Ber. Bunsen Ges. Phys. Chem. 97, 163-171 (1993)

Protein Dynamics and EPR-Spectroscopy: Comparison of Molecular Dynamic Simulations with Experiment.

Steinhoff HJ and Karim C

Institut fur Biophysik, Ruhr-Universitat Bochum, Germany

Electron paramagnetic resonance (EPR) experiments and molecular dynamics simulations on the residual motion of hemoglobin bound spin labels provide information about dynamical and rate processes in proteins. Rapid (ps time range) reorientational fluctuations of the nitroxide ring of the spin labels within a conformational substate can be experimentally characterized and distinguished from low frequency (ns time range) transitions between the conformational substates which are observed above 200K in solved samples. A comparison of the experimentally determined magnitudes and frequencies of the reorientational motions and the results of molecular dynamics simulations for several nitroxide locations yields good agreement for the short time dynamics. Evidence for relatively large scale motions involving rare jumps are observed in the molecular dynamic trajectories. A simple approach using Kramers'theory and a two state jump model permits to combine EPR results and molecular dynamics simulations in the case of these rare events.