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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• 作者：Kathleen Wood ; Douglas J. Tobias ; Brigitte Kessler ; Frank Gabel ; Dieter Oesterhelt ; Frans A. A. Mulder ; Giuseppe Zaccai ; Martin Weik
• 刊名：Journal of the American Chemical Society
• 出版年：2010
• 出版时间：April 14, 2010
• 年：2010
• 卷：132
• 期：14
• 页码：4990-4991
• 全文大小：106K
• 年卷期：v.132,no.14(April 14, 2010)
• ISSN：1520-5126

文摘

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.