Human D-amino acid oxidase: an update and review.

The flavoprotein D-amino acid oxidase (DAO) degrades the gliotransmitter D-Ser, a potent activator of N-methyl-D-aspartate-type glutamate receptors. A body of evidence suggests that DAO, together with its activator, G72 protein, may play a key role in the pathophysiology of schizophrenia. It has also been suggested that 3,4-dihydroxy-D-phenylalanine (D-DOPA), the stereoisomer of 3,4-dihydroxy-L-phenylalanine (L-DOPA), is oxidized by DAO and converted to dopamine via an alternative biosynthetic pathway. We determined the crystal structures of human DAO in complex with the reaction products of two clinically important substrates, D-Ser and D-DOPA. Kinetic data show that the maximum velocity is much greater for D-DOPA than that for D-Ser, which strongly supports the proposed alternative pathway for dopamine biosynthesis in the treatment of Parkinson's disease. In addition, biochemical characterization of human DAO indicates that it binds FAD more weakly than does porcine D-amino acid oxidase (pDAO) and exists as a stable homodimer, even in the apoprotein form. Determination of the structures of human DAO in various states reveals that, in contrast to pDAO, the hydrophobic-Val-Ala-Ala-Gly-Leu (VAAGL) stretch (residues 47-51, structurally ambivalent peptide) located at the si-face of the flavin ring assumes a uniquely stable conformation, which provides a structural basis for the unique kinetic features of human DAO.