Bacillus subtilis β-1, 4-Endoglucanase Products from Intact and Truncated Genes Are Secreted into the Extracellular Medium by Escherichia coli

Abstract

We compared the secretion of a Bacillus subtilis endo-β-1,4-glucanase (EC 3.2.1.4) in B. subtilis and of the product from the cloned gene (pC6.3) expressed in Escherichia coli. The cloned enzyme has been isolated previously as the 52.2-kilodalton (kDa) species predicted from the gene sequence (R. M. MacKay, A. Lo, G. Willick, M. Zuker, S. Baird, M. Dove, F. Moranelli, and V. Seligy, Nucleic Acids Res., 14:9159-9170, 1986); this 52.2-kDa species is then converted to an active 35.8-kDa species. The 35.8-kDa species has a segment removed from the COOH terminus. Endoglucanase products were identified by use of an antibody directed to the 35.8-kDa enzyme. Time course studies of the secretion in B. subtilis showed that the enzyme was first secreted as a 52.2-kDa proenzyme. This was cleaved progressively to a product of about 32 kDa. Time course analysis of the expression of the cloned product from pC6.3 in E. coli showed that about 70% of the endoglucanase activity was found extracellularly. Analysis of active products from three deletion clones showed that the expression pattern of the endoglucanase was not affected by removal of the transcription termination signal and that neither expression nor secretion was substantially altered by removal of a region coding for up to 163 residues of the carboxyl terminus.