Crystal Structures of Native and Ligand Bound Cysteine Dioxygenase

Abstract

Cysteine dioxygenase is a mononuclear iron-dependent enzyme responsible for the oxidation of cysteine with molecular oxygen to form cysteinsulfinate. This reaction commits cysteine to either catabolism to sulfate and pyruvate or to taurine. Recombinant rat CDO was heterologously expressed, purified and crystallized, and its activity profile was characterized. The rCDO had a high catalytic activity and kinetic parameters similar to those observed for the enzyme in nonpurified preparations of rat liver. We determined the crystal structure of native, unliganded cysteine dioxygenase to 1.5 Å and the structure with bound ligand to 1.8 Å. The crystal structure reveals a monomer in the asymmetric unit. Cysteine dioxygenase has the canonical cupin β-sandwich folding conformation observed for other cupin proteins. Analysis of the active site of the enzyme reveals an iron atom coordinated with three histidine residues (His86, His88, and His140) and a water molecule. The sulfur of cysteine replaces the water molecule. These results suggest that cysteine dioxygenase may have a unique active site geometry that facilitates the catalysis of thiol dioxygenation, a reaction quite different from that catalyzed by other known mononuclear iron enzymes.