Arg305 of streptomyces l-glutamate oxidase plays a crucial role for substrate recognition

Recently, we have solved the crystal structure of l-glutamate oxidase (LGOX) from Streptomyces sp. X-119-6 (PDB code: 2E1M), the substrate specificity of which is strict toward l-glutamate. By a docking simulation using l-glutamate and structure of LGOX, we selected three residues, Arg305, His312, and Trp564 as candidates of the residues associating with recognition of l-glutamate. The activity of LGOX toward l-glutamate was significantly reduced by substitution of selected residues with Ala. However, the enzyme, Arg305 of which was substituted with Ala, exhibited catalytic activity toward various l-amino acids. To investigate the role of Arg305 in substrate specificity, we constructed Arg305 variants of LGOX. In all mutants, the substrate specificity of LGOX was markedly changed by the mutation. The results of kinetics and pH dependence on activity indicate that Arg305 of LGOX is associated with the interaction of enzyme and side chain of substrate.