Identification and characterization of a novel bifunctional cellulase/hemicellulase from a soil metagenomic library

Microbes, especially the uncultured microbes, have been considered as an important resource for discovery of novel cellulases. In this study, a novel bifunctional cellulase/hemicellulase (ZFYN184) was identified by functional screening of a soil metagenomic library. Sequence analysis indicated that ZFYN184 shared at best 39% identity with glycoside hydrolase family 44 (GH44) proteins and contained a glutamic acid residue at 235 acting as the catalytic proton donor in hydrolysis of polysaccharides. The recombinant ZFYN184 was expressed inEscherichia coliBL21 (DE3), and the biochemical profiles of the enzyme, including optimum pH and temperature, pH and thermal stabilities, tolerance to various additives, and substrate specificity, were determined. ZFYN184 possessed strong endo-beta-1,4-glucanase and endo-1,4-beta-mannanase activities, as well as weak xylanase activity, while all these hydrolytic activities were derived from a single catalytic domain in this GH44 enzyme.