Expression, purification, crystallization and preliminary X-ray analysis of a novel N-substituted branched-chain L-amino-acid dioxygenase from Burkholderia ambifaria AMMD

Ferrous ion- and α-ketoglutarate-dependent dioxygenase from Burkholderia ambifaria AMMD (SadA) catalyzes the C3-hydroxylation of N-substituted branched-chain L-amino acids, especially N-succinyl-L-leucine, coupled to the conversion of α-ketoglutarate to succinate and CO₂. SadA was expressed in Escherichia coli, purified and crystallized using the sitting-drop vapour-diffusion method at 293 K. Crystals of selenomethionine-substituted SadA were obtained using a reservoir solution containing PEG 3000 as the precipitant at pH 9.5 and diffracted X-rays to 2.4 Å resolution. The crystal belonged to space group P2₁2₁2₁, with unit-cell parameters a = 49.3, b = 70.9, c = 148.2 Å. The calculated Matthews coefficient (V_M = 2.1 ų Da⁻¹, 41% solvent content) suggested that the crystal contains two molecules per asymmetric unit.