orals 5th Asia-Pacific NMR Symposium 2013

Orientation selective DEER (PELDOR) using spin labels and Fe-S clusters as applied to a mitochondrial complex I and a P450 protein-protein complex (#76)

Jeffrey Harmer 1 2
  1. Previous address: Department of Chemistry, Centre for Advanced Electron Spin Resonance, University of Oxford, Oxford, OX1 3QR, UK
  2. University of Queensland, St Lucia, Qld, Australia

The dipolar coupling between two paramagnetic centres depends upon their spin-spin distance and relative orientation with respect to the spectrometer field vector B0.1 Generally most double electron-electron resonance (DEER) spectroscopy experiments (or synonymously pulsed electron double resonance (PELDOR)) are carried out under conditions where the signal only reports on the spin-spin distance and for this type of dipolar data sophisticated analysis method for obtaining the distance distribution have been developed. Recently there has been an increasing number of studies on systems where the DEER response depends upon both distance and spin-spin orientation. In our case we have been interested in employing DEER spectroscopy to gain structural information with biological system containing iron-sulfur clusters, a spin which provides good orientation selectively in DEER experiments.

This contribution will present the salient points to consider when analysing data from orientation selective DEER experiments, and discuss two applications: a) assignment of the redox potentials and corresponding paramagnetic iron-sulfur clusters comprising the molecular wire of mitochondrial complex I to a structural model using DEER spectroscopy,2 and b) determining the 3D structure of an electron-transfer protein-protein complex in a P450 system using DEER measurements between paramagnetic iron-sulfur clusters and MTLS spin labels.3

  1. Bowen A.M., Tait C.E., Timmel C.R., Harmer J.R. (2013) Orientation selective DEER using Rigid Spin Labels, Cofactors, Metals, and Clusters’, In: Timmel CR, Harmer J (eds) Spin-labels and intrinsic paramagnetic centres in the biosciences: structural information from distance measurements. Struct Bond, Springer-Verlag Berlin Heidelberg, doi: 10.1007/430_2013_115.
  2. Roessler MM, King MS, Robinson AJ, Armstrong FA, Harmer J, Hirst J (2010) Direct assignment of EPR spectra to structurally defined iron-sulfur clusters in complex I by double electron-electron resonance. PNAS 107 (5):1930-1935. doi:10.1073/pnas.0908050107
  3. Lovett JE, Bowen AM, Timmel CR, Jones MW, Dilworth JR, Caprotti D, Bell SG, Wong LL, Harmer J (2009) Structural information from orientationally selective DEER spectroscopy. PCCP 11 (31):6840-6848.