Streptomyces属放線菌由来の高基質特異性l-グルタミン酸オキシダーゼに関する研究

l-glutamate oxidase (LGOX) from Streptomyces sp. is a heterohexameric flavin enzyme that catalyzes the oxidative deamination of l-glutamate to form α-ketoglutarate with ammonia and hydrogen peroxide. LGOX shows strict substrate specificity for l-Glu. In addition, it is highly thermostable and pH stable. Because of these properties, LGOX is currently used as a biosensor for the trace determination of l-Glu in the food industry and clinical laboratories. The full-length cDNA is 2103 bp and is encoded by a single polypeptide chain consisting of 701 residues including subunits α-γ-β. The LGOX gene was heterologously expressed in Escherichia coli JM109. The LGOX precursor expressed in E. coli is a homodimer with weak enzymatic activity and becomes a heterohexamer upon activation by protease treatment. X-ray crystallography and docking studies of purified recombinant LGOX suggest that the Arg305 residue is a key residue for substrate recognition. Mutant analysis showed that Arg305 is essential for substrate recognition, as the activity toward l-Glu was greatly reduced and substrate specificity was changed in some enzymes. The functional analysis of R305E-LGOX, which is an l-Arg oxidase, revealed that R305E-LGOX can be used as a enzyme biosensor for l-Arg.

総合論文 (Comprehensive paper)