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Biomolecular Concepts Jun 2015Ion channels are integral membrane proteins that undergo important conformational changes as they open and close to control transmembrane flux of different ions. The... (Review)
Review
Ion channels are integral membrane proteins that undergo important conformational changes as they open and close to control transmembrane flux of different ions. The molecular underpinnings of these dynamic conformational rearrangements are difficult to ascertain using current structural methods. Several functional approaches have been used to understand two- and three-dimensional dynamic structures of ion channels, based on the reactivity of the cysteine side-chain. Two-dimensional structural rearrangements, such as changes in the accessibility of different parts of the channel protein to the bulk solution on either side of the membrane, are used to define movements within the permeation pathway, such as those that open and close ion channel gates. Three-dimensional rearrangements – in which two different parts of the channel protein change their proximity during conformational changes – are probed by cross-linking or bridging together two cysteine side-chains. Particularly useful in this regard are so-called metal bridges formed when two or more cysteine side-chains form a high-affinity binding site for metal ions such as Cd2+ or Zn2+. This review describes the use of these different techniques for the study of ion channel dynamic structure and function, including a comprehensive review of the different kinds of conformational rearrangements that have been studied in different channel types via the identification of intra-molecular metal bridges. Factors that influence the affinities and conformational sensitivities of these metal bridges, as well as the kinds of structural inferences that can be drawn from these studies, are also discussed.
Topics: Animals; Cell Membrane; Cysteine; Humans; Ion Channels; Metals; Mutation; Protein Conformation
PubMed: 26103632
DOI: 10.1515/bmc-2015-0013 -
FEBS Letters Sep 2017Ion channels facilitate diffusion of ions across cell membranes for such diverse purposes as neuronal signaling, muscular contraction, and fluid homeostasis. Solute... (Review)
Review
Ion channels facilitate diffusion of ions across cell membranes for such diverse purposes as neuronal signaling, muscular contraction, and fluid homeostasis. Solute transporters often utilize ionic gradients to move aqueous solutes up their concentration gradient, also fulfilling a wide variety of tasks. Recently, an increasing number of ion channel-transporter ('chansporter') complexes have been discovered. Chansporter complex formation may overcome what could otherwise be considerable spatial barriers to rapid signal integration and feedback between channels and transporters, the ions and other substrates they transport, and environmental factors to which they must respond. Here, current knowledge in this field is summarized, covering both heterologous expression structure/function findings and potential mechanisms by which chansporter complexes fulfill contrasting roles in cell signaling in vivo.
Topics: Animals; Cell Membrane; Humans; Ion Channels; Signal Transduction
PubMed: 28718502
DOI: 10.1002/1873-3468.12755 -
Cardiology 2023The coronavirus disease 2019 (COVID-19) pandemic has led to millions of confirmed cases and deaths worldwide and has no approved therapy. Currently, more than 700 drugs...
Hydroxychloroquine Attenuates hERG Channel by Promoting the Membrane Channel Degradation: Computational Simulation and Experimental Evidence for QT-Interval Prolongation with Hydroxychloroquine Treatment.
INTRODUCTION
The coronavirus disease 2019 (COVID-19) pandemic has led to millions of confirmed cases and deaths worldwide and has no approved therapy. Currently, more than 700 drugs are tested in the COVID-19 clinical trials, and full evaluation of their cardiotoxicity risks is in high demand.
METHODS
We mainly focused on hydroxychloroquine (HCQ), one of the most concerned drugs for COVID-19 therapy, and investigated the effects and underlying mechanisms of HCQ on hERG channel via molecular docking simulations. We further applied the HEK293 cell line stably expressing hERG-wild-type channel (hERG-HEK) and HEK293 cells transiently expressing hERG-p.Y652A or hERG-p.F656A mutants to validate our predictions. Western blot analysis was used to determine the hERG channel, and the whole-cell patch clamp was utilized to record hERG current (IhERG).
RESULTS
HCQ reduced the mature hERG protein in a time- and concentration-dependent manner. Correspondingly, chronic and acute treatment of HCQ decreased the hERG current. Treatment with brefeldin A (BFA) and HCQ combination reduced hERG protein to a greater extent than BFA alone. Moreover, disruption of the typical hERG binding site (hERG-p.Y652A or hERG-p.F656A) rescued HCQ-mediated hERG protein and IhERG reduction.
CONCLUSION
HCQ can reduce the mature hERG channel expression and IhERG via enhancing channel degradation. The QT prolongation effect of HCQ is mediated by typical hERG binding sites involving residues Tyr652 and Phe656.
Topics: Humans; COVID-19; COVID-19 Drug Treatment; ERG1 Potassium Channel; Ether-A-Go-Go Potassium Channels; HEK293 Cells; Hydroxychloroquine; Ion Channels; Molecular Docking Simulation; Mutation
PubMed: 37231805
DOI: 10.1159/000531132 -
American Journal of Physiology. Cell... Sep 2018Of the three pannexins in vertebrate proteomes, pannexin1 (Panx1) is the only one well characterized, and it is generally accepted that Panx1 functions as an ATP release...
Of the three pannexins in vertebrate proteomes, pannexin1 (Panx1) is the only one well characterized, and it is generally accepted that Panx1 functions as an ATP release channel for signaling to other cells. However, the ATP permeability of the channel is only observed with certain stimuli, including low oxygen, mechanical stress, and elevated extracellular potassium ion concentration. Otherwise, the Panx1 channel is selective for chloride ions and exhibits no ATP permeability when stimulated simply by depolarization to positive potentials. A third, irreversible activation of Panx1 follows cleavage of carboxyterminal amino acids by caspase 3. The selectivity/permeability properties of the caspase cleaved channel are unclear as it reportedly has features of both channel conformations. Here we describe the biophysical properties of the channel formed by the truncation mutant Panx1Δ378, which is identical to the caspase-cleaved protein. Consistent with previous findings for the caspase-activated channel, the Panx1Δ378 channel was constitutively active. However, like the voltage-gated channel, the Panx1Δ378 channel had high chloride selectivity, lacked cation permeability, and did not mediate ATP release unless stimulated by extracellular potassium ions. Thus, the caspase-cleaved Panx1 channel should be impermeable to ATP, contrary to previous claims.
Topics: Adenosine Triphosphate; Animals; Caspases; Cell Membrane Permeability; Connexins; Female; Ion Channels; Nerve Tissue Proteins; Potassium; Xenopus Proteins; Xenopus laevis
PubMed: 29719171
DOI: 10.1152/ajpcell.00302.2017 -
Nature Communications Feb 2023Inorganic polyphosphate (polyP) is an ancient energy metabolite and phosphate store that occurs ubiquitously in all organisms. The vacuolar transporter chaperone (VTC)...
Inorganic polyphosphate (polyP) is an ancient energy metabolite and phosphate store that occurs ubiquitously in all organisms. The vacuolar transporter chaperone (VTC) complex integrates cytosolic polyP synthesis from ATP and polyP membrane translocation into the vacuolar lumen. In yeast and in other eukaryotes, polyP synthesis is regulated by inositol pyrophosphate (PP-InsP) nutrient messengers, directly sensed by the VTC complex. Here, we report the cryo-electron microscopy structure of signal-activated VTC complex at 3.0 Å resolution. Baker's yeast VTC subunits Vtc1, Vtc3, and Vtc4 assemble into a 3:1:1 complex. Fifteen trans-membrane helices form a novel membrane channel enabling the transport of newly synthesized polyP into the vacuolar lumen. PP-InsP binding orients the catalytic polymerase domain at the entrance of the trans-membrane channel, both activating the enzyme and coupling polyP synthesis and membrane translocation. Together with biochemical and cellular studies, our work provides mechanistic insights into the biogenesis of an ancient energy metabolite.
Topics: Polyphosphates; Cryoelectron Microscopy; Saccharomyces cerevisiae; Cytosol; Ion Channels
PubMed: 36759618
DOI: 10.1038/s41467-023-36466-4 -
The Journal of General Physiology Jun 2014Protein S-acylation, the reversible covalent fatty-acid modification of cysteine residues, has emerged as a dynamic posttranslational modification (PTM) that controls... (Review)
Review
Protein S-acylation, the reversible covalent fatty-acid modification of cysteine residues, has emerged as a dynamic posttranslational modification (PTM) that controls the diversity, life cycle, and physiological function of numerous ligand- and voltage-gated ion channels. S-acylation is enzymatically mediated by a diverse family of acyltransferases (zDHHCs) and is reversed by acylthioesterases. However, for most ion channels, the dynamics and subcellular localization at which S-acylation and deacylation cycles occur are not known. S-acylation can control the two fundamental determinants of ion channel function: (1) the number of channels resident in a membrane and (2) the activity of the channel at the membrane. It controls the former by regulating channel trafficking and the latter by controlling channel kinetics and modulation by other PTMs. Ion channel function may be modulated by S-acylation of both pore-forming and regulatory subunits as well as through control of adapter, signaling, and scaffolding proteins in ion channel complexes. Importantly, cross-talk of S-acylation with other PTMs of both cysteine residues by themselves and neighboring sites of phosphorylation is an emerging concept in the control of ion channel physiology. In this review, I discuss the fundamentals of protein S-acylation and the tools available to investigate ion channel S-acylation. The mechanisms and role of S-acylation in controlling diverse stages of the ion channel life cycle and its effect on ion channel function are highlighted. Finally, I discuss future goals and challenges for the field to understand both the mechanistic basis for S-acylation control of ion channels and the functional consequence and implications for understanding the physiological function of ion channel S-acylation in health and disease.
Topics: Aminoacylation; Animals; Cysteine; Fatty Acids; Humans; Ion Channel Gating; Ion Channels; Models, Biological; Structure-Activity Relationship
PubMed: 24821965
DOI: 10.1085/jgp.201411176 -
Biophysical Journal Jul 2012Mechanosensors are important for many life functions, including the senses of touch, balance, and proprioception; cardiovascular regulation; kidney function; and... (Review)
Review
Mechanosensors are important for many life functions, including the senses of touch, balance, and proprioception; cardiovascular regulation; kidney function; and osmoregulation. Many channels from an assortment of families are now candidates for eukaryotic mechanosensors and proprioception, as well as cardiovascular regulation, kidney function, and osmoregulation. Bacteria also possess two families of mechanosensitive channels, termed MscL and MscS, that function as osmotic emergency release valves. Of the two channels, MscL is the most conserved, most streamlined in structure, and largest in conductance at 3.6 nS with a pore diameter in excess of 30 Å; hence, the structural changes required for gating are exaggerated and perhaps more easily defined. Because of these properties, as well as its tractable nature, MscL represents a excellent model for studying how a channel can sense and respond to biophysical changes of a lipid bilayer. Many of the properties of the MscL channel, such as the sensitivity to amphipaths, a helix that runs along the membrane surface and is connected to the pore via a glycine, a twisting and turning of the transmembrane domains upon gating, and the dynamic changes in membrane interactions, may be common to other candidate mechanosensors. Here we review many of these properties and discuss their structural and functional implications.
Topics: Bacterial Proteins; Ion Channels; Mechanotransduction, Cellular; Models, Biological; Pressure; Protein Structure, Secondary
PubMed: 22853893
DOI: 10.1016/j.bpj.2012.06.021 -
American Journal of Physiology. Cell... May 2021Ion channels in plasma membrane play a principal role in different physiological processes, including cell volume regulation, signal transduction, and modulation of... (Review)
Review
Ion channels in plasma membrane play a principal role in different physiological processes, including cell volume regulation, signal transduction, and modulation of membrane potential in living cells. Actin-based cytoskeleton, which exists in a dynamic balance between monomeric and polymeric forms (globular and fibrillar actin), can be directly or indirectly involved in various cellular responses including modulation of ion channel activity. In this mini-review, we present an overview of the role of submembranous actin dynamics in the regulation of ion channels in excitable and nonexcitable cells. Special attention is focused on the important data about the involvement of actin assembly/disassembly and some actin-binding proteins in the control of the epithelial Na channel (ENaC) and mechanosensitive Piezo channels whose integral activity has a potential impact on membrane transport and multiple coupled cellular reactions. Growing evidence suggests that actin elements of the cytoskeleton can represent a "converging point" of various signaling pathways modulating the activity of ion transport proteins in cell membranes.
Topics: Actin Cytoskeleton; Actins; Animals; Cell Membrane; Epithelial Sodium Channels; Humans; Ion Channel Gating; Ion Channels; Mechanotransduction, Cellular; Protein Conformation; Structure-Activity Relationship
PubMed: 33471624
DOI: 10.1152/ajpcell.00368.2020 -
Microbiology and Molecular Biology... Feb 2020General principles in biology have often been elucidated from the study of bacteria. This is true for the bacterial mechanosensitive channel of large conductance, MscL,... (Review)
Review
General principles in biology have often been elucidated from the study of bacteria. This is true for the bacterial mechanosensitive channel of large conductance, MscL, the channel highlighted in this review. This channel functions as a last-ditch emergency release valve discharging cytoplasmic solutes upon decreases in osmotic environment. Opening the largest gated pore, MscL passes molecules up to 30 Å in diameter; exaggerated conformational changes yield advantages for study, including assays. MscL contains structural/functional themes that recur in higher organisms and help elucidate how other, structurally more complex, channels function. These features of MscL include (i) the ability to directly sense, and respond to, biophysical changes in the membrane, (ii) an α helix ("slide helix") or series of charges ("knot in a rope") at the cytoplasmic membrane boundary to guide transmembrane movements, and (iii) important subunit interfaces that, when disrupted, appear to cause the channel to gate inappropriately. MscL may also have medical applications: the modality of the MscL channel can be changed, suggesting its use as a triggered nanovalve in nanodevices, including those for drug targeting. In addition, recent studies have shown that the antibiotic streptomycin opens MscL and uses it as one of the primary paths to the cytoplasm. Moreover, the recent identification and study of novel specific agonist compounds demonstrate that the channel is a valid drug target. Such compounds may serve as novel-acting antibiotics and adjuvants, a way of permeabilizing the bacterial cell membrane and, thus, increasing the potency of commonly used antibiotics.
Topics: Anti-Bacterial Agents; Bacteria; Bacterial Physiological Phenomena; Cell Membrane; Escherichia coli; Escherichia coli Proteins; Ion Channels; Osmoregulation
PubMed: 31941768
DOI: 10.1128/MMBR.00055-19 -
Biochimica Et Biophysica Acta Feb 2014The interplay between actin and 10 membrane channel proteins that have been shown to directly bind to actin are reviewed. The 10 membrane channel proteins covered in... (Review)
Review
The interplay between actin and 10 membrane channel proteins that have been shown to directly bind to actin are reviewed. The 10 membrane channel proteins covered in this review are aquaporin 2 (AQP2), cystic fibrosis transmembrane conductance regulator (CFTR), ClC2, short form of ClC3 (sClC3), chloride intracellular channel 1 (CLIC1), chloride intracellular channel 5 (CLIC5), epithelial sodium channel (ENaC), large-conductance calcium-activated potassium channel (Maxi-K), transient receptor potential vanilloid 4 (TRPV4), and voltage-dependent anion channel (VDAC), with particular attention to AQP2. In regard to AQP2, most reciprocal interactions between actin and AQP2 occur during intracellular trafficking, which are largely mediated through indirect binding. Actin and the actin cytoskeleton work as cables, barriers, stabilizers, and force generators for motility. However, as with ENaC, the effects of actin cytoskeleton on channel gating should be investigated further. This article is part of a Special Issue entitled: Reciprocal influences between cell cytoskeleton and membrane channels, receptors and transporters. Guest Editor: Jean Claude Hervé.
Topics: Actins; Animals; Aquaporin 2; Biological Transport; Humans; Ion Channels
PubMed: 23770358
DOI: 10.1016/j.bbamem.2013.06.004