Speaker
Description
Current NMR methods for studying proteins are primarily focused on backbone resonances and on methyl bearing side chains. In contrast, NMR of aromatic side chains has been less pursued although these moieties form a large portion of the hydrophobic protein cores. This is in part due to the complexity of aromatic side-chain spectra, which appear in a narrow and crowded spectral region. 13C-dispersion of spectra reduces the complexity but the large carbon-carbon and carbon-proton couplings make spectra difficult to analyze. The TROSY effect of aromatic carbons has been realized early on as an approach to make aromatic spin systems more accessible, and alternate 13C labeling with judiciously chosen pyruvate precursors can render rather well resolved aromatic spectra that can yield NOE contacts with and between aromatic side chains in larger proteins. With the ability to introduce 19F-labeled aromatic residues into proteins, we explored whether we could utilize the large CSA of fluorine to create a 19F-13C TROSY effect for more efficient detection of aromatic signals in large proteins. Indeed, simulation of the relaxation properties using the Spinach program indicated that 13C detected FC TROSY experiments can yield very sharp signals but need specific labeling strategies. Similar advances can also be made with 19F-13C labeled nucleotide bases, some of which promise to yield very sharp TROSY signals that are expected to deteriorate little with larger systems. NMR access to mobility and interactions of aromatic side chains is particularly interesting for elucidating mechanisms of signal transduction of membrane protein receptors where binding of agonists or antagonists may cause small structural and dynamic changes to define signaling.