scholarly journals Structure and assembly of calcium homeostasis modulator proteins

2019 ◽  
Author(s):  
Johanna L Syrjanen ◽  
Kevin Michalski ◽  
Tsung-Han Chou ◽  
Timothy Grant ◽  
Shanlin Rao ◽  
...  
Keyword(s):  
Calcium Homeostasis ◽  
Neuronal Excitability ◽  
Dependent Manner ◽  
Transmembrane Helices ◽  
Cryo Electron Microscopy ◽  
Large Pore ◽  
Oligomeric Assembly ◽  
Voltage Dependent ◽  
Bona Fide ◽  
Dynamics Simulations

AbstractBiological membranes of many tissues and organs contain large-pore channels designed to permeate a wide variety of ions and metabolites. Examples include connexin, innexin, and pannexin, which form gap junctions and/or bona fide cell surface channels. The most recently identified large-pore channels are the calcium homeostasis modulators (CALHMs), which permeate ions and ATP in a voltage-dependent manner to control neuronal excitability, taste signaling, and pathologies of depression and Alzheimer’s disease. Despite such critical biological roles, the structures and patterns of oligomeric assembly remain unclear. Here, we reveal the first structures of two CALHMs, CALHM1 and CALHM2, by single particle cryo-electron microscopy, which show novel assembly of the four transmembrane helices into channels of 8-mers and 11-mers, respectively. Furthermore, molecular dynamics simulations suggest that lipids can favorably assemble into a bilayer within the larger CALHM2 pore, but not within CALHM1, demonstrating the potential correlation between pore-size, lipid accommodation, and channel activity.

scholarly journals Cryo-EM structure of the calcium homeostasis modulator 1 channel

2020 ◽  
Vol 6 (29) ◽  
pp. eaba8161
Author(s):  
Yue Ren ◽  
Tianlei Wen ◽  
Zhiqin Xi ◽  
Shunjin Li ◽  
Jing Lu ◽  
...  
Keyword(s):  
Calcium Homeostasis ◽  
Transmembrane Helix ◽  
Atp Release ◽  
Ion Permeation ◽  
Extracellular Loop ◽  
Release Channel ◽  
Dimer Interface ◽  
Cryo Electron Microscopy ◽  
Gating Mechanism ◽  
Oligomeric Assembly

Calcium homeostasis modulator 1 (CALHM1) is a voltage-gated ATP release channel that plays an important role in neural gustatory signaling and the pathogenesis of Alzheimer’s disease. Here, we present a cryo–electron microscopy structure of full-length Ca2+-free CALHM1 from Danio rerio at an overall resolution of 3.1 Å. Our structure reveals an octameric architecture with a wide pore diameter of ~20 Å, presumably representing the active conformation. The overall structure is substantially different from that of the isoform CALHM2, which forms both undecameric hemichannels and gap junctions. The N-terminal small helix folds back to the pore and forms an antiparallel interaction with transmembrane helix 1. Structural analysis revealed that the extracellular loop 1 region within the dimer interface may contribute to oligomeric assembly. A positive potential belt inside the pore was identified that may modulate ion permeation. Our structure offers insights into the assembly and gating mechanism of the CALHM1 channel.

The Voltage-Dependent K+ Channel Family

2019 ◽  
Author(s):  
Hanne B. Rasmussen ◽  
James S. Trimmer
Keyword(s):  
Ion Channels ◽  
Neuronal Excitability ◽  
Expression Patterns ◽  
Basic Knowledge ◽  
K Channel ◽  
Dependent Manner ◽  
Kv Channels ◽  
Voltage Dependent ◽  
The Individual ◽  
Α Subunits

Voltage-dependent K+ (potassium; Kv) channels are ion channels that critically impact neuronal excitability and function. Four principal α subunits assemble to create a membrane-spanning pore that opens in a voltage-dependent manner to allow the selective passage of K+ ions across the cell membrane. Forty human genes encoding Kv channel α subunits have been identified, and most of them are expressed in the nervous system. The individual Kv subunits display unique cellular and subcellular expression patterns and co-assemble into distinct homo- and hetero-tetrameric channels that differ in their electrophysiological and pharmacological properties, and their sensitivity to dynamic modulation, by cellular signaling pathways. The resulting diversity allows Kv channels to impact all steps in electrical information processing, as well as numerous other aspects of neuronal functions, including those in which they appear to play a non-conducting role. This chapter reviews the current basic knowledge about this large and important family of ion channels.

scholarly journals Cryo-EM structure of the mechanically activated ion channel OSCA1.2

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
Sebastian Jojoa-Cruz ◽  
Kei Saotome ◽  
Swetha E Murthy ◽  
Che Chun Alex Tsui ◽  
Mark SP Sansom ◽  
...  
Keyword(s):  
Ion Channels ◽  
Turgor Pressure ◽  
Ion Permeation ◽  
Membrane Tension ◽  
Transmembrane Helices ◽  
Channel Conductance ◽  
Cryo Electron Microscopy ◽  
Stress Sensing ◽  
Dynamics Simulations

Mechanically activated ion channels underlie touch, hearing, shear-stress sensing, and response to turgor pressure. OSCA/TMEM63s are a newly-identified family of eukaryotic mechanically activated ion channels opened by membrane tension. The structural underpinnings of OSCA/TMEM63 function are not explored. Here, we elucidate high resolution cryo-electron microscopy structures of OSCA1.2, revealing a dimeric architecture containing eleven transmembrane helices per subunit and surprising topological similarities to TMEM16 proteins. We locate the ion permeation pathway within each subunit by demonstrating that a conserved acidic residue is a determinant of channel conductance. Molecular dynamics simulations reveal membrane interactions, suggesting the role of lipids in OSCA1.2 gating. These results lay a foundation to decipher how the structural organization of OSCA/TMEM63 is suited for their roles as MA ion channels.

Cryo-Electron Microscopy and Correlation Averaging of Frozen-Hydrated, Polymorphic 2D Crystals of the Mitochondrial Outer Membrane Channel

1990 ◽  
Vol 48 (1) ◽  
pp. 100-101
Author(s):  
Xiao-Wei Guo
Keyword(s):  
Outer Membrane ◽  
Hexagonal Lattice ◽  
Mitochondrial Outer Membrane ◽  
Rectangular Lattice ◽  
Electron Microscopic ◽  
Cryo Electron Microscopy ◽  
Voltage Dependent ◽  
Outer Membrane Channel ◽  
2D Crystals ◽  
Vdac Channel

Voltage-dependent, anion-selective channels (VDAC) are formed in the mitochondrial outer membrane (mitOM) by a 30-kDa polypeptide. These channels form ordered 2D arrays when mitOMs from Neurospora crassa are treated with soluble phospholipase A2. We obtain low-dose electron microscopic images of unstained specimens of VDAC crystals preserved in vitreous ice, using a Philips EM420 equipped with a Gatan cryo-transfer stage. We then use correlation analysis to compute average projections of the channel crystals. The procedure involves Fourier-filtration of a region within a crystal field to obtain a preliminary average that is subsequently cross-correlated with the entire crystal. Subregions are windowed from the crystal image at coordinates of peaks in the cross-correlation function (CCF, see Figures 1 and 2) and summed to form averages (Figure 3).The VDAC channel forms several different types of crystalline arrays in mitOMs. The polymorph first observed during phospholipase treatment is a parallelogram array (a=13 run, b=11.5 run, θ==109°) containing 6 water-filled pores per unit cell. Figure 1 shows the CCF of a sub-field of such an “oblique” array used to compute the correlation average of Figure 3A. With increased phospholipase treatment, other polymorphs are observed, often co-existing within the same crystal. For example, two distinct (but closely related) types of lattices occur in the field corresponding to the CCF of Figure 2: a “contracted” version of the parallelogram lattice (a=13 run, b=10 run, θ=99°), and a near-rectangular lattice (a=8.5 run, b=5 nm). The pattern of maxima in this CCF suggests that a third, near-hexagonal lattice (a=4.5 nm) may also be present. The correlation averages of Figures 3B-D were computed from polycrystalline fields, using peak coordinates in regions of CCFs corresponding to each of the three lattice types.

Effects of cytochrome c on the mitochondrial apoptosis-induced channel MAC

2004 ◽  
Vol 286 (5) ◽  
pp. C1109-C1117 ◽  
Author(s):  
Liang Guo ◽  
Dawn Pietkiewicz ◽  
Evgeny V. Pavlov ◽  
Sergey M. Grigoriev ◽  
John J. Kasianowicz ◽  
...  
Keyword(s):  
Cytochrome C ◽  
Outer Membrane ◽  
Cell Types ◽  
Rnase A ◽  
Mitochondrial Outer Membrane ◽  
Dependent Manner ◽  
Mitochondrial Apoptosis ◽  
Noise Type ◽  
Voltage Dependent

Recent studies indicate that cytochrome c is released early in apoptosis without loss of integrity of the mitochondrial outer membrane in some cell types. The high-conductance mitochondrial apoptosis-induced channel (MAC) forms in the outer membrane early in apoptosis of FL5.12 cells. Physiological (micromolar) levels of cytochrome c alter MAC activity, and these effects are referred to as types 1 and 2. Type 1 effects are consistent with a partitioning of cytochrome c into the pore of MAC and include a modest decrease in conductance that is dose and voltage dependent, reversible, and has an increase in noise. Type 2 effects may correspond to “plugging” of the pore or destabilization of the open state. Type 2 effects are a dose-dependent, voltage-independent, and irreversible decrease in conductance. MAC is a heterogeneous channel with variable conductance. Cytochrome c affects MAC in a pore size-dependent manner, with maximal effects of cytochrome c on MAC with conductance of 1.9–5.4 nS. The effects of cytochrome c, RNase A, and high salt on MAC indicate that size, rather than charge, is crucial. The effects of dextran molecules of various sizes indicate that the pore diameter of MAC is slightly larger than that of 17-kDa dextran, which should be sufficient to allow the passage of 12-kDa cytochrome c. These findings are consistent with the notion that MAC is the pore through which cytochrome c is released from mitochondria during apoptosis.

Halothane Inhibition of Recombinant Cardiac L-type Ca2+ Channels Expressed in HEK-293 Cells

2005 ◽  
Vol 103 (6) ◽  
pp. 1156-1166 ◽  
Author(s):  
Kevin J. Gingrich ◽  
Son Tran ◽  
Igor M. Nikonorov ◽  
Thomas J. Blanck
Keyword(s):  
Charge Transfer ◽  
Calcium Channels ◽  
Dependent Manner ◽  
Current Time ◽  
Hek 293 ◽  
Hek 293 Cells ◽  
293 Cells ◽  
Dependent Inactivation ◽  
Voltage Dependent

Background Volatile anesthetics depress cardiac contractility, which involves inhibition of cardiac L-type calcium channels. To explore the role of voltage-dependent inactivation, the authors analyzed halothane effects on recombinant cardiac L-type calcium channels (alpha1Cbeta2a and alpha1Cbeta2aalpha2/delta1), which differ by the alpha2/delta1 subunit and consequently voltage-dependent inactivation. Methods HEK-293 cells were transiently cotransfected with complementary DNAs encoding alpha1C tagged with green fluorescent protein and beta2a, with and without alpha2/delta1. Halothane effects on macroscopic barium currents were recorded using patch clamp methodology from cells expressing alpha1Cbeta2a and alpha1Cbeta2aalpha2/delta1 as identified by fluorescence microscopy. Results Halothane inhibited peak current (I(peak)) and enhanced apparent inactivation (reported by end pulse current amplitude of 300-ms depolarizations [I300]) in a concentration-dependent manner in both channel types. alpha2/delta1 coexpression shifted relations leftward as reported by the 50% inhibitory concentration of I(peak) and I300/I(peak)for alpha1Cbeta2a (1.8 and 14.5 mm, respectively) and alpha1Cbeta2aalpha2/delta1 (0.74 and 1.36 mm, respectively). Halothane reduced transmembrane charge transfer primarily through I(peak) depression and not by enhancement of macroscopic inactivation for both channels. Conclusions The results indicate that phenotypic features arising from alpha2/delta1 coexpression play a key role in halothane inhibition of cardiac L-type calcium channels. These features included marked effects on I(peak) inhibition, which is the principal determinant of charge transfer reductions. I(peak) depression arises primarily from transitions to nonactivatable states at resting membrane potentials. The findings point to the importance of halothane interactions with states present at resting membrane potential and discount the role of inactivation apparent in current time courses in determining transmembrane charge transfer.

Association between Hsp90 and the ClC-2 chloride channel upregulates channel function

2006 ◽  
Vol 290 (1) ◽  
pp. C45-C56 ◽  
Author(s):  
Alexandre Hinzpeter ◽  
Joanna Lipecka ◽  
Franck Brouillard ◽  
Maryvonne Baudoin-Legros ◽  
Michal Dadlez ◽  
...  
Keyword(s):  
Chloride Channel ◽  
Fluid Transport ◽  
Cell Swelling ◽  
Dependent Manner ◽  
Patch Clamp Technique ◽  
Mass Spectrometry Identification ◽  
Voltage Dependent ◽  
Channel Expression ◽  
Associated Proteins ◽  
Cellular Stresses

The voltage-dependent ClC-2 chloride channel has been implicated in a variety of physiological functions, including fluid transport across specific epithelia. ClC-2 is activated by hyperpolarization, weakly acidic external pH, intracellular Cl−, and cell swelling. To add more insight into the mechanisms involved in ClC-2 regulation, we searched for associated proteins that may influence ClC-2 activity. With the use of immunoprecipitation of ClC-2 from human embryonic kidney-293 cells stably expressing the channel, followed by electrophoretic separation of coimmunoprecipitated proteins and mass spectrometry identification, Hsp70 and Hsp90 were unmasked as possible ClC-2 interacting partners. Association of Hsp90 with ClC-2 was confirmed in mouse brain. Inhibition of Hsp90 by two specific inhibitors, geldanamycin or radicicol, did not affect total amounts of ClC-2 but did reduce plasma membrane channel abundance. Functional experiments using the whole cell configuration of the patch-clamp technique showed that inhibition of Hsp90 reduced ClC-2 current amplitude and impaired the intracellular Cl− concentration [Cl−]-dependent rightward shift of the fractional conductance. Geldanamycin and radicicol increased both the slow and fast activation time constants in a chloride-dependent manner. Heat shock treatment had the opposite effect. These results indicate that association of Hsp90 with ClC-2 results in greater channel activity due to increased cell surface channel expression, facilitation of channel opening, and enhanced channel sensitivity to intracellular [Cl−]. This association may have important pathophysiological consequences, enabling increased ClC-2 activity in response to cellular stresses such as elevated temperature, ischemia, or oxidative reagents.

Pharmacological mechanism of topiramate in the prophylaxis and treatment of migraine: a review

2018 ◽  
pp. 190-195
Author(s):  
Emanuela Paz Rosas ◽  
Raisa Ferreira Costa ◽  
Silvania Tavares Paz ◽  
Ana Paula Fernandes da Silva ◽  
Manuela Freitas Lyra de Freitas
Keyword(s):  
Cortical Spreading Depression ◽  
Molecular Mechanisms ◽  
Spreading Depression ◽  
Neuronal Excitability ◽  
Mechanisms Of Action ◽  
World Population ◽  
Gamma Aminobutyric Acid ◽  
Pharmacological Mechanism ◽  
Calcium Ion Channels ◽  
Voltage Dependent

Objective: This review sought to bring evidence of studies addressing the mechanisms of action of topiramate in the prevention and treatment of migraine. Background: Migraine is a neurovascular disorder that affects a large part of the world population. The use of prophylactics contributes to the decrease in the frequency and severity of this disease. Among the antiepileptic drugs, the topiramate, has proven to be the most effective for the treatment of migraine. Although the mechanism of action of this drug is still not well elucidated in the literature, there are several molecular mechanisms proposed. Methodology: A survey was carried out in the literature, from February to March 2018, in different databases, using the descriptors: topiramate, migraine and mechanisms of action. After a careful selection, 25 manuscripts were chosen for this review. Results: Evidence from a number of studies has indicated that the main mechanisms of action of topiramate are related to the modulation of voltage-dependent sodium and calcium ion channels, blockade of excitatory glutamate transmission and inhibition by gamma-aminobutyric acid receptors (GABA), AMPA/kainate and some isoenzymes of carbonic anhydrase. In addition, topiramate is involved in the suppression of cortical spreading depression, besides influencing trigeminovascular activity, and neuronal excitability. Conclusion: Thus, topiramate could be involved in the prevention of major events of the pathophysiology of migraine. Acting directly on cortical spreading depression (DAC), trigeminovascular signals and decreased central sensitization of migraine pain.

scholarly journals Modulation of High-Voltage Activated Ca2+ Channels in the Rat Periaqueductal Gray Neurons by μ-Type Opioid Agonist

1997 ◽  
Vol 77 (3) ◽  
pp. 1418-1424 ◽  
Author(s):  
Chang-Ju Kim ◽  
Jeong-Seop Rhee ◽  
Norio Akaike
Keyword(s):  
G Proteins ◽  
Opioid Receptor ◽  
High Voltage ◽  
Inhibitory Effect ◽  
Periaqueductal Gray ◽  
Dependent Manner ◽  
Opioid Agonist ◽  
Voltage Clamp Condition ◽  
Voltage Dependent ◽  
Clamp Condition

Kim, Chang-Ju, Jeong-Seop Rhee, and Norio Akaike. Modulation of high-voltage activated Ca2+ channels in the rat periaqueductal gray neurons by μ-type opioid agonist. J. Neurophysiol. 77: 1418–1424, 1997. The effect of μ-type opioid receptor agonist, D-Ala2,N-MePhe4,Gly5-ol-enkephalin (DAMGO), on high-voltage-activated (HVA) Ca2+ channels in the dissociated rat periaqueductal gray (PAG) neurons was investigated by the use of nystatin-perforated patch recording mode under voltage-clamp condition. Among 118 PAG neurons tested, the HVA Ca2+ channels of 38 neurons (32%) were inhibited by DAMGO (DAMGO-sensitive cells), and the other 80 neurons (68%) were not affected by DAMGO (DAMGO-insensitive cells). The N-, P-, L-, Q-, and R-type Ca2+ channel components in DAMGO-insensitive cells shared 26.9, 37.1, 22.3, 7.9, and 5.8%, respectively, of the total Ca2+ channel current. The channel components of DAMGO-sensitive cells were 45.6, 25.7, 21.7, 4.6, and 2.4%, respectively. The HVA Ca2+ current of DAMGO-sensitive neurons was inhibited by DAMGO in a concentration-, time-, and voltage-dependent manner. Application of ω-conotoxin-GVIA occluded the inhibitory effect of DAMGO ∼70%. So, HVA Ca2+ channels inhibited by DAMGO were mainly the N-type Ca2+ channels. The inhibitory effect of DAMGO on HVA Ca2+ channels was prevented almost completely by the pretreatment of pertussis toxin (PTX) for 8–10 h, suggesting that DAMGO modulation on N-type Ca2+ channels in rat PAG neurons is mediated by PTX-sensitive G proteins. These results indicate that μ-type opioid receptor modulates N-type HVA Ca2+ channels via PTX-sensitive G proteins in PAG neurons of rats.

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