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Spatio-Temporal Manipulation of Small GTPase Activity at Subcellular Level and on Timescale of Seconds in Living Cells
Published on: March 9, 2012
Modification of Rab5 with a photoactivatable analog of geranylgeranyl diphosphate
G J Quellhorst1, C M Allen, M Wessling-Resnick
1Department of Nutrition, Harvard School of Public Health, Boston, Massachusetts 02115, USA. gquellho@hsph.harvard.edu
The Journal of Biological Chemistry
|August 28, 2001
Summary
Researchers developed a novel photoaffinity probe to study Rab5 protein interactions. This technique reveals that soluble factors bind Rab5 via protein-protein interactions, not prenyl-lipid attachments.
Area of Science:
- Molecular Biology
- Protein Biochemistry
- Cell Signaling
Background:
- Rab proteins are crucial for intracellular membrane trafficking.
- Prenylation, a post-translational modification, is essential for Rab protein function.
- The precise mechanisms of Rab protein interactions with prenyltransferases and other factors remain incompletely understood.
Purpose of the Study:
- To develop a novel photoaffinity labeling technique for characterizing prenyl-binding sites.
- To investigate the interaction mechanisms between Rab5 and its modifying enzymes and binding partners.
- To elucidate whether Rab5 associates with soluble or membrane-bound factors through prenyl-lipid or protein-protein interactions.
Main Methods:
- Synthesis and application of a geranylgeranyl diphosphate analog, DATFP-FPP, as a photoprobe.
- In vitro prenylation assays using modified Rab5 and rabbit reticulocyte lysate.
- Gel mobility shift, Triton X-114 phase separation, and sucrose density gradient ultracentrifugation to analyze protein complexes.
- UV cross-linking of DATFP-modified Rab5 to identify interacting partners.
- Immunoprecipitation to confirm the identity of cross-linked proteins (Rab escort protein, GDI-1).
- Disuccinimidyl suberate cross-linking to investigate membrane-associated factor interactions.
Main Results:
- DATFP-FPP successfully inhibited and modified Rab5, confirming its use as a substrate by Rab geranylgeranyl transferase.
- DATFP-modified Rab5 formed larger complexes with soluble factors in the lysate, including Rab escort protein and GDI-1, identified via UV cross-linking and immunoprecipitation.
- While prenylated Rab5 associated with membranes, UV cross-linking failed to identify prenyl-binding membrane proteins, suggesting protein-protein interactions mediate these associations.
Conclusions:
- The novel DATFP-FPP photoprobe is effective for characterizing prenyl-binding sites and protein interactions.
- Soluble factors like Rab escort protein and GDI-1 bind Rab5 through protein-protein interactions.
- Membrane association of Rab5 likely involves protein-protein interactions rather than direct protein-prenyl-lipid interactions.
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