Deciphering biased-agonism complexity reveals a new active AT1 receptor entity

Area of Science:

• Pharmacology
• Molecular Biology
• Biochemistry

Background:

• Functional selectivity of G protein-coupled receptors (GPCRs) is a key characteristic, but complex signaling pathways hinder its understanding.
• Deciphering GPCR functional selectivity is challenging due to pleiotropic and crosstalk signaling.
• Understanding the initial active receptor conformation is crucial for decoding biased agonism.

Purpose of the Study:

• To develop novel, highly sensitive bioluminescence resonance energy transfer (BRET)-based probes for direct detection of G protein activation across all isoforms.
• To investigate the G protein-coupling activity of [(1)Sar(4)Ile(8)Ile]-angiotensin II (SII), a previously characterized biased agonist.
• To elucidate the precise signaling mechanism of SII at the angiotensin II type 1 (AT(1)) receptor.

Main Methods:

• Development of specific and sensitive BRET-based probes for real-time monitoring of G protein activation.
• Multiplexing assays to simultaneously measure receptor conformation and downstream signaling events.
• Evaluation of SII's G protein-coupling activity in both recombinant and primary cell systems.

Main Results:

• SII was identified as an agonist that stabilizes a unique G protein-dependent AT(1A) receptor signaling module.
• This SII-induced signaling module is distinct from that mediated by the physiological agonist, angiotensin II.
• The study provides direct evidence of G protein activation by SII, challenging previous assumptions of its G protein independence.

Conclusions:

• Biased agonists may not simply select a subset of effects from a physiological agonist but can stabilize novel, distinct active receptor conformations.
• The developed BRET probes offer a powerful tool for dissecting complex GPCR signaling and functional selectivity.
• This research redefines the understanding of biased agonism, highlighting the potential for creating new pharmacological receptor entities.