Isolation and Characterization of an Acidic, Salt-Tolerant Endoglucanase Cel5A from a Bacterial Strain Martelella endophytica YC6887 Genome

A Martelella endophytica (M. endophytica) strain YC6887 was previously isolated from the roots of a halophyte, Rosa rugosa, which was sequenced and characterized. The genomic and proteomic analysis showed a carbohydrate-degrading enzyme, endoglucanase Cel5A which was further characterized. The protein analysis revealed that this endoglucanase belongs to glycosidic hydrolase family 5 (GH5) with catalytic domain. This gene encodes 349-residue polypeptide and shows closest similarity with cellulases of other Martelella species. The protein was purified to homogeneity and shown that it was a 39 kDa protein. The purified recombinant Cel5A endoglucanase exhibited maximum activity at 50 degrees C and pH 4.5. The enzyme was salt tolerant and retained more than 50% residual activity up to 15% NaCl. The homology model structure of Cel5A displayed that it is stable and compact protein structure consisting of eleven alpha-helical structures and eight beta-sheets. According to the predicted ligand binding site after superimposition with Pseudomonas stutzeri endoglucanase Cel5A (PDB ID: 4LX4), it consisted of five amino acid Asn157, Tyr116, Glu158, Glu270 and Trp303 that may be the expected active site of Cel5A from YC6887. This presented that our strain M. endophytica YC6887 that produces cellulase partially degrade the insoluble polysaccharides into reducing sugars.