Distributions and Fluctuations of Protein Structures Investigated by X-Ray Analysis and Mössbauer Spectroscopy
The X-ray structure determination of myoglobin at five temperatures allows an estimation of the structural order at 0 K Extrapolation to 0 K of the < x 2> x -values determined between 80 K and 300 K shows that this protein has a large zero point disorder indicating a distribution of slightly different structures. At temperatures above 200 K, Mössbauer spectroscopy measures structural fluctuations of the molecules at a time scale between 10-7 to 10-9 s occurring within the distribution of structures obtained by X-ray methods. These fluctuations can be described as a diffusive motion of segments of the molecule within a limited space. RSMR-experiments show that the characteristic size of these segments is larger than 5Å but smaller than the diameter of the molecule.
Investigations of model compounds prove that forming and breaking of hydrogen bridges plays an important role for protein specific motions on the time scale between 10-7 and 10-9 s. Water serves as a plasticizer but also dry myoglobin reveals protein dynamics. Mössbauer spectroscopy on membrane proteins gives < x2 >y-values similar to those of myoglobin crystals. The onset of protein specific motions occurs, however, at lower temperatures.
KeywordsMossbauer Spectroscopy Backbone Atom Diffusive Motion Hydrogen Bridge Mossbauer Spectrum
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