Glycosylation of caffeic acid and structural analogues catalyzed by novel glucansucrases from Leuconostoc and Weissella species

Abstract

Twelve Leuconostoc and seven Weissella strains with extracellular glucansucrase activity were obtained from an analysis of 41 lactic acid bacteria. Culture supernatants of all glucansucrase positive strains catalyzed the glycosylation of caffeic acid with sucrose as donor substrate. Eighteen enzymes produced one major peak, which was identified as caffeic acid-4′-O-α-D-monoglucoside by LC-MS and NMR spectroscopy. Only W. beninensis DSM 22752 formed significant amounts of the corresponding 3´-O-α-D-monoglucoside. The Weissella strain and five Leuconostoc strains with high glycosylation activity were selected for further studies. All glucansucrases catalyzed the glycosylation of the catechol protocatechuic acid, a side-chain truncated analogue of caffeic acid. The Leuconostoc enzymes displayed a preference for the 4′-O-α-D isomer, while the DSM 22752 glucansucrase also produced the protocatechuic acid-3′-O-α-D-monoglucoside. Lower activities with non-catecholic caffeic acid derivatives and no activity with mono-methylated caffeic acid were observed with all glucansucrases. Time-course analyses confirmed that glucansucrase from L. citreum DSM 5577 was the most efficient biocatalyst for catechol glucosylation with yields of up to 74% caffeic acid glucosides after 24 h. The enzyme displayed a high regio-preference for the 4′-O-α-d-isomer and formed less than 10% oligoglucosides. Gel electrophoretic analysis and activity staining of the PEG-enriched enzyme showed a single protein band with a molecular mass of 171 kDa. The DSM 5577 glucansucrase was tolerant against the co-solvents dimethyl sulfoxide and ethanol. Kinetic analysis revealed a KM of 27.6 mM for caffeic acid and 31 mM for sucrose with kcat values of 131 s−1 and 438 s−1.