Gene cloning and characterization of a cold-adapted β-glucosidase belonging to glycosyl hydrolase family 1 from a psychrotolerant bacterium Micrococcus antarcticus

The gene bgIU encoding a cold-adapted beta-glucosidase (BgIU) was cloned from Micrococcus antarcticus. Sequence analysis revealed that the bgIU contained an open reading frame of 1419 bp and encoded a protein of 472 amino acid residues. Based on its putative catalytic domains, BgIU was classified as a member of the glycosyl hydrolase family 1 (GH1). BgIU possessed lower arginine content and Arg/(Arg + Lys) ratio than mesophilic GH1 beta-glucosidases. Recombinant BgIU was purified with Ni2+ affinity chromatography and subjected to enzymatic characterization. SDS-PAGE and native staining showed that it was a monomeric protein with an apparent molecular mass of 48 kDa. BgIU was particularly thermolabile since its half-life time was only 30 min at 30 degrees C and it exhibited maximal activity at 25 degrees C and pH 6.5. Recombinant BgIU could hydrolyze a wide range of aryl-beta-glucosides and beta-linked oligosaccharides with highest activity towards cellobiose and then p-nitrophenyl-beta-D-glucopyranoside (pNPG). Under the optimal conditions with pNPG as substrate, the K-m and k(cat) were 7 mmol/L and 7.85 x 103/s, respectively. This is the first report of cloning and characterization of a cold-adapted beta-glucosidase belonging to GH1 from a psychrotolerant bacterium. (C) 2011 Elsevier Inc. All rights reserved.