Protein backbone atoms

The accuracy of protein structures determined by NMR is very dependent on the quantity and quality of data that can be obtained. It has been known that the highest quality NMR structures have accuracies comparable to the medium-resolution X-ray structures (2.0-2.5A) for protein backbone atomic coordinates.3 To improve the structural qualities and utilize them for biological system studies, it is important to re-emphasize factors having a critical impact on quality as summarized below. 

As remarked, hydrated protein samples exhibit a sudden onset of motions of the protein side-chains. Protein backbone atoms also show the dynamic transition and as expected the amplitude of fluctuations is less here compared to those of side-chain atoms. This onset of motion could be related to either of the two phenomena mentioned above but could also be the result of a new phenomenon arising from the coupling between the protein and water. 

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