GPCR structure and function relationship: identification of a biased apelin receptor mutant

Area of Science:

• Pharmacology
• Molecular Biology
• Biochemistry

Background:

• Biased ligands for G protein-coupled receptors (GPCRs) offer potential therapeutic advantages but their mechanisms are poorly understood.
• Investigating the molecular basis of GPCR biased signaling is crucial for developing safer and more effective drugs.

Purpose of the Study:

• To elucidate the molecular mechanisms underlying biased signaling in GPCRs using the apelin receptor (APJ) as a model.
• To identify specific amino acid residues influencing APJ signaling bias.

Main Methods:

• Systematic investigation of amino acid residues around the APJ orthosteric binding site.
• Site-directed mutagenesis, including the I109A mutation in transmembrane domain 3 (TM3).
• Molecular dynamics simulations to analyze conformational changes and interactions.

Main Results:

• A single mutation, I109A in TM3 of APJ, converted the receptor to a biased signaling profile.
• The I109A mutant retained ligand binding and G protein activation but showed defects in GRK/β-arrestin recruitment and ERK activation.
• Molecular dynamics revealed that the mutation created space, allowing apelin's Phe-13 to interact with TM3 residues, stabilizing a biased conformation.

Conclusions:

• The I109A mutation in APJ provides a model for understanding GPCR biased signaling mechanisms.
• Specific hydrophobic interactions involving Phe-13 and TM3 residues dictate APJ signaling bias.
• These findings facilitate the design of novel APJ-targeting therapeutics with improved selectivity.