Glucosylation of catechol with the GTFA glucansucrase enzyme from Lactobacillus reuteri and sucrose as donor substrate

Lactic acid bacteria use glucansucrase enzymes for synthesis of gluco-oligosaccharides and polysaccharides (α-glucans) from sucrose. Depending on the glucansucrase enzyme, specific α-glucosidic linkages are introduced. GTFA-ΔN (N-terminally truncated glucosyltransferase A) is a glucansucrase enzyme of Lactobacillus reuteri 121 that synthesizes the reuteran polysaccharide with (α1→4) and (α1→6) glycosidic linkages. Glucansucrases also catalyze glucosylation of various alternative acceptor substrates. At present it is unclear whether the linkage specificity of these enzymes is the same in oligo/polysaccharide synthesis and in glucosylation of alternative acceptor substrates. Our results show that GTFA-ΔN glucosylates catechol into products with up to at least 5 glucosyl units attached. These catechol glucosides were isolated and structurally characterized using 1D/2D 1H NMR spectroscopy. They contained 1 to 5 glucose units with different (α1→4) and (α1→6) glycosidic linkage combinations. Interestingly, also a branched catechol glucoside was formed and a catechol glucoside with 2 successive (α1→6) glycosidic linkages, products that are absent when only sucrose is used as both glycosyl donor and acceptor substrate