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

Abstract

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 I (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.