H-1-NMR STUDY OF THE FE4S4 CENTER IN FERREDOXIN-I FROM DESULFOVIBRIO-DESULFURICANS NORWAY - SEQUENCE-SPECIFIC ASSIGNMENT OF THE CLUSTER-LIGATED CYSTEINES

The oxidized and reduced forms of the /Fe4S4/ ferredoxin I from Desulf ovibrio desulfuricans Norway were investigated by H-1 NMR spectroscopy with the aim of obtaining the complete assignment of the cysteines li gating the cluster. A combination of TOCSY and NOESY measurements toge ther with information from the x-ray crystallographic structure of rel ated ferredoxins provided the sequence-specific assignment of the four cysteines coordinated to the cluster. Through EXSY experiments, the h yperfine 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 beh avior; that identifies Cys 9 (I) and Cys 15 (III) as ligated to the mi xed-valence iron ions.