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 primarily because they are too large and therefore tumble too slowly for optimal NMR performance. In addition, initial tests of a high through-put strategy for solving structures by X-ray crystallography or by standard NMR spectroscopy indicate that the vast majority of proteins will simply fail to result in appropriate samples. Clearly, ancillary approaches are going to be required. This proposal seeks to continue the development of a novel approach to using an NMR-based method. The primary idea is to simply arrange for the large 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 such as liquid ethane. Protein assemblies as large as 200 kDa could, in principle, 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 approach has been demonstrated with soluble and reasonably well-behaved proteins. Furthermore, proteins that tend to aggregate or even form insoluble precipitates have been successfully encapsulated and proteins that are relatively unstable and therefore incompletely folded in vitro have been forced to fold in the confined space of the reverse micelle. Despite these successful applications, the method has not been generally adopted by the NMR community. The reasons for this are clear: The apparatus necessary for the routine and safe preparation and manipulation of the highly pressurized and flammable samples that are necessary is not commercially available. This proposal seeks to develop the apparatus necessary to allow academic and non-academic structural biologists employing NMR spectroscopy to use the approach and thereby gain access to proteins that are not amenable to standard NMR methods or to crystallography.
