Molecular cloning and characterization of a glycosyl hydrolase family 9 cellulase distributed throughout the digestive tract of the cricket Teleogryllus emma

A novel endogenous β-1,4-endoglucanase (EG) gene belonging to the glycosyl hydrolase family 9 (GHF 9) that is distributed throughout the digestive tract of the cricket Teleogryllus emma was cloned and characterized. This gene, named TeEG-I, consists of eight exons encoding 453 amino acid residues and exists as a single copy in the T. emma genome. TeEG-I possesses all the features, including signature motifs and catalytic domains, of GHF 9 members, sharing high levels of identity with the termite, Mastotermes darwiniensis (64% protein sequence identity), and the cockroach, Panesthia cribrata (62%), GHF 9 cellulases. Recombinant TeEG-I, which is expressed as a 47-kDa polypeptide in baculovirus-infected insect Sf9 cells, showed an optimal pH and temperature of pH 5.0 and 40 °C. The K_m and V_max values for digestion of carboxymethyl cellulose were 5.4 mg/ml and 3118.4 U/mg, respectively. Northern and Western blot analyses revealed that TeEG-I is present throughout the digestive tract, which correlated with the TeEG-I distribution and cellulase activity in the digestive tract as assayed by immunofluorescence staining and enzyme activity assay, respectively. These results indicate that TeEG-I is distributed throughout the entire digestive tract of T. emma, suggesting a functional role of endogenous TeEG-I in a sequential cellulose digestion process throughout the T. emma digestion tract.