Expression and characterization of recombinant β-glucosidases from Aspergillus nidulans AN2227

Abstract

Recombinant β-glucosidase (EC 3.2.1.21) from Aspergillus nidulans AN2227 was expressed using Buffered Methanol Complex Medium (BMMY). Purification was conducted using ammonium sulphate precipitation and anion exchange chromatography on DEAE-Sephadex A-50 column. The enzyme was purified 2.58 fold from the crude extract. β-glucosidase was purified to electrophoretic homogeneity and had a relative molecular weight of 100 kDa as determined by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). The enzyme had an optimum pH and temperature of 6.0 and 40 ^oC respectively. The most striking characteristics of this enzyme are the dramatically broad pH and temperature profile. The enzyme also had a K_m of 0.42 mM for 4-Nitrophenyl-β-D-glucopyranoside (pNPG). The activity of the enzyme was inhibited by HgCl₂ and slightly activated by CoCl₂, FeCl₃, CaCl₂, FeCl₂ and ZnCl₂ suggesting that the enzyme may not be a metalloprotein and therefore does not require metal ions for optimum activity.

Keywords: Aspergillus nidulans, Cellulase, β-glucosidase, p-nitrophenol-β-glucopyranoside.