A D-glucose- and D-xylose-tolerant GH1 β-glucosidase from Cellulosimicrobium funkei HY-13, a fibrolytic gut bacterium of Eisenia fetida

Abstract

The GluM gene (1491-bp) coding for a β-glucosidase comprising a single catalytic glycoside hydrolase family 1 domain from an earthworm (Eisenia fetida)-symbiotic bacterium, Cellulosimicrobium funkei HY-13, was cloned and over-expressed in Escherichia coli BL21. The recombinant histidine-tagged enzyme (rGluM: 56 kDa) displayed the highest cleavage activity toward p-nitrophenyl (pNP)-β-D-glucopyranoside at pH 5.0 and 40 °C. The β-glucosidase activity of rGluM was enhanced over 1.8-fold of its original activity in the presence of 1 mM Ca2+, Ni2+, Mn2+, and Co2+ ions, respectively, while it was highly sensitive to 5 mM N-bromosuccinimide and 1 mM Hg2+. The susceptibility of some pNP-sugar derivatives and D-cellobiose to rGluM was evaluated to be in the order of pNP-β-D-glucopyranoside > pNP-β-D-galactopyranoside > D-cellobiose > pNP-β-D-cellobioside > pNP-β-D-mannopyranoside. The kcat/Km values of rGluM toward pNP-β-D-glucopyranoside, pNP-β-D-galactopyranoside, and D-cellobiose were 302.28, 179.73, and 6.40 mM-1 s-1, respectively. At a concentration below 1.0 M, D-galactose was a potent activator of rGluM with β-glucosidase activity enhanced by approximately 160% in a dose-dependent manner. Moreover, the D-glucose (< 400 mM) and D-xylose (≤ 700 mM) stimulation of rGluM suggests that it can be exploited as a potential biocatalyst to generate D-glucose molecules in D-cellobiose degradation.