Characterization of a lichenase isolated from soil metagenome.

A lichenase gene (mt-lic) was identified for the first time through function-based screening of a soil metagenomic library. Its deduced amino acid sequence exhibited a high degree of homology with endo-β-1,3-1,4-glucanase (having both lichenase and chitosanase activities), encoded by the bgc gene of Bacillus circulans WL-12. The recombinant lichenase overexpressed and purified from Escherichia coli was able to efficiently hydrolyze both barley β-glucan and lichenan. The enzyme showed maximal activity at a pH of 6.0 at 50°C, with Azo-barley-glucan as the substrate. The metal ions Mn(2+), Mg(2+), Ca(2+), and Fe(2+) enhanced the enzymatic activity, whereas the Cu(2+) and Zn(2+) ions inhibited the enzymatic activity. The Km and Vmax values of the purified lichenase were determined to be 0.45 mg/ml and 24.83 U/min/mg of protein, respectively.