7qn9
Cryo-EM structure of human full-length extrasynaptic alpha4beta3delta GABA(A)R in complex with GABA, histamine and nanobody Nb25 in a pre-open/closed state
Structural highlights
FunctionGBRA4_HUMAN Alpha subunit of the heteropentameric ligand-gated chloride channel gated by gamma-aminobutyric acid (GABA), a major inhibitory neurotransmitter in the brain (PubMed:35355020). GABA-gated chloride channels, also named GABA(A) receptors (GABAAR), consist of five subunits arranged around a central pore and contain GABA active binding site(s) located at the alpha and beta subunit interface(s) (PubMed:35355020). When activated by GABA, GABAARs selectively allow the flow of chloride anions across the cell membrane down their electrochemical gradient (PubMed:35355020). GABAARs containing alpha-4 are predominantly extrasynaptic, contributing to tonic inhibition in dentate granule cells and thalamic relay neurons (By similarity). Extrasynaptic alpha-4-containing GABAARs control levels of excitability and network activity (By similarity). GABAAR containing alpha-4-beta-3-delta subunits can simultaneously bind GABA and histamine where histamine binds at the interface of two neighboring beta subunits, which may be involved in the regulation of sleep and wakefulness (PubMed:35355020).[UniProtKB:Q9D6F4][1] Publication Abstract from PubMedType A gamma-aminobutyric acid receptors (GABA(A)Rs) are pentameric ligand-gated chloride channels that mediate fast inhibitory signalling in neural circuits(1,2) and can be modulated by essential medicines including general anaesthetics and benzodiazepines(3). Human GABA(A)R subunits are encoded by 19 paralogous genes that can, in theory, give rise to 495,235 receptor types. However, the principles that govern the formation of pentamers, the permutational landscape of receptors that may emerge from a subunit set and the effect that this has on GABAergic signalling remain largely unknown. Here we use cryogenic electron microscopy to determine the structures of extrasynaptic GABA(A)Rs assembled from alpha4, beta3 and delta subunits, and their counterparts incorporating gamma2 instead of delta subunits. In each case, we identified two receptor subtypes with distinct stoichiometries and arrangements, all four differing from those previously observed for synaptic, alpha1-containing receptors(4-7). This, in turn, affects receptor responses to physiological and synthetic modulators by creating or eliminating ligand-binding sites at subunit interfaces. We provide structural and functional evidence that selected GABA(A)R arrangements can act as coincidence detectors, simultaneously responding to two neurotransmitters: GABA and histamine. Using assembly simulations and single-cell RNA sequencing data(8,9), we calculated the upper bounds for receptor diversity in recombinant systems and in vivo. We propose that differential assembly is a pervasive mechanism for regulating the physiology and pharmacology of GABA(A)Rs. Differential assembly diversifies GABA(A) receptor structures and signalling.,Sente A, Desai R, Naydenova K, Malinauskas T, Jounaidi Y, Miehling J, Zhou X, Masiulis S, Hardwick SW, Chirgadze DY, Miller KW, Aricescu AR Nature. 2022 Apr;604(7904):190-194. doi: 10.1038/s41586-022-04517-3. Epub 2022 , Mar 30. PMID:35355020[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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