Ion-channel properties of mastoparan, a 14-residue peptide from wasp venom, and of MP3, a 12-residue analogue

1990 ◽  
Vol 239 (1296) ◽  
pp. 383-400 ◽  
Keyword(s):  
Ion Channels ◽  
Lipid Bilayers ◽  
Type I ◽  
Type Ii ◽  
Channel Formation ◽  
Channel Inactivation ◽  
Ion Channel Properties ◽  
Discrete Channel ◽  
Voltage Dependent ◽  
Channel Properties

Mastoparan, a 14-residue peptide, has been investigated with respect to its ability to form ion channels in planar lipid bilayers. In the presence of 0.3 - 3.0 μ M mastoparan, two types of activity are seen. Type I activity is characterized by discrete channel openings, exhibiting multiple con­ductance levels in the range 15-700 pS. Type II activity is characterized by transient increases in bilayer conductance, up to a maximum of about 650 pS. Both type I and type II activities are voltage dependent. Channel activation occurs if the compartment containing mastoparan is held at a positive potential; channel inactivation if the same compartment is held at a negative potential. Channel formation is dependent on ionic strength; channel openings are only observed at KCl concentrations of 0.3 M or above. Furthermore, raising the concentration of KCl to 3.0 M stabilizes the open form of the channel. Mastoparan channels are weakly cation selective, P K/Cl ≈ 2. A 12-residue analogue, des -Ile 1 , Asn 2 mastoparan, preferentially forms type I channels. The ion channels formed by these short peptides may be modelled in terms of bundles of transmembrane α -helices.

scholarly journals Genome Delivery and Ion Channel Properties Are Altered in VP4 Mutants of Poliovirus

2003 ◽  
Vol 77 (9) ◽  
pp. 5266-5274 ◽  
Author(s):  
Pranav Danthi ◽  
Magdalena Tosteson ◽  
Qi-han Li ◽  
Marie Chow
Keyword(s):  
Ion Channels ◽  
Lipid Bilayers ◽  
Conformational Transition ◽  
Channel Structure ◽  
Host Cells ◽  
Lethal Mutant ◽  
Ion Channel Properties ◽  
Type 3

ABSTRACT During entry into host cells, poliovirus undergoes a receptor-mediated conformational transition to form 135S particles with irreversible exposure of VP4 capsid sequences and VP1 N termini. To understand the role of VP4 during virus entry, the fate of VP4 during infection by site-specific mutants at threonine-28 of VP4 (4028T) was compared with that of the parental Mahoney type 1 virus. Three virus mutants were studied: the entry-defective, nonviable mutant 4028T.G and the viable mutants 4028T.S and 4028T.V, in which residue threonine-28 was changed to glycine, serine, and valine, respectively. We show that mutant and wild-type (WT) VP4 proteins are localized to cellular membranes after the 135S conformational transition. Both WT and viable 4028T mutant particles interact with lipid bilayers to form ion channels, whereas the entry-defective 4028T.G particles do not. In addition, the electrical properties of the channels induced by the mutant viruses are different from each other and from those of WT Mahoney and Sabin type 3 viruses. Finally, uncoating and/or cytoplasmic delivery of the viral genome is altered in the 4028T mutants: the 4028T.G lethal mutant does not release its genome into the cytoplasm, and genome delivery is slower during infection by mutant 4028T.V 135S particles than by mutant 4028T.S or WT 135S particles. The distinctive electrical characteristics of the different 4028T mutant channels indicate that VP4 sequences might form part of the channel structure. The different entry phenotypes of these VP4 mutants suggest that the ion channels may be related to VP4's role during genome uncoating and/or delivery.

Effects of intracellular pH and calcium activity on ion currents in internally perfused neurons of the snail Lymnaea stagnalis

1987 ◽  
Vol 65 (5) ◽  
pp. 994-1000 ◽  
Author(s):  
William J. Moody ◽  
Lou Byerly
Keyword(s):  
Ion Channel ◽  
Lymnaea Stagnalis ◽  
Ionic Composition ◽  
Channel Current ◽  
Ion Channel Properties ◽  
Internal Ph ◽  
Voltage Dependent ◽  
Ion Sensitive Microelectrodes ◽  
Degree Of Control ◽  
Channel Properties

The suction pipet method of intracellular dialysis and voltage clamp of cells has proven extremely useful in analysing the electrical properties of cells too small for the application of conventional microelectrode techniques and in larger cells for studying the effects of alterations in the internal ionic composition. Using neurons of the snail Lymnaea stagnalis, we have analysed several problems involved in the latter application of this technique and present several solutions to them. One major problem centers around the degree of control over the ionic composition of the cytoplasm achieved by altering the pipet solution. Using ion-sensitive microelectrodes during internal dialysis, we found that the efficiency of exchange between pipet and cytoplasm was much poorer for highly buffered ions such as H+ and Ca2+, than for K+, for example. Special precautions are described that can help this situation. The second problem involves the study of the effects of low internal pH on ion-channel properties. We summarize evidence for a specific voltage-dependent hydrogen ion channel, current through which becomes prominent at low internal pH. We analyse how the presence of this heretofore unrecognized current can seriously confuse the results of experiments designed to study the effects of low internal pH on other voltage-dependent currents.

scholarly journals Binding of Ca2+-Independent C2 Domains to Lipid Membranes: a Multi-Scale Molecular Dynamics Study

2020 ◽  
Author(s):  
Andreas Haahr Larsen ◽  
Mark S.P. Sansom
Keyword(s):  
Molecular Dynamics ◽  
Lipid Bilayers ◽  
Md Simulations ◽  
Multiscale Simulation ◽  
Coarse Grained ◽  
Type I ◽  
Type Ii ◽  
Binding Modes ◽  
C2 Domains ◽  
Anionic Lipids

AbstractC2 domains facilitate protein-lipid interaction in cellular recognition and signalling processes. They possess a β-sandwich structure, with either type I or type II topology. C2 domains can interact with anionic lipid bilayers in either a Ca2+-dependent or a Ca2+-independent manner. The mechanism of recognition of anionic lipids by Ca2+-independent C2 domains is incompletely understood. We have used molecular dynamics (MD) simulations to explore the membrane interactions of six Ca2+– independent C2 domains, from KIBRA, PI3KC2α, RIM2, PTEN, SHIP2, and Smurf2. In coarse grained MD simulations these C2 domains bound to lipid bilayers, forming transient interactions with zwitterionic (phosphatidylcholine, PC) bilayers compared to long lived interactions with anionic bilayers also containing either phosphatidylserine (PS) or PS and phosphatidylinositol bisphosphate (PIP2). Type I C2 domains bound non-canonically via the front, back or side of the β sandwich, whereas type II C2 domains bound canonically, via the top loops (as is typically the case for Ca2+-dependent C2 domains). C2 domains interacted strongly (up to 120 kJ/mol) with membranes containing PIP2 causing the bound anionic lipids to clustered around the protein. The C2 domains bound less strongly to anionic membranes without PIP2 (<50 kJ/mol), and most weakly to neutral membranes (<33 kJ/mol). Productive binding modes were identified and further analysed in atomistic simulations. For PTEN and SHIP2, CG simulations were also performed of the intact enzymes (i.e. phosphatase domain plus C2 domain) with PIP2-contating bilayers and the roles of the two domains in membrane localization were compared. From a methodological perspective, these studies establish a multiscale simulation protocol for studying membrane binding/recognition proteins, capable of revealing binding modes alongside details of lipid binding affinity and specificity.

Ion Channel Sensor on a Silicon Support

2004 ◽  
Vol 820 ◽  
Author(s):  
Michael Goryll ◽  
Seth Wilk ◽  
Gerard M. Laws ◽  
Stephen M. Goodnick ◽  
Trevor J. Thornton ◽  
...  
Keyword(s):  
Ion Channels ◽  
Ion Channel ◽  
Lipid Bilayer ◽  
Lipid Bilayers ◽  
Chemical Vapor ◽  
Fast Method ◽  
Fluorocarbon Films ◽  
Novel Approach ◽  
Voltage Dependent ◽  
Assembled Monolayers

AbstractWe are building a biosensor based on ion channels inserted into lipid bilayers that are suspended across an aperture in silicon. The process flow only involves conventional optical lithography and deep Si reactive ion etching to create micromachined apertures in a silicon wafer. In order to provide surface properties for lipid bilayer attachment that are similar to those of the fluorocarbon films that are currently used, we coated the silicon surface with a fluoropolymer using plasma-assisted chemical vapor deposition. When compared with the surface treatment methods using self-assembled monolayers of fluorocarbon chemicals, this novel approach towards modifying the wettability of a silicon dioxide surface provides an easy and fast method for subsequent lipid bilayer formation. Current-Voltage measurements on OmpF ion channels incorporated into these membranes show the voltage dependent gating action expected from a working porin ion channel.

Diversity in the Structure and Function of Ion Channels

The Neuron ◽  
2015 ◽  
pp. 127-150
Author(s):  
Irwin B. Levitan ◽  
Leonard K. Kaczmarek
Keyword(s):  
Ion Channels ◽  
Potassium Channels ◽  
Messenger Rna ◽  
Individual Gene ◽  
Calcium Dependent ◽  
Electrophysiological Measurements ◽  
Voltage Dependent ◽  
And Function ◽  
Inward Rectifier Channels ◽  
Channel Properties

Voltage clamp and patch clamp techniques are used to reveal heterogeneity of ion currents carried through voltage-dependent sodium, calcium, and potassium channels. Advances in channel molecular biology have made it clear that the diversity of ion channels is even greater than was suspected from these electrophysiological measurements. This diversity is achieved by several different mechanisms, including the existence of multiple genes for the pore-forming α‎ subunits of ion channels, alternative splicing of the messenger RNA transcribed from each individual gene, formation of heterotetramers containing different α‎ subunits of potassium channels, and modulation of channel properties by auxiliary subunits that may themselves comprise a large and diverse family of proteins. Moreover, potassium channels can be further categorized into voltage-dependent, calcium-dependent, sodium-dependent, two-pore, and inward rectifier channels. Emerging evidence suggests that many human diseases are associated with dysfunction of individual classes of ion channels in neurons.

scholarly journals Single Channel Properties of Rat Acid–sensitive Ion Channel-1α, -2a, and -3 Expressed in Xenopus Oocytes

2002 ◽  
Vol 120 (4) ◽  
pp. 553-566 ◽  
Author(s):  
Ping Zhang ◽  
Cecilia M. Canessa
Keyword(s):  
Ion Channels ◽  
Xenopus Oocytes ◽  
Single Channel ◽  
Patch Clamp Technique ◽  
Open Probability ◽  
Acid Sensing Ion Channels ◽  
Voltage Dependent ◽  
Subconductance States ◽  
Kinetics Of ◽  
Channel Properties

The mammalian nervous system expresses proton-gated ion channels known as acid-sensing ion channels (ASICs). Depending on their location and specialization some neurons express more than one type of ASIC where they may form homo- or heteromeric channels. Macroscopic characteristics of the ASIC currents have been described, but little is known at the single channel level. Here, we have examined the properties of unitary currents of homomeric rat ASIC1α, ASIC2a, and ASIC3 expressed in Xenopus oocytes with the patch clamp technique. We describe and characterize properties unique to each of these channels that can be used to distinguish the various types of ASIC channels expressed in mammalian neurons. The amplitudes of the unitary currents in symmetrical Na+ are similar for the three types of channels (23–18 pS) and are not voltage dependent. However, ASIC1α exhibits three subconductance states, ASIC2a exhibits only one, and ASIC3 none. The kinetics of the three types of channels are different: ASIC1α and ASIC2a shift between modes of activity, each mode has different open probability and kinetics. In contrast, the kinetics of ASIC3 are uniform throughout the burst of activity. ASIC1α, ASIC2a, and ASIC3 are activated by external protons with apparent pH50 of 5.9, 5.0, and 5.4, respectively. Desensitization in the continual presence of protons is fast and complete in ASIC1α and ASIC3 (2.0 and 4.5 s−1, respectively) but slow and only partial in ASIC2a (0.045 s−1). The response to external Ca2+ also differs: μM concentrations of extracellular Ca2+ are necessary for proton gating of ASIC3 (EC50 = 0.28 μM), whereas ASIC1α and ASIC2a do not require Ca2+. In addition, Ca2+ inhibits ASIC1α (KD = 9.2 ± 2 mM) by several mechanisms: decrease in the amplitude of unitary currents, shortening of the burst of activity, and decrease in the number of activated channels. Contrary to previous reports, our results indicate that the Ca2+ permeability of ASIC1α is very small.

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