NMR spectroscopic studies of paramagnetic proteins: iron-sulfur proteins.

Newer NMR methods, particularly in conjunction with stable isotope labeling, offer exciting approaches to structure-function studies of paramagnetic proteins. This review examines progress in NMR spectroscopy of iron-sulfur proteins. The application of multidimensional multinuclear NMR spectroscopy to iron-sulfur proteins and the optimization of NMR pulse sequences for rapidly relaxing spins have allowed investigators to determine sequence-specific assignments for numerous NMR signals in rubredoxins, ferredoxins, and high-potential iron proteins, including those from the cysteine residues that ligate iron ions or iron-sulfur clusters. These advances enable one to interpret the wealth of information derived from NMR parameters, such as the temperature and pH dependence of chemical shifts and the relaxation properties of the resonances that report on interactions between nuclei and between nuclei and unpaired electron density. This information is being used to test theoretical descriptions of electron distribution within these molecules and to model the structures and dynamic properties of the proteins in solution. Mutagenesis of these proteins, in conjunction with NMR studies, is beginning to reveal which residues are important for cluster formation and stability and which residues play a role in electron transfer to and from redox partner proteins.