Insoluble glucan synthesis by Streptococcus mutans serotype c strains

Abstract

Both dextransucrase and mutansynthetase activities have been purified from the culture fluids of Streptococcus mutans GS-5 (serotype c). Although homogeneous dextransucrase preparations normally synthesize little insoluble glucan, essentially all of the glucan synthesized by this enzyme in the presence of 1.5 M (NH4)2SO4 was water insoluble. Linkage analysis of the insoluble glucans indicated that the presence of NH4' increased the portion of ca-1,3-glucose linkages relative to a-1,6-glucose units in the product. Chromatofocusing of aggregated glucosyltransferase fractions synthesizing predominantly insoluble glucan yielded primarily dextransucrase activity separable from relatively low levels of mutansynthetase activity. The latter enzyme was detected only in 18-h assays and synthesized primer-dependent insoluble glucan, which was decreased in the presence of NH4+. In the absence of primer dextran T10, the addition of dextransucrase also stimulated insoluble glucan synthesis by mutansynthetase. Dextransucrase and mutansynthetase appear to be distinct enzymes, since the latter possesses a higher molecular weight (155,000 compared to 140,000), a much lower isoelectric point, and did not cross-react with antibody directed against dextransucrase. These results are discussed relative to the mechanism of insoluble glucan synthesis by S. mutans serotype c strains.

Molecular analyses of glucosyltransferase genes among strains of Streptococcus mutans

“…It was notable that the catalytic domain was completely conserved in the alignments in these three di¡erent types of GTases. The glucan binding domain is composed of a series of repeat sequences called direct repeating units and each unit contains approximately 65 amino acids with high proportions of hydroxy amino acid [10]. Similar repeating units are also found in a glucan binding protein of S. mutans [12] and the carboxyl-terminal region of Clostridium di¤cile toxin A and B [13].…”

“…Although information about GTase genes of S. mutans has been accumulated using a single strain GS-5 [10], no extensive comparative sequence analyses have been performed. In this study, we cloned the three GTase genes from several strains of S. mutans representing serotype c, e, or f, and comparison of the sequences was performed.…”

Utilization of a mini‐mu transposon to construct defined mutants in Streptococcus mutans

“…Streptococcus mutans. produce glucosyltransferase (EC 2,4.1.5; GTF) activities which catalyse the formation of extracellular glucans (Ciardi, 1983), Previous results {Fukushima et al, 1981;Kuramitsu and Wondrack. 1983) have indicated that the glucans involved in colonization are synthesized by the concerted action of at least two distinct GTFs: GTF-I producing primarily a-1,3-linked glucans and GTF-S synthesizing a-1.6-glucans.…”

Construction of Streptococcus mutans glucosyltransferase mutants utilizing a cloned gene fragment

“…The present communication describes a procedure based on a strategy recently utilized in this laboratory for mapping cloned genes of S. mutans GS-5 [5] for generating mutants defective in GTF-I activity [6]. Although mutants defective in GTF activity have been previously described [3], the nature of the genetic lesions involved remains unknown.…”