Modern nuclear magnetic resonance (NMR) spectroscopy continues to be a central technique in the characterization of the structure and dynamics of proteins, nucleic acids and their complexes. Nevertheless, a significant fraction of the proteins that are known through the analysis of the genomic sequence are inaccessible to solution NMR methods. This is because they are too large, either by themselves or because they require association with large assemblies of lipids, and therefore tumble too slowly for optimal NMR performance. This proposal seeks to continue the development of a novel approach to rendering the NMR relaxation properties of large proteins amenable to the comprehensive and efficient application of modern triple resonance and related solution NMR techniques. The basic approach is to simply arrange for the protein molecule to tumble as a much smaller protein. This is achieved by encapsulating the protein in a reverse micelle system and dissolving the entire assembly in a low viscosity fluid. We calculate protein assemblies as large as 100 kDa could be made to tumble with sufficiently short correlation times to allow the full battery of existing triple resonance techniques to be applied, even without benefit of deuteration. The basic approach has been demonstrated with a small model protein, ubiquitin. Using a set of well-characterized proteins, we will determine the conditions necessary to adequately encapsulate large proteins. This method is also potentially applicable to membrane proteins and we will also adapt the technology for this purpose and apply it to several membrane proteins. A number of technical advances will be explored and include the use of cryogenic probe technology and development of a method of partial alignment to allow access to residual dipolar couplings for structural restraints. Should this general strategy prove successful, it would provide a powerful approach to using high-resolution solution NMR techniques to characterize proteins up to 100 kDa in size.
