1oqb
From Proteopedia
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The Crystal Structure of the one-iron form of the di-iron center in Stearoyl Acyl Carrier Protein Desaturase from Ricinus Communis (Castor Bean).
Overview
Delta9 stearoyl-acyl carrier protein (ACP) desaturase is a mu-oxo-bridged, di-iron enzyme, which belongs to the structural class I of large helix, bundle proteins and that catalyzes the NADPH and O2-dependent formation of, a cis-double bond in stearoyl-ACP. The crystal structures of complexes, with azide and acetate, respectively, as well as the apoand single-iron, forms of Delta9 stearoyl-ACP desaturase from Ricinus communis have been, determined. In the azide complex, the ligand forms a mu-1,3-bridge between, the two iron ions in the active site, replacing a loosely bound water, molecule. The structure of the acetate complex is similar, with acetate, bridging the di-iron center in the same orientation with respect to the, di-iron center. However, in this complex, the iron ligand Glu196 has, changed its coordination mode from bidentate to monodentate, the first, crystallographic observation of a carboxylate shift in Delta9 stearoyl-ACP, desaturase. The two complexes are proposed to mimic a mu-1,2 peroxo, intermediate present during catalytic turnover. There are striking, structural similarities between the di-iron center in the Delta9, stearoyl-ACP desaturase-azide complex and in the reduced, rubrerythrin-azide complex. This suggests that Delta9 stearoyl-ACP, desaturase might catalyze the formation of water from exogenous hydrogen, peroxide at a low rate. From the similarity in iron center structure, we, propose that the mu-oxo-bridge in oxidized desaturase is bound to the, di-iron center as in rubrerythrin and not as reported for the R2 subunit, of ribonucleotide reductase and the hydroxylase subunit of methane, monooxygenase. The crystal structure of the one-iron depleted desaturase, species demonstrates that the affinities for the two iron ions comprising, the di-iron center are not equivalent, Fe1 being the higher affinity site, and Fe2 being the lower affinity site.
About this Structure
1OQB is a Single protein structure of sequence from Ricinus communis with FE2 as ligand. Active as [acyl-carrier-protein_desaturase Acyl-[acyl-carrier-protein] desaturase], with EC number 1.14.19.2 Full crystallographic information is available from OCA.
Reference
Azide and acetate complexes plus two iron-depleted crystal structures of the di-iron enzyme delta9 stearoyl-acyl carrier protein desaturase. Implications for oxygen activation and catalytic intermediates., Moche M, Shanklin J, Ghoshal A, Lindqvist Y, J Biol Chem. 2003 Jul 4;278(27):25072-80. Epub 2003 Apr 18. PMID:12704186 [[Category: Acyl-[acyl-carrier-protein] desaturase]]
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