Structural elucidation of a water-insoluble glucan produced by a cariogenic oral Streptococcus

The structure of a water-insoluble polysaccharide produced by the D-glucosyl-transferase of Streptococcus mutans 6715 has been elucidated through periodate oxidation, Smith degradation, dextranase digestion, concanavalin A binding studies, and methylation combined with g.l.c.-m.s. analysis. These studies show that the D-glucan is comprised of 67% alpha-(1----3) linkages in a contiguous backbone with the remaining 33% as alpha-(1----6) linkages, possibly as linear residues extending from alpha-(1----6) branch points. Of the residues, 14% are branch points and the ratio of linear alpha-(1----3) residues in the backbone to alpha-(1----6) residues in the side chain was found to be 5:2. Dextranase digestion and Smith degradation both gave rise to a high-molecular-weight fraction that is only alpha-(1----3) linked.