Refined crystal structure of the 2[4Fe-4S] ferredoxin from Clostridium acidurici at 1.84 Å resolution

The D13C variant of Bacillus schlegelii 7Fe ferredoxin is an 8Fe ferredoxin as revealed by 1H‐NMR spectroscopy

“…The remaining resonances A, E, and I must originate from the new 4Fe cluster in the D13C mutant that is ligated by Cys 8 , Cys 13 assigned to Cys 49 HpV This assignment is also consistent with the expected dipolar connectivities of Cys 47 H0 2 in the X-ray structure of C. acidi-urici 8Fe ferredoxin [19] since this proton (corresponding to Cys 49 H(3 2 in the D13C mutant of B. schlegeliis ferredoxin) is close to two Ha protons (those of residues i-3 and i+3, respectively). Signal I can be tentatively assigned to Cys 8 .…”

“…The latter resonance is characterized by its NOE to a resonance at 4.24 ppm, presumably Asp 23 Ha. This assignment is supported by the fact that the structurally characterized cubane ferredoxins share a turn involving the fourth cysteine of the cluster binding sequence (C(IV)PXX) as a highly conserved structural element [16][17][18][19][20][21][22][23]. Owing to this turn, a strong NOE connectivity is expected between CysIV H(3 2 and the Ha of amino acid i+3 with respect to CysIV (Asp 23 in the present case).…”

“…The overall tertiary structure of B. schlegeliis ferredoxin maintains the pseudo 2-fold symmetry of all dicluster ferredoxins [19,21,22,24,25]. This is evident from the similarity of the ID spectra of the two proteins and the observation of the expected NOE between Hf$i of CysIII of cluster I and H(3i of CysIII of cluster II in both cases.…”

The Two [4Fe-4S] Clusters in Chromatium vinosumFerredoxin Have Largely Different Reduction Potentials

“…3) shows little, if any, change in the relatively weak negative band around 200 nm. These observations are consistent with the lack of extensive secondary structure elements in clostridial ferredoxins (21). Moreover, they suggest that only small global structural changes are induced by adding one electron to each cluster.…”

Identification of Residues of Rhodobacter capsulatus Ferredoxin I Important for Its Interaction with Nitrogenase

“…In order to study the role of FdI and especially its interaction with nitrogenase, we have undertaken to generate sitedirected mutants of FdI as a means to identify functionally im-portant residues. In this study, a three-dimensional representation of FdI has been constructed by computer-modelling using as a reference the crystal structure of the ferredoxin from Clostridium acidurici (CaFd) (Duke et al, 1994). Based on this information, residues were chosen for site-directed mutagenesis.…”