'''The Crystal Structure of the one-iron form of the di-iron center in Stearoyl Acyl Carrier Protein Desaturase from Ricinus Communis (Castor Bean).'''
===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==
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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.
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==About this Structure==
==About this Structure==
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[[Category: Fatty acid biosynthesis]]
[[Category: Fatty acid biosynthesis]]
[[Category: Four-helix bundle]]
[[Category: Four-helix bundle]]
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Revision as of 14:03, 28 July 2008
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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
