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Updated: May 5, 2026
Comparative Strategies for Ubiquitination Detection in Mammalian Cell Lysates Using SMAD2/SMURF2 as a Model
Published on: April 17, 2026
Differences in the regulation of K-Ras and H-Ras isoforms by monoubiquitination
Rachael Baker1, Emily M Wilkerson, Kazutaka Sumita
1From the Departments of Biochemistry and Biophysics and.
Abstract:
Ras GTPases are signaling switches that control critical cellular processes including gene expression, differentiation, and apoptosis. The major Ras isoforms (K, H, and N) contain a conserved core GTPase domain, but have distinct biological functions. Among the three Ras isoforms there are clear differences in post-translational regulation, which contribute to differences in localization and signaling output. Modification by ubiquitination was recently reported to activate Ras signaling in cells, but the mechanisms of activation are not well understood. Here, we show that H-Ras is activated by monoubiquitination and that ubiquitination at Lys-117 accelerates intrinsic nucleotide exchange, thereby promoting GTP loading. This mechanism of Ras activation is distinct from K-Ras monoubiquitination at Lys-147, which leads to impaired regulator-mediated GTP hydrolysis. These findings reveal that different Ras isoforms are monoubiquitinated at distinct sites, with distinct mechanisms of action, but with a common ability to chronically activate the protein in the absence of a receptor signal or oncogenic mutation.
Insights
Monoubiquitination activates H-Ras by enhancing GTP loading, distinct from K-Ras activation. This post-translational modification provides a novel mechanism for chronic Ras signaling activation.
Area of Science:
- Molecular Biology
- Cell Signaling
Background:
- Ras GTPases are crucial regulators of cellular processes like gene expression and apoptosis.
- Distinct biological functions of Ras isoforms (K, H, N) arise from differences in post-translational regulation and localization.
- Ubiquitination has been implicated in Ras signaling activation, but the precise mechanisms remain unclear.
Purpose of the Study:
- To elucidate the mechanism by which H-Ras is activated by monoubiquitination.
- To compare the ubiquitination-mediated activation mechanisms of H-Ras and K-Ras.
Main Methods:
- Investigated the role of monoubiquitination in H-Ras activation.
- Analyzed the specific ubiquitination site (Lys-117) on H-Ras and its effect on nucleotide exchange.
- Compared H-Ras ubiquitination mechanism with K-Ras ubiquitination at Lys-147.
Main Results:
- H-Ras is activated by monoubiquitination at Lys-117, which accelerates intrinsic nucleotide exchange and promotes GTP loading.
- This activation mechanism differs from K-Ras monoubiquitination at Lys-147, which impairs GTP hydrolysis.
- Different Ras isoforms exhibit distinct ubiquitination sites and mechanisms, yet all can lead to chronic activation.
Conclusions:
- Monoubiquitination at Lys-117 is a novel mechanism for H-Ras activation, distinct from K-Ras.
- Ras isoform-specific ubiquitination sites and mechanisms contribute to differential Ras signaling.
- Ubiquitination offers a pathway for chronic Ras activation independent of receptor signals or mutations.
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