The g-tensor of the flavin cofactor in (6–4) photolyase: a 360 GHz/12.8 T electron paramagnetic resonance study

Abstract

The g-tensor of the neutral radical form of the flavin adenine dinucleotide cofactor FADH^• of (6–4) photolyase from Xenopus laevis has been determined by very high-magnetic-field/high-microwave-frequency electron-paramagnetic resonance (EPR) performed at 360 GHz/12.8 T. Due to the high spectral resolution the anisotropy of the g-tensor could be fully resolved in the frozen-solution continuous-wave EPR spectrum. By least square fittings of spectral simulations to experimental data, the principal values of the g-tensor have been established: g_X  = 2.00433(5), g_Y  = 2.00368(5), g_Z  = 2.00218(7). A comparison of very high-field EPR data and proton and deuteron electron-nuclear double resonance measurements yielded precise information concerning the orientation of the g-tensor with respect to the molecular frame. This data allowed a comparison to be made between the principal values of the g-tensors of the FADH^• cofactors of photolyases involved in the repair of two different DNA lesions: the cyclobutane pyrimidine dimer (CPD) and the (6–4) photoproduct. It was found that g_X and g_Z are similar in both enzymes, whereas the g_Y component is slightly larger in (6–4) photolyase. This result clearly shows the sensitivity of the g-tensor to subtle differences in the protein environment experienced by the flavin.

Acknowledgements

We thank Martin Fuchs for making available his EPR simulation program and Evgenia Kirilina for assistance with the 360 GHz EPR measurements. Continuous support by Robert Bittl is gratefully acknowledged. This work was supported by the Deutsche Forschungsgemeinschaft (Sfb-498 (TP A2) and SPP-1051 [for high-field instrumentation]), and the VolkswagenStiftung (project I/77100).

Notes

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Additional information

Notes on contributors

S. Weber∗

∗[email protected]