Related Experiment Videos
Characterization of the interaction between RhoGDI and Cdc42Hs using fluorescence spectroscopy
1Department of Biochemistry, Molecular and Cell Biology, Cornell University, Ithaca, New York 14853, USA.
The Journal of Biological Chemistry
|April 26, 1996
Summary
A new fluorescence assay directly measures GDP-dissociation inhibitor (GDI) binding to Cdc42Hs, revealing a 30 nM affinity. This method differentiates GDI from LD4 proteins, identifying a key binding region.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Signaling
Background:
- GDP-dissociation inhibitor (GDI) regulates Rho-like GTP-binding proteins through multiple biochemical activities.
- Understanding GDI's interaction with Cdc42Hs is crucial for elucidating its regulatory mechanisms.
Purpose of the Study:
- To develop a direct fluorescence spectroscopic assay for GDI binding to Cdc42Hs.
- To characterize the binding kinetics and identify regions responsible for differential binding affinities.
Main Methods:
- Utilized N-methylanthraniloyl GDP (Mant-GDP) fluorescence quenching assay.
- Employed Spodoptera frugiperda-expressed and Escherichia coli-expressed Cdc42Hs, including a carboxyl-terminal mutant.
- Performed fluorescence titrations to determine binding affinities (Kd) and analyzed GDI/LD4 chimeras.
Main Results:
- GDI binding to Cdc42Hs-Mant-GDP induced a ~20% fluorescence quench, dependent on isoprenylation.
- The assay revealed a 1:1 binding stoichiometry with an apparent Kd of 30 nM for GDP-bound Cdc42Hs and 28 nM for GTP-bound Cdc42Hs.
- Differences in functional potency between GDI and LD4 correlated with their binding affinities, pinpointing a carboxyl-terminal GDI region for high-affinity binding.
Conclusions:
- The fluorescence assay provides a direct readout for GDI-Cdc42Hs interaction.
- GDI exhibits similar binding affinities for both GDP- and GTP-bound Cdc42Hs.
- A specific region in the GDI carboxyl-terminus mediates higher affinity binding to Cdc42Hs compared to LD4.