Protein fluctuations explored by inelastic neutron scattering and dielectric relaxation spectroscopy

Abstract

Glasses, supercooled liquids and proteins share common properties, in particular the existence of an energy landscape and the presence of two types of fluctuations, α and β. While the effect of α fluctuations on proteins has been known for a few years, the effect of β fluctuations has not been fully understood. By comparing neutron-scattering data on the protein myoglobin with β fluctuations in the hydration shell measured by dielectric relaxation spectroscopy, we show that the internal protein motions are slaved to these fluctuations. We also show that there is no ‘dynamical transition’ in proteins near 200 K. The rapid increase in the mean-square displacement with temperature in many neutron-scattering experiments can be quantitatively predicted by β fluctuations in the hydration shell.

Keywords:

• protein dynamics
• hydration shell
• β fluctuations
• inelastic neutron scattering
• dielectric relaxation spectroscopy
• no dynamical transitions

Acknowledgements

We thank Joel Berendzen and Benjamin McMahon for illuminating discussions, and Izabela Mihut-Stroe, Jonathan Betts and Albert Migliori for assistance with the dielectric relaxation spectroscopy experiments. GC acknowledges the financial support of the Laboratory Directed Research and Development program (20080138DR) at Los Alamos National Laboratory. This research is performed under U.S. Department of Energy contract DE-AC5206NA25396.