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The low-temperature inflection observed in neutron scattering measurements of proteins is due to methyl rotation: Direct evidence using isotope labeling and molecular dynamics simulations

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  • Kathleen Wood, Institut Laue-Langevin, France
  • Douglas J. Tobias, University of California, Unknown
  • Brigitte Kessler, Max Planck Institute of Biochemistry, Unknown
  • Frank Gabel, CEA Grenoble, Unknown
  • Dieter Oesterhelt, Max Planck Institute of Biochemistry, Germany
  • Frans A A Mulder
  • Giuseppe Zaccai, Institut Laue-Langevin, Unknown
  • Martin Weik, CEA Grenoble, France

There is increasing interest in the contribution of methyl groups to the overall dynamics measured by neutron scattering experiments of proteins. In particular an inflection observed in atomic mean square displacements measured as a function of temperature on high resolution spectrometers (1 μeV) was explained by the onset of methyl group rotations. By specifically labeling a non-methyl-containing side-chain in a native protein system, the purple membrane, and performing neutron scattering measurements, we here provide direct experimental evidence that the observed inflection is indeed due to methyl group rotations. Molecular dynamics simulations reproduce the experimental data, and their analysis suggests that the apparent transition is due to methyl group rotation entering the finite instrumental resolution of the spectrometer. Methyl group correlation times measured by solid state NMR in the purple membrane, taken from previous work, support the interpretation.

Original languageEnglish
JournalJournal of the American Chemical Society
Volume132
Issue14
Pages (from-to)4990-4991
Number of pages2
ISSN0002-7863
DOIs
Publication statusPublished - 14 Apr 2010
Externally publishedYes

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