1H NMR studies of the FeS4 center in ferredoxin I from desulfovibrio desulfuricans norway: sequence-specific assignment of the cluster liganted cysteines
Résumé
The oxidized and reduced forms of the [Fe4-S4] ferredoxin I from Desulfovibrio desulfuricans Norway were investigated by 1H NMR spectroscopy with the aim of obtaining the complete assignment of the cysteines ligating the cluster. A combination of TOCSY and NOESY measurements together with information from the x-ray crystallographic structure of related ferredoxins provided the sequence-specific assignment of the four cysteines coordinated to the cluster. Through EXSY experiments, the hyperfine shifted resonance signals in the reduced ferredoxin were also assigned. The temperature dependence of the contact-shifted cysteinyl residues of the reduced ferredoxin reveals that two cysteines exhibit anti-Curie behavior whereas the other two cysteines display Curie behavior; that identifies Cys 9 (I) and Cys 15 (III) as ligated to the mixed-valence iron ions.