Mutastein, a new inhibitor of adhesive-insoluble glucan synthesis by glucosyltransferases of Streptococcus mutans.

Mutastein, a new inhibitor of glucosyltransferases (GTase) of Streptococcus mutans, was isolated from cultural broth of Aspergillus terreus M3328.Mutastein was a heat-stable protein and was sensitive to pronase digestion.In the formation of glucans, that of adhesive waterinsoluble glucans of S. mutans was specifically inhibited by mutastein.Water-insoluble glucans (IG) synthesized by Streptococcus mutans form sucrose are known to be a major virulence factor for induction of dental caries in man and animals.'"')These glucans, which are synthesized by the action of glucosyltransferases (GTase) of S. mutans, firmly coat the tooth surfaces, forming a barrier which prevents the diffusion of acids produced by the bacteria.Many chemical and enzymatic procedures for eliminating S. mutans from tooth surfaces have been explored.3)Among these approaches, several were related to active compounds that specifically inhibit GTase, which include periodate-oxidized clinical dextran,4) several amino sugars5) and a-glucosidase inhibitors of microbial origin.6)Recently, OKAMI et al.7) isolated a specific GTase inhibitor, ribocitrin, from a culture filtrate of a strain of Streptomyces sp.In the course of search for substances that inhibit GTase activity of S. mutans, we found a new inhibitor, named mutastein, in the culture filtrate of a strain of Aspergillus terreus.This report describes the isolation of mutastein and its effects on IG synthesis from sucrose by cell-free GTase of S. mutans. Materials and MethodsPreparation of Cell-free GTase S. mutans B13, serotype d (kindly supplied by K. FUKUSHIMA, Nihon University School of Dentistry, Matsudo, Chiba-ken) was grown at 37°C for 18 hours in brain heart infusion (BHI) broth (Nissui Medical Co., Tokyo).To produce cell-free GTase, the culture supernatant was brought to 60% saturation with (NH4)2SO4.The precipitate formed was isolated by centrifugation, dissolved in 5 mM potassium phosphate buffer (KPB), pH 6.5, and dialyzed against the same buffer.The preparations were stored at -80°C until use.