Protein chemical shift analysis: a practical guide.

Proper protein chemical shift analysis requires careful experimental measurements and the implementation of standardized referencing procedures. In this article we outline the steps necessary to ensure proper chemical shift referencing and the selection criteria for choosing appropriate "random coil" amino acid chemical shift values for predicting, comparing, and assigning 1H, 13C, and 15N resonances in proteins. By making use of these standardized conditions we demonstrate how several recently developed methods, namely homologous assignment techniques and empirical chemical shift contour maps (or hypersurfaces), can significantly improve the accuracy of chemical shift prediction for 1H, 13C, and 15N nuclei. In addition to illustrating the potential utility of chemical shift prediction, we also outline procedures for identifying secondary structure elements through heteronuclear chemical shift analysis and further demonstrate how empirical shift contour maps can actually be used to refine, and more importantly generate, reasonably good three-dimensional protein structures.