Purification and characterization of a thermostable intra-cellular beta-glucosidase with transglycosylation properties from filamentous fungus Termitomyces clypeatus

摘要

An intra-cellular p-glucosidase was purified to homogeneity by gel filtration, ion exchange chromatography and HPGPLC from mycelial extract of Termitomyces clypeatus in the presence of the glycosylation inhibitor 2-deoxy-d-glucose. CD spectroscopy demonstrated that the purified enzyme exhibited alpha-helical conformation. MALDI-TOF identified the enzyme's molecular weight as 6688 Daltons, but SDS-PAGE and immunoblotting indicated that the enzyme formed aggregates. The enzyme also showed unique properties of co-aggregation with sucrase in the fungus. The enzyme showed around 80% stability up to 60 degrees C and residual activity was 80-100% between pH ranges 5-8. The enzyme had higher specific activity against p-nitrophenyl-D-glucopyranoside than cellobiose and HPLC showed that the enzyme possesses transglycosylation activity and synthesizes cello-oligosaccharides by addition of glucose. The enzyme will be useful in synthetic biology to produce complex bioactive glycosides and to avoid chemical hazards. This is the first report of a beta-glucosidase enzyme with such a low monomeric unit size.