Resonance Raman studies of the [4Fe‐4S] to [2Fe‐2S] cluster conversion in the iron protein of nitrogenase

Abstract

Resonance Raman spectroscopy has been used to investigate the Fe-S stretching modes of the [4Fe-4SP+ cluster in the oxidized iron protein of Closfri~iron pusrertrianrrm nitrogenase. The results are consistent with a cubane [4Fe_4S] cluster having effective Td symmetry with cysteinyl coordination for each iron. In accord with previous optical and EPR studies [(1984) Biochemistry 23,21 lg-21221. treatment with the iron chelator CI,GL'-dipyyidyl in the presence of MgATP is shown to effect cluster conversion to a [ZFe-2SlZ+ cluster. Resonance Raman data also indicate that partial conversion to a [2Fe-tS]*+ cluster is induced by thionine-oxidation in the presence of MgATP in the absence of an iron chelator. This result suggests new explanations for the dramatic change in the CD spectrum that accompanies MgATP-binding to the oxidized Fe protein and the anomalous resonance Raman spectra of thionine-oxidized Clnsrridiunr pusreuriunum bidirectional hydrogenase.

Escherichia coli RIC Is Able to Donate Iron to Iron-Sulfur Clusters

“…The shoulders at 336 and 356 cm −1 are indicative of bridging and terminal modes of oxidized [4Fe-4S] 2+/1+ clusters, and these bands were also previously observed in the spectrum of E. coli IscU after a reconstitution reaction promoted by frataxin (CyaY) [29]. The modes assigned to the [2Fe-2S] 2+/1+ center show slight downshifts in comparison with those reported for E. coli IscU [29], but are consistent with the energies of vibrational modes observed in other [2Fe-2S] 2+/1+ clusters [12], [24], [27], [28], [30]. The origin of the intense band at 308 cm −1 is not clear at this point; nevertheless, it might be due to contribution from a non-resolved ice lattice mode [31].…”

“…These bands are absent from the spectrum of the control reaction done in the absence of RIC (Figure 2B, spectrum b). Vibrational modes at 295, 345, 395 and 420 cm −1 fall into the range of frequencies characteristic of oxidized [2Fe-2S] 2+/1+ clusters [12], [24], [27]-[29]; the bands at 295 cm −1 and 345 cm −1 correspond to the terminal modes B 3u and A g , respectively, and the 396 cm −1 and 420 cm −1 bands to A g and B 2u bridging modes of a newly formed [2Fe-2S] 2+/1+ oxidized cluster in E. coli IscU [30]. The shoulders at 336 and 356 cm −1 are indicative of bridging and terminal modes of oxidized [4Fe-4S] 2+/1+ clusters, and these bands were also previously observed in the spectrum of E. coli IscU after a reconstitution reaction promoted by frataxin (CyaY) [29].…”

Design and fine-tuning redox potentials of metalloproteins involved in electron transfer in bioenergetics

“…Interestingly, different types of FeS clusters can convert into each other within the same protein scaffold via a process called cluster interconversion. The most common type of interconversion is from [4Fe-4S] to [2Fe-2S], which is observed in nitrogenase [121,122], ribonucleotide reductase [123], pyruvate-formate activating enzyme [124], and fumarate nitrate reduction transcription factor [125–128]. Interconversions between [4Fe-4S] to [3Fe-4S] [129–131] and between [2Fe-2S] to [4Fe-4S] have also been reported [132].…”

Dynamics of the [4Fe-4S] Cluster in Pyrococcus furiosus D14C Ferredoxin via Nuclear Resonance Vibrational and Resonance Raman Spectroscopies, Force Field Simulations, and Density Functional Theory Calculations

“…RR spectroscopy has also used to probe [4Fe-4S]→[3Fe-4S] interconversion (28–30), reductive coupling of [2Fe-4S] to [4Fe-4S] clusters on the IscU scaffold protein (31), partial [4Fe-4S]→[2Fe-4S] transformation in the nitrogenase Fe protein (32), and changes in electron localization in ferredoxin:thioredoxin reductase (33). …”