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Most general anaesthetics and classical benzodiazepine drugs act through positive modulation of [gamma]-aminobutyric acid type A (GABA.sub.A) receptors to dampen neuronal activity in the brain.sup.1-5. However, direct structural information on the mechanisms of general anaesthetics at their physiological receptor sites is lacking. Here we present cryo-electron microscopy structures of GABA.sub.A receptors bound to intravenous anaesthetics, benzodiazepines and inhibitory modulators. These structures were solved in a lipidic environment and are complemented by electrophysiology and molecular dynamics simulations. Structures of GABA.sub.A receptors in complex with the anaesthetics phenobarbital, etomidate and propofol reveal both distinct and common transmembrane binding sites, which are shared in part by the benzodiazepine drug diazepam. Structures in which GABA.sub.A receptors are bound by benzodiazepine-site ligands identify an additional membrane binding site for diazepam and suggest an allosteric mechanism for anaesthetic reversal by flumazenil. This study provides a foundation for understanding how pharmacologically diverse and clinically essential drugs act through overlapping and distinct mechanisms to potentiate inhibitory signalling in the brain. Cryo-electron microscopy structures of GABA.sub.A receptors bound to intravenous anaesthetics and benzodiazepines reveal both common and distinct transmembrane binding sites, and show that the mechanisms of action of anaesthetics partially overlap with those of benzodiazepines., Author(s): Jeong Joo Kim [sup.1] , Anant Gharpure [sup.1] , Jinfeng Teng [sup.1] , Yuxuan Zhuang [sup.2] , Rebecca J. Howard [sup.2] , Shaotong Zhu [sup.1] , Colleen M. Noviello [...]

γ-Aminobutyric acid type A (GABAA) receptors mediate fast inhibitory signaling in the brain and are targets of numerous drugs and endogenous neurosteroids. A subset of neurosteroids are GABAA receptor positive allosteric modulators; one of these, allopregnanolone, is the only drug approved specifically for treating postpartum depression. There is a consensus emerging from structural, physiological and photolabeling studies as to where positive modulators bind, but how they potentiate GABA activation remains unclear. Other neurosteroids are negative modulators of GABAA receptors, but their binding sites remain debated. Here we present structures of a synaptic GABAA receptor bound to allopregnanolone and two inhibitory sulfated neurosteroids. Allopregnanolone binds at the receptor-bilayer interface, in the consensus potentiator site. In contrast, inhibitory neurosteroids bind in the pore. MD simulations and electrophysiology support a mechanism by which allopregnanolone potentiates channel activity and suggest the dominant mechanism for sulfated neurosteroid inhibition is through pore block. Legesse et al. present structural studies of a human GABAA receptor in complex with positive and negative modulator neurosteroids, uncovering mechanisms of potentiation and inhibition. [ABSTRACT FROM AUTHOR]

Voltage-gated sodium channels play an important role in electrical signaling in excitable cells. In response to changes in membrane potential, they cycle between nonconducting and conducting conformations. With recent advances in structural biology, structures of sodium channels have been captured in several distinct conformations, which are thought to represent different functional states. However, it has been difficult to capture the intrinsically transient open state. We recently showed that a proposed open state of the bacterial sodium channel NavMs was not conductive and that a conformational change involving a transition to a p-helix in the pore-lining S6 helix converted this structure into a conducting state. However, the relevance of this structural feature in other sodium channels, and its implications for the broader gating cycle, remained unclear. Here, we propose a comparable open state of another class of bacterial channel from Aliarcobacter butzleri (NavAb) with characteristic pore hydration, ion permeation, and drug binding properties. Furthermore, we show that a p-helix transition can lead to pore opening and that such a conformational change blocks fenestrations in the inner helix bundle. We also discover that a region in the C-terminal domain can undergo a disordering transition proposed to be important for pore opening. These results support a role for a p-helix transition in the opening of NavAb, enabling new proposals for the structural annotation and drug modulation mechanisms in this important sodium channel model. [ABSTRACT FROM AUTHOR]