scholarly journals Segregation of lipids near acetylcholine-receptor channels imaged by cryo-EM

IUCrJ ◽  
2017 ◽  
Vol 4 (4) ◽  
pp. 393-399 ◽  
Author(s):  
Nigel Unwin
Keyword(s):  
Membrane Lipids ◽  
Electrical Response ◽  
Postsynaptic Membrane ◽  
Chemical Synapse ◽  
Transmembrane Helices ◽  
Time Resolved ◽  
Presynaptic Nerve Terminal ◽  
Local Rigidity ◽  
Outer Leaflet ◽  
Lipid Distribution

Rapid communication at the chemical synapse depends on the action of ion channels residing in the postsynaptic membrane. The channels open transiently upon the binding of a neurotransmitter released from the presynaptic nerve terminal, eliciting an electrical response. Membrane lipids also play a vital but poorly understood role in this process of synaptic transmission. The present study examines the lipid distribution around nicotinic acetylcholine (ACh) receptors in tubular vesicles made from postsynaptic membranes of theTorpedoray, taking advantage of the recent advances in cryo-EM. A segregated distribution of lipid molecules is found in the outer leaflet of the bilayer. Apparent cholesterol-rich patches are located in specific annular regions next to the transmembrane helices and also in a more extended `microdomain' between the apposed δ subunits of neighbouring receptors. The particular lipid distribution can be interpreted straightforwardly in relation to the gating movements revealed by an earlier time-resolved cryo-EM study, in which the membranes were exposed briefly to ACh. The results suggest that in addition to stabilizing the protein, cholesterol may play a mechanical role by conferring local rigidity to the membrane so that there is productive coupling between the extracellular and membrane domains, leading to opening of the channel.

scholarly journals Interhelical H-Bonds Modulate the Activity of a Polytopic Transmembrane Kinase

Biomolecules ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 938
Author(s):  
Juan Cruz Almada ◽  
Ana Bortolotti ◽  
Jean Marie Ruysschaert ◽  
Diego de Mendoza ◽  
María Eugenia Inda ◽  
...  
Keyword(s):  
Histidine Kinase ◽  
Adaptive Response ◽  
Catalytic Domain ◽  
Membrane Lipids ◽  
Signal Transmission ◽  
Expression System ◽  
Lipid Homeostasis ◽  
Transmembrane Helices ◽  
Transmembrane Region

DesK is a Histidine Kinase that allows Bacillus subtilis to maintain lipid homeostasis in response to changes in the environment. It is located in the membrane, and has five transmembrane helices and a cytoplasmic catalytic domain. The transmembrane region triggers the phosphorylation of the catalytic domain as soon as the membrane lipids rigidify. In this research, we study how transmembrane inter-helical interactions contribute to signal transmission; we designed a co-expression system that allows studying in vivo interactions between transmembrane helices. By Alanine-replacements, we identified a group of polar uncharged residues, whose side chains contain hydrogen-bond donors or acceptors, which are required for the interaction with other DesK transmembrane helices; a particular array of H-bond- residues plays a key role in signaling, transmitting information detected at the membrane level into the cell to finally trigger an adaptive response.

scholarly journals Processing of ARIA and release from isolated nerve terminals

1999 ◽  
Vol 354 (1381) ◽  
pp. 411-416 ◽  
Author(s):  
Bomie Han ◽  
Gerald D. Fischbach
Keyword(s):  
Neuromuscular Junction ◽  
Action Potential ◽  
Acetylcholine Receptors ◽  
Molecular Layer ◽  
Postsynaptic Membrane ◽  
High Density ◽  
Small Contribution ◽  
Presynaptic Nerve Terminal ◽  
Voltage Gated

The neuromuscular junction is a specialized synapse in that every action potential in the presynaptic nerve terminal results in an action potential in the postsynaptic membrane, unlike most interneuronal synapses where a single presynaptic input makes only a small contribution to the population postsynaptic response. The postsynaptic membrane at the neuromuscular junction contains a high density of neurotransmitter (acetylcholine) receptors and a high density of voltage–gated Na + channels. Thus, the large acetylcholine activated current occurs at the same site where the threshold for action potential generation is low. Acetylcholine receptor inducing activity (ARIA), a 42 kD protein, that stimulates synthesis of acetylcholine receptors and voltage–gated Na + channels in cultured myotubes, probably plays the same roles at developing and mature motor endplates in vivo . ARIA is synthesized as part of a larger, transmembrane, precursor protein called proARIA. Delivery of ARIA from motor neuron cell bodies in the spinal cord to the target endplates involves several steps, including proteolytic cleavage of proARIA. ARIA is also expressed in the central nervous system and it is abundant in the molecular layer of the cerebellum. In this paper we describe our first experiments on the processing and release of ARIA from subcellular fractions containing synaptosomes from the chick cerebellum as a model system.

scholarly journals Crystal structure of a human plasma membrane phospholipid flippase

2020 ◽  
Vol 295 (30) ◽  
pp. 10180-10194 ◽  
Author(s):  
Hanayo Nakanishi ◽  
Katsumasa Irie ◽  
Katsumori Segawa ◽  
Kazuya Hasegawa ◽  
Yoshinori Fujiyoshi ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Human Plasma ◽  
Binding Sites ◽  
The Other ◽  
Asymmetric Distribution ◽  
Transmembrane Helices ◽  
Outer Leaflet ◽  
Extracellular Side ◽  
Phospholipid Flippase ◽  
Plasma Membrane Phospholipid

ATP11C, a member of the P4-ATPase flippase, translocates phosphatidylserine from the outer to the inner plasma membrane leaflet, and maintains the asymmetric distribution of phosphatidylserine in the living cell. We present the crystal structures of a human plasma membrane flippase, ATP11C–CDC50A complex, in a stabilized E2P conformation. The structure revealed a deep longitudinal crevice along transmembrane helices continuing from the cell surface to the phospholipid occlusion site in the middle of the membrane. We observed that the extension of the crevice on the exoplasmic side is open, and the complex is therefore in an outward-open E2P state, similar to a recently reported cryo-EM structure of yeast flippase Drs2p–Cdc50p complex. We noted extra densities, most likely bound phosphatidylserines, in the crevice and in its extension to the extracellular side. One was close to the phosphatidylserine occlusion site as previously reported for the human ATP8A1–CDC50A complex, and the other in a cavity at the surface of the exoplasmic leaflet of the bilayer. Substitutions in either of the binding sites or along the path between them impaired specific ATPase and transport activities. These results provide evidence that the observed crevice is the conduit along that phosphatidylserine traverses from the outer leaflet to its occlusion site in the membrane and suggest that the exoplasmic cavity is important for phospholipid recognition. They also yield insights into how phosphatidylserine is incorporated from the outer leaflet of the plasma membrane into the transmembrane.

Temporal electrical response of chiral smectic liquid crystal displays with V/W-shaped electrooptical characteristic

2008 ◽  
Vol 16 (2) ◽  
Author(s):  
J. Pena ◽  
I. Pérez ◽  
V. Urruchi ◽  
J. Torres ◽  
J. Otón
Keyword(s):  
Liquid Crystal ◽  
Electrical Response ◽  
Work Time ◽  
Electrical Equivalent Circuit ◽  
Time Resolved ◽  
Smectic Liquid Crystal ◽  
Domain Variations ◽  
Analogue Circuits ◽  
Crystal Cells ◽  
Electrooptical Response

AbstractChiral smectic liquid crystal cells showing V-shaped electrooptical switching have been reported as one of the most promising technologies for high-end display applications. In this work, time-resolved electrical behaviour of these devices has been obtained through a set of systematic measurements. The electrical equivalent circuit has been derived, a number of simulations at different frequencies have been performed using commercial software for analogue circuits. Performance of this electrical model to account for time domain variations of switching currents in chiral smectic LC displays with V/W-shaped electrooptical response has been analyzed as well.

scholarly journals Cryo-electron microscopy revealed TACAN is extensively and specifically associated with membrane lipids

2021 ◽  
Author(s):  
Zhen Wang ◽  
Fengying Fan ◽  
Lili Dong ◽  
Qingxia Wang ◽  
Yue Zhou ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Ion Channel ◽  
Membrane Lipids ◽  
The Body ◽  
Mechanical Hyperalgesia ◽  
Transmembrane Helices ◽  
Lipid Core ◽  
Cryo Electron Microscopy ◽  
Mechanosensitive Ion Channel

TACAN is not a mechanosensitive ion channel but significantly linked to the mechanical hyperalgesia. In this study, we show that the human TACAN is a homodimer with each monomer consisting of a body, a spring and a blade domains. The body domain contains six transmembrane helices that forms an independent channel. The spring domain adapts a loop-helix-loop configuration with the helix running within and parallel to the membrane. The blade domain is composed of two cytoplasmic helices. In addition, we found that all the helices of the body and the spring domains are specifically associated with membrane lipids. Particularly, a lipid core, residing within a cavity formed by the two body and spring domains, contacts with the helices from the body and spring domains and extends to reach two symmetrically arranged lipid clusters. These results extremely imply that the membrane lipids coordinate with the membrane-embedded protein to sense and transduce the mechanic signal.

scholarly journals Redistribution of cholesterol from vesicle to plasmalemma controls fusion pore geometry

2020 ◽  
Author(s):  
Boštjan Rituper ◽  
Alenka Guček ◽  
Marjeta Lisjak ◽  
Urszula Gorska ◽  
Aleksandra Šakanović ◽  
...  
Keyword(s):  
Pore Diameter ◽  
Membrane Lipids ◽  
Radial Force ◽  
Fusion Pore ◽  
Pore Geometry ◽  
Cholesterol Depletion ◽  
List Type ◽  
Vesicle Membrane ◽  
Membrane Pore ◽  
Outer Leaflet

ABSTRACTEukaryotic vesicles fuse with the plasmalemma to form the fusion pore, previously considered to be unstable with widening of the pore diameter. Recent studies established that the pore diameter is stable, reflecting balanced forces of widening and closure. Proteins are considered key regulators of the fusion pore, whereas the role of membrane lipids remains unclear. Super-resolution microscopy revealed that lactotroph secretory vesicles discharge cholesterol after stimulation of exocytosis; subsequently, vesicle cholesterol redistributes to the outer leaflet of the plasmalemma. Cholesterol depletion in lactotrophs and astrocytes evokes release of vesicle hormone, indicating that cholesterol constricts the fusion pore. A new model of cholesterol-dependent fusion pore diameter regulation is proposed. High-resolution measurements of fusion pore conductance confirmed that the fusion pore widens with cholesterol depletion and constricts with cholesterol enrichment. In fibroblasts lacking the Npc1 protein, in which cholesterol accumulates in vesicles, the fusion pore is narrower than in controls, showing that cholesterol regulates fusion pore geometry.Graphical AbstractTop: stages through which a vesicle interacts with the plasmalemma. Stage A denotes hemifusion, which proceeds to stage B, with a narrow fusion pore, which can then reversibly open (stage C), before widening fully (stage D). Bottom: redistribution of cholesterol from the vesicle to the outer leaflet of the plasmalemma controls fusion pore constriction.In BriefA membrane pore is formed when the vesicle membrane fuses with the plasmalemma. Proteins were considered key regulators of the opening and closing of this fusion pore. Here, evidence is provided to show that cholesterol, a membrane constituent, determines a radial force constricting the fusion pore, revealing that the fusion pore functions as a proteolipidic structure.HighlightsIntravesicular cholesterol redistributes to the outer leaflet of the plasmalemma.Cholesterol depletion widens the fusion pore, whereas cholesterol enrichment constricts the fusion pore.A model of cholesterol-dependent force preventing fusion pore widening is developed.Disease-related increase in vesicle cholesterol constricts the fusion pore.

Physiology of a bidirectional, excitatory, chemical synapse

1985 ◽  
Vol 53 (3) ◽  
pp. 821-835 ◽  
Author(s):  
P. A. Anderson
Keyword(s):  
Motor Nerve ◽  
Electrical Coupling ◽  
Reversal Potential ◽  
Postsynaptic Membrane ◽  
Synaptic Delay ◽  
Chemical Synapse ◽  
Patch Clamp Recording ◽  
Postsynaptic Response ◽  
Chemical Synapses ◽  
The Relationship

Neurons of the motor nerve net of the jellyfish Cyanea are connected by chemical synapses that, from their ultrastructure, appear to be bidirectional chemical synapses. These synapses were examined physiologically, by recording intracellularly from synaptically connected cells, with the whole cell configuration of the patch-clamp recording technique. Subthreshold depolarizations produced neither small voltage responses indicative of electrical coupling, nor unitary depolarizations suggestive of excitatory postsynaptic potentials (EPSP). Synaptic transmission was affected only when the presynaptic cell was depolarized above spike threshold. The synaptic delay was slightly less than 1 ms at room temperature. The postsynaptic response was initially suprathreshold, resulting in an action potential, but with time this gave way to a large 60 mV amplitude EPSP that did not produce action potentials. The amplitude of the EPSP was directly related to the postsynaptic membrane potential and extrapolated to a reversal potential close to zero mV. Reversal of the EPSP was never observed, even in the presence of intracellular tetrathylammonium (TEA). The relationship between presynaptic depolarization and postsynaptic response was difficult to examine in normal conditions, but in the presence of extracellular lidocaine, which blocked the Na+ and K+ channels in these membranes, a distinct relationship was apparent. The synapse was physiologically nonpolarized and conducted equally well in either direction with a constant synaptic delay.

scholarly journals Tracking Membrane Protein Dynamics in Real Time

2021 ◽  
Author(s):  
Fredrik Orädd ◽  
Magnus Andersson
Keyword(s):  
Membrane Protein ◽  
Protein Dynamics ◽  
Structural Dynamics ◽  
Protein Function ◽  
Md Simulation ◽  
Membrane Lipids ◽  
Time Resolved ◽  
Biological Time ◽  
Membrane Protein Dynamics ◽  
Membrane Protein Function

Abstract Membrane proteins govern critical cellular processes and are central to human health and associated disease. Understanding of membrane protein function is obscured by the vast ranges of structural dynamics—both in the spatial and time regime—displayed in the protein and surrounding membrane. The membrane lipids have emerged as allosteric modulators of membrane protein function, which further adds to the complexity. In this review, we discuss several examples of membrane dependency. A particular focus is on how molecular dynamics (MD) simulation have aided to map membrane protein dynamics and how enhanced sampling methods can enable observing the otherwise inaccessible biological time scale. Also, time-resolved X-ray scattering in solution is highlighted as a powerful tool to track membrane protein dynamics, in particular when combined with MD simulation to identify transient intermediate states. Finally, we discuss future directions of how to further develop this promising approach to determine structural dynamics of both the protein and the surrounding lipids. Graphic Abstract

scholarly journals Clustering and Lateral Concentration of Raft Lipids by the MAL Protein

2009 ◽  
Vol 20 (16) ◽  
pp. 3751-3762 ◽  
Author(s):  
Lee Goldstein Magal ◽  
Yakey Yaffe ◽  
Jeanne Shepshelovich ◽  
Juan Francisco Aranda ◽  
Maria del Carmen de Marco ◽  
...  
Keyword(s):  
Transmembrane Domain ◽  
Apical Membrane ◽  
Membrane Lipids ◽  
Site Directed Mutagenesis ◽  
Bimolecular Fluorescence Complementation ◽  
Membrane Domains ◽  
Transmembrane Helices ◽  
Binding Motifs ◽  
Detergent Resistant Membranes ◽  
Apical Sorting

MAL, a compact hydrophobic, four-transmembrane-domain apical protein that copurifies with detergent-resistant membranes is obligatory for the machinery that sorts glycophosphatidylinositol (GPI)-anchored proteins and others to the apical membrane in epithelia. The mechanism of MAL function in lipid-raft–mediated apical sorting is unknown. We report that MAL clusters formed by two independent procedures—spontaneous clustering of MAL tagged with the tandem dimer DiHcRED (DiHcRED-MAL) in the plasma membrane of COS7 cells and antibody-mediated cross-linking of FLAG-tagged MAL—laterally concentrate markers of sphingolipid rafts and exclude a fluorescent analogue of phosphatidylethanolamine. Site-directed mutagenesis and bimolecular fluorescence complementation analysis demonstrate that MAL forms oligomers via ϕxxϕ intramembrane protein–protein binding motifs. Furthermore, results from membrane modulation by using exogenously added cholesterol or ceramides support the hypothesis that MAL-mediated association with raft lipids is driven at least in part by positive hydrophobic mismatch between the lengths of the transmembrane helices of MAL and membrane lipids. These data place MAL as a key component in the organization of membrane domains that could potentially serve as membrane sorting platforms.

scholarly journals Contribution of Membrane Lipids to Postsynaptic Protein Organization

2021 ◽  
Vol 13 ◽  
Author(s):  
Manon Westra ◽  
Yolanda Gutierrez ◽  
Harold D. MacGillavry
Keyword(s):  
Synaptic Transmission ◽  
Protein Interactions ◽  
Membrane Lipids ◽  
Postsynaptic Membrane ◽  
Synaptic Membrane ◽  
Protein Distribution ◽  
Receptor Complexes ◽  
Postsynaptic Protein ◽  
Technical Developments ◽  
Lipid Species

The precise subsynaptic organization of proteins at the postsynaptic membrane controls synaptic transmission. In particular, postsynaptic receptor complexes are concentrated in distinct membrane nanodomains to optimize synaptic signaling. However, despite the clear functional relevance of subsynaptic receptor organization to synaptic transmission and plasticity, the mechanisms that underlie the nanoscale organization of the postsynaptic membrane remain elusive. Over the last decades, the field has predominantly focused on the role of protein-protein interactions in receptor trafficking and positioning in the synaptic membrane. In contrast, the contribution of lipids, the principal constituents of the membrane, to receptor positioning at the synapse remains poorly understood. Nevertheless, there is compelling evidence that the synaptic membrane is enriched in specific lipid species and that deregulation of lipid homeostasis in neurons severely affects synaptic functioning. In this review we focus on how lipids are organized at the synaptic membrane, with special emphasis on how current models of membrane organization could contribute to protein distribution at the synapse and synaptic transmission. Finally, we will present an outlook on how novel technical developments could be applied to study the dynamic interplay between lipids and proteins at the postsynaptic membrane.

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