Al. Macedo et al., 2-DIMENSIONAL H-1-NMR STUDIES ON DESULFOVIBRIO-GIGAS FERREDOXINS - ASSIGNMENT OF THE IRON-SULFUR CLUSTER CYSTEINYL LIGAND PROTONS, Magnetic resonance in chemistry, 31, 1993, pp. 190000059-190000067
1D and 2D H-1 NMR studies are reported on the oxidized and reduced [4F
e-4S] cluster of Desulfovibrio gigas ferredoxin I (FdI). Several low-f
ield contact shifted resonances (fast relaxing) are assigned to beta-C
H2 and alpha-CH coordinated cysteinyl residues. NOESY patterns (suppor
ted by 1D NOE experiments) resolves four pairs of geminal beta-CH2 pro
tons at low-field. The cluster ligands are assigned non-specifically t
o Cys8, Cys11, Cys14 and Cys50, based on the X-ray structural analysis
available for the oligomeric form, FdII, that contains a single [3Fe-
4S] cluster. It was indicated in this case that Cys11 is not bound to
the trinuclear cluster but is tilted towards the solvent. The presence
of four pairs of geminal beta-CH2 protons for FdI unambiguously prove
s the occupancy of the fourth site of the [3Fe-4S] complex and implies
the coordination of the Cys11 at the cluster. Analysis of the oxidize
d form of FdII, using the same methodology as described for FdI, suppo
rts the presence of three cysteinyl ligands in the [3Fe-4S] core. Furt
her, the combined use of the X-ray coordinates enables the specific as
signment of the three cysteinyl ligands of the cluster, extending a pr
evious assignment of Cys50. In addition, very broad resonances were de
tected for the reduced form of FdII in the low-field region around 200
ppm and in the high field region around -80 ppm.