Identification and characterization of a new acid-stable endoglucanase from a metagenomic library

A new endoglucanase gene cel124 was cloned from a metagenomic library and expressed in Escherichia coli. Catalytic triad analysis showed that the catalytic triad sites were different from the known endoglucanases. Cel124, a 34 kDa protein, exhibited a specific activity (29.08 U mg(-1)) toward 1% of sodium carboxymethyl cellulose and was stable at 50 C for 30 mm. The optimal temperature and pH for its catalytic activity were 50 degrees C and pH 5.5 respectively. Cel124 could hydrolyze soluble cellulose, but not insoluble cellulose or other polysaccharides. The kinetic parameters (5.63 mg ml(-1) for K-m and 0.0397 mmol min(-1) mg(-1) for V-max) were measured. 3 M NaCl in the system could increase its activity by 2 fold. Site-directed mutation and circular dichroism spectra test suggested that the residue (Glu41) was essential for its activity, might be a potential active site. Based on our data, we proposed that Cell 24 might represent a new type of endoglucanase. (C) 2014 Elsevier Inc. All rights reserved.