Journal
GLYCOBIOLOGY
Volume 26, Issue 11, Pages 1157-1170Publisher
OXFORD UNIV PRESS INC
DOI: 10.1093/glycob/cww074
Keywords
Bradyrhizobium diazoefficiens; beta-D-glucans; non-Leloir beta-glucosyltransferase; oligosaccharide synthesis; structural analysis
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Funding
- EU [265992 AMYLOMICS]
- Icelandic Research Fund [70209021, 141341-052]
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Recently, we have shown that glycoside hydrolases enzymes of family GH17 from proteobacteria (genera Pseudomonas, Azotobacter) catalyze elongation transfer reactions with laminarioligosaccharides generating (beta 1 -> 3) linkages preferably and to a lesser extent (beta 1 -> 6) or (beta 1 -> 4) linkages. In the present study, the cloning and characterization of the gene encoding the structurally very similar GH17 domain of the NdvB enzyme from Bradyrhizobium diazoefficiens, designated Glt20, as well as its catalytic properties are described. The Glt20 enzyme was strikingly different from the previously investigated bacterial GH17 enzymes, both regarding substrate specificity and product formation. The Azotobacter and Pseudomonas enzymes cleaved the donor laminarioligosaccharide substrates three or four moieties from the non-reducing end, generating linear oligosaccharides. In contrast, the Glt20 enzyme cleaved donor laminari-oligosaccharide substrates two glucose moieties from the reducing end, releasing laminaribiose and transferring the remainder to laminari-oligosaccharide acceptor substrates creating only (beta 1 -> 3)(beta 1 -> 6) branching points. This enables Glt20 to transfer larger oligosaccharide chains than the other type of bacterial enzymes previously described, and helps explain the biologically significant formation of cyclic beta-glucans in B. diazoefficiens.
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