Structural insights into constitutive activity of 5-HT₆ receptor

Area of Science:

• Neuroscience
• Structural Biology
• Pharmacology

Background:

• G-protein-coupled receptors (GPCRs) research often targets agonist activation, overlooking intrinsic constitutive activity with therapeutic potential.
• Constitutive activity of the brain-specific serotonin 5-HT₆ receptor (5-HT₆R) is linked to cognitive/memory deficits in neuropsychiatric disorders.
• The structural underpinnings of 5-HT₆R's constitutive activity remain largely unknown.

Purpose of the Study:

• To determine the cryo-EM structure of the serotonin-bound human 5-HT₆R-Gs heterotrimer.
• To identify key structural determinants responsible for the constitutive activity of 5-HT₆R.
• To develop structure-guided tools for modulating 5-HT₆R constitutive activity.

Main Methods:

• Cryo-electron microscopy (cryo-EM) to resolve the 5-HT₆R-Gs heterotrimer structure at 3.0-Å resolution.
• Detailed structural analysis and signaling interrogation.
• Structure-guided mutagenesis and nanobody development.

Main Results:

• The cryo-EM structure revealed the serotonin-bound human 5-HT₆R-Gs heterotrimer.
• Key structural determinants essential for constitutive 5-HT₆R activity were identified.
• A nanobody mimic Gαs was developed, capable of reducing 5-HT₆R constitutive activity.

Conclusions:

• The study provides crucial insights into the molecular basis of 5-HT₆R constitutive activity.
• These findings will accelerate the development of novel therapeutics for neuropsychiatric disorders by targeting constitutive activity.
• The developed nanobody offers a potential therapeutic strategy for modulating 5-HT₆R function.