Yang M, Luoh S M, Goddard A, Reilly D, Henzel W, Bass S
Department of Molecular Biology, Genentech Inc., South San Francisco, CA 94080-4990, USA.
Microbiology (Reading). 1996 Jul;142 ( Pt 7):1659-65. doi: 10.1099/13500872-142-7-1659.
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.
一个编码β-D-葡萄糖苷酶（EC 3.2.1.21）的新型大肠杆菌基因bgIX已得到鉴定。bgIX基因位于大肠杆菌染色体上47.8分钟处或2225 kb处，与dld基因相邻。来自该区域的一个2.6 kb DNA片段的序列显示有一个大的开放阅读框，编码一个含765个氨基酸的蛋白质。BgIX蛋白是从周质中纯化得到的，氨基末端测序表明成熟蛋白源自一个20个残基信号肽的切割。对序列数据库的搜索显示，BgIX是来自多种细菌、真菌以及植物拟南芥的一个β-葡萄糖苷酶大家族的成员。它在序列以及位于周质而非细胞质这一位置方面与其他四种大肠杆菌磷酸β-葡萄糖苷酶不同。对于比色底物邻硝基苯基β-D-吡喃葡萄糖苷，BgIX酶的Km为18±1 mM，Vmax为3±0.7 μmol min-1。
