A novel metagenome-derived beta-galactosidase: gene cloning, overexpression, purification and characterization.

A novel beta-galactosidase gene, zd410, was isolated by screening a soil metagenomic library. Sequence analysis revealed that zd410 encodes a protein of 672 amino acids with a predicted molecular weight of 78.6 kDa. The recombinant ZD410 was expressed and purified in Pichia pastoris, with a yield of ca. 300 mg from 1 L culture. The purified enzyme displayed optimal activity at 38 degrees C and pH 7.0. Given that the enzyme had 54% of the maximal activity at 20 degrees C and 11% of the maximal activity at close to 0 degrees C, ZD410 was regarded as a cold-adapted beta-galactosidase. ZD410 displays high enzymatic activity for its synthetic substrate-ONPG (o-nitrophenyl-beta-D-galactopyranoside, 243 U/mg) and its natural substrate-lactose (25.4 U/mg), while its activity was slightly stimulated by addition of Na(+), K(+), or Ca(2+) at low concentrations. ZD410 is a good candidate of beta-galactosidases for food industry after further study.