Diverse Mechanisms of G Protein Regulation by Monoubiquitination Public Deposited

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  • March 19, 2019
Creator
  • Baker, Rachael Ann
    • Affiliation: School of Medicine, Department of Biochemistry and Biophysics
Abstract
  • Cell signaling pathways convert information from the extracellular environment into an intracellular response. It is essential that these pathways be turned on and off on the appropriate timescales. Post-translational modifications are one essential mechanism used to maintain proper signaling. One post-translational modification that is emerging as a key regulator of cell signaling is monoubiquitination. Monoubiquitination is dynamic and reversible, making it ideal for temporal and spatial regulation. It has recently become evident that monoubiquitination regulates G proteins, which are the molecular switches that turn signaling pathways on and off. However, the mechanisms by which monoubiquitination acts on these enzymes is not known. We used a chemical ubiquitination approach coupled with biochemical and biophysical assays to elucidate the mechanisms by which two G proteins, the small G protein Ras and the heterotrimeric G protein Gpa1, are regulated by monoubiquitination. Monoubiquitination at one position activates K-Ras by impeding regulator-mediated hydrolysis while monoubiquitination at a distinct site activates H-Ras by increasing intrinsic nucleotide exchange. Together, these results demonstrate that monoubiquitination contributes to isoform-dependent regulation of Ras in a site-specific manner. Furthermore, we found that the site of ubiquitination on Gpa1 was in a unique domain that is essential for trafficking but does not contribute to enzymatic activity. The G protein substrates we chose exhibited diverse mechanisms of regulation by monoubiquitination including altering protein interactions (K-Ras), intrinsic activity (H-Ras), and localization (Gpa1). In summary, our results represent the first mechanistic study of G protein regulation by monoubiquitination and contribute to understanding Ras and Gpa1 regulation specifically as well as regulation of G proteins by monoubiquitination generally. More broadly, these results illustrate the diverse roles for monoubiquitination in the regulation of cell signaling.
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  • In Copyright
Advisor
  • Dohlman, Henrik
Degree
  • Doctor of Philosophy
Graduation year
  • 2013
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