The structure of iron superoxide dismutase from Pseudomonas ovalis complexed with the inhibitor azide

The 2.9 Å resolution structure of iron superoxide dismutase(FeSOD) (EC 1.15.1.1 EC] ) from Pseudomonas ovalis complexed withthe inhibitor azide was solved. Comparison of this structurewith free enzyme shows that the inhibitor is bound at the opencoordination position of the iron, with a bond length of 2.0Å. The metal moves by 0.4 Å into the trigonal planeto produce an orthogonal geometry at the iron. Binding of theinhibitor also causes a movement of the axial ligand (histidine26) away from the metal, a lengthening of the iron—histidinebond, and a rotation of the histidine 74 ring. The inhibitorpossesses contacts in the binding pocket with a pair of conservedtryptophan residues and with the side chains of tyrosine 34and glutamine 70. This glutamine is conserved between all FeSODs,but is absent in MnSOD. Comparisons with MnSOD show that a differentglutamine which possesses the same interactions in the activesite as Gln70 in FeSOD is conserved at position 154 in the overallSOD sequence, implying that while manganese and FeSODs are structuralhomologues in a global sense, their functional and evolutionaryrelationship is that of second-site mutation revertants.