Does Divergent Binding Pocket Closure Drive Ligand Bias for Class A GPCRs?

Area of Science:

• Biochemistry
• Molecular Pharmacology
• Cell Signaling

Background:

• G protein-coupled receptors (GPCRs) are crucial cell surface receptors involved in numerous physiological processes.
• GPCRs mediate cellular responses by coupling to intracellular transducer proteins.
• Allosteric coupling describes the reciprocal conformational changes between the ligand-binding pocket and intracellular interfaces.

Purpose of the Study:

• To investigate the mechanism by which agonists with extended binding modes induce ligand bias in GPCR signaling.
• To explore the hypothesis that interference with binding pocket closure underlies divergent allosteric coupling and functional selectivity.

Main Methods:

• Computational modeling of GPCR-ligand interactions.
• Allosteric network analysis.
• Functional assays to measure pathway-specific signaling.

Main Results:

• Agonists with extended binding modes were shown to selectively inhibit the closure of the GPCR extracellular ligand binding pocket.
• This inhibition of pocket closure leads to altered allosteric coupling pathways.
• The divergent allosteric coupling results in biased signaling, favoring specific downstream pathways over others.

Conclusions:

• Ligand binding mode is a critical determinant of GPCR functional selectivity.
• Interference with allosteric coupling, specifically binding pocket closure, provides a mechanistic explanation for agonist-induced ligand bias.
• This understanding can inform the design of novel therapeutics targeting GPCRs with improved selectivity.