Different Benzodiazepines Bind with Distinct Binding Modes to GABA_A Receptors

Area of Science:

• Neuroscience
• Pharmacology
• Computational Chemistry

Background:

• Benzodiazepines are key drugs targeting GABA_A receptors, enhancing neuronal inhibition.
• The precise structural basis of benzodiazepine binding to GABA_A receptors remains controversial, with conflicting computational models.
• Chiral centers in benzodiazepines may influence receptor subtype selectivity and binding modes.

Purpose of the Study:

• To investigate the binding modes of different benzodiazepine chemotypes at various GABA_A receptor subtypes.
• To determine if structurally related benzodiazepines share a common binding mode or exhibit distinct interactions.
• To correlate in silico predictions with experimental data regarding ligand binding and functional activity.

Main Methods:

• Computational docking of diazepam into homology models of GABA_A receptors.
• Synthesis and testing of R and S isomers for three distinct benzodiazepine chemotypes (diazepam, imidazobenzodiazepine, triazolam derivatives).
• Radioligand displacement assays and two-electrode voltage clamp electrophysiology on GABA_A receptors (α1β3γ2, α2β3γ2, α3β3γ2, α5β3γ2).

Main Results:

• Imidazobenzodiazepine isomers showed similar binding affinities, unlike other chemotypes.
• For diazepam and triazolam derivatives, R isomers had reduced binding, while S isomers retained activity.
• Experimental findings align with in silico studies, suggesting distinct binding modes for imidazobenzodiazepines versus other tested benzodiazepines.

Conclusions:

• Chemically related benzodiazepines can interact with GABA_A receptors through distinct binding modes.
• The binding mode is not conserved across all benzodiazepine chemotypes.
• This study provides crucial insights into the structural basis of benzodiazepine-GABA_A receptor interactions, resolving previous controversies.