Broad-temperature range spectroscopy of the two-centre modular redox metalloprotein Desulfovibrio desulfuricans desulfoferrodoxin

The electronic-vibrational couplings of the two-centre non-heme iron protein Desulfovibrio desulfuricans desulfoferrodoxin (DFx) in three oxidation states, i.e. fully oxidised (grey), half-oxidised (pink), and fully reduced (colourless), have been investigated by variable temperature (VT) UV/VIS, MCD, CD, and EPR spectroscopy. The UV/VIS spectra of grey DFx at room temperature is characterised by broad charge transfer (CT) transitions associated with oxidised centre 1 (495 and 368 nm) and II (335 and 635 nm). The transitions are resolved at 78 K, substantiated by VT-MCD and -CD. The data offer novel information about the electronic-vibrational couplings of the transitions. Multiphonon bandshape analysis discloses strong contributions from both local Fe-S and S-C stretching and solvent/protein modes. A number of transitions are blue- or red-shifted compared with monomeric desulforedoxin, superoxide reductase or dismutase, and cloned Desulfovibrio vulgaris DFx fragments. Conversion from grey to pink DFx is accompanied by drastic electronic-vibrational changes of both centres. The data suggest that electron transfer and optical CT-transitions of DFx are controlled by environmental reorganization in the whole region between the metal centres.