β-Glucosidase, exo-β-glucanase and pyridoxine transglucosylase activities of rice BGlu1

Abstract

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.