Magnetic and optical anisotropy of Clostridium pasteurianum rubredoxin from optically detected electron paramagnetic resonance

Abstract

The high-spin Fe͑III͒-center of oxidized rubredoxin from Clostridium pasteurianum shows a complicated, temperature-dependent EPR spectrum. We combine conventional EPR spectroscopy with optically detected EPR ͑ODEPR͒ to elucidate the electronic structure of this protein metal center. The ODEPR experiment, which can be considered as coherent Raman scattering or modulated magnetic circular dichroism ͑MCD͒, yields spectra that depend on the relative orientation of optical and magnetic dipole moments. A detailed analysis of the spectra shows that they correspond to a zero-field splitting of Dϭϩ46.3 GHz and a strong rhombic distortion with E/D ϭ0.25. In the frozen solution, conformational strain gives rise to variation of the rhombicity, which can be measured quantitatively from the EPR line shape. Analysis of the ODEPR line shapes yields the orientation of the optical anisotropy with respect to the magnetic g-tensor. We compare the results from this study to published results on EPR, optical spectroscopy, and MCD.

Continuous-wave EPR at 275GHz: Application to high-spin Fe3+ systems

“…The high magnetic field at which the spectra were recorded made it possible to determine reliable g-values directly. These g-values are clearly different from the gvalues that were determined earlier, indirectly, from X-band spectra [45].…”

“…Börger et al interpreted the complicated frozen solution spectrum of rubredoxin at X-band by including E/D-strain into their simulations [45]. From X-band spectra the strain in D and E can not be determined independently.…”

“…Rubredoxin from several organisms has been studied at the standard EPR frequency of 9 GHz [29,38,[43][44][45]. The D-values are around 50 GHz and the rhombicity parameter k is around 0.26.…”

Coherent Raman detected electron spin resonance spectroscopy of metalloproteins: linking electron spin resonance and magnetic circular dichroism

“…The first experiments were on ruby (Cr 3+ :Al 2 O 3 ) [13], an exceptionally well understood material that can be used as a calibration standard. Metalloproteins with a wide range of physical properties have now been studied by us: low-spin ferric haem cytochrome c 551 [11,14]; a type-1 'blue' copper protein azurin [15,16]; the Cu A centre of N 2 OR (nitrous oxide reductase) [17]; rubredoxin, a mononuclear iron-sulfur high-spin ferric ion [18]; and a [3Fe-4S] cluster with spin ½ in ferredoxin I, Azotobacter chroococcum (L. Udovicic, D. Suter, A.J. Thomson and S.J.…”

Laser‐Assisted Magnetic Resonance: Principles and Applications

“…The first high spin system, to which ODEPR was applied, is oxidised rubredoxin from Clostridium pasteurianum [92]. This electron transfer protein contains a single high-spin iron sulfur cluster.…”