Intrinsic conformational equilibria position arrestin-2 for activation

Area of Science:

• Molecular and Structural Biology
• Biochemistry
• Cell Signaling

Background:

• Arrestins (arrestin-2) are key regulators of G protein-coupled receptor (GPCR) signaling, mediating receptor desensitization and internalization.
• Arrestin activation involves large conformational changes, but the pre-activation conformational equilibria in solution are not well understood.
• Previous studies identified minor conformational states but could not link them to activation due to signal broadening upon receptor binding.

Purpose of the Study:

• To characterize the intrinsic conformational landscape of full-length human arrestin-2 in solution.
• To identify pre-existing conformational equilibria that precede receptor binding and activation.
• To provide a solution-state framework for understanding arrestin pre-activation dynamics.

Main Methods:

• Multinuclear NMR spectroscopy was employed to study the conformational dynamics of arrestin-2.
• Dynamic analyses, including backbone relaxation measurements, were used to probe conformational exchange on various timescales (μs-ms).

Main Results:

• Two distinct pre-existing conformational equilibria were identified in arrestin-2 solution states.
• A slow exchange equilibrium populates a receptor-bound-like, interdomain-twisted conformation at physiological temperatures.
• A faster equilibrium populates a state consistent with C-terminal tail release, indicating arrestin-2 acts as a preorganized scaffold intrinsically sampling relevant conformations.

Conclusions:

• Arrestin-2 exists as a preorganized scaffold that intrinsically samples conformations relevant to receptor binding in the absence of ligands.
• These findings provide a solution-state model for arrestin pre-activation.
• This study establishes a dynamic fingerprint for future investigations into ligand-dependent arrestin activation.