Analysis of functional domains of Streptococcus sobrinus glucosyltransferase U

The group of enzymes collectively called glucosyltransferases (GTF) plays an important role in dental plaque formation and colonization of cariogenic bacteria on the tooth surface. Streptococcus mutans and Streptococcus sobrinus are predominant mutans streptococci species presented in the human oral cavity. Three kinds of GTFs (GtfB, GtfC, and GtfD) are from S. mutans, and 4 kinds (GTFI, GTFS, GTFT, and GTFU) from S. sobrinus. Recently, the gtfU gene has been molecularly cloned, and nucleotide sequences of the gene were completely analyzed. Thus, all gtf genes are now defined in the DNA database. Detailed information of structure and function of GTFs is important not only in evaluating the nature of virulence but also for the development of a vaccine against dental caries. GTFs have 3 major functional domains, including an N-terminal highly variable region (CD1), a conserved core catalytic region (CD2), and a C-terminal glucan-binding region (GBD). In this study, 3 functional domains in 7 GTFs were compared from motif search results using a protein motif database Pfam. Putative catalytic domains CD1 and CD2 were well maintained in all 7 GTFs while numbers of putative GBD repeat were different in GTFs, and GTFU has a large number of the repeat.