Crystal Structure of a Novel N-Substituted L-Amino Acid Dioxygenase from Burkholderia ambifaria AMMD

A novel dioxygenase from Burkholderia ambifaria AMMD (SadA) stereoselectively catalyzes the C3-hydroxylation of Nsubstituted branched-chain or aromatic L-amino acids, especially N-succinyl-L-leucine, coupled with the conversion of alpha-ketoglutarate to succinate and CO2. To elucidate the structural basis of the substrate specificity and stereoselective hydroxylation, we determined the crystal structures of the SadA. Zn(II) and SadA. Zn(II). alpha-KG complexes at 1.77 angstrom and 1.98 angstrom resolutions, respectively. SadA adopted a double-stranded beta-helix fold at the core of the structure. In addition, an HXD/EXnH motif in the active site coordinated a Zn(II) as a substitute for Fe(II). The alpha-KG molecule also coordinated Zn(II) in a bidentate manner via its 1-carboxylate and 2-oxo groups. Based on the SadA. Zn(II). alpha-KG structure and mutation analyses, we constructed substrate-binding models with N-succinyl-L-leucine and N-succinyl-L-phenylalanine, which provided new insight into the substrate specificity. The results will be useful for the rational design of SadA variants aimed at the recognition of various N-succinyl L-amino acids.