Three-dimensional modelling of the catalytic domain of Streptococcus mutans glucosyltransferase GtfB

Glucosyltransferases (GtfB/C/D) of Streptococcus mutans, a pathogen for human dental caries, synthesize water-insoluble glucan through
the hydrolysis of sucrose. Genetic and biochemical approaches have identified several active sites of these enzymes, but no three-dimensional
(3D) structural evidence is yet available to elucidate the subdomain arrangement and molecular mechanism of catalysis. Based on a
combined sequence and secondary structure alignment against known crystal structures of segments from closely related proteins, we
propose here the 3D model of an N-terminal domain essential for the sucrose binding and splitting in GtfB. A Tim-barrel of (K/L)8
structural characteristics is revealed and the structural correlation for two peptides is described.