Mutational and crystallographic analysis of l-amino acid oxidase/monooxygenase from Pseudomonas sp. AIU 813: Interconversion between oxidase and monooxygenase activities.

In this study, it was shown for the first time that l-amino acid oxidase of Pseudomonas sp. AIU813, renamed as l-amino acid oxidase/monooxygenase (l-AAO/MOG), exhibits l-lysine 2-monooxygenase as well as oxidase activity. l-Lysine oxidase activity of l-AAO/MOG was increased in a p-chloromercuribenzoate (p-CMB) concentration-dependent manner to a final level that was five fold higher than that of the non-treated enzyme. In order to explain the effects of modification by the sulfhydryl reagent, saturation mutagenesis studies were carried out on five cysteine residues, and we succeeded in identifying l-AAO/MOG C254I mutant enzyme, which showed five-times higher specific activity of oxidase activity than that of wild type. The monooxygenase activity shown by the C254I variant was decreased significantly. Moreover, we also determined a high-resolution three-dimensional structure of l-AAO/MOG to provide a structural basis for its biochemical characteristics. The key residue for the activity conversion of l-AAO/MOG, Cys-254, is located near the aromatic cage (Trp-418, Phe-473, and Trp-516). Although the location of Cys-254 indicates that it is not directly involved in the substrate binding, the chemical modification by p-CMB or C254I mutation would have a significant impact on the substrate binding via the side chain of Trp-516. It is suggested that a slight difference of the binding position of a substrate can dictate the activity of this type of enzyme as oxidase or monooxygenase.

Crystal structures of glycoside hydrolase family 51 α-L-arabinofuranosidase from Thermotoga maritima.

α-L-Arabinofuranosidase from the hyperthermophilic bacterium Thermotoga maritima (Tm-AFase) is an extremely thermophilic enzyme belonging to glycoside hydrolase family 51. It can catalyze the transglycosylation of a novel glycosyl donor, 4,6-dimethoxy-1,3,5-triazin-2-yl (DMT)-ß-D-xylopyranoside. In this study we determined the crystal structures of Tm-AFase in substrate-free and complex forms with arabinose and xylose at 1.8-2.3 Å resolution to determine the architecture of the substrate binding pocket. Subsite -1 of Tm-AFase is similar to that of α-L-arabinofuranosidase from Geobacillus stearothermophilus, but the substrate binding pocket of Tm-AFase is narrower and more hydrophobic. Possible substrate binding modes were investigated by automated docking analysis.