Abstract
β-glucosidases catalyze the final step of cellulose hydrolysis and are essential in cellulose degradation. A β-glucosidase gene, cen502, was identified and isolated from a metagenomic library from Bursaphelenchus xylophilus via functional screening. Analyses indicated that cen502 encodes a 465 amino acid polypeptide that contains a catalytic domain belonging to the glycoside hydrolase family 1 (GH1). Cen502 was heterologously expressed, purified, and biochemically characterized. Recombinant Cen502 displayed optimum enzymatic activity at pH 8.0 and 38 °C. The enzyme had highest specific activity to p-nitrophenyl-β-D-glucopyranoside (pNPG; 180.3 U/mg) and had Km and Vmax values of 2.334 mol/ml and 9.017 μmol/min/mg, respectively. The addition of Fe2+ and Mn2+ significantly increased Cen502 β-glucosidase activity by 60% and 50%, respectively, while 10% and 25% loss of β-glucosidase activity was induced by addition of Pb2+ and K+, respectively. Cen502 exhibited activity against a broad array of substrates, including cellobiose, lactose, salicin, lichenan, laminarin, and sophorose. However, Cen502 displayed a preference for the hydrolysis of β-1,4 glycosidic bonds rather than β-1,3, β-1,6, or β-1,2 bonds. Our results indicate that Cen502 is a novel β-glucosidase derived from bacteria associated with B. xylophilus and may represent a promising target to enhance the efficiency of cellulose bio-degradation in industrial applications.
Highlights
Cen[502] displayed optimum enzymatic activity at pH 8.0 and 38 °C
Β-glucosidases (EC 3.2.1.21), which are widely distributed naturally, cleave the disaccharide cellobiose into two molecules of glucose that represent the end products of cellulose hydrolysis5–13. β-glucosidase activity is considered the rate-limiting factor in cellulose degradation by eliminating cellobiose inhibition on EGs and CBHs, allowing more efficient cellulolytic enzyme function
There has been little investigation of β-glucosidases from the pinewood nematode (PWN), Bursaphelenchus xylophilus (Bx), which feeds on plant cells of trees
Summary
Cen[502] displayed optimum enzymatic activity at pH 8.0 and 38 °C. The enzyme had highest specific activity to p-nitrophenyl-β-D-glucopyranoside (pNPG; 180.3 U/mg) and had Km and Vmax values of 2.334 mol/ml and 9.017 μmol/min/mg, respectively. A single clone, Cen[502], was obtained that expressed relatively strong β-glucosidase activity, as indicated by the production of the largest black halo in β-glucosidase screening (Fig. 1). The ORF comprised a full-length β-glucosidase gene (cen502) that encoded a protein consisting of 465 amino acids.
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