Structures of larger proteins in solution: three- and four-dimensional heteronuclear NMR spectroscopy.

Three- and four-dimensional heteronuclear nuclear magnetic resonance (NMR) spectroscopy offers dramatic improvements in spectral resolution by spreading through-bond and through-space correlations in three and four orthogonal frequency axes. Simultaneously, large heteronuclear couplings are exploited to circumvent problems due to the larger linewidths that are associated with increasing molecular weight. These novel experiments have been designed to extend the application of NMR as a method for determining three-dimensional structures of proteins in solution beyond the limits of conventional two-dimensional NMR (approximately 100 residues) to molecules in the 150- to 300-residue range. This potential has recently been confirmed with the determination of the high-resolution NMR structure of a protein greater than 150 residues, namely, interleukin-1 beta.