IMMUNOLOGICAL CHARACTERISTICS OF A STREPTOCOCCUS-MUTANS GLUCOSYLTRANSFERASE-B SUCROSE-BINDING SITE PEPTIDE-CHOLERA TOXIN B-SUBUNIT CHIMERICPROTEIN

Glucosyltransferases (Gtfs) produced by the mutans streptococci are re cognized as virulence factors in dental caries, and the inhibition of Gtfs by secretory immunoglobulin A is predicted to provide protection against this disease, The basis of such mucosal immunity is linked to the ability to reliably stimulate production of secretory immunoglobul in A against Gtfs. In this regard, we are exploring tile immungeniciti es of various Gtf peptides genetically fused to the B subunit of chole ra toxin (CTB), a known mucosal adjuvant, In this work, we have create d a gene fusion linking the GtfB active-site (AS) peptide DANFDSIRVDAV DNVDADLLQIA to the amino terminus of CTB. This sequence, deduced from the nucleotide sequence of gtfB from Streptococcus mutans GS5, has bee n found to be strongly conserved in Gtfs from several mutans streptoco cci, We have purified this recombinant protein (AS:CTB) from Escherich ia coli carrying the fusion gene under the control of the lactose oper on promoter, This protein was immunogenic in rabbits and produced spec ific serum antibodies against both the Gtf peptide and the CTB moiety. The antiserum was tested for its ability to inhibit GtfB activity obt ained from a mutant of S. mutans able to make only this enzyme and non e of the other usual Gtfs or fructosyltransferase. Approximately 50% o f the GtfB activity tvas inhibited in such assays. These results sugge st that the AS of this enzyme is accessible to antibody binding and th at this region of the protein may be considered a vulnerable target fo r vaccine design and development, The AS:CTB was able to bind GM(1) ga nglioside in enzyme-linked immunosorbent assays, indicating that tile recombinant protein retained this property, which is thought to be cri tical to the mucosal immunoadjuvant properties of CTB, Thus, this prot ein may be promising as a candidate anticaries vaccinogen alone or in combination with other Gtf peptides or conjugates.