X-ray structure analysis of a unique D-amino-acid oxidase from the thermophilic fungus Rasamsonia emersonii strain YA.

D-Amino-acid oxidases (DAAOs) catalyze the oxidative deamination of neutral and basic D-amino acids. The DAAO from the thermophilic fungus Rasamsonia emersonii strain YA (ReDAAO) has a high thermal stability and a unique broad substrate specificity that includes the acidic D-amino acid D-Glu as well as various neutral and basic D-amino acids. In this study, ReDAAO was crystallized by the hanging-drop vapor-diffusion method and its crystal structure was determined at a resolution of 2.00 Å. The crystal structure of the enzyme revealed that unlike other DAAOs, ReDAAO forms a homotetramer and contains an intramolecular disulfide bond (Cys230-Cys285), suggesting that this disulfide bond is involved in the higher thermal stability of ReDAAO. Moreover, the structure of the active site and its vicinity in ReDAAO indicates that Arg97, Lys99, Lys114 and Ser231 are candidates for recognizing the side chain of D-Glu.