites with dissociation constants of the order of 10(-10) mol/L and 10(-9) mol/L. The binding to SHA of the C-terminal one-third of AgI/II which corresponds to AgII was less than one-fifth that of the whole molecule and did not show evidence of saturation. The binding of 125I-AgI/II was inhibited by native or recombinant fragments that mapped in the N-terminal part of the molecule and that contained the alanine-rich repeat region, whereas fragments mapping at the central or C-terminal one-third had no effect. As with binding to SHA, the regions of AgI/II which inhibited aggregation mapped at the N-terminal part of the molecule, but, in addition, a recombinant segment mapping at the central part and containing the proline-rich repeat region was also inhibitory. The S. mutans-aggregating activity of SAG or whole saliva was inhibited by amino compounds, and most strongly by L-lysine and analogues possessing omega-primary amine groups. These data support the role of AgI/II as an adhesin with high-affinity binding for SHA receptors, mediated by the N-terminal part of the molecule. This region is also involved in SAG-induced S. mutans aggregation, which is sensitive to amino compounds.
authors.affiliation: Department of Microbiology, University of Alabama at Birmingham 35294-2170.
authors.forename: G
authors.initials: G
authors.lastname: Hajishengallis
authors.forename: T
authors.initials: T
authors.lastname: Koga
authors.forename: M W
authors.initials: MW
authors.lastname: Russell
mesh_terms: D018829:Adhesins, Bacterial / Q000276:immunology; D000373:Agglutinins / Q000378:metabolism; D000942:Antigens, Bacterial / Q000276:immunology*; D001422:Bacterial Adhesion / Q000187:drug effects / Q000276:immunology; D001426:Bacterial Proteins / Q000276:immunology*; D002241:Carbohydrates / Q000494:pharmacology; D044622:Dental Pellicle; D004306:Dose-Response Relationship, Immunologic; D017886:Durapatite / Q000737:chemistry; D000939:Epitopes; D006801:Humans; D007457:Iodine Radioisotopes; D007700:Kinetics; D008239:Lysine / Q000494:pharmacology; D011485:Protein Binding; D011946:Receptors, Antigen / Q000276:immunology; D011994:Recombinant Proteins; D012463:Saliva / Q000276:immunology*; D012709:Serum Albumin / Q000378:metabolism; D013295:Streptococcus mutans / Q000276:immunology*
chemical_list: D018829:Adhesins, Bacterial; D000373:Agglutinins; D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D002241:Carbohydrates; D000939:Epitopes; D007457:Iodine Radioisotopes; D011946:Receptors, Antigen; D011994:Recombinant Proteins; D012709:Serum Albumin; D017886:Durapatite; D008239:Lysine