Analysis of NMR data and global fold of the [Fe 4 –S 4 ] ferredoxin I from Desulfovibrio desulfuricans norway

The oxidized form of the[Fe 4 –S 4 ] ferredoxin I from Desulfovibrio desulfuricans Norway ( Dd N Fd I)was investigated by 1 H and 13 C NMR spectroscopy.The sequence‐specific 1 H assignments of 93%of the amino acid residues of the whole protein, a completedetermination of its secondary structure and an identification of adisulfide bridge are reported. The secondary structure of Dd NFd I was determined from both sequential and spatial NOEs. These NOEsreveal two anti‐parallel β‐sheets includingThr1–Ile4 and Glu59–Ile56, Val22–Ile26 andThr35–Lys31, one helical segment (ranging from Ala41 toAsp49) and three tight turns. Three‐dimensional featuresof Dd N Fd I were evidenced from long‐range NOE crosspeaks between the secondary structural elements of the protein. Amongthem, a possible disulfide bridge, located between the pair ofcysteines which are not coordinated to the cluster, was indicated by a 13 C– 1 H HSQC experiment at naturalabundance. The comparison of secondary structural elements andtertiary contacts of Dd N Fd I protein with those of ferredoxinsfrom mesophilic bacteria Desulfovibrio gigas and Desulfovibrio africanus and that from the hyperthermostablearchaeon Thermococcus litoralis confirms that Dd N Fd Iexhibits the same global protein folding topology as the others. Thechemical shifts of Dd N Fd I were compared with those of othermonocluster‐type ferredoxins. They show a peculiar conservationof the hydrophobic core of these ferredoxins. © 1998 John Wiley& Sons, Ltd.