Identification and Characterization of a Glycoside Hydrolase Family 9 Member from the Digestive Gland of the Snail Achatina fulica

Biomass-degrading enzymes can aid the development of new technologies to increase the production efficiency of green fuels like ethanol. This study reports the identification and characterization of a novel glycoside hydrolase family 9 (GH9) member from the digestive gland of the snail Achatina fulica, an endo-β-1,4-glucanase named AfEG66. The enzyme has a high level of identity with other mollusk endoglucanases and harbors a family 2 carbohydrate-binding module (CBM2) linked to a GH9 domain. Recombinant AfEG66 was expressed in Escherichia coli and purified by immobilized metal ion affinity chromatography followed by ion exchange chromatography. The enzyme was active against barley β-glucan, lichenan, and showed a specific activity of 41.56 ± 1.21 IU/mg towards carboxymethyl cellulose. AfEG66 showed higher activities at pH 6.0–6.5 and 45 °C, being stable at temperatures equal or below 37 °C. The enzyme activity on cello-oligosaccharides with different glucose units was evaluated by thin-layer chromatography and showed the hydrolysis of substrates containing at least three glucose residues. A structural model was obtained to perform docking assays that clarified the hydrolytic properties of this enzyme. The results presented here show that A. fulica has an endogenous cellulase gene that encodes a GH9 endoglucanase associated to a putative CBM2 with β-1,4 glycoside hydrolase activity.