Effects of antibodies to glucosyltransferase on soluble and insolubilized enzymes

Previous studies have shown that glucosyltransferase enzymes (Gtfs) of Streptococcus mutans adsorbed to saliva coated hydroxyapatite (sHA) have distinct properties from the same enzymes in solution. The purpose of the present study was to determine the effects on enzyme activity of polyclonal antibodies raised to Gtfs in a soluble form and bound to sHA.

Antiserum was raised in six New Zealand White rabbits using the purified glucosyltransferase enzymes (Gtfs) of S. mutans, GtfB, GtfC, or GtfD as soluble antigens or adsorbed to hydroxyapatite (HA, insolubilized). The antisera were examined for their ability to react to these Gtfs and Gtf from Streptococcus sanguis (GtfSs) in Western blot formats as well as inhibit enzyme activity in solution and insolubilized.

Antibodies raised against GtfB or GtfC detected all Gtf enzymes examined in Western blots; antibodies raised to GtfD reacted strongly to GtfD and GtfSs, poorly to GtfC, and was non-reactive with GtfB. Antibodies to GtfB or GtfC inhibited activity of GtfB and GtfC in solution by 90% or more. Enzyme activity adsorbed to sHA was inhibited from 70% to 80% by the same antisera. These same antibodies possessed no specific effect on the activities of either GtfD or GtfSs. Antibodies raised to the GtfD enzyme inhibited activity of GtfD (80% to 90% inhibition) and GtfSs activity (50% to 80%) in solution. In contrast the GtfD antibodies had no effect on the activity of either GtfB or GtfC enzymes in solution. Modest inhibitory effects were noted on GtfC and GtfSs enzymes bound to sHA, but no inhibition was observed for sHA-bound GtfB or GtfD.

These data show that some antibodies effective against enzymes in solution may have significantly lesser inhibitory effects against the same enzymes insolubilized. Further, presentation of Gtf antigen immobilized to HA has only a minor influence on the production of antibodies inhibitory to Gtf activity.