Redox-dependent structural changes in archaeal and bacterial Rieske-type [2Fe-2S] clusters

Abstract

Proteins containing Rieske-type [2Fe-2S] clusters play important roles in many biological electron transfer reactions. Typically, [2Fe-2S] clusters are not directly involved in the catalytic transformation of substrate, but rather supply electrons to the active site. We report herein X-ray absorption spectroscopic (XAS) data that directly demonstrate an average increase in the iron-histidine bond length of at least 0.1 A upon reduction of two distantly related Rieske-type clusters in archaeal Rieske ferredoxin from Sulfolobus solfataricus strain P-1 and bacterial anthranilate dioxygenases from Acinetobacter sp. strain ADP1. This localized redox-dependent structural change may fine tune the protein-protein interaction (in the case of ARF) or the interdomain interaction (in AntDO) to facilitate rapid electron transfer between a lower potential Rieske-type cluster and its redox partners, thereby regulating overall oxygenase reactions in the cells.

Fig. 1.

EXAFS (top) and sulfur phase-corrected Fourier transforms (bottom, over k = 2–13.5 Å⁻¹) of oxidized (a) and reduced (b) ARF (solid) and AntDO (dashed). The vertical line in the Fourier transform is positioned to illustrate the shift to longer distance of the shoulder of the first shell peak, which represents the Fe-N_imid scattering shell. X-ray absorption Fe K edge spectra (bottom, inset) for oxidized (a) and reduced (b) ARF (solid) and AntDO (dashed).

Fig. 2.

Comparison of the goodness-of-fit value (f`) with the Fe-N_imid bond distance for oxidized (dashed) and reduced (solid) ARF (open circles) and AntDO (filled circles) in fits where the Fe-N_imid distance was constrained to the specified value and the Fe-N_imid Debye-Waller factor was constrained to be 0.0020 Ų. Lines connect the points for visual comparison.