The value of chemical shift parameters in the description of protein solution structures

An increasing number of protein solution structures, calculated on the basis of nuclear Overhauser enhancement cross-peak intensities observed in two- or higher dimensional NOESY experiments, are becoming available. Among these structures regions of uncertainty are frequently observed particularly with respect to loops and surface side chains. These are commonly ascribed to either a lack of NOE constraints or to some intrinsic mobility within the protein. A powerful method of structural analysis which may resolve this problem is based on the information content of the chemical shift. The value of such an analysis is illustrated here with cytochromes b5 and c, proteins for which high-quality crystallographic and NMR data are available. Comparison of these using a pseudocontact shift-based analysis indicates that NOE data should be combined with the chemical shift data in order to uncover fully the ensemble of protein states and their dynamics in solution.