Characteristics of the endoglucanase encoded by a cel gene from Bacteroides succinogenes expressed in Escherichia coli

Abstract

A cel gene from Bacteroides succinogenes inserted into the vector pUC8 coded for an enzyme which exhibited high hydrolytic activity on carboxymethylcellulose, p-nitrophenylcellobioside, and lichenan and low activity on laminarin and xylan. The enzyme was not synthesized by the Escherichia coli host when cells were cultured in complex medium containing added glucose. In the absence of added glucose, the endoglucanase and cellobiosidase activities synthesized were partitioned into the periplasmic space during growth, and practically all enzyme was located in the periplasm when the stationary phase of growth was reached. The enzyme exhibited 17- and sixfold higher Km values for the hydrolysis of carboxymethylcellulose and lichenan, respectively, than did the extracellular endoglucanase complex from B. succinogenes. The Cel endoglucanase had a pH optimum similar to that of the B. succinogenes enzyme except that the range was narrower, and the Cel endoglucanase was more readily inactivated on exposure to high temperature, detergents, and certain metals. Its activity was stimulated by calcium and magnesium. Nondenaturing polyacrylamide gel electrophoresis at different acrylamide concentrations revealed the presence of three endoglucanase components, two with molecular weights of 43,000 and one with a molecular weight of 55,000.