GABA, Valium, and Xanax
GABA (Gamma-Aminobutyric Acid) is the main inhibitory neurotransmitter in the mammalian central nervous system. It is a small molecule that reduces the activity of the neurons it binds to.
GABA binds two types of receptors, GABA-A and GABA-B. GABA-A receptors act by directly controlling the flow of ions across the cell membrane. GABA-B receptors activate intracellular signaling pathways that ultimately lead to changes in the cell's function.
Many drugs that affect GABA signaling have important medical applications. For example, benzodiazepines like Valium and Xanax enhance the activity of GABA-A receptors, leading to anxiolytic, sedative, and anticonvulsant effects. Barbiturates also enhance GABA-A receptor activity but have a higher risk of overdose and dependence. GABA-B agonists like Baclofen are used to treat spasticity and muscle rigidity in conditions like multiple sclerosis and spinal cord injury.
GABA receptor visualized in Nanome, PDB 6DW0.png
An unexpected effect
GABA-A receptor negative allosteric modulators (GABAaRNAMs) are a class of compounds that bind to a specific site on the GABA-A receptor and can increase arousal and seizures.
Scientists at the University of Saint Joseph (CT) found out that pathological sleep in humans can be reversed with a benzodiazepine antagonist and a macrolide antibiotic, which led them to wonder: what other drugs normally associated with sleep disruption can modulate arousal?
They screened 11 compounds that have been reported to influence arousal. The goal was to see if these compounds shared a GABA-related mechanism, and if it could be leveraged to improve arousal in patients suffering from diseases associated with excessive daytime sleepiness.
The computational modeling of modulator–receptor interactions predicted drug action at canonical binding sites and novel orphan sites on the receptor.
The 11 compounds had different chemical structures, yet they all modulated GABA-A receptor activation and had the ability to impair arousal in humans. From a structure–activity perspective, this may seem counterintuitive.
Modeling data provided an insight into this paradox, and showed how the GABA-A receptor can act as a connection for these compounds by binding them at multiple sites that in turn impair receptor activation, translating the binding of disparate molecular structures into changes in a common pathway.
The findings of the study suggest that multiple avenues are now open to investigate large and brain-penetrant molecules for the treatment of patients with an Excitation/Inhibition imbalance.
Common therapeutics involved inarousal inhibit GABAaR activation
Exploring the GABA receptor in VR
Professor Asher Brandt from the University of Saint Joseph walked Nanome’s scientist Daniel Gruffat on a journey to discover the GABA-A receptor structure for the first time in the history of Nanome’s YouTube channel!
In this video they go through the oligomeric structure of the receptor and then focus on different potential binding sites. Prof. Brandt shows us that GABA shares the same binding site as small antibiotics, while larger ones are likely to target a different region.
During the session, Nanome’s docking plugin came in handy for exploring several docking poses of Pentylenetetrazol, one of the compounds evaluated in the study.
Scientists visualize the GABA receptor in Nanome
Watch the full video here: https://youtu.be/EsLZceJ4CmQ
References:
Kaplan et al (2023). Commonly Used Therapeutics Associated with Changes in Arousal Inhibit GABAaR Activation. Biomolecules. 15;13(2):365. doi: 10.3390/biom13020365.