THE BGLX GENE LOCATED AT 47.8-MIN ON THE ESCHERICHIA-COLI CHROMOSOME ENCODES A PERIPLASMIC BETA-GLUCOSIDASE

A new Escherichia coil gene, bglX, encoding a beta-D-glucosidase (EC 3 .2.1.21) has been characterized. The bglX gene is located adjacent to the did gene at 47.8 min or 2225 kb on the E. coil chromosome. The seq uence of a 2.6 kb DNA fragment from this region revealed a large open reading frame encoding a protein of 765 amino acids. The BglX protein was purified from the periplasm, and amino-terminal sequencing suggest s that the mature protein is derived from cleavage of a 20 residue sig nal peptide. A search of the sequence databases revealed that BglX is a member of a large family of beta-glucosidases from a variety of bact eria and fungi, and the plant Arabidopsis thaliana. It differs from th e other four E. coil phospho-beta-glucosidases in sequence and in its periplasmic rather than cytoplasmic location. The BglX enzyme has a K- m of 18 +/- 1 mM and a V-max of 3 +/- 0.7 mu mol min(-1) for the color imetric substrate o-nitrophenyl beta-D-glucopyranoside.