Structural characterization of a putative recombinant l-amino acid oxidase from Leptospira interrogans

Amino acid oxidases (AOs) are flavin adenine dinucleotide (FAD)-dependent dimeric enzymes that stereo specifically catalyse the deamination of an  -amino acid leading to an  -keto acid. Putative Leptospira interrogans recombinant L -amino acid oxidase ( Li -rLAO; lacking 20 residues corresponding to the N-terminal signal sequence) was cloned, expressed, purified, and i ts three-dimensional structure was determined by X-ra y crystallography at a resolution of 1.8 Å. The active site could be easily identified by the presence of electron density corresponding to a non-covalently bound FAD in both protomers of the dimeric enzyme. Structural analysis of Li- rLAO revealed that its polypeptide fold is similar to those of the previously determined homologous structures as available in the Protein Data Bank. However, a substrate-binding residue found at the activ e site of other previously determined homologous structures was not conserved in Li- rLAO, suggesting that its specificity may differ from those of earlier reported structures. Not surprisingly, Li- rLAO showed no activity for most amino acids and amines; it exhibited a low activity only with L -arginine as the substrate. The cata-lytic properties of Li- rLAO could be rationalized in terms of its three-dimensional structure.