Lactose- and cellobiose-derived branched trisaccharides and a sucrose-containing trisaccharide produced by acceptor reactions of Weissella confusa dextransucrase

Dextran-producing Weissella have received significant attention. However, except for maltose, the acceptor reactions of Weissella dextransucrases with different sugars have not been investigated. The action of recombinant Weissella confusa VTT E-90392 dextransucrase was tested with several potential acceptors, particularly, analogs lactose and cellobiose. The major acceptor products of both disaccharides were identified as branched trisaccharides, with a glucosyl residue α-(1→2)-linked to the acceptor's reducing end. An additional product, isomelezitose (6Fru-α-Glcp-sucrose), was also produced when using lactose as an acceptor. This is the first report of the synthesis of isomelezitose by a dextransucrase. The NMR spectra of the three trisaccharides were fully assigned, and their structures were confirmed by selective enzymatic hydrolysis. The trisaccharides prepared from 13C6glc sucrose and lactose were analyzed by ESI-MSn, and the fragmentation patterns of these compounds were characterized.