RESEARCH

GTPases: Aberrant regulation RAS and RHO GTPases is linked to a variety of disease states, including cancer, cardiovascular and neurological disorders. RAS, in particular, has been a topic of intense investigation, as oncogenic RAS mutations cause constitutive RAS activation and are prevalent in cancer. We have a longstanding history studying RAS proteins. In our earlier studies, we applied novel four dimensional nuclear magnetic resonance (NMR) approaches to determine the first solution structure of the RAS proto-oncogene. Subsequently, my group at the University of North Carolina identified and solved the NMR solution structure of a novel RAS binding site in the RAF kinase, that is required for RAF activation of the mitogen activated protein kinase cascade. Our work has also elucidated how post-translational modifications of RAS, in particular, cysteine oxidation and ubiquitin modification lead to RAS activation. Through these efforts, our lab developed novel chemical ligation and radical detection methods to characterize RAS post-translational modifications. Importantly, redox and ubiquitin modification of RAS contributes to RAS-mediated tumorigenesis. Our lab also showed that other members of the RAS superfamily (e.g., RHO GTPases) are regulated by these post-translational modifications, indicating conservation of these important regulatory mechanisms within the RAS superfamily of GTPases. We have recently extended these studies to investigate additional lysine modifications (acetylation, methylation) in RAS proteins. A current research interest in our lab lies in characterizing how residue and site-specific mutation differences in Ras proteins lead to distinct signaling and tumorigenic signatures. In a recent paper with the Sharpless lab (UNC), we characterized two different oncogenic Ras mutations to elucidate why one activating mutation promotes Melanoma whereas the other does not. Understanding these differences could lead to mutation specific anti-cancer therapies. We have most recently initiated NMR structural studies on the heterotrimeric Gai subunit, in collaboration with the Dohlman lab at UNC. Heterotrimeric G proteins are molecular switches that stimulate intracellular signalling cascades in response to activation of G-protein-coupled receptors (GPCRs) by extracellular stimuli. Our efforts here are centered on identification and characterization of inhibitors and mutations that activate and deactivate the Ga subunit.