Expression, purification and characterization of two thermostable endoglucanases cloned from a lignocellulosic decomposing fungi Aspergillus fumigatus Z5 isolated from compost

Two genes encoding endoglucanase, designated as eg12 and eg13, were cloned from a lignocellulosic decomposing fungus Aspergillus fumigatus Z5 and were successfully expressed in Pichia pastoris X33. The deduced amino acid sequences encoded by eg12 and eg13 showed strong similarity with the sequence of glycoside hydrolase family 5. SDS-PAGE and western blot assays indicated that the recombinant enzymes were secreted into the culture medium and the zymogram analysis confirmed that both recombinant enzymes had endoglucanase activity. Several biochemical properties of the two recombinant enzymes were studied: Eg12 and Eg13 showed optimal activity at pH 5.0 and 4.0, respectively, and at 50 and 60 degrees C, respectively. Eg12 and Eg13 showed good pH stability in the range of 4-7, and both enzymes demonstrated good thermostability ranging from 30 to 60 degrees C. The K(m) and V(max) values using carboxymethyl cellulose (CMC, soluble cellulose, polymerized by beta-1, 4-linked glucose residues) as the substrate at optimal conditions were determined. The activities of the enzymes on a variety of cello-oligosaccharide substrates were investigated, and Eg12 can hydrolyze cellotetraose and cellopentaose but not cellobiose and cellotriose, whereas Eg13 can hydrolyze all cello-oligosaccharides, except cellobiose. (C) 2011 Elsevier Inc. All rights reserved.