The bglu1 cDNA for a β-glucosidase cloned from rice (Oryza sativa L.) seedlings was expressed as a soluble and active protein in Escherichia coli and designated BGlu1. This enzyme hydrolysed β-1,4-linked oligosaccharides with increasing catalytic efficiency (kcat/Km) values as the DP (degree of polymerization) increased from 2 to 6. In contrast, hydrolysis of β-1,3-linked oligosaccharides decreased from DP 2 to 3, and polymers with a DP greater than 3 were not hydrolysed. The enzyme also hydrolysed p-nitrophenyl β-d-glycosides and some natural glucosides but with lower catalytic efficiency than β-linked oligosaccharides. Pyridoxine 5´-O-β-d-glucoside was the most efficiently hydrolysed natural glycoside tested. BGlu1 also had high transglucosylation activity towards pyridoxine, producing pyridoxine 5´-O-β-d-glucopyranoside in the presence of the glucose donor p-nitrophenyl β-d-glucoside.
Abbreviations used: Ai, subsite affinity; DP, degree of polymerization; GH, glycosyl hydrolase; pNP, p-nitrophenyl; pNPG, p-nitrophenyl β-d-glucoside; H,H-COSY, two-dimensional homonuclear correlation spectroscopy; HMQC, heteronuclear multiple quantum coherence; HMBC, heteronuclear multiple bond correlation.