The Origin of Protein Sidechain Order Parameter Distributions
Robert B. Best, Jane Clarke, and Martin Karplus
J. Am. Chem. Soc.; 2004; 126(25) pp 7734 - 7735
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Abstract:

Previous work by Wand et al. (Nature 2001, 411, 501-504) showed that the NMR order parameters characterizing the amplitude of motion of protein side chains seemed to form a multimodal distribution. At the time, no detailed explanation of this at the molecular level was offered, yet three "classes" of motion were inferred. We have analyzed a larger published data set and found that, although the distribution is multimodal, the evidence for three classes is weak. More significantly, we have been able to provide a simple physical explanation for the distributions based on the results of molecular dynamics simulations. This result will aid in the interpretation of data from NMR dynamics experiments.