Influence of antibody on the structure of glucans

Glucosyltransferase (GTF) plays an essential role in the formation of the biofilm known as dental plaque and in the pathogenesis of dental caries. Mutans streptococci produce at least three distinct GTFs (GtfB, C and D), each of which forms a glucan polymer from sucrose. Glucan is a major constituent of plaque biofilm. GTF adsorbed to a surface forms glucans that differ in structure from those formed by the same enzyme in solution. In the present study, activities of GtfB and GtfC in solution or adsorbed on a surface were inhibited in the presence of a polyclonal antiserum (DS-1) to a mixture of GTFs and by immunoglobulin G (IgG) prepared from DS-1; in contrast, enzyme activity was enhanced by normal rabbit serum (NRS) and IgG from NRS. GtfD activity on a surface was enhanced by both antiserum DS-1 and NRS, and IgG prepared from either serum; GtfD activity in solution was slightly inhibited by each of the sera. The structure of GtfB and GtfC glucans formed in the presence of antiserum differed from that of controls based on linkage analyses, and on their susceptibilities to the glucanohydrolases mutanase (alpha-1,3 hydrolase) and dextranase (alpha-1,6 hydrolase); soluble products from the enzymatic digestion also differed. The results show that the effects of antibody on enzyme activity are more complex than simple inhibition or enhancement and that the presence of antibody may influence glucan structure, which clearly could impact plaque formation. The results have implications for the formation and properties of biofilms formed in other environments.