Nuclear Magnetic Resonance (NMR) became during the two last decades an important method for biomolecular structure determination. NMR permits to study biomolecules in solution and gives access to the molecular flexibility at atomic level on a complete structure: in that respect, it is occupying a unique place in structural biology. During the first years of its development, NMR was trying to meet the requirements previously defined in X-ray crystallography. But, NMR then started to determine its own criteria for the definition of a structure. Indeed, the atomic coordinates of an NMR structure are calculated using restraints on geometrical parameters (angles and distances) of the structure, which are only indirectly related to atom positions: in that respect, NMR and X-ray crystallography are very different. The indirect relation between the NMR measurements and the molecular structure and dynamics makes critical the precision and the interpretation of the NMR parameters and the development of quantitative analysis methods. The methods published since 1997 for liquid-NMR of proteins are reviewed here. First, methods for structure determination are presented, as well as methods for spectral assignment and for structure quality assessment. Second, the quantitative analysis of structure mobility is reviewed.
Keywords: X-ray crystallography, TOUCHSTONEX approach, J-coupling restraints, 3D NMR, nuclear Overhauser effects (NOE), structure determination