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Structural basis for the interaction of Ras with RalGDS
1Department of Chemistry and E.O. Lawrence Berkeley National Laboratory, University of California, Berkeley 94720, USA.
Abstract:
The Ras protein signals to a number of distinct pathways by interacting with diverse downstream effectors. Among the effectors of Ras are the Raf kinase and RalGDS, a guanine nucleotide dissociation stimulator specific for Ral. Despite the absence of significant sequence similarities, both effectors bind directly to Ras, but with different specificities. We report here the 2.1 A crystal structure of the complex between Ras and the Ras-interacting domain (RID) of RalGDS. This structure reveals that the beta-sheet of the RID joins the switch I region of Ras to form an extended beta-sheet with a topology similar to that found in the Rap-Raf complex. However, the side chain interactions at the joining junctions of the two interacting systems and the relative orientation of the two binding domains are distinctly different. Furthermore, in the case of the Ras-RID complex a second RID molecule also interacts with a different part of the Ras molecule, the switch II region. These findings account for the cross-talk between the Ras and Ral pathways and the specificity with which Ras distinguishes the two effectors.
Insights
The Ras protein interacts with RalGDS, a key signaling molecule, revealing a unique structural complex. This structure explains how Ras differentiates between RalGDS and other effectors, clarifying pathway signaling.
Area of Science:
- Molecular Biology
- Structural Biology
- Cell Signaling
Background:
- Ras proteins are critical regulators of cellular signaling pathways.
- Ras interacts with various downstream effectors, including Raf kinase and Ral Guanine Nucleotide Dissociation Stimulator (RalGDS).
- Despite functional similarities, Ras effectors exhibit distinct binding specificities and sequence variations.
Purpose of the Study:
- To elucidate the structural basis of Ras-RalGDS interaction.
- To understand the molecular mechanisms underlying Ras effector specificity.
- To explain the cross-talk between Ras and Ral signaling pathways.
Main Methods:
- X-ray crystallography was employed to determine the 2.1 Å structure of the Ras-RalGDS Ras-Interacting Domain (RID) complex.
- Structural analysis focused on the interfaces between Ras and RalGDS, including beta-sheet formation and side chain interactions.
- Comparison of the Ras-RalGDS complex with other Ras-effector complexes, such as Rap-Raf.
Main Results:
- The Ras-RalGDS complex structure reveals an extended beta-sheet formed by the RalGDS RID and Ras switch I region.
- This topology is similar to the Rap-Raf complex, but with distinct side chain interactions and domain orientations.
- A novel finding is the interaction of a second RalGDS RID molecule with the Ras switch II region.
- These structural features explain the specific binding of Ras to RalGDS and potential pathway cross-talk.
Conclusions:
- The determined structure provides atomic-level insights into Ras-RalGDS binding.
- The dual interaction of RalGDS with Ras accounts for the specificity and cross-talk observed in Ras signaling.
- Understanding these interactions is crucial for deciphering complex cellular signaling networks and potential therapeutic targets.