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 fusion
protein PAcA-GB, a fusion of the saliva-binding
alanine-rich region (PAcA) of PAc with the
glucan binding (GB) domain of GTF-I, an
enzyme catalyzing the synthesis of water-insoluble
glucan from
sucrose, and fusion
protein PAcA-SB, a fusion of PAcA with 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. Water-insoluble
glucan synthesis by cell-associated and cell-free GTF preparations from S. mutans as well as total
glucan synthesis by GTF-I was markedly inhibited by anti-PAcA-GB
immunoglobulin G (
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 not in the presence of
sucrose. Immunization with the fusion
protein PAcA-GB may be useful for controlling the colonization of teeth by S. mutans.