Nicotinic acetylcholine receptors are ligand-gated ion channels that mediate fast chemical neurotransmission at the neuromuscular junction and have diverse signalling roles in the central nervous ...system. The nicotinic receptor has been a model system for cell-surface receptors, and specifically for ligand-gated ion channels, for well over a century. In addition to the receptors' prominent roles in the development of the fields of pharmacology and neurobiology, nicotinic receptors are important therapeutic targets for neuromuscular disease, addiction, epilepsy and for neuromuscular blocking agents used during surgery. The overall architecture of the receptor was described in landmark studies of the nicotinic receptor isolated from the electric organ of Torpedo marmorata. Structures of a soluble ligand-binding domain have provided atomic-scale insights into receptor-ligand interactions, while high-resolution structures of other members of the pentameric receptor superfamily provide touchstones for an emerging allosteric gating mechanism. All available high-resolution structures are of homopentameric receptors. However, the vast majority of pentameric receptors (called Cys-loop receptors in eukaryotes) present physiologically are heteromeric. Here we present the X-ray crystallographic structure of the human α4β2 nicotinic receptor, the most abundant nicotinic subtype in the brain. This structure provides insights into the architectural principles governing ligand recognition, heteromer assembly, ion permeation and desensitization in this prototypical receptor class.
Most general anaesthetics and classical benzodiazepine drugs act through positive modulation of γ-aminobutyric acid type A (GABA
) receptors to dampen neuronal activity in the brain
. 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
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
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
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.
The ability of oligomeric membrane proteins to assemble in different functional ratios of subunits is a common feature across many systems. Recombinant expression of hetero-oligomeric proteins with ...defined stoichiometries facilitates detailed structural and functional analyses, but remains a major challenge. Here we present two methods for overcoming this challenge: one for rapid virus titration and another for stoichiometry determination. When these methods are coupled, they allow for efficient dissection of the heteromer stoichiometry problem and optimization of homogeneous protein expression. We demonstrate the utility of the methods in a system that to date has proved resistant to atomic-scale structural study, the nicotinic acetylcholine receptor. Leveraging these two methods, we have successfully expressed, purified, and grown diffraction-quality crystals of this challenging target.
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•Streamlined bacmam virus titration method•Fluorescent protein fusion approach for estimation of subunit ratio in a heteromer•Expression and crystallization of a defined nicotinic receptor stoichiometry
Morales-Perez et al. developed a pair of methods to efficiently express defined stoichiometries of heteromeric membrane proteins. Application of this approach to a nicotinic acetylcholine receptor that can assemble in multiple functional ratios of subunits has yielded diffraction-quality crystals of the receptor.
The nicotinic acetylcholine receptor, a pentameric ligand-gated ion channel, converts the free energy of binding of the neurotransmitter acetylcholine into opening of its central pore. Here we ...present the first high-resolution structure of the receptor type found in muscle-endplate membrane and in the muscle-derived electric tissues of fish. The native receptor was purified from Torpedo electric tissue and functionally reconstituted in lipids optimal for cryo-electron microscopy. The receptor was stabilized in a closed state by the binding of α-bungarotoxin. The structure reveals the binding of a toxin molecule at each of two subunit interfaces in a manner that would block the binding of acetylcholine. It also reveals a closed gate in the ion-conducting pore, formed by hydrophobic amino acid side chains, located ∼60 Å from the toxin binding sites. The structure provides a framework for understanding gating in ligand-gated channels and how mutations in the acetylcholine receptor cause congenital myasthenic syndromes.
•High-resolution structure of a native muscle-type nicotinic acetylcholine receptor•Previously unresolved structural elements contribute to neurotoxin binding•Channel is stabilized in a closed conformation by α-bungarotoxin from snake venom•Transduction mechanism and myasthenic disease mutations
Rahman et al. report the high-resolution single-particle cryo-EM structure of a native muscle-type nicotinic acetylcholine receptor from the Torpedo electric ray, in complex with α-bungarotoxin from the banded krait. The structure was obtained in a lipidic environment shown to support channel function and reveals a closed, hydrophobic ion channel gate.
Long non-coding RNAs (lncRNAs) represent a novel class of non-coding RNAs having a crucial role in many biological processes. The identification of long non-coding homologs among different species is ...essential to investigate such roles in model organisms as homologous genes tend to retain similar molecular and biological functions. Alignment-based metrics are able to effectively capture the conservation of transcribed coding sequences and then the homology of protein coding genes. However, unlike protein coding genes the poor sequence conservation of long non-coding genes makes the identification of their homologs a challenging task.
In this study we compare alignment-based and alignment-free string similarity metrics and look at promoter regions as a possible source of conserved information. We show that promoter regions encode relevant information for the conservation of long non-coding genes across species and that such information is better captured by alignment-free metrics. We perform a genome wide test of this hypothesis in human, mouse, and zebrafish.
The obtained results persuaded us to postulate the new hypothesis that, unlike protein coding genes, long non-coding genes tend to preserve their regulatory machinery rather than their transcribed sequence. All datasets, scripts, and the prediction tools adopted in this study are available at https://github.com/bioinformatics-sannio/lncrna-homologs .
The α7 nicotinic acetylcholine receptor is a pentameric ligand-gated ion channel that modulates neuronal excitability, largely by allowing Ca2+ permeation. Agonist binding promotes transition from a ...resting state to an activated state, and then rapidly to a desensitized state. Recently, cryogenic electron microscopy (cryo-EM) structures of the human α7 receptor in nanodiscs were reported in multiple conformations. These were selectively stabilized by inhibitory, activating, or potentiating compounds. However, the functional annotation of these structures and their differential interactions with unresolved lipids and ligands remain incomplete. Here, we characterized their ion permeation, membrane interactions, and ligand binding using computational electrophysiology, free-energy calculations, and coarse-grained molecular dynamics. In contrast to nonconductive structures in apparent resting and desensitized states, the structure determined in the presence of the potentiator PNU-120596 was consistent with an activated state permeable to Ca2+. Transition to this state was associated with compression and rearrangement of the membrane, particularly in the vicinity of the peripheral MX helix. An intersubunit transmembrane site was implicated in selective binding of either PNU-120596 in the activated state or cholesterol in the desensitized state. This substantiates functional assignment of all three lipid-embedded α7-receptor structures with ion-permeation simulations. It also proposes testable models of their state-dependent interactions with lipophilic ligands, including a mechanism for allosteric modulation at the transmembrane subunit interface.
Abstract
γ-Aminobutyric acid type A (GABA
A
) receptors mediate fast inhibitory signaling in the brain and are targets of numerous drugs and endogenous neurosteroids. A subset of neurosteroids are ...GABA
A
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 GABA
A
receptors, but their binding sites remain debated. Here we present structures of a synaptic GABA
A
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.
Introduction
Non-Alcoholic Fatty Liver Disease (NAFLD) is currently the most common form of liver disease worldwide affecting all ages and ethnic groups and it has become a consistent threat even in ...young people. Our aim was to estimate the effect of a Low Glycemic Index Mediterranean Diet (LGIMD) on the NAFLD score as measured by a Liver Ultrasonography (LUS).
Design
NUTRIzione in EPAtologia (NUTRIEPA) is a population-based Double-Blind RCT. Data were collected in 2011 and analyzed in 2013-14.
Setting/participants
98 men and women coming from Putignano (Puglia, Southern Italy) were drawn from a previous randomly sampled population-based study and identified as having moderate or severe NAFLD.
Intervention
The intervention strategy was the assignment of a LGIMD or a control diet.
Outcome measures
The main outcome measure was NAFLD score, defined by LUS.
Results
After randomization, 50 subjects were assigned to a LGIMD and 48 to a control diet. The study lasted six months and all participants were subject to monthly controls/checks. Adherence to the LGIMD as measured by Mediterranean Adequacy Index (MAI) showed a median of 10.1. A negative interaction between time and LGIMD on the NAFLD score (-4.14, 95% CI -6.78,-1.49) was observed, and became more evident at the sixth month (-4.43, 95%CI -7.15, -1.71). A positive effect of the interaction among LGIMD, time and age (Third month: 0.07, 95% CI 0.02, 0.12; Sixth month: 0.08, 95% CI 0.03,0.13) was also observed.
Conclusions
LGIMD was found to decrease the NAFLD score in a relatively short time. Encouraging those subjects who do not seek medical attention but still have NAFLD to follow a LGIMD and other life-style interventions, may reduce the degree of severity of the disease. Dietary intervention of this kind, could also form the cornerstone of primary prevention of Type 2 Diabetes Mellitus (T2DM) and cardiovascular disease.
Background and Purpose
AVE 0991 (AVE) is a non‐peptide compound, mimic of the angiotensin (Ang)‐(1–7) actions in many tissues and pathophysiological states. Here, we have investigated the effect of ...AVE on pulmonary remodelling in a murine model of ovalbumin (OVA)‐induced chronic allergic lung inflammation.
Experimental Approach
We used BALB/c mice (6–8 weeks old) and induced chronic allergic lung inflammation by OVA sensitization (20 μg·mouse−1, i.p., four times, 14 days apart) and OVA challenge (1%, nebulised during 30 min, three times per·week, for 4 weeks). Control and AVE groups were given saline i.p and challenged with saline. AVE treatment (1 mg·kg−1·per day, s.c.) or saline (100 μL·kg−1·per day, s.c.) was given during the challenge period. Mice were anaesthetized 72 h after the last challenge and blood and lungs collected. In some animals, primary bronchi were isolated to test contractile responses. Cytokines were evaluated in bronchoalveolar lavage (BAL) and lung homogenates.
Key Results
Treatment with AVE of OVA sensitised and challenged mice attenuated the altered contractile response to carbachol in bronchial rings and reversed the increased airway wall and pulmonary vasculature thickness and right ventricular hypertrophy. Furthermore, AVE reduced IL‐5 and increased IL‐10 levels in the BAL, accompanied by decreased Ang II levels in lungs.
Conclusions and Implications
AVE treatment prevented pulmonary remodelling, inflammation and right ventricular hypertrophy in OVA mice, suggesting that Ang‐(1–7) receptor agonists are a new possibility for the treatment of pulmonary remodelling induced by chronic asthma.
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