scholarly journals Tarantula toxins use common surfaces for interacting with Kv and ASIC ion channels

eLife ◽  
2015 ◽  
Vol 4 ◽  
Author(s):  
Kanchan Gupta ◽  
Maryam Zamanian ◽  
Chanhyung Bae ◽  
Mirela Milescu ◽  
Dmitriy Krepkiy ◽  
...  
Keyword(s):  
Ion Channels ◽  
Ion Channel ◽  
Extracellular Domain ◽  
Voltage Sensor ◽  
Concave Surface ◽  
Voltage Sensing ◽  
Membrane Interaction ◽  
Computational Approaches ◽  
Physical Environments

Tarantula toxins that bind to voltage-sensing domains of voltage-activated ion channels are thought to partition into the membrane and bind to the channel within the bilayer. While no structures of a voltage-sensor toxin bound to a channel have been solved, a structural homolog, psalmotoxin (PcTx1), was recently crystalized in complex with the extracellular domain of an acid sensing ion channel (ASIC). In the present study we use spectroscopic, biophysical and computational approaches to compare membrane interaction properties and channel binding surfaces of PcTx1 with the voltage-sensor toxin guangxitoxin (GxTx-1E). Our results show that both types of tarantula toxins interact with membranes, but that voltage-sensor toxins partition deeper into the bilayer. In addition, our results suggest that tarantula toxins have evolved a similar concave surface for clamping onto α-helices that is effective in aqueous or lipidic physical environments.

scholarly journals Tarantula Toxins Interact with Voltage Sensors within Lipid Membranes

2007 ◽  
Vol 130 (5) ◽  
pp. 497-511 ◽  
Author(s):  
Mirela Milescu ◽  
Jan Vobecky ◽  
Soung H. Roh ◽  
Sung H. Kim ◽  
Hoi J. Jung ◽  
...  
Keyword(s):  
Ion Channels ◽  
Lipid Membranes ◽  
Voltage Sensor ◽  
Structural Motif ◽  
Membrane Interaction ◽  
Voltage Sensors ◽  
Kv Channels ◽  
Channel Interactions ◽  
The Stability ◽  
Electrical Signaling

Voltage-activated ion channels are essential for electrical signaling, yet the mechanism of voltage sensing remains under intense investigation. The voltage-sensor paddle is a crucial structural motif in voltage-activated potassium (Kv) channels that has been proposed to move at the protein–lipid interface in response to changes in membrane voltage. Here we explore whether tarantula toxins like hanatoxin and SGTx1 inhibit Kv channels by interacting with paddle motifs within the membrane. We find that these toxins can partition into membranes under physiologically relevant conditions, but that the toxin–membrane interaction is not sufficient to inhibit Kv channels. From mutagenesis studies we identify regions of the toxin involved in binding to the paddle motif, and those important for interacting with membranes. Modification of membranes with sphingomyelinase D dramatically alters the stability of the toxin–channel complex, suggesting that tarantula toxins interact with paddle motifs within the membrane and that they are sensitive detectors of lipid–channel interactions.

How Does an Ion Channel Sense Voltage?

Physiology ◽  
1997 ◽  
Vol 12 (5) ◽  
pp. 203-210 ◽  
Author(s):  
DM Papazian ◽  
F Bezanilla
Keyword(s):  
Ion Channels ◽  
Electric Field ◽  
Ion Channel ◽  
Voltage Sensor ◽  
Significant Fraction ◽  
Channel Activity ◽  
Transmembrane Segments ◽  
Voltage Dependent ◽  
Ion Conducting ◽  
Muscle Excitability

Voltage-dependent ion channels underlie nerve and muscle excitability. Recent studies have increased our understanding of how voltage controls channel activity. Charged residues in transmembrane segments that contribute to the voltage sensor have been identified. During activation, voltage-sensing residues traverse a significant fraction of the transmembrane electric field, dramatically increasing the probability that the channel will enter an open, ion-conducting state.

scholarly journals Divergent functional and conformational outcomes in an ion channel-peptide interaction

2021 ◽  
Author(s):  
Christian Bernsen Borg ◽  
Stephanie Andrea Heusser ◽  
Janne Colding ◽  
Stephan Alexander Pless
Keyword(s):  
Ion Channels ◽  
Synaptic Transmission ◽  
Ion Channel ◽  
Extracellular Domain ◽  
Cation Channels ◽  
Precise Control ◽  
Acid Sensing Ion Channels ◽  
Subunit Interface ◽  
Ligand Interactions ◽  
Peptide Interaction

Acid-sensing ion channels (ASICs) are trimeric proton-gated cation channels that contribute to fast synaptic transmission. Pharmacological inhibition of ASIC1a has been shown to reduce neurotoxicity and infarct volumes during stroke. The cysteine knot toxin Psalmotoxin-1 (PcTx1) is one of the most potent and selective inhibitors of ASIC1a. PcTx1 binds at the subunit interface, but both the stoichiometric requirements and the dynamics of the conformational consequences of the ion channel-peptide interaction remain unknown. Here, we use a combination of electrophysiology, voltage-clamp fluorometry and subunit concatenation to decipher the mechanism of PcTx1 inhibition. We observe a long-lived PcTx1-induced conformational change in the ASIC1a extracellular domain that is destabilized by the F350L mutation at the PcTx1 binding site. Concatemeric channel constructs show that two WT ASIC1a subunits are sufficient for WT-like current inhibition, while the presence of a single mutated subunit is enough to destabilize the PcTx1-induced conformation. Our results therefore demonstrate a divergence between the functional effects of PcTx1 on the pore and its conformational consequences in the extracellular domain. It further highlights how engineering of ion channels enables precise control over individual subunits for pharmacological and conformational assessment to determine the mechanism of ion channel-ligand interactions.

scholarly journals The Dragon’s Paralysing Spell: Evidence of Sodium and Calcium Ion Channel Binding Neurotoxins in Helodermatid and Varanid Lizard Venoms

Toxins ◽  
2021 ◽  
Vol 13 (8) ◽  
pp. 549
Author(s):  
James S. Dobson ◽  
Richard J. Harris ◽  
Christina N. Zdenek ◽  
Tam Huynh ◽  
Wayne C. Hodgson ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Electrical Stimulation ◽  
Ion Channels ◽  
Ion Channel ◽  
Large Body ◽  
Tissue Preparation ◽  
Clinical Effects ◽  
Voltage Sensing ◽  
Biolayer Interferometry ◽  
Voltage Sensing Domain

Bites from helodermatid lizards can cause pain, paresthesia, paralysis, and tachycardia, as well as other symptoms consistent with neurotoxicity. Furthermore, in vitro studies have shown that Heloderma horridum venom inhibits ion flux and blocks the electrical stimulation of skeletal muscles. Helodermatids have long been considered the only venomous lizards, but a large body of robust evidence has demonstrated venom to be a basal trait of Anguimorpha. This clade includes varanid lizards, whose bites have been reported to cause anticoagulation, pain, and occasionally paralysis and tachycardia. Despite the evolutionary novelty of these lizard venoms, their neuromuscular targets have yet to be identified, even for the iconic helodermatid lizards. Therefore, to fill this knowledge gap, the venoms of three Heloderma species (H. exasperatum, H. horridum and H. suspectum) and two Varanus species (V. salvadorii and V. varius) were investigated using Gallus gallus chick biventer cervicis nerve–muscle preparations and biolayer interferometry assays for binding to mammalian ion channels.. Incubation with Heloderma venoms caused the reduction in nerve-mediated muscle twitches post initial response of avian skeletal muscle tissue preparation assays suggesting voltage-gated sodium (NaV) channel binding. Congruent with the flaccid paralysis inducing blockage of electrical stimulation in the skeletal muscle preparations, the biolayer interferometry tests with Heloderma suspectum venom revealed binding to the S3–S4 loop within voltage-sensing domain IV of the skeletal muscle channel subtype, NaV1.4. Consistent with tachycardia reported in clinical cases, the venom also bound to voltage-sensing domain IV of the cardiac smooth muscle calcium channel, CaV1.2. While Varanus varius venom did not have discernable effects in the avian tissue preparation assay at the concentration tested, in the biointerferometry assay both V. varius and V. salvadorii bound to voltage-sensing domain IV of both NaV1.4 and CaV1.2, similar to H. suspectum venom. The ability of varanid venoms to bind to mammalian ion channels but not to the avian tissue preparation suggests prey-selective actions, as did the differential potency within the Heloderma venoms for avian versus mammalian pathophysiological targets. This study thus presents the detailed characterization of Heloderma venom ion channel neurotoxicity and offers the first evidence of varanid lizard venom neurotoxicity. In addition, the data not only provide information useful to understanding the clinical effects produced by envenomations, but also reveal their utility as physiological probes, and underscore the potential utility of neglected venomous lineages in the drug design and development pipeline.

scholarly journals TOK Homologue in Neurospora crassa: First Cloning and Functional Characterization of an Ion Channel in a Filamentous Fungus

2003 ◽  
Vol 2 (1) ◽  
pp. 181-190 ◽  
Author(s):  
Stephen K. Roberts
Keyword(s):  
Ion Channels ◽  
Ion Channel ◽  
Neurospora Crassa ◽  
Filamentous Fungus ◽  
Single Channel ◽  
Functional Characterization ◽  
Reversal Potential ◽  
Channel Activity ◽  
Biophysical Properties ◽  
Patch Clamp Technique

ABSTRACT In contrast to animal and plant cells, very little is known of ion channel function in fungal physiology. The life cycle of most fungi depends on the “filamentous” polarized growth of hyphal cells; however, no ion channels have been cloned from filamentous fungi and comparatively few preliminary recordings of ion channel activity have been made. In an attempt to gain an insight into the role of ion channels in fungal hyphal physiology, a homolog of the yeast K+ channel (ScTOK1) was cloned from the filamentous fungus, Neurospora crassa. The patch clamp technique was used to investigate the biophysical properties of the N. crassa K+ channel (NcTOKA) after heterologous expression of NcTOKA in yeast. NcTOKA mediated mainly time-dependent outward whole-cell currents, and the reversal potential of these currents indicated that it conducted K+ efflux. NcTOKA channel gating was sensitive to extracellular K+ such that channel activation was dependent on the reversal potential for K+. However, expression of NcTOKA was able to overcome the K+ auxotrophy of a yeast mutant missing the K+ uptake transporters TRK1 and TRK2, suggesting that NcTOKA also mediated K+ influx. Consistent with this, close inspection of NcTOKA-mediated currents revealed small inward K+ currents at potentials negative of EK. NcTOKA single-channel activity was characterized by rapid flickering between the open and closed states with a unitary conductance of 16 pS. NcTOKA was effectively blocked by extracellular Ca2+, verapamil, quinine, and TEA+ but was insensitive to Cs+, 4-aminopyridine, and glibenclamide. The physiological significance of NcTOKA is discussed in the context of its biophysical properties.

Ion channel activities of cultured rat mesangial cells

1991 ◽  
Vol 261 (5) ◽  
pp. F808-F814 ◽  
Author(s):  
H. Matsunaga ◽  
N. Yamashita ◽  
Y. Miyajima ◽  
T. Okuda ◽  
H. Chang ◽  
...  
Keyword(s):  
Angiotensin Ii ◽  
Ion Channels ◽  
Patch Clamp ◽  
Ion Channel ◽  
Arginine Vasopressin ◽  
Mesangial Cells ◽  
Cation Channel ◽  
K Channel ◽  
Patch Clamp Technique ◽  
Inside Out

We used the patch-clamp technique to clarify the nature of ion channels in renal mesangial cells in culture. In the cell-attached mode most patches were silent in the absence of agonists. In some patches a 25-pS nonselective channel was observed. This 25-pS cation channel was consistently observed in inside-out patches, and it was activated by intracellular Ca2+. Excised patch experiments also revealed the existence of a 40-pS K+ channel, which was activated by intracellular Ca2+. This 40-pS K+ channel was observed infrequently in the cell-attached mode. The activities of both channels were increased by arginine vasopressin or angiotensin II, resulting from an increase in intracellular Ca2+ concentration.

scholarly journals Proper Voltage-Dependent Ion Channel Function in Dysferlin-Deficient Cardiomyocytes

2015 ◽  
Vol 36 (3) ◽  
pp. 1049-1058 ◽  
Author(s):  
Lena Rubi ◽  
Vaibhavkumar S. Gawali ◽  
Helmut Kubista ◽  
Hannes Todt ◽  
Karlheinz Hilber ◽  
...  
Keyword(s):  
Ion Channels ◽  
Muscular Dystrophy ◽  
Ion Channel ◽  
Cardiac Electrophysiology ◽  
Cardiac Complications ◽  
Membrane Repair ◽  
Patch Clamp Technique ◽  
Cardiac Ion Channels ◽  
Ventricular Cardiomyocytes ◽  
Voltage Dependent

Background/Aims: Dysferlin plays a decisive role in calcium-dependent membrane repair in myocytes. Mutations in the encoding DYSF gene cause a number of myopathies, e.g. limb-girdle muscular dystrophy type 2B (LGMD2B). Besides skeletal muscle degenerative processes, dysferlin deficiency is also associated with cardiac complications. Thus, both LGMD2B patients and dysferlin-deficient mice develop a dilated cardiomyopathy. We and others have recently reported that dystrophin-deficient ventricular cardiomyocytes from mouse models of Duchenne muscular dystrophy show significant abnormalities in voltage-dependent ion channels, which may contribute to the pathophysiology in dystrophic cardiomyopathy. The aim of the present study was to investigate if dysferlin, like dystrophin, is a regulator of cardiac ion channels. Methods and Results: By using the whole cell patch-clamp technique, we compared the properties of voltage-dependent calcium and sodium channels, as well as action potentials in ventricular cardiomyocytes isolated from the hearts of normal and dysferlin-deficient (dysf) mice. In contrast to dystrophin deficiency, the lack of dysferlin did not impair the ion channel properties and left action potential parameters unaltered. In connection with normal ECGs in dysf mice these results suggest that dysferlin deficiency does not perturb cardiac electrophysiology. Conclusion: Our study demonstrates that dysferlin does not regulate cardiac voltage-dependent ion channels, and implies that abnormalities in cardiac ion channels are not a universal characteristic of all muscular dystrophy types.

scholarly journals Computational Ion Channel Research: from the Application of Artificial Intelligence to Molecular Dynamics Simulations.

2020 ◽  
Vol 55 (S3) ◽  
pp. 14-45
Keyword(s):  
Artificial Intelligence ◽  
Molecular Dynamics ◽  
Ion Channels ◽  
Ion Channel ◽  
Computational Methods ◽  
Homology Modelling ◽  
Channel Structure ◽  
Learning Approaches ◽  
Qsar Analysis ◽  
Wide Range

Although ion channels are crucial in many physiological processes and constitute an important class of drug targets, much is still unclear about their function and possible malfunctions that lead to diseases. In recent years, computational methods have evolved into important and invaluable approaches for studying ion channels and their functions. This is mainly due to their demanding mechanism of action where a static picture of an ion channel structure is often insufficient to fully understand the underlying mechanism. Therefore, the use of computational methods is as important as chemical-biological based experimental methods for a better understanding of ion channels. This review provides an overview on a variety of computational methods and software specific to the field of ion-channels. Artificial intelligence (or more precisely machine learning) approaches are applied for the sequence-based prediction of ion channel family, or topology of the transmembrane region. In case sufficient data on ion channel modulators is available, these methods can also be applied for quantitative structureactivity relationship (QSAR) analysis. Molecular dynamics (MD) simulations combined with computational molecular design methods such as docking can be used for analysing the function of ion channels including ion conductance, different conformational states, binding sites and ligand interactions, and the influence of mutations on their function. In the absence of a three-dimensional protein structure, homology modelling can be applied to create a model of your ion channel structure of interest. Besides highlighting a wide range of successful applications, we will also provide a basic introduction to the most important computational methods and discuss best practices to get a rough idea of possible applications and risks.

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