Changes in linkage pattern of glucan products induced by substitution of Lys residues in the dextransucrase

Dextransucrase S (DSRS) is the only active glucansucrase that has been found in Leuconostoc mesenteroides NRRL B‐512F strain. Native DSRS produces mainly 6‐linked glucopyranosyl residue (Glc p ), while Escherichia coli recombinant DSRS was observed to produce a glucan consisting of 70% 6‐linked Glc p and 15% 3,6‐Glc p . Lys residues were introduced at the N‐terminal end of the core domain by site‐directed mutagenesis. In glucans produced by the one‐point mutants T350K and S455K, the amount of 6‐linked Glc p was increased to about 85% of the total glucan produced, more similar in structure to native B‐512F dextran. The double mutant T350K/S455K produced adhesive, water‐insoluble glucan with 77% 6‐linked Glc p , 8% 3,6‐linked Glc p and 4% 2,6‐linked Glc p . The T350K/S455K mutant exhibited a 10‐fold increase in glucosyltransferase activity over those of the parental DSRS‐His 6 and its T350K and S455K mutants. This is the first report demonstrating a change in the properties of a dextransucrase or a related glucosyltransferase through simple site‐directed mutagenesis to create 2,6‐linked Glc p .