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Catalytic domain of the p120 Ras GAP binds to RAb5 and stimulates its GTPase activity
1Department of Biochemistry and Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73190, USA.
Abstract:
Ras is a master GTPase switch controlling multiple signal transduction cascades in the regulation of cell proliferation and differentiation. Rab5 is a local GTPase switch that is localized on early endosomes and controls early endosome fusion. This study demonstrates that the catalytic domain of p120 GTPase-activating protein (GAP), a well known Ras GAP, is able to interact physically with Rab5 and stimulate its GTPase activity. This GAP activity toward Rab5, however, cannot be extended to other Rab GTPases such as Rab3, Rab4, and Rab6, indicating that it is not a generic GAP for the Rab family of GTPases that regulate intracellular membrane fusion during endocytosis and exocytosis. The findings indicate a level of structural similarity between Ras and Rab5 unexpected from their primary sequences. They also suggest a possible signal transduction regulation of the Rab5-dependent endosome fusion via the Ras GAP.
Insights
p120 GTPase-activating protein (GAP), a Ras GAP, physically interacts with Rab5, stimulating its GTPase activity. This specific interaction suggests a novel signaling pathway regulating endosome fusion via Ras GAP.
Area of Science:
- Molecular Biology
- Cell Biology
- Signal Transduction
Background:
- Ras GTPase is a key regulator of cell proliferation and differentiation.
- Rab5 GTPase controls early endosome fusion.
- GTPase-activating proteins (GAPs) regulate GTPase activity.
Purpose of the Study:
- To investigate the interaction between p120 GAP and Rab5.
- To determine if p120 GAP can stimulate Rab5 GTPase activity.
- To explore the implications of this interaction for signal transduction.
Main Methods:
- Co-immunoprecipitation to assess physical interaction.
- In vitro GTPase assays to measure enzyme activity.
- Testing activity against various Rab GTPases (Rab3, Rab4, Rab6).
Main Results:
- The catalytic domain of p120 GAP directly interacts with Rab5.
- p120 GAP significantly stimulates the GTPase activity of Rab5.
- This GAP activity is specific to Rab5 and not observed for Rab3, Rab4, or Rab6.
- Structural similarities between Ras and Rab5 were noted, despite differing primary sequences.
Conclusions:
- p120 GAP specifically targets Rab5, suggesting a non-generic role.
- The findings reveal a potential link between Ras signaling and Rab5-dependent endosome fusion.
- This interaction may represent a novel mechanism for regulating endosomal trafficking.