Development of Immunological Procedure for Prevention of Dental Caries Using Fusion Protein of Colonization Factors

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Cell-surface protein antigen (PAc) and glucosyltransferases (GTFs) produced by Streptococcus mutans are considered to be major colonization factors of the organism, and the inhibition of these two factors is predicted to provide protection against dental caries. In this study, we have constructed a fusion protein PAcA : GB of the salivabinding alanine-rich region (PAcA) of PAc and the glucan-binding (GB) domain of GTF-I,an enzyme catalyzing the synthesis of water-insoluble glucan from sucrose, and a fusion protein PAcA : SB of PAcA and the sucrose-binding (SB) domain of GTF-I.The recombinant fusion proteins were purified from cell extracts of Escherichia coli harboring the fusion genes, and rabbit antibodies against these fusion proteins were prepared. The water-insoluble glucan synthesis by cell-associated and cell-free GTF preparations from S.mutans and the total glucan synthesis by GTF-I was markedly inhibited by anti-PAcA : GB IgG antibodies, but not by anti-PAcA : SB IgG antibodies. Significant inhibition of the sucrose-independent and sucrose-dependent adhesion of S.mutans to saliva-coated hydroxyapatite beads was observed when anti-PAcA : GB antibodies were added to the reaction mixture. Anti-PAcA : SB antibodies inhibited the adhesion of S.mutans to the beads in the absence of sucrose, but did not in the presence of sucrose. Immunization with the fusion protein PAcA : GB may be useful for controlling the colonization of teeth by the organism.