Water-soluble and water-insoluble glucans produced by Escherichia coli recombinant dextransucrases from Leuconostoc mesenteroides NRRL B-512F

Two dextransucrase genes, dsrS and dsrT5, from Leuconostoc mesenteroides NRRL B-512F were expressed in Escherichia coli, and recombinant dsrT5 dextransucrase was shown to produce a water-insoluble glucan. In contrast, native dextran from L. mesenteroides B-512F is water-soluble. The water-insoluble glucan was shown by 13C NMR and glycosyl-linkage composition analysis to contain about 50% 6-linked Glc p and 40% 3-linked Glc p. The ‘primitive’ B-512F strain is suggested to have produced water-insoluble glucan containing 3-linked Glc p. The glucans produced by dextransucrases expressed in E. coli contained 4-linked Glc p, as shown by glycosyl-linkage composition analysis. The amount of 4-linked Glc p was increased when the truncated, water-insoluble, glucan-producing dextransucrase, which does not have C-terminal repeating units, was added to the water-soluble, glucan-producing dextransucrase. Trace amounts of 4-linked Glc p were also detected in the dextran obtained from the B-512F culture supernatant, in dextran produced by dextransucrase purified from the B-512F strain culture supernatant, and in clinical dextran. The results of glycosyl-linkage composition analysis suggest that dextransucrases produce 4-linked Glc p as well as 6- and 3-linked Glc p. The glucan produced by recombinant DSRS was mostly water-soluble, and contained about 65% 6-linked Glc p, 10% 3,6-linked Glc p, and 15% 4-linked Glc p. The glucan produced by recombinant dextransucrase DSRT5 was mostly water-insoluble, and contained about 50% 6-linked Glc p and 40% 3-linked Glc p.