The BglX Gene Located at 47.8 Min on the Escherichia Coli Chromosome Encodes a Periplasmic Beta-glucosidase

A new Escherichia coli gene, bgIX, encoding a beta-D-glucosidase (EC 3.2.1.21) has been characterized. The bgIX gene is located adjacent to the dld gene at 47.8 min or 2225 kb on the E. coli chromosome. The sequence of a 2.6 kb DNA fragment from this region revealed a large open reading frame encoding a protein of 765 amino acids. The BgIX protein was purified from the periplasm, and amino-terminal sequencing suggests that the mature protein is derived from cleavage of a 20 residue signal peptide. A search of the sequence databases revealed that BgIX is a member of a large family of beta-glucosidases from a variety of bacteria and fungi, and the plant Arabidopsis thaliana. It differs from the other four E. coli phospho-beta-glucosidases in sequence and in its periplasmic rather than cytoplasmic location. The BgIX enzyme has a Km of 18 +/- 1 mM and a Vmax of 3 +/- 0.7 mumol min-1 for the colorimetric substrate o-nitrophenyl beta-D-glucopyranoside.