Ion Channel Properties of a Cation Channelrhodopsin, Gt_CCR4

We previously reported a cation channelrhodopsin, Gt_CCR4, which is one of the 44 types of microbial rhodopsins from a cryptophyte flagellate, Guillardia theta. Due to the modest homology of amino acid sequences with a chlorophyte channelrhodopsin such as Cr_ChR2 from Chlamydomonas reinhardtii, it has been proposed that a family of cryptophyte channelrhodopsin, including Gt_CCR4, has a distinct molecular mechanism for channel gating and ion permeation. In this study, we compared the photocurrent properties, cation selectivity and kinetics between well-known Cr_ChR2 and Gt_CCR4 by a conventional path clamp method. Large and stable light-induced cation conduction by Gt_CCR4 at the maximum absorbing wavelength (530 nm) was observed with only small inactivation (15%), whereas the photocurrent of Cr_ChR2 exhibited significant inactivation (50%) and desensitization. The light sensitivity of Gt_CCR4 was higher (EC50 = 0.13 mW/mm2) than that of Cr_ChR2 (EC50 = 0.80 mW/mm2) while the channel open life time (photocycle speed) was in the same range as that of Cr_ChR2 (25~30 ms for Gt_CCR4 and 10~15 ms for Cr_ChR2). This observation implies that Gt_CCR4 enables optical neuronal spiking with weak light in high temporal resolution when applied in neuroscience. Furthermore, we demonstrated high Na+ selectivity of Gt_CCR4 in which the selectivity ratio for Na+ was 37-fold larger than that for Cr_ChR2, which primarily conducts H+. On the other hand, Gt_CCR4 conducted almost no H+ and no Ca2+ under physiological conditions. These results suggest that ion selectivity in Gt_CCR4 is distinct from that in Cr_ChR2. In addition, a unique red-absorbing and stable intermediate in the photocycle was observed, indicating a photochromic property of Gt_CCR4.

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Molecular dynamics simulations of the Cx26 hemichannel: Evaluation of structural models with Brownian dynamics

The Journal of General Physiology ◽

10.1085/jgp.201110679 ◽

2011 ◽

Vol 138 (5) ◽

pp. 475-493 ◽

Cited By ~ 62

Author(s):

Taekyung Kwon ◽

Andrew L. Harris ◽

Angelo Rossi ◽

Thaddeus A. Bargiello

Keyword(s):

Crystal Structure ◽

Molecular Dynamics ◽

Posttranslational Modifications ◽

Brownian Dynamics ◽

Ion Selectivity ◽

Physiological Role ◽

Md Simulations ◽

Cation Selectivity ◽

Gap Junction Channel ◽

Channel Properties

The recently published crystal structure of the Cx26 gap junction channel provides a unique opportunity for elucidation of the structure of the conductive connexin pore and the molecular determinants of its ion permeation properties (conductance, current–voltage [I-V] relations, and charge selectivity). However, the crystal structure was incomplete, most notably lacking the coordinates of the N-terminal methionine residue, which resides within the pore, and also lacking two cytosolic domains. To allow computational studies for comparison with the known channel properties, we completed the structure. Grand canonical Monte Carlo Brownian dynamics (GCMC/BD) simulations of the completed and the published Cx26 hemichannel crystal structure indicate that the pore is too narrow to permit significant ion flux. The GCMC/BD simulations predict marked inward current rectification and almost perfect anion selectivity, both inconsistent with known channel properties. The completed structure was refined by all-atom molecular dynamics (MD) simulations (220 ns total) in an explicit solvent and POPC membrane system. These MD simulations produced an equilibrated structure with a larger minimal pore diameter, which decreased the height of the permeation barrier formed by the N terminus. GCMC/BD simulations of the MD-equilibrated structure yielded more appropriate single-channel conductance and less anion/cation selectivity. However, the simulations much more closely matched experimentally determined I-V relations when the charge effects of specific co- and posttranslational modifications of Cx26 previously identified by mass spectrometry were incorporated. We conclude that the average equilibrated structure obtained after MD simulations more closely represents the open Cx26 hemichannel structure than does the crystal structure, and that co- and posttranslational modifications of Cx26 hemichannels are likely to play an important physiological role by defining the conductance and ion selectivity of Cx26 channels. Furthermore, the simulations and data suggest that experimentally observed heterogeneity in Cx26 I-V relations can be accounted for by variation in co- and posttranslational modifications.

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Faculty Opinions recommendation of Ion channel properties underlying axonal action potential initiation in pyramidal neurons.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1007335.92105 ◽

2002 ◽

Author(s):

Alain Destexhe

Keyword(s):

Action Potential ◽

Ion Channel ◽

Pyramidal Neurons ◽

Ion Channel Properties ◽

Action Potential Initiation ◽

Potential Initiation ◽

Channel Properties

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Antimicrobial Peptides and their Pore/Ion Channel Properties in Neutralization of Pathogenic Microbes

Current Topics in Medicinal Chemistry ◽

10.2174/1568026615666150703115454 ◽

2015 ◽

Vol 16 (1) ◽

pp. 46-53 ◽

Cited By ~ 22

Author(s):

Shruti Sharma ◽

Nirakar Sahoo ◽

Anirban Bhunia

Keyword(s):

Antimicrobial Peptides ◽

Ion Channel ◽

Ion Channel Properties ◽

Pathogenic Microbes ◽

Channel Properties

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A Model for Predicting Cation Selectivity and Permeability in AMPA and NMDA Receptors Based on Receptor Subunit Composition

Frontiers in Synaptic Neuroscience ◽

10.3389/fnsyn.2021.779759 ◽

2021 ◽

Vol 13 ◽

Author(s):

Sampath Kumar ◽

Sanjay S. Kumar

Keyword(s):

Experimental Data ◽

Divalent Cations ◽

Ion Selectivity ◽

Gene Families ◽

Subunit Composition ◽

Receptor Subunit ◽

Cation Selectivity ◽

Subunit Stoichiometry ◽

Ampa And Nmda Receptors

Glutamatergic AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) and NMDA (N-methyl-D-aspartate) receptors are implicated in diverse functions ranging from synaptic plasticity to cell death. They are heterotetrameric proteins whose subunits are derived from multiple distinct gene families. The subunit composition of these receptors determines their permeability to monovalent and/or divalent cations, but it is not entirely clear how this selectivity arises in native and recombinantly-expressed receptor populations. By analyzing the sequence of amino acids lining the selectivity filters within the pore forming membrane helices (M2) of these subunits and by correlating subunit stoichiometry of these receptors with their ability to permeate Na+ and/or Ca2+, we propose here a mathematical model for predicting cation selectivity and permeability in these receptors. The model proposed is based on principles of charge attractivity and charge neutralization within the pore forming region of these receptors; it accurately predicts and reconciles experimental data across various platforms including Ca2+ permeability of GluA2-lacking AMPARs and ion selectivity within GluN3-containing di- and tri-heteromeric NMDARs. Additionally, the model provides insights into biophysical mechanisms regulating cation selectivity and permeability of these receptors and the role of various subunits in these processes.

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Tuning the ion selectivity of glutamate transporter–associated uncoupled conductances

The Journal of General Physiology ◽

10.1085/jgp.201511556 ◽

2016 ◽

Vol 148 (1) ◽

pp. 13-24 ◽

Cited By ~ 6

Author(s):

Rosemary J. Cater ◽

Robert J. Vandenberg ◽

Renae M. Ryan

Keyword(s):

Excitatory Amino Acid ◽

Ion Selectivity ◽

Glutamate Transporter ◽

Amino Acid Transporters ◽

Primary Role ◽

Cation Selectivity ◽

Anion Selectivity ◽

Transport Domain ◽

Cl Conductance

The concentration of glutamate within a glutamatergic synapse is tightly regulated by excitatory amino acid transporters (EAATs). In addition to their primary role in clearing extracellular glutamate, the EAATs also possess a thermodynamically uncoupled Cl− conductance. This conductance is activated by the binding of substrate and Na+, but the direction of Cl− flux is independent of the rate or direction of substrate transport; thus, the two processes are thermodynamically uncoupled. A recent molecular dynamics study of the archaeal EAAT homologue GltPh (an aspartate transporter from Pyrococcus horikoshii) identified an aqueous pore at the interface of the transport and trimerization domains, through which anions could permeate, and it was suggested that an arginine residue at the most restricted part of this pathway might play a role in determining anion selectivity. In this study, we mutate this arginine to a histidine in the human glutamate transporter EAAT1 and investigate the role of the protonation state of this residue on anion selectivity and transporter function. Our results demonstrate that a positive charge at this position is crucial for determining anion versus cation selectivity of the uncoupled conductance of EAAT1. In addition, because the nature of this residue influences the turnover rate of EAAT1, we reveal an intrinsic link between the elevator movement of the transport domain and the Cl− channel.

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