Crystal structure of the Rac1-RhoGDI complex involved in nadph oxidase activation

Area of Science:

• Molecular biology
• Structural biology
• Biochemistry

Background:

• Rac1 and Rho GDP dissociation inhibitor (RhoGDI) are key regulators of cellular processes.
• Understanding their interaction is crucial for deciphering signaling pathways.
• NADPH oxidase activation involves Rac1, but the precise mechanism remains incompletely understood.

Purpose of the Study:

• To elucidate the structural basis of the Rac1-RhoGDI complex.
• To investigate the mechanism of NADPH oxidase activation by the Rac1-RhoGDI complex.

Main Methods:

• Purification of prenylated Rac1-RhoGDI heterodimer.
• Small angle neutron scattering (SANS) for stoichiometry determination.
• X-ray crystallography for high-resolution structure determination (2.7 Å).

Main Results:

• Confirmed a 1:1 stoichiometry of the Rac1-RhoGDI complex.
• Determined the crystal structure, revealing Rac1 bound to GDP with a mixed conformation in switch regions.
• Identified critical lipid-protein interactions and hydrogen/hydrophobic bonds stabilizing the complex.
• Showed that accessible effector loops in the complex facilitate NADPH oxidase activation.

Conclusions:

• The Rac1-RhoGDI complex is competent for NADPH oxidase activation.
• Specific structural interactions dictate the complex's stability and function.
• The structure provides insights into the regulation of Rac1 activity and downstream signaling.