Hydration dependence of active core fluctuations in bacteriorhodopsin
Kathleen Wood 1, Ursula Lehnert 1, Brigitte Kessler 2, Giuseppe Zaccai 1* and Dieter Oesterhelt 2
1 Institut Laue Langevin
2 MPI Biochemie
* To whom correspondence should be addressed. E-mail: zaccai{at}ill.fr.
Submitted on August 22, 2007
Revised on October 4, 2007
Accepted on 23 January 2008
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Abstract |
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We used neutron scattering and specific hydrogen-deuterium labeling to investigate the thermal dynamics of isotope labeled amino acids and retinal, predominantly in the active core and extra-cellular moiety of bacteriorhodopsin (BR) in the purple membrane (PM) and its response to hydration. Measurements on two neutron spectrometers allowed two populations of motions to be characterised. The lower amplitude motions are found to be the same for both the labeled amino acids and retinal of BR and the global membrane. The larger amplitude dynamics of the labeled part were found to be more resilient however than the average membrane, suggesting their functional importance. The response to hydration was characterised, showing that the labeled part of BR are not shielded from hydration effects. The results suggest that the inhibition of high amplitude motions by lowering hydration may play a key role in the slowing down of the photocycle and the proton pumping activity of BR.
Key Words:
hydrogen-deuterium labelling, local thermal motions, mean square displacement, neutron scattering, purple membrane
