Inhibitory effect of bovine milk lactoferrin on the interaction between a streptococcal surface protein antigen and human salivary agglutinin

Human whole saliva induces aggregation of Streptococcus mutans cells via an interaction between a surface protein antigen (PAc) of the organism and sa livary agglutinin, Bovine milk inhibits the saliva-induced aggregation of S , mutans, In this study, the milk component that possesses inhibitory activ ity against this aggregation was isolated and found to be lactoferrin, Surf ace plasmon resonance analysis indicated that bovine lactoferrin binds more strongly to salivary agglutinin, especially to high molecular mass glycopr otein, which is a component of the agglutinin, than to recombinant PAc. The binding of bovine lactoferrin to salivary agglutinin was thermostable, and the optimal pH for binding was 4.0, To identify the saliva-binding region of bovine lactoferrin, 11 truncated bovine lactoferrin fragments were const ructed. A fragment corresponding to the C-terminal half of the lactoferrin molecule had a strong inhibitory effect on the saliva-induced aggregation o f S. mutans, whereas a fragment corresponding to the N-terminal half had a weak inhibitory effect. Seven shorter fragments corresponding to lactoferri n residues 473-538 also showed a high ability to inhibit the aggregation of S. mutans. These results suggest that residues 473-538 of bovine lactoferr in are important in the inhibition of saliva-induced aggregation of S. muta ns.