GABA A receptors (GABA A Rs) are pentameric ligand-gated ion channels that mediate inhibitory neurotransmission in central nervous system. Their gating transitions depend on precise extracellular domain (ECD) rearrangements, where loops C and F play central roles in ligand efficacy which directs the pore dynamics. Glycosylation, an important post-translational modification, is known to influence GABA A Rs function. Several glycosylation sites have been identified across GABA A Rs subunits. Many of them are also conserved in the pentameric ligand-gated ion channel super family (pLGIC) and are located near orthosteric binding sites. This similarity suggests a general modulatory mechanism for these glycans. The mechanism underlying this conserved functional role remains unknown. To investigate this, we performed 100 μs of all-atom unbiased molecular dynamics simulations on fully glycosylated α1β2γ2 GABA A Rs and a non-glycosylated system under saturating GABA concentrations. The trajectories were analyzed to capture the glycan-dependent differences in stability, dynamics, and ligand binding. Our results reveal that surface glycans stabilize Loop C and F through hydrogen bonds that help to maintain the structural integrity of the orthosteric pocket. This stabilization was characterized by a stable pre-binding conformation that prime the binding sites for GABA capture. We directly observed spontaneous GABA binding into the canonical pocket during the simulation time without applying any biasing force, providing the first report of this critical molecular process. In addition, the glycans shield large portions of the receptor surface, limiting access to alternative interfaces and binding sites, while leaving the orthosteric pockets relatively exposed. This selective shielding may facilitate GABA recognition and binding by guiding ligands toward the orthosteric site. These findings show how surface glycosylation promotes ligand binding and channel opening in GABA A receptors. This mechanism could be a shared process across the pLGICs that uses glycans to fine-tune neurotransmitter signaling at synapses.
Ahangar et al. (Sun,) studied this question.