G Protein Mono-ubiquitination by the Rsp5 Ubiquitin Ligase
Program in Systems Biology
Medical Subject Headings
Endosomal Sorting Complexes Required for Transport; GTP-Binding Protein alpha Subunits, Gq-G11; Mutation; Proteasome Endopeptidase Complex; Protein Processing, Post-Translational; Saccharomyces cerevisiae; Saccharomyces cerevisiae Proteins; Ubiquitin-Protein Ligase Complexes; Ubiquitination; Vacuoles
Emerging evidence suggests that ubiquitination serves as a protein trafficking signal in addition to its well characterized role in promoting protein degradation. The yeast G protein alpha subunit Gpa1 represents a rare example of a protein that undergoes both mono- and poly-ubiquitination. Whereas mono-ubiquitinated Gpa1 is targeted to the vacuole, poly-ubiquitinated Gpa1 is directed instead to the proteasome. Here we investigate the structural requirements for mono- and poly-ubiquitination of Gpa1. We find that variants of Gpa1 engineered to be unstable are more likely to be poly-ubiquitinated and less likely to be mono-ubiquitinated. In addition, mutants that cannot be myristoylated are no longer mono-ubiquitinated but are still polyubiquitinated. Finally, we show that the ubiquitin ligase Rsp5 is necessary for Gpa1 mono-ubiquitination in vivo and that the purified enzyme is sufficient to catalyze Gpa1 mono-ubiquitination in vitro. Taken together, these data indicate that mono- and poly-ubiquitination have distinct enzyme and substrate recognition requirements; whereas poly-ubiquitination targets misfolded protein for degradation, a distinct ubiquitination apparatus targets the fully mature, fully myristoylated G protein for mono-ubiquitination and delivery to the vacuole.
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Citation: Torres MP, Lee MJ, Ding F, Purbeck C, Kuhlman B, Dokholyan NV, Dohlman HG. G Protein Mono-ubiquitination by the Rsp5 Ubiquitin Ligase. J Biol Chem. 2009 Mar 27;284(13):8940-50. doi: 10.1074/jbc.M809058200. Link to article on publisher's site
The Journal of biological chemistry
Torres, Matthew P.; Lee, Michael J.; Ding, Feng; Purbeck, Carrie; Kuhlman, Brian; Dokholyan, Nikolay V.; and Dohlman, Henrik G., "G Protein Mono-ubiquitination by the Rsp5 Ubiquitin Ligase" (2009). Program in Systems Biology Publications and Presentations. 41.