Structural Studies of Proteins in Solution Using Proton Nuclear Magnetic Resonance

Nuclear magnetic resonance (NMR) spectroscopy has become established in recent years as a uniquely powerful technique for studying the structures of proteins in solution. In a ¹ H spectrum, each hydrogen atom in the molecule gives rise to an individual signal, and in favorable cases, it is possible to resolve each of them and assign each to an identified atom. The power of the method then lies in the wealth of information that can be obtained concerning both through-bond and through-space connectivities between individual nuclei. This makes it possible to determine in detail the three-dimensional (3D) conformation from NMR data, and that is the major subject of this chapter. The feasibility of such a full structure determination depends crucially on the completeness with which signals can be assigned to individual nuclei and conformation-dependent parameters determined. The key to achieving this has been the development of two-dimensional (2D) NMR, which, by dispersing the signals more thoroughly and in a structurally significant manner, permits the resolution of large numbers of resonances and elucidation of the connectivities between them. The principles of 2D NMR and the particular experiments that are commonly employed in studies of proteins will be outlined, together with the strategies employed to make specific resonance assignments. A number of approaches are then possible to turning the accumulated spectral information into structural detail, and these are reviewed briefly. Such a detailed analysis is not always feasible, however, because it may not be possible to resolve and assign the spectrum in sufficient detail—in that case, the structural information that can be obtained will necessarily be more limited, though it may nonetheless be valuable. We illustrate briefly how “partial answers” to some structural questions may be obtained.