Abstract

One of the leading components in the development of alcohol-induced neuroplasticity of the brain is the neuroadaptive changes in the GABAA receptor. GABAAR belongs to the family of cis-loop receptors, it is a heteromeric protein complex consisting of five subunits that form a central ion-conducting pore and is an anion-selective (CL-) channel responsible for rapid inhibitory transmission in the CNS. GABAAR are targets of various drugs, including tranquilizers and alcohol. The existence of 19 different subunits (α1–6, β1–3, γ1–3, δ, ε, π, θ, ρ1–3) results in a multiplicity of GABAAR subtypes with distinct subunit compositions and different pharmacology. Specific receptor subunits can mediate alcohol- or drug-related behavior. The most common GABAAR subunit combination in the CNS is the α1β2γ2 subtype. The crystal structure of the α1β2γ2 GABAAR heteropentamer represents a receptor model optimized for studying interactions with agonists and allosteric modulators that bind to their target sites of the GABAR. A modern approach to molecular modeling using computer design and computational platforms in combination with molecular and quantum mechanics (molecular docking) allows to estimate the geometry of ligand-receptor interactions of new medicinal compounds based on their mechanism of action and structure. Molecular docking was performed to study the complexation of the Galodif molecule - meta-chloro-benzhydryl urea (m-Cl-BGM) with the determination of the orientation and conformation of the ligand in the binding site of the GABAAR. For docking, a model crystal structure of the α1β2γ2 GABAAR heteropentamer was used, characterized by high accuracy and optimized for assessing the interaction of ligands with the benzodiazepine site of GABAAR. It was established by the results of molecular docking (Schrödinger (Glide) program) that the m-Cl-BGM molecule is complementary to the benzodiazepine binding site of GABAAR. The key amino acids responsible for ligand binding at the GABAAR site are: α1F64, α1R66, α1L117, α1R119, α1T129, α1R131, β2Y97, β2E155, β2Y157, β2F200, β2S201, β2T202, β2G203, β2Y205, β2R207. According to the results of docking, it was established that the m-Cl-BGM molecule is complementary to the benzodiazepine binding site GABAR (binding energy is quite low) and interacts with key amino acids at the α1γ2 interface: Tyr159 (hydrogen bonds), Tyr209, H101 Phe77 (π-π interaction) with a high degree of model compliance - dG insertion: 0.74. Our molecular modeling data are consistent with our experiments on the effect of m-Cl-BGM on the binding of the selective ligand [3H]flunitrazepam to GABA/benzodiazepine receptors (BZDR). When m-Cl-BGM was administered intragastrically in 1% starch suspension (100 mg/kg per day - 1/20 LD50) for 14 days to male Wistar rats under conditions of 10 months of consumption of 15% ethanol solution by alcohol-preferring animals under conditions of free access to alcohol and water, we found an increase in the affinity of benzodiazepine binding sites-receptors (BZDR) of the GABA receptor complex (a decrease in the values of the dissociation constant of the ligand-receptor complex - Kd) of BZDR in the cerebral cortex of rats to the level of Kd values of receptors in rats not subjected to chronic alcoholization. The obtained data indicate an increase in the affinity of receptors to the selective ligand - [3H]flunitrazepam in these animals under the influence of the introduction of m-Cl-BGM. Thus, the m-Cl-BGM molecule, located in the narrow binding pocket of the benzodiazepine - diazepam, having a similar stoichiometry to the diazepam molecule, but a lower molecular weight and less bulky geometry of the molecule, exerts allosteric modulation of the GABA/benzodiazepine receptor, increasing its affinity for GABA and stimulates GABAergic neuronal function in the CNS. m-Cl-BGM modulates GABAAR through conformational changes in the receptor.