# Conformational Heterogeneity Underlying Divergent Signaling in Class A G Protein-Coupled Receptors

## TL;DR

This paper explores how different shapes of GPCRs lead to varied signaling and drug responses, highlighting new methods to study these shapes.

## Contribution

The paper introduces new biophysical techniques to identify transient GPCR conformations missed by traditional methods.

## Key findings

- GPCRs have multiple active and inactive conformations that influence signaling pathways.
- Transient conformations can be detected using techniques like NMR and fluorescence microscopy.
- Ligands targeting specific conformations could improve drug efficacy and safety.

## Abstract

Class A G protein-coupled
receptors (GPCRs) are targets
for ∼36%
of commercial drugs. GPCRs in their apo-forms exhibit conformational
heterogeneity, and more than a single active and inactive conformation
exists in equilibrium. Distinct transient conformational states can
be significantly populated and can be coupled with different agonists,
transducers, and effectors, giving rise to divergent signaling pathways.
The characterization of such transient conformational states, which
may have eluded identification by X-ray crystallography and cryogenic
electron microscopy, can be achieved through a combination of biophysical
techniques, such as nuclear magnetic resonance, double electron–electron
resonance spectroscopy, single-molecule fluorescence microscopy, molecular
dynamics simulations, and mass spectrometry. We review findings about
the functional, conformational states of four class A GPCRs, including
detailed results for the adenosine A2A and β2 adrenergic receptors and important observations for the β1 and μ opioid receptors. The identification of ligands
that can bind to distinct conformations, e.g., agonists that activate
favorable pathways while inhibiting deleterious ones, represents an
important goal in drug development.