15. Enzymatic Transglycosylation for Synthesis of Novel Glycosides from Renewable Galacto- and Glucomannan
Hemicellulose, such as softwood galactoglucomannan is promising renewable bioresource. Degradation is possible with a combination of Glycoside Hydrolases (GHs), e.g family GH27 ɑ-galactosidase and GH5 β-mannanase in cooperation. These enzymes can also synthesize new glycosidic bonds during the catalysis in the presence of other acceptor molecules besides water, referred to as transglycosylation. In our work, we have demonstrated synergy between α-galactosidase and β-mannanase in formation of transglycosylation products using galactomannan as donor substrate through covalent fusion of mannose or galactose units to allyl alcohol.
We have shown that using HPLC for product screening in conjunction with NMR for structural determination of novel glycosides is a powerful approach for monitoring this reaction. Coincubation of GHs with complimentary activities has potential to result in improved substrate conversion and increased synthesis yields of allyl glycosides. These reactive glycosides could be utilized for downstream applications such as production of biomaterials and for surface modification. Furthermore, an engineered subsite +1/+2 variant of Trichoderma reesei B-mannanase TrMan5A showed enhanced allyl mannoside synthesis capacity, when compared to the wild-type. This application allows for generation of numerous different novel glycosides such as using allyl- or propargyl alcohol as the acceptor, allowing for downstream application in thiol-ene or -yne click chemistry respectively.