1
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Tewes N, Kubitzki B, Bytyqi F, Metko N, Mach S, Thiel G, Rauh O. Mutation in pore-helix modulates interplay between filter gate and Ba2+ block in a Kcv channel pore. J Gen Physiol 2024; 156:e202313514. [PMID: 38652099 DOI: 10.1085/jgp.202313514] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2023] [Revised: 03/05/2024] [Accepted: 04/09/2024] [Indexed: 04/25/2024] Open
Abstract
The selectivity filter of K+ channels catalyzes a rapid and highly selective transport of K+ while serving as a gate. To understand the control of this filter gate, we use the pore-only K+ channel KcvNTS in which gating is exclusively determined by the activity of the filter gate. It has been previously shown that a mutation at the C-terminus of the pore-helix (S42T) increases K+ permeability and introduces distinct voltage-dependent and K+-sensitive channel closures at depolarizing voltages. Here, we report that the latter are not generated by intrinsic conformational changes of the filter gate but by a voltage-dependent block caused by nanomolar trace contaminations of Ba2+ in the KCl solution. Channel closures can be alleviated by extreme positive voltages and they can be completely abolished by the high-affinity Ba2+ chelator 18C6TA. By contrast, the same channel closures can be augmented by adding Ba2+ at submicromolar concentrations to the cytosolic buffer. These data suggest that a conservative exchange of Ser for Thr in a crucial position of the filter gate increases the affinity of the filter for Ba2+ by >200-fold at positive voltages. While Ba2+ ions apparently remain only for a short time in the filter-binding sites of the WT channel before passing the pore, they remain much longer in the mutant channel. Our findings suggest that the dwell times of permeating and blocking ions in the filter-binding sites are tightly controlled by interactions between the pore-helix and the selectivity filter.
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Affiliation(s)
- Noel Tewes
- Membrane Biophysics, Technische Universität Darmstadt , Darmstadt, Germany
| | - Beatrice Kubitzki
- Membrane Biophysics, Technische Universität Darmstadt , Darmstadt, Germany
| | - Flandrit Bytyqi
- Membrane Biophysics, Technische Universität Darmstadt , Darmstadt, Germany
| | - Nikola Metko
- Membrane Biophysics, Technische Universität Darmstadt , Darmstadt, Germany
| | - Sebastian Mach
- Membrane Biophysics, Technische Universität Darmstadt , Darmstadt, Germany
| | - Gerhard Thiel
- Membrane Biophysics, Technische Universität Darmstadt , Darmstadt, Germany
- Centre for Synthetic Biology, Technische Universität Darmstadt , Darmstadt, Germany
| | - Oliver Rauh
- Membrane Biophysics, Technische Universität Darmstadt , Darmstadt, Germany
- Centre for Synthetic Biology, Technische Universität Darmstadt , Darmstadt, Germany
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2
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Yoo H, Lee HR, Kang SB, Lee J, Park K, Yoo H, Kim J, Chung TD, Lee KM, Lim HH, Son CY, Sun JY, Oh SS. G-Quadruplex-Filtered Selective Ion-to-Ion Current Amplification for Non-Invasive Ion Monitoring in Real Time. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2023; 35:e2303655. [PMID: 37433455 DOI: 10.1002/adma.202303655] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2023] [Revised: 07/08/2023] [Accepted: 07/10/2023] [Indexed: 07/13/2023]
Abstract
Living cells efflux intracellular ions for maintaining cellular life, so intravital measurements of specific ion signals are of significant importance for studying cellular functions and pharmacokinetics. In this work, de novo synthesis of artificial K+ -selective membrane and its integration with polyelectrolyte hydrogel-based open-junction ionic diode (OJID) is demonstrated, achieving a real-time K+ -selective ion-to-ion current amplification in complex bioenvironments. By mimicking biological K+ channels and nerve impulse transmitters, in-line K+ -binding G-quartets are introduced across freestanding lipid bilayers by G-specific hexylation of monolithic G-quadruplex, and the pre-filtered K+ flow is directly converted to amplified ionic currents by the OJID with a fast response time at 100 ms intervals. By the synergistic combination of charge repulsion, sieving, and ion recognition, the synthetic membrane allows K+ transport exclusively without water leakage; it is 250× and 17× more permeable toward K+ than monovalent anion, Cl- , and polyatomic cation, N-methyl-d-glucamine+ , respectively. The molecular recognition-mediated ion channeling provides a 500% larger signal for K+ as compared to Li+ (0.6× smaller than K+ ) despite the same valence. Using the miniaturized device, non-invasive, direct, and real-time K+ efflux monitoring from living cell spheroids is achieved with minimal crosstalk, specifically in identifying osmotic shock-induced necrosis and drug-antidote dynamics.
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Affiliation(s)
- Hyebin Yoo
- Department of Materials Science & Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Gyeongbuk, 37673, South Korea
| | - Hyun-Ro Lee
- Department of Materials Science & Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Gyeongbuk, 37673, South Korea
| | - Soon-Bo Kang
- Department of Materials Science & Engineering, Seoul National University, Seoul, 08826, South Korea
| | - Juhwa Lee
- Department of Chemistry, Pohang University of Science and Technology (POSTECH), Pohang, Gyeongbuk, 37673, South Korea
| | - Kunwoong Park
- Neurovascular Unit Research Group, Korea Brain Research Institute (KBRI), Daegu, 41062, South Korea
| | - Hyunjae Yoo
- Department of Materials Science & Engineering, Seoul National University, Seoul, 08826, South Korea
| | - Jinmin Kim
- Department of Materials Science & Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Gyeongbuk, 37673, South Korea
| | - Taek Dong Chung
- Department of Chemistry, Seoul National University, Seoul, 08826, South Korea
| | - Kyung-Mi Lee
- Department of Biochemistry and Molecular Biology, Korea University College of Medicine, Seoul, 02841, South Korea
| | - Hyun-Ho Lim
- Neurovascular Unit Research Group, Korea Brain Research Institute (KBRI), Daegu, 41062, South Korea
| | - Chang Yun Son
- Department of Chemistry, Pohang University of Science and Technology (POSTECH), Pohang, Gyeongbuk, 37673, South Korea
- Institute for Convergence Research and Education in Advanced Technology (I-CREATE), Yonsei University, Incheon, 21983, South Korea
| | - Jeong-Yun Sun
- Department of Materials Science & Engineering, Seoul National University, Seoul, 08826, South Korea
- Research Institute of Advanced Materials (RIAM), Seoul National University, Seoul, 08826, South Korea
| | - Seung Soo Oh
- Department of Materials Science & Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Gyeongbuk, 37673, South Korea
- Institute for Convergence Research and Education in Advanced Technology (I-CREATE), Yonsei University, Incheon, 21983, South Korea
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3
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Singh M, Sapkota K, Sakimura K, Kano M, Cowell RM, Overstreet-Wadiche L, Hablitz JJ, Nakazawa K. Maturation of GABAergic Synaptic Transmission From Neocortical Parvalbumin Interneurons Involves N-methyl-D-aspartate Receptor Recruitment of Cav2.1 Channels. Neuroscience 2023; 513:38-53. [PMID: 36682446 DOI: 10.1016/j.neuroscience.2023.01.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2022] [Revised: 01/02/2023] [Accepted: 01/08/2023] [Indexed: 01/21/2023]
Abstract
N-methyl-D-aspartate receptor (NMDAR) hypofunction during brain development is likely to contribute to the manifestation of schizophrenia (SCZ) in young adulthood. The cellular targets of NMDAR hypofunction appear to be at least in part corticolimbic fast-spiking (FS) interneurons. However, functional alterations in parvalbumin (PV)-positive FS interneurons following NMDAR hypofunction are poorly understood. Paired patch-clamp recordings from murine cortical PV interneurons and pyramidal neurons revealed that genetic deletion of NMDAR subunit Grin1 in prospective PV interneurons before the second postnatal week impaired evoked- and synchronized-GABA release. Whereas intrinsic excitability and spiking characteristics were also disturbed by Grin1 deletion, neither restoring their excitability by K+ channel blockade nor increasing extracellular Ca2+ rescued the GABA release. GABA release was also insensitive to the Cav2.1 channel antagonist ω-agatoxin IVA. Heterozygous deletion of Cacna1a gene (encoding Cav2.1) in PV interneurons produced a similar GABA release phenotype as the Grin1 mutants. Treatment with the Cav2.1/2.2 channel agonist GV-58 augmented somatic Ca2+ currents and GABA release in Cacna1a-haploinsufficient PV interneurons, but failed to enhance GABA release in the Grin1-deleted PV interneurons. Taken together, our results suggest that Grin1 deletion in prospective PV interneurons impairs proper maturation of membrane excitability and Cav2.1-recruited evoked GABA release. This may increase synaptic excitatory/inhibitory ratio in principal neurons, contributing to the emergence of SCZ-like phenotypes.
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Affiliation(s)
- Mahendra Singh
- Department of Neuroscience, Scientific Platforms, Southern Research, Birmingham, AL 35205, USA; Department of Neurobiology, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
| | - Kiran Sapkota
- Department of Neuroscience, Scientific Platforms, Southern Research, Birmingham, AL 35205, USA
| | - Kenji Sakimura
- Department of Animal Model Development, Brain Research Institute, Niigata University, Niigata 951-8585, Japan
| | - Masanobu Kano
- Department of Neurophysiology, Graduate School of Medicine, The University of Tokyo, Tokyo 113-0033, Japan; International Research Center for Neurointelligence (WPI-IRCN), The University of Tokyo Institutes for Advanced Study (UTIAS), The University of Tokyo, Tokyo 113-0033, Japan
| | - Rita M Cowell
- Department of Neuroscience, Scientific Platforms, Southern Research, Birmingham, AL 35205, USA; Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, Birmingham, AL 35294, USA; Department of Neurology, University of Alabama at Birmingham, Birmingham, AL 35294, USA
| | | | - John J Hablitz
- Department of Neurobiology, University of Alabama at Birmingham, Birmingham, AL 35294, USA
| | - Kazu Nakazawa
- Department of Neuroscience, Scientific Platforms, Southern Research, Birmingham, AL 35205, USA; Department of Neurobiology, University of Alabama at Birmingham, Birmingham, AL 35294, USA; Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, Birmingham, AL 35294, USA
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4
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A distinct mechanism of C-type inactivation in the Kv-like KcsA mutant E71V. Nat Commun 2022; 13:1574. [PMID: 35322021 PMCID: PMC8943062 DOI: 10.1038/s41467-022-28866-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2021] [Accepted: 02/01/2022] [Indexed: 11/08/2022] Open
Abstract
C-type inactivation is of great physiological importance in voltage-activated K+ channels (Kv), but its structural basis remains unresolved. Knowledge about C-type inactivation has been largely deduced from the bacterial K+ channel KcsA, whose selectivity filter constricts under inactivating conditions. However, the filter is highly sensitive to its molecular environment, which is different in Kv channels than in KcsA. In particular, a glutamic acid residue at position 71 along the pore helix in KcsA is substituted by a valine conserved in most Kv channels, suggesting that this side chain is a molecular determinant of function. Here, a combination of X-ray crystallography, solid-state NMR and MD simulations of the E71V KcsA mutant is undertaken to explore inactivation in this Kv-like construct. X-ray and ssNMR data show that the filter of the Kv-like mutant does not constrict under inactivating conditions. Rather, the filter adopts a conformation that is slightly narrowed and rigidified. On the other hand, MD simulations indicate that the constricted conformation can nonetheless be stably established in the mutant channel. Together, these findings suggest that the Kv-like KcsA mutant may be associated with different modes of C-type inactivation, showing that distinct filter environments entail distinct C-type inactivation mechanisms.
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5
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Identification of a G-Protein-Independent Activator of GIRK Channels. Cell Rep 2021; 31:107770. [PMID: 32553165 DOI: 10.1016/j.celrep.2020.107770] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2019] [Revised: 03/24/2020] [Accepted: 05/22/2020] [Indexed: 12/18/2022] Open
Abstract
G-protein-gated inwardly rectifying K+ (GIRK) channels are essential effectors of inhibitory neurotransmission in the brain. GIRK channels have been implicated in diseases with abnormal neuronal excitability, including epilepsy and addiction. GIRK channels are tetramers composed of either the same subunit (e.g., homotetramers) or different subunits (e.g., heterotetramers). Compounds that specifically target subsets of GIRK channels in vivo are lacking. Previous studies have shown that alcohol directly activates GIRK channels through a hydrophobic pocket located in the cytoplasmic domain of the channel. Here, we report the identification and functional characterization of a GIRK1-selective activator, termed GiGA1, that targets the alcohol pocket. GiGA1 activates GIRK1/GIRK2 both in vitro and in vivo and, in turn, mitigates the effects of a convulsant in an acute epilepsy mouse model. These results shed light on the structure-based development of subunit-specific GIRK modulators that could provide potential treatments for brain disorders.
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6
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Cosseddu SM, Choe EJ, Khovanov IA. Unraveling of a Strongly Correlated Dynamical Network of Residues Controlling the Permeation of Potassium in KcsA Ion Channel. ENTROPY (BASEL, SWITZERLAND) 2021; 23:E72. [PMID: 33418985 PMCID: PMC7825352 DOI: 10.3390/e23010072] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Revised: 12/23/2020] [Accepted: 01/02/2021] [Indexed: 12/26/2022]
Abstract
The complicated patterns of the single-channel currents in potassium ion channel KcsA are governed by the structural variability of the selectivity filter. A comparative analysis of the dynamics of the wild type KcsA channel and several of its mutants showing different conducting patterns was performed. A strongly correlated dynamical network of interacting residues is found to play a key role in regulating the state of the wild type channel. The network is centered on the aspartate D80 which plays the role of a hub by strong interacting via hydrogen bonds with residues E71, R64, R89, and W67. Residue D80 also affects the selectivity filter via its backbones. This network further compromises ions and water molecules located inside the channel that results in the mutual influence: the permeation depends on the configuration of residues in the network, and the dynamics of network's residues depends on locations of ions and water molecules inside the selectivity filter. Some features of the network provide a further understanding of experimental results describing the KcsA activity. In particular, the necessity of anionic lipids to be present for functioning the channel is explained by the interaction between the lipids and the arginine residues R64 and R89 that prevents destabilizing the structure of the selectivity filter.
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Affiliation(s)
| | | | - Igor A. Khovanov
- School of Engineering, University of Warwick, Coventry CV4 7AL, UK; (S.M.C.); (E.J.C.)
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7
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Selectivity filter ion binding affinity determines inactivation in a potassium channel. Proc Natl Acad Sci U S A 2020; 117:29968-29978. [PMID: 33154158 DOI: 10.1073/pnas.2009624117] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Potassium channels can become nonconducting via inactivation at a gate inside the highly conserved selectivity filter (SF) region near the extracellular side of the membrane. In certain ligand-gated channels, such as BK channels and MthK, a Ca2+-activated K+ channel from Methanobacterium thermoautotrophicum, the SF has been proposed to play a role in opening and closing rather than inactivation, although the underlying conformational changes are unknown. Using X-ray crystallography, identical conductive MthK structures were obtained in wide-ranging K+ concentrations (6 to 150 mM), unlike KcsA, whose SF collapses at low permeant ion concentrations. Surprisingly, three of the SF's four binding sites remained almost fully occupied throughout this range, indicating high affinities (likely submillimolar), while only the central S2 site titrated, losing its ion at 6 mM, indicating low K+ affinity (∼50 mM). Molecular simulations showed that the MthK SF can also collapse in the absence of K+, similar to KcsA, but that even a single K+ binding at any of the SF sites, except S4, can rescue the conductive state. The uneven titration across binding sites differs from KcsA, where SF sites display a uniform decrease in occupancy with K+ concentration, in the low millimolar range, leading to SF collapse. We found that ions were disfavored in MthK's S2 site due to weaker coordination by carbonyl groups, arising from different interactions with the pore helix and water behind the SF. We conclude that these differences in interactions endow the seemingly identical SFs of KcsA and MthK with strikingly different inactivating phenotypes.
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8
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A Functional K + Channel from Tetraselmis Virus 1, a Member of the Mimiviridae. Viruses 2020; 12:v12101107. [PMID: 33003637 PMCID: PMC7650704 DOI: 10.3390/v12101107] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2020] [Revised: 09/25/2020] [Accepted: 09/25/2020] [Indexed: 12/05/2022] Open
Abstract
Potassium ion (K+) channels have been observed in diverse viruses that infect eukaryotic marine and freshwater algae. However, experimental evidence for functional K+ channels among these alga-infecting viruses has thus far been restricted to members of the family Phycodnaviridae, which are large, double-stranded DNA viruses within the phylum Nucleocytoviricota. Recent sequencing projects revealed that alga-infecting members of Mimiviridae, another family within this phylum, may also contain genes encoding K+ channels. Here we examine the structural features and the functional properties of putative K+ channels from four cultivated members of Mimiviridae. While all four proteins contain variations of the conserved selectivity filter sequence of K+ channels, structural prediction algorithms suggest that only two of them have the required number and position of two transmembrane domains that are present in all K+ channels. After in vitro translation and reconstitution of the four proteins in planar lipid bilayers, we confirmed that one of them, a 79 amino acid protein from the virus Tetraselmis virus 1 (TetV-1), forms a functional ion channel with a distinct selectivity for K+ over Na+ and a sensitivity to Ba2+. Thus, virus-encoded K+ channels are not limited to Phycodnaviridae but also occur in the members of Mimiviridae. The large sequence diversity among the viral K+ channels implies multiple events of lateral gene transfer.
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9
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Rohaim A, Gong L, Li J, Rui H, Blachowicz L, Roux B. Open and Closed Structures of a Barium-Blocked Potassium Channel. J Mol Biol 2020; 432:4783-4798. [PMID: 32615129 DOI: 10.1016/j.jmb.2020.06.012] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2020] [Revised: 05/27/2020] [Accepted: 06/12/2020] [Indexed: 11/26/2022]
Abstract
Barium (Ba2+) is a classic permeant blocker of potassium (K+) channels. The "external lock-in effect" in barium block experiments, whereby the binding of external K+ impedes the forward translocation of the blocker, provides a powerful avenue to investigate the selectivity of the binding sites along the pore of potassium channels. Barium block experiments show that the external lock-in site is highly selective for K+ over Na+. Wild-type KcsA was crystallized in low K+ conditions, and the crystals were soaked in solutions containing various concentrations of barium. Structural analysis reveals open and closed gate conformations of the KcsA channel. Anomalous diffraction experiments show that Ba2+ primarily binds to the innermost site S4 of the selectivity filter of the open-gate conformation and also the site S2, but no binding is detected with the closed-gate conformation. Alchemical free-energy perturbation calculations indicate that the presence of a Ba2+ ion in the selectivity filter boosts the specificity of K+ binding relative to Na+ in the external sites S0-S2.
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Affiliation(s)
- Ahmed Rohaim
- Department of Biochemistry and Molecular Biology, University of Chicago, Gordon Center for Integrative Science, 929 E 57th St, Chicago, IL 60637, USA; Department of Biophysics, Faculty of Science, Cairo University, Giza 12613, Egypt
| | - LiDong Gong
- School of Chemistry and Chemical Engineering, Liaoning Normal University, Dalian 116029, China
| | - Jing Li
- Department of Biochemistry and Molecular Biology, University of Chicago, Gordon Center for Integrative Science, 929 E 57th St, Chicago, IL 60637, USA
| | - Huan Rui
- Department of Biochemistry and Molecular Biology, University of Chicago, Gordon Center for Integrative Science, 929 E 57th St, Chicago, IL 60637, USA
| | - Lydia Blachowicz
- Department of Biochemistry and Molecular Biology, University of Chicago, Gordon Center for Integrative Science, 929 E 57th St, Chicago, IL 60637, USA
| | - Benoît Roux
- Department of Biochemistry and Molecular Biology, University of Chicago, Gordon Center for Integrative Science, 929 E 57th St, Chicago, IL 60637, USA.
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10
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Eckert D, Schulze T, Stahl J, Rauh O, Van Etten JL, Hertel B, Schroeder I, Moroni A, Thiel G. A small viral potassium ion channel with an inherent inward rectification. Channels (Austin) 2020; 13:124-135. [PMID: 31010373 PMCID: PMC6527081 DOI: 10.1080/19336950.2019.1605813] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Some algal viruses have coding sequences for proteins with structural and functional characteristics of pore modules of complex K+ channels. Here we exploit the structural diversity among these channel orthologs to discover new basic principles of structure/function correlates in K+ channels. The analysis of three similar K+ channels with ≤ 86 amino acids (AA) shows that one channel (Kmpv1) generates an ohmic conductance in HEK293 cells while the other two (KmpvSP1, KmpvPL1) exhibit typical features of canonical Kir channels. Like Kir channels, the rectification of the viral channels is a function of the K+ driving force. Reconstitution of KmpvSP1 and KmpvPL1 in planar lipid bilayers showed rapid channel fluctuations only at voltages negative of the K+ reversal voltage. This rectification was maintained in KCl buffer with 1 mM EDTA, which excludes blocking cations as the source of rectification. This means that rectification of the viral channels must be an inherent property of the channel. The structural basis for rectification was investigated by a chimera between rectifying and non-rectifying channels as well as point mutations making the rectifier similar to the ohmic conducting channel. The results of these experiments exclude the pore with pore helix and selectivity filter as playing a role in rectification. The insensitivity of the rectifier to point mutations suggests that tertiary or quaternary structural interactions between the transmembrane domains are responsible for this type of gating.
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Affiliation(s)
- Denise Eckert
- a Membrane Biophysics , Technische Universität Darmstadt , Darmstadt , Germany
| | - Tobias Schulze
- a Membrane Biophysics , Technische Universität Darmstadt , Darmstadt , Germany
| | - Julian Stahl
- a Membrane Biophysics , Technische Universität Darmstadt , Darmstadt , Germany
| | - Oliver Rauh
- a Membrane Biophysics , Technische Universität Darmstadt , Darmstadt , Germany
| | - James L Van Etten
- b Department of Plant Pathology and Nebraska Center for Virology , University of Nebraska Lincoln , Lincoln , NE , USA
| | - Brigitte Hertel
- a Membrane Biophysics , Technische Universität Darmstadt , Darmstadt , Germany
| | - Indra Schroeder
- a Membrane Biophysics , Technische Universität Darmstadt , Darmstadt , Germany
| | - Anna Moroni
- c Department of Biosciences and CNR IBF-Mi , Università degli Studi di Milano , Milano , Italy
| | - Gerhard Thiel
- a Membrane Biophysics , Technische Universität Darmstadt , Darmstadt , Germany
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11
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Otsuka R, Hirata K, Sasaki Y, Lisy JM, Ishiuchi S, Fujii M. Alkali and Alkaline Earth Metal Ions Complexes with a Partial Peptide of the Selectivity Filter in K
+
Channels Studied by a Cold Ion Trap Infrared Spectroscopy. Chemphyschem 2020; 21:712-724. [DOI: 10.1002/cphc.202000033] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2020] [Revised: 02/12/2020] [Indexed: 12/15/2022]
Affiliation(s)
- Remina Otsuka
- Laboratory for Chemistry and Life ScienceInstitute of Innovative Research, Tokyo Institute of Technology 4259 Nagatsuta-cho, Midori-ku Yokohama 226-8503 Japan
- School of Life Science and TechnologyTokyo Institute of Technology 4259 Nagatsuta-cho, Midori-ku Yokohama, Kanagawa 226-8503 Japan
| | - Keisuke Hirata
- Laboratory for Chemistry and Life ScienceInstitute of Innovative Research, Tokyo Institute of Technology 4259 Nagatsuta-cho, Midori-ku Yokohama 226-8503 Japan
- School of Life Science and TechnologyTokyo Institute of Technology 4259 Nagatsuta-cho, Midori-ku Yokohama, Kanagawa 226-8503 Japan
| | - Yuta Sasaki
- Laboratory for Chemistry and Life ScienceInstitute of Innovative Research, Tokyo Institute of Technology 4259 Nagatsuta-cho, Midori-ku Yokohama 226-8503 Japan
- School of Life Science and TechnologyTokyo Institute of Technology 4259 Nagatsuta-cho, Midori-ku Yokohama, Kanagawa 226-8503 Japan
| | - James M. Lisy
- Tokyo Tech World Research Hub Initiative (WRHI)Institute of Innovation Research, Tokyo Institute of Technology 4259, Nagatsuta-cho, Midori-ku Yokohama 226-8503 Japan
- Department of ChemistryUniversity of Illinois at Urbana-Champaign Urbana IL 61801 USA
| | - Shun‐ichi Ishiuchi
- Laboratory for Chemistry and Life ScienceInstitute of Innovative Research, Tokyo Institute of Technology 4259 Nagatsuta-cho, Midori-ku Yokohama 226-8503 Japan
- School of Life Science and TechnologyTokyo Institute of Technology 4259 Nagatsuta-cho, Midori-ku Yokohama, Kanagawa 226-8503 Japan
| | - Masaaki Fujii
- Laboratory for Chemistry and Life ScienceInstitute of Innovative Research, Tokyo Institute of Technology 4259 Nagatsuta-cho, Midori-ku Yokohama 226-8503 Japan
- School of Life Science and TechnologyTokyo Institute of Technology 4259 Nagatsuta-cho, Midori-ku Yokohama, Kanagawa 226-8503 Japan
- Tokyo Tech World Research Hub Initiative (WRHI)Institute of Innovation Research, Tokyo Institute of Technology 4259, Nagatsuta-cho, Midori-ku Yokohama 226-8503 Japan
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12
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Chaudhari MI, Vanegas JM, Pratt LR, Muralidharan A, Rempe SB. Hydration Mimicry by Membrane Ion Channels. Annu Rev Phys Chem 2020; 71:461-484. [PMID: 32155383 DOI: 10.1146/annurev-physchem-012320-015457] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Ions transiting biomembranes might pass readily from water through ion-specific membrane proteins if these protein channels provide environments similar to the aqueous solution hydration environment. Indeed, bulk aqueous solution is an important reference condition for the ion permeation process. Assessment of this hydration mimicry concept depends on understanding the hydration structure and free energies of metal ions in water in order to provide a comparison for the membrane channel environment. To refine these considerations, we review local hydration structures of ions in bulk water and the molecular quasi-chemical theory that provides hydration free energies. In doing so, we note some current views of ion binding to membrane channels and suggest new physical chemical calculations and experiments that might further clarify the hydration mimicry concept.
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Affiliation(s)
- Mangesh I Chaudhari
- Department of Computational Biology and Biophysics, Sandia National Laboratories, Albuquerque, New Mexico 87185, USA;
| | - Juan M Vanegas
- Department of Computational Biology and Biophysics, Sandia National Laboratories, Albuquerque, New Mexico 87185, USA; .,Current affiliation: Department of Physics, University of Vermont, Burlington, Vermont 05405, USA
| | - L R Pratt
- Department of Chemical and Biomolecular Engineering, Tulane University, New Orleans, Louisiana 70118, USA
| | - Ajay Muralidharan
- Department of Chemical and Biomolecular Engineering, Tulane University, New Orleans, Louisiana 70118, USA.,Current affiliation: Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706, USA
| | - Susan B Rempe
- Department of Computational Biology and Biophysics, Sandia National Laboratories, Albuquerque, New Mexico 87185, USA;
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Sumikama T, Oiki S. Queueing arrival and release mechanism for K + permeation through a potassium channel. J Physiol Sci 2019; 69:919-930. [PMID: 31456113 PMCID: PMC10717923 DOI: 10.1007/s12576-019-00706-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2019] [Accepted: 08/18/2019] [Indexed: 01/26/2023]
Abstract
The mechanism underlying ion permeation through potassium channels still remains controversial. K+ ions permeate across a narrow selectivity filter (SF) in a single file. Conventional scenarios assume that K+ ions are tightly bound in the SF, and, thus, they are displaced from their energy well by ion-ion repulsion with an incoming ion. This tight coupling between entering and exiting ions has been called the "knock-on" mechanism. However, this paradigm is contradicted by experimental data measuring the water-ion flux coupling ratio, demonstrating fewer ion occupancies. Here, the results of molecular dynamics simulations of permeation through the KcsA potassium channel revealed an alternative mechanism. In the aligned ions in the SF (an ion queue), the outermost K+ was readily and spontaneously released toward the extracellular space, and the affinity of the relevant ion was ~ 50 mM. Based on this low-affinity regime, a simple queueing mechanism described by loose coupling of entering and exiting ions is proposed.
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Affiliation(s)
- Takashi Sumikama
- Department of Molecular Physiology and Biophysics, Faculty of Medical Sciences, University of Fukui, Fukui, 910-1193, Japan
- Nano Life Science Institute (WPI-NanoLSI), Kanazawa University, Kakuma-machi, Kanazawa, 920-1192, Japan
| | - Shigetoshi Oiki
- Department of Molecular Physiology and Biophysics, Faculty of Medical Sciences, University of Fukui, Fukui, 910-1193, Japan.
- Biomedical Imaging Research Center, University of Fukui, Fukui, 910-1193, Japan.
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14
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Song Z, Cao X, Horng TL, Huang H. Selectivity of the KcsA potassium channel: Analysis and computation. Phys Rev E 2019; 100:022406. [PMID: 31574673 DOI: 10.1103/physreve.100.022406] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2019] [Indexed: 11/07/2022]
Abstract
Ion channels regulate the flux of ions through cell membranes and play significant roles in many physiological functions. Most of the existing literature focuses on computational approaches based on molecular dynamics simulation or numerical solution of the modified Poisson-Nernst-Planck (PNP) system. In this paper, we present an analytical and computational study of a mathematical model of the KcsA potassium channel, including the effects of ion size (Bikerman model) and solvation energy (Born model). Under equilibrium conditions, we obtain an analytical solution of our modified PNP system, which is used to explain selectivity of KcsA of various ions (K^{+}, Na^{+}, Cl^{-}, Ca^{2+}, and Ba^{2+}) due to negative permanent charges inside the filter region and the effect of ion sizes. Our results show that K^{+} is always selected over Na^{+}, as smaller Na^{+} ions have larger solvation energy. As the amount of negative charges in the filter exceeds a critical value, divalent ions (Ca^{2+} and Ba^{2+}) can enter the filter region and block the KcsA channel. For the nonequilibrium cases, due to difficulties associated with a pure analytical or numerical approach, we use a hybrid analytical-numerical method to solve the modified PNP system. Our predictions of selectivity of KcsA channels and saturation phenomenon of the current-voltage (I-V) curve agree with experimental observations.
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Affiliation(s)
- Zilong Song
- Department of Mathematics and Statistics, York University, Toronto, Ontario, Canada M3J 1P3
| | - Xiulei Cao
- Department of Mathematics and Statistics, York University, Toronto, Ontario, Canada M3J 1P3
| | - Tzyy-Leng Horng
- Department of Applied Mathematics, Feng Chia University, Taichung 40724, Taiwan and National Center for Theoretical Sciences, Taipei Office, Taipei, Taiwan 10617
| | - Huaxiong Huang
- Department of Mathematics and Statistics, York University, Toronto, Ontario, Canada M3J 1P3 and Fields Institute for Research in Mathematical Sciences, Toronto, Ontario, Canada M5T 3J1
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15
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Xu Y, McDermott AE. Inactivation in the potassium channel KcsA. JOURNAL OF STRUCTURAL BIOLOGY-X 2019; 3:100009. [PMID: 32647814 PMCID: PMC7337057 DOI: 10.1016/j.yjsbx.2019.100009] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/16/2018] [Revised: 05/17/2019] [Accepted: 06/04/2019] [Indexed: 12/17/2022]
Abstract
C-type inactivation in potassium channels is a nearly universal regulatory mechanism. A major hypothesis states that C-type inactivation involves ion loss at the selectivity filter as an allosteric response to activation. NMR is used to probe protein conformational changes in response to pH and [K+], demonstrating that H+ and K+ binding are allosterically coupled in KcsA. The lipids are integrated parts of potassium channels in terms of structure, energetics and function.
Inactivation, the slow cessation of transmission after activation, is a general feature of potassium channels. It is essential for their function, and malfunctions in inactivation leads to numerous pathologies. The detailed mechanism for the C-type inactivation, distinct from the N-type inactivation, remains an active area of investigation. Crystallography, computational simulations, and NMR have greatly enriched our understanding of the process. Here we review the major hypotheses regarding C-type inactivation, particularly focusing on the key role played by NMR studies of the prokaryotic potassium channel KcsA, which serves as a good model for voltage gated mammalian channels.
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Affiliation(s)
- Yunyao Xu
- Department of Chemistry, Columbia University, New York, NY 10027, United States
| | - Ann E McDermott
- Department of Chemistry, Columbia University, New York, NY 10027, United States
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16
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Eichmann C, Frey L, Maslennikov I, Riek R. Probing Ion Binding in the Selectivity Filter of the KcsA Potassium Channel. J Am Chem Soc 2019; 141:7391-7398. [DOI: 10.1021/jacs.9b01092] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Cédric Eichmann
- Laboratory of Physical Chemistry, ETH Zurich, 8093 Zurich, Switzerland
| | - Lukas Frey
- Laboratory of Physical Chemistry, ETH Zurich, 8093 Zurich, Switzerland
| | | | - Roland Riek
- Laboratory of Physical Chemistry, ETH Zurich, 8093 Zurich, Switzerland
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17
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Chaudhari MI, Rempe SB. Strontium and barium in aqueous solution and a potassium channel binding site. J Chem Phys 2018; 148:222831. [PMID: 29907035 DOI: 10.1063/1.5023130] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Ion hydration structure and free energy establish criteria for understanding selective ion binding in potassium (K+) ion channels and may be significant to understanding blocking mechanisms as well. Recently, we investigated the hydration properties of Ba2+, the most potent blocker of K+ channels among the simple metal ions. Here, we use a similar method of combining ab initio molecular dynamics simulations, statistical mechanical theory, and electronic structure calculations to probe the fundamental hydration properties of Sr2+, which does not block bacterial K+ channels. The radial distribution of water around Sr2+ suggests a stable 8-fold geometry in the local hydration environment, similar to Ba2+. While the predicted hydration free energy of -331.8 kcal/mol is comparable with the experimental result of -334 kcal/mol, the value is significantly more favorable than the -305 kcal/mol hydration free energy of Ba2+. When placed in the innermost K+ channel blocking site, the solvation free energies and lowest energy structures of both Sr2+ and Ba2+ are nearly unchanged compared with their respective hydration properties. This result suggests that the block is not attributable to ion trapping due to +2 charge, and differences in blocking behavior arise due to free energies associated with the exchange of water ligands for channel ligands instead of free energies of transfer from water to the binding site.
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Affiliation(s)
- Mangesh I Chaudhari
- Center for Biological and Engineering Sciences, Sandia National Laboratories, Albuquerque, New Mexico 87185, USA
| | - Susan B Rempe
- Center for Biological and Engineering Sciences, Sandia National Laboratories, Albuquerque, New Mexico 87185, USA
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18
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Iwamoto M, Elfaramawy MA, Yamatake M, Matsuura T, Oiki S. Concurrent In Vitro Synthesis and Functional Detection of Nascent Activity of the KcsA Channel under a Membrane Potential. ACS Synth Biol 2018; 7:1004-1011. [PMID: 29566487 DOI: 10.1021/acssynbio.7b00454] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Processes involved in the functional formation of prokaryotic membrane proteins have remained elusive. Here, we developed a new in vitro membrane protein expression system to detect nascent activities of the KcsA potassium channel in lipid bilayers under an applied membrane potential. The channel was synthesized using a reconstituted Escherichia coli-based in vitro transcription/translation system (IVTT) in a water-in-oil droplet lined by a membrane. The synthesized channels spontaneously incorporated into the membrane even without the translocon machinery (unassisted pathway) and formed functional channels with the correct orientation. The single-channel current of the first appearing nascent channel was captured, followed by the subsequent appearance of multiple channels. Notably, the first appearance time shortened substantially as the membrane potential was hyperpolarized. Under a steadily applied membrane potential, this system serves as a production line of membrane proteins via the unassisted pathway, mimicking the bacterial synthetic membrane.
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Affiliation(s)
- Masayuki Iwamoto
- Department of Molecular Physiology and Biophysics, University of Fukui, Eiheiji-cho, Fukui 910-1193, Japan
| | - Maie A. Elfaramawy
- Department of Biotechnology, Division of Advanced Science and Biotechnology, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan
| | - Mariko Yamatake
- Department of Molecular Physiology and Biophysics, University of Fukui, Eiheiji-cho, Fukui 910-1193, Japan
| | - Tomoaki Matsuura
- Department of Biotechnology, Division of Advanced Science and Biotechnology, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan
| | - Shigetoshi Oiki
- Department of Molecular Physiology and Biophysics, University of Fukui, Eiheiji-cho, Fukui 910-1193, Japan
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19
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Mineral profiling of ostrich (Struthio camelus) seminal plasma and its relationship with semen traits and collection day. Anim Reprod Sci 2018; 193:98-106. [PMID: 29653829 DOI: 10.1016/j.anireprosci.2018.04.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2018] [Revised: 03/17/2018] [Accepted: 04/05/2018] [Indexed: 11/24/2022]
Abstract
Successful assisted reproduction techniques, with specific focus on in vitro semen storage for artificial insemination, are dependent on certain key elements which includes the biochemical profiling of semen. The objective of this study was to complete an ostrich seminal plasma (SP) evaluation by inductively coupled plasma mass spectrometry (ICP-MS) among seven males at different daily intervals (day 1, 3, 7, 11, 15, 19, 21, 23, 25, 26, 27, 28) for a period of 28 days during spring (August to September) for mineral profiling. The effect of collection day and male on sperm concentration, semen volume and seminal plasma volume, was explored as well as the relationships amongst these specific sperm traits and SP minerals. Variation amongst SP mineral concentrations, accounted for by the fixed effects of sperm concentration, semen volume, seminal plasma volume, collection day and male, ranged from 18% to 77%. Male had the largest effect on variation in SP minerals, namely: phosphorus (P), potassium (K), calcium (Ca), sodium (Na), boron (B), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), molybdenum (Mo), barium (Ba), arsenic (As) and selenium (Se). Sperm concentration instigated fluctuations of P, magnesium (Mg), B, zinc (Zn), Fe, aluminium (Al), Se, manganese (Mn) and lead (Pb). Semen volume had an effect on Na, K, B, Pb and Ba while seminal plasma volume only influenced variation in Na. There were fluctuations among collection days of specific micro minerals, Ni and Mo, with initial Ni concentrations being relatively greater and Mo at lesser concentrations. Semen volume, seminal plasma volume and sperm concentration varied amongst males. Sperm concentrations during the initial collection days, 1 and 3, were less than that for days 7 to 28. Significant variation of SP minerals and sperm characteristics among ejaculates and males suggest an association of these specific elements with sperm function and are, therefore, considered to be of potential importance to success of assisted reproduction technology for the ostrich. The relationship amongst sperm concentration and collection day confirms the need to conduct an initial period of collection to stabilise a greater sperm concentration to optimise sperm numbers for artificial insemination purposes.
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20
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Winterstein LM, Kukovetz K, Rauh O, Turman DL, Braun C, Moroni A, Schroeder I, Thiel G. Reconstitution and functional characterization of ion channels from nanodiscs in lipid bilayers. J Gen Physiol 2018; 150:637-646. [PMID: 29487088 PMCID: PMC5881443 DOI: 10.1085/jgp.201711904] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2017] [Revised: 12/20/2017] [Accepted: 01/30/2018] [Indexed: 11/20/2022] Open
Abstract
Recent studies have shown that membrane proteins can be efficiently synthesized in vitro before spontaneously inserting into soluble nanoscale lipid bilayers called nanodiscs (NDs). In this paper, we present experimental details that allow a combination of in vitro translation of ion channels into commercially available NDs followed by their direct reconstitution from these nanobilayers into standard bilayer setups for electrophysiological characterization. We present data showing that two model K+ channels, Kcv and KcsA, as well as a recently discovered dual-topology F- channel, Fluc, can be reliably reconstituted from different types of NDs into bilayers without contamination from the in vitro translation cocktail. The functional properties of Kcv and KcsA were characterized electrophysiologically and exhibited sensitivity to the lipid composition of the target DPhPC bilayer, suggesting that the channel proteins were fully exposed to the target membrane and were no longer surrounded by the lipid/protein scaffold. The single-channel properties of the three tested channels are compatible with studies from recordings of the same proteins in other expression systems. Altogether, the data show that synthesis of ion channels into NDs and their subsequent reconstitution into conventional bilayers provide a fast and reliable method for functional analysis of ion channels.
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Affiliation(s)
| | - Kerri Kukovetz
- Plant Membrane Biophysics, Technische Universität Darmstadt, Darmstadt, Germany
| | - Oliver Rauh
- Plant Membrane Biophysics, Technische Universität Darmstadt, Darmstadt, Germany
| | - Daniel L Turman
- Department of Biochemistry and Howard Hughes Medical Institute, Brandeis University, Waltham, MA
| | - Christian Braun
- Plant Membrane Biophysics, Technische Universität Darmstadt, Darmstadt, Germany
| | - Anna Moroni
- Department of Biosciences and Consiglio Nazionale delle Ricerche - Istituto di Biofisica, Università degli Studi di Milano, Milano, Italy
| | - Indra Schroeder
- Plant Membrane Biophysics, Technische Universität Darmstadt, Darmstadt, Germany
| | - Gerhard Thiel
- Plant Membrane Biophysics, Technische Universität Darmstadt, Darmstadt, Germany
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21
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Transmembrane allosteric energetics characterization for strong coupling between proton and potassium ion binding in the KcsA channel. Proc Natl Acad Sci U S A 2017; 114:8788-8793. [PMID: 28768808 DOI: 10.1073/pnas.1701330114] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The slow spontaneous inactivation of potassium channels exhibits classic signatures of transmembrane allostery. A variety of data support a model in which the loss of K+ ions from the selectivity filter is a major factor in promoting inactivation, which defeats transmission, and is allosterically coupled to protonation of key channel activation residues, more than 30 Å from the K+ ion binding site. We show that proton binding at the intracellular pH sensor perturbs the potassium affinity at the extracellular selectivity filter by more than three orders of magnitude for the full-length wild-type KcsA, a pH-gated bacterial channel, in membrane bilayers. Studies of F103 in the hinge of the inner helix suggest an important role for its bulky sidechain in the allosteric mechanism; we show that the energetic strength of coupling of the gates is strongly altered when this residue is mutated to alanine. These results provide quantitative site-specific measurements of allostery in a bilayer environment, and highlight the power of describing ion channel gating through the lens of allosteric coupling.
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22
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Chaudhari MI, Pratt LR, Rempe SB. Utility of chemical computations in predicting solution free energies of metal ions. MOLECULAR SIMULATION 2017. [DOI: 10.1080/08927022.2017.1342127] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- Mangesh I. Chaudhari
- Center for Biological and Engineering Sciences, Sandia National Laboratories, Albuquerque, NM, USA
| | - Lawrence R. Pratt
- Department of Chemical and Biomolecular Engineering, Tulane University, New Orleans, LA, USA
| | - Susan B. Rempe
- Center for Biological and Engineering Sciences, Sandia National Laboratories, Albuquerque, NM, USA
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23
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Hysteresis of KcsA potassium channel's activation- deactivation gating is caused by structural changes at the channel's selectivity filter. Proc Natl Acad Sci U S A 2017; 114:3234-3239. [PMID: 28265056 DOI: 10.1073/pnas.1618101114] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Mode-shift or hysteresis has been reported in ion channels. Voltage-shift for gating currents is well documented for voltage-gated cation channels (VGCC), and it is considered a voltage-sensing domain's (VSD) intrinsic property. However, uncoupling the Shaker K+ channel's pore domain (PD) from the VSD prevented the mode-shift of the gating currents. Consequently, it was proposed that an open-state stabilization of the PD imposes a mechanical load on the VSD, which causes its mode-shift. Furthermore, the mode-shift displayed by hyperpolarization-gated cation channels is likely caused by structural changes at the channel's PD similar to those underlying C-type inactivation. To demonstrate that the PD of VGCC undergoes hysteresis, it is imperative to study its gating process in the absence of the VSD. A back-door strategy is to use KcsA (a K+ channel from the bacteria Streptomyces lividans) as a surrogate because it lacks a VSD and exhibits an activation coupled to C-type inactivation. By directly measuring KcsA's activation gate opening and closing in conditions that promote or halt C-type inactivation, we have found (i) that KcsA undergoes mode-shift of gating when having K+ as the permeant ion; (ii) that Cs+ or Rb+, known to halt C-inactivation, prevented mode-shift of gating; and (iii) that, in the total absence of C-type inactivation, KcsA's mode-shift was prevented. Finally, our results demonstrate that an allosteric communication causes KcsA's activation gate to "remember" the conformation of the selectivity filter, and hence KcsA requires a different amount of energy for opening than for closing.
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24
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Turman DL, Stockbridge RB. Mechanism of single- and double-sided inhibition of dual topology fluoride channels by synthetic monobodies. J Gen Physiol 2017; 149:511-522. [PMID: 28258203 PMCID: PMC5379923 DOI: 10.1085/jgp.201611747] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2016] [Accepted: 02/03/2017] [Indexed: 11/30/2022] Open
Abstract
Fibronectin domain monobodies bind to both sides of Fluc Fl− channels in a negatively cooperative way, but crystal structures show two monobodies binding simultaneously. Turman and Stockbridge resolve this contradiction by showing that monobodies block channel pores by means of a negatively charged loop. The Fluc family of proteins comprises small, electrodiffusive fluoride channels, which prevent accumulation of toxic F− ions in microorganisms. Recent crystal structures have confirmed their unusual architecture, in which a pair of antiparallel subunits convenes to form a dimer with a twofold symmetry axis parallel to the plane of the membrane. These structures have also revealed the interactions between Fluc channels and several different fibronectin domain monobodies that inhibit Fluc-mediated F− currents; in all structures, each channel binds to two monobodies symmetrically, one on either side of the membrane. However, these structures do not reveal the mechanism of monobody inhibition. Moreover, the results appear to diverge from a recent electrophysiological study indicating that monobody binding is negatively cooperative; that is, a bound monobody on one side of a Fluc channel decreases the affinity of an oppositely bound monobody by ∼10-fold. In this study, we reconcile these observations by probing the mechanism of monobody binding and its negative cooperativity using electrophysiological experiments in planar lipid bilayers. Our results indicate that monobody inhibition occurs via a pore-blocking mechanism and that negative cooperativity arises from electrostatic repulsion between the oppositely bound monobodies. A single glutamate residue, on a loop of the monobody that extends into the channel interior, is responsible for negatively cooperative binding. This glutamate side chain also confers voltage dependence and sensitivity to the concentration of trans-F− ion to monobody binding. Neutralization by mutation to glutamine abolishes these electrostatic effects. Monobodies that are amenable to cocrystallization with Fluc channels lack an analogous negatively charged side chain and bind independently to opposite sides of the channel. Thus, this work reveals the source of voltage dependence and negative cooperativity of monobody binding to Fluc channels along with the pore-blocking mechanism.
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Affiliation(s)
- Daniel L Turman
- Department of Biochemistry and Howard Hughes Medical Institute, Brandeis University, Waltham, MA 02454
| | - Randy B Stockbridge
- Program in Biophysics, University of Michigan, Ann Arbor, MI 48109 .,Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109
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25
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Abstract
Specific ion binding by carboxylates (-COO-) is a broadly important topic because -COO- is one of the most common functional groups coordinated to metal ions in metalloproteins and synthetic polymers. We apply quantum chemical methods and the quasi-chemical free-energy theory to investigate how variations in the number of -COO- ligands in a binding site determine ion-binding preferences. We study a series of monovalent (Li+, Na+, K+, Cs+) and divalent (Zn2+, Ca2+) ions relevant to experimental work on ion channels and ionomers. Of two competing hypotheses, our results support the ligand field strength hypothesis and follow the reverse Hofmeister series for ion solvation and ion transfer from aqueous solution to binding sites with the preferred number of ligands. New insight arises from the finding that ion-binding sequences can be manipulated and even reversed just by constraining the number of carboxylate ligands in the binding sites. Our results help clarify the discrepancy in ion association between molecular ligands in aqueous solutions and ionomers, and their chemical analogues in ion-channel binding sites.
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Affiliation(s)
- Mark J Stevens
- Center for Integrated Nanotechnologies and ‡Biological and Engineering Sciences, Sandia National Laboratories , Albuquerque, New Mexico 87185, United States
| | - Susan L B Rempe
- Center for Integrated Nanotechnologies and ‡Biological and Engineering Sciences, Sandia National Laboratories , Albuquerque, New Mexico 87185, United States
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26
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Zheng H, Lee S, Llaguno MC, Jiang QX. bSUM: A bead-supported unilamellar membrane system facilitating unidirectional insertion of membrane proteins into giant vesicles. ACTA ACUST UNITED AC 2016; 147:77-93. [PMID: 26712851 PMCID: PMC4692488 DOI: 10.1085/jgp.201511448] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
KvAP conjugated to beads via a C-terminal His-tag seeds formation of a supported bilayer with unidirectional channel orientation for functional studies. Fused or giant vesicles, planar lipid bilayers, a droplet membrane system, and planar-supported membranes have been developed to incorporate membrane proteins for the electrical and biophysical analysis of such proteins or the bilayer properties. However, it remains difficult to incorporate membrane proteins, including ion channels, into reconstituted membrane systems that allow easy control of operational dimensions, incorporation orientation of the membrane proteins, and lipid composition of membranes. Here, using a newly developed chemical engineering procedure, we report on a bead-supported unilamellar membrane (bSUM) system that allows good control over membrane dimension, protein orientation, and lipid composition. Our new system uses specific ligands to facilitate the unidirectional incorporation of membrane proteins into lipid bilayers. Cryo–electron microscopic imaging demonstrates the unilamellar nature of the bSUMs. Electrical recordings from voltage-gated ion channels in bSUMs of varying diameters demonstrate the versatility of the new system. Using KvAP as a model system, we show that compared with other in vitro membrane systems, the bSUMs have the following advantages: (a) a major fraction of channels are orientated in a controlled way; (b) the channels mediate the formation of the lipid bilayer; (c) there is one and only one bilayer membrane on each bead; (d) the lipid composition can be controlled and the bSUM size is also under experimental control over a range of 0.2–20 µm; (e) the channel activity can be recorded by patch clamp using a planar electrode; and (f) the voltage-clamp speed (0.2–0.5 ms) of the bSUM on a planar electrode is fast, making it suitable to study ion channels with fast gating kinetics. Our observations suggest that the chemically engineered bSUMs afford a novel platform for studying lipid–protein interactions in membranes of varying lipid composition and may be useful for other applications, such as targeted delivery and single-molecule imaging.
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Affiliation(s)
- Hui Zheng
- Department of Cell Biology, Department of Physiology, and Department of Biophysics, The University of Texas Southwestern Medical Center, Dallas, TX 75390 Department of Cell Biology, Department of Physiology, and Department of Biophysics, The University of Texas Southwestern Medical Center, Dallas, TX 75390
| | - Sungsoo Lee
- Department of Cell Biology, Department of Physiology, and Department of Biophysics, The University of Texas Southwestern Medical Center, Dallas, TX 75390 Department of Cell Biology, Department of Physiology, and Department of Biophysics, The University of Texas Southwestern Medical Center, Dallas, TX 75390
| | - Marc C Llaguno
- Department of Cell Biology, Department of Physiology, and Department of Biophysics, The University of Texas Southwestern Medical Center, Dallas, TX 75390 Department of Cell Biology, Yale University, New Haven, CT 06510
| | - Qiu-Xing Jiang
- Department of Cell Biology, Department of Physiology, and Department of Biophysics, The University of Texas Southwestern Medical Center, Dallas, TX 75390 Department of Microbiology and Cell Science, University of Florida, Gainesville, FL 32611
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27
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Naranjo D, Moldenhauer H, Pincuntureo M, Díaz-Franulic I. Pore size matters for potassium channel conductance. J Gen Physiol 2016; 148:277-91. [PMID: 27619418 PMCID: PMC5037345 DOI: 10.1085/jgp.201611625] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2016] [Accepted: 08/10/2016] [Indexed: 01/31/2023] Open
Abstract
Ion channels are membrane proteins that mediate efficient ion transport across the hydrophobic core of cell membranes, an unlikely process in their absence. K+ channels discriminate K+ over cations with similar radii with extraordinary selectivity and display a wide diversity of ion transport rates, covering differences of two orders of magnitude in unitary conductance. The pore domains of large- and small-conductance K+ channels share a general architectural design comprising a conserved narrow selectivity filter, which forms intimate interactions with permeant ions, flanked by two wider vestibules toward the internal and external openings. In large-conductance K+ channels, the inner vestibule is wide, whereas in small-conductance channels it is narrow. Here we raise the idea that the physical dimensions of the hydrophobic internal vestibule limit ion transport in K+ channels, accounting for their diversity in unitary conductance.
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Affiliation(s)
- David Naranjo
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Playa Ancha, Valparaíso 2360103, Chile
| | - Hans Moldenhauer
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Playa Ancha, Valparaíso 2360103, Chile
| | - Matías Pincuntureo
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Playa Ancha, Valparaíso 2360103, Chile Programa de Doctorado en Ciencias, mención Biofísica y Biología Computacional, Universidad de Valparaíso, Valparaíso 2360103, Chile
| | - Ignacio Díaz-Franulic
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Playa Ancha, Valparaíso 2360103, Chile Center for Bioinformatics and Integrative Biology, Universidad Andrés Bello, Santiago 8370146, Chile Fraunhofer Chile Research, Las Condes 7550296, Chile
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Medovoy D, Perozo E, Roux B. Multi-ion free energy landscapes underscore the microscopic mechanism of ion selectivity in the KcsA channel. BIOCHIMICA ET BIOPHYSICA ACTA 2016; 1858:1722-32. [PMID: 26896693 PMCID: PMC4939264 DOI: 10.1016/j.bbamem.2016.02.019] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/29/2015] [Revised: 01/20/2016] [Accepted: 02/13/2016] [Indexed: 11/28/2022]
Abstract
Potassium (K(+)) channels are transmembrane proteins that passively and selectively allow K(+) ions to flow through them, after opening in response to an external stimulus. One of the most critical functional aspects of their function is their ability to remain very selective for K(+) over Na(+) while allowing high-throughput ion conduction at a rate close to the diffusion limit. Classically, it is assumed that the free energy difference between K(+) and Na(+) in the pore relative to the bulk solution is the critical quantity at the origin of selectivity. This is the thermodynamic view of ion selectivity. An alternative view assumes that kinetic factors play the dominant role. Recent results from a number of studies have also highlighted the great importance of the multi-ion single file on the selectivity of K(+) channels. The data indicate that having multiple K(+) ions bound simultaneously is required for selective K(+) conduction, and that a reduction in the number of bound K(+) ions destroys the multi-ion selectivity mechanism utilized by K(+) channels. In the present study, multi-ion potential of mean force molecular dynamics computations are carried out to clarify the mechanism of ion selectivity in the KcsA channel. The computations show that the multi-ion character of the permeation process is a critical element for establishing the selective ion conductivity through K(+)-channels. This article is part of a Special Issue entitled: Membrane Proteins edited by J.C. Gumbart and Sergei Noskov.
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Affiliation(s)
- David Medovoy
- Biochemistry and Molecular Biology, Institute for Biophysical Dynamics, Gordon Center for Integrative Science, The University of Chicago, 929 E 57th Street, Chicago, IL 60637, USA
| | - Eduardo Perozo
- Biochemistry and Molecular Biology, Institute for Biophysical Dynamics, Gordon Center for Integrative Science, The University of Chicago, 929 E 57th Street, Chicago, IL 60637, USA
| | - Benoît Roux
- Biochemistry and Molecular Biology, Institute for Biophysical Dynamics, Gordon Center for Integrative Science, The University of Chicago, 929 E 57th Street, Chicago, IL 60637, USA.
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29
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Piermarini PM, Dunemann SM, Rouhier MF, Calkins TL, Raphemot R, Denton JS, Hine RM, Beyenbach KW. Localization and role of inward rectifier K(+) channels in Malpighian tubules of the yellow fever mosquito Aedes aegypti. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2015; 67:59-73. [PMID: 26079629 DOI: 10.1016/j.ibmb.2015.06.006] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/03/2015] [Revised: 06/03/2015] [Accepted: 06/07/2015] [Indexed: 05/04/2023]
Abstract
Malpighian tubules of adult female yellow fever mosquitoes Aedes aegypti express three inward rectifier K(+) (Kir) channel subunits: AeKir1, AeKir2B and AeKir3. Here we 1) elucidate the cellular and membrane localization of these three channels in the Malpighian tubules, and 2) characterize the effects of small molecule inhibitors of AeKir1 and AeKir2B channels (VU compounds) on the transepithelial secretion of fluid and electrolytes and the electrophysiology of isolated Malpighian tubules. Using subunit-specific antibodies, we found that AeKir1 and AeKir2B localize exclusively to the basolateral membranes of stellate cells and principal cells, respectively; AeKir3 localizes within intracellular compartments of both principal and stellate cells. In isolated tubules bathed in a Ringer solution containing 34 mM K(+), the peritubular application of VU590 (10 μM), a selective inhibitor of AeKir1, inhibited transepithelial fluid secretion 120 min later. The inhibition brings rates of transepithelial KCl and fluid secretion to 54% of the control without a change in transepithelial NaCl secretion. VU590 had no effect on the basolateral membrane voltage (Vbl) of principal cells, but it significantly reduced the cell input conductance (gin) to values 63% of the control within ∼90 min. In contrast, the peritubular application of VU625 (10 μM), an inhibitor of both AeKir1 and AeKir2B, started to inhibit transepithelial fluid secretion as early as 60 min later. At 120 min after treatment, VU625 was more efficacious than VU590, inhibiting transepithelial KCl and fluid secretion to ∼35% of the control without a change in transepithelial NaCl secretion. Moreover, VU625 caused the Vbl and gin of principal cells to respectively drop to values 62% and 56% of the control values within only ∼30 min. Comparing the effects of VU590 with those of VU625 allowed us to estimate that AeKir1 and AeKir2B respectively contribute to 46% and 20% of the transepithelial K(+) secretion when the tubules are bathed in a Ringer solution containing 34 mM K(+). Thus, we uncover an important role of AeKir1 and stellate cells in transepithelial K(+) transport under conditions of peritubular K(+) challenge. The physiological role of AeKir3 in intracellular membranes of both stellate and principal cells remains to be determined.
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Affiliation(s)
- Peter M Piermarini
- Department of Entomology, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster, OH 44691, USA.
| | - Sonja M Dunemann
- Department of Entomology, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster, OH 44691, USA
| | - Matthew F Rouhier
- Department of Entomology, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster, OH 44691, USA
| | - Travis L Calkins
- Department of Entomology, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster, OH 44691, USA
| | - Rene Raphemot
- Department of Anesthesiology, Vanderbilt University School of Medicine, Nashville, TN 37232, USA; Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
| | - Jerod S Denton
- Department of Anesthesiology, Vanderbilt University School of Medicine, Nashville, TN 37232, USA; Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
| | - Rebecca M Hine
- Department of Biomedical Sciences, VRT 8004, Cornell University, Ithaca, NY 14853, USA
| | - Klaus W Beyenbach
- Department of Biomedical Sciences, VRT 8004, Cornell University, Ithaca, NY 14853, USA
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Designer and natural peptide toxin blockers of the KcsA potassium channel identified by phage display. Proc Natl Acad Sci U S A 2015; 112:E7013-21. [PMID: 26627718 DOI: 10.1073/pnas.1514728112] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Peptide neurotoxins are powerful tools for research, diagnosis, and treatment of disease. Limiting broader use, most receptors lack an identified toxin that binds with high affinity and specificity. This paper describes isolation of toxins for one such orphan target, KcsA, a potassium channel that has been fundamental to delineating the structural basis for ion channel function. A phage-display strategy is presented whereby ∼1.5 million novel and natural peptides are fabricated on the scaffold present in ShK, a sea anemone type I (SAK1) toxin stabilized by three disulfide bonds. We describe two toxins selected by sorting on purified KcsA, one novel (Hui1, 34 residues) and one natural (HmK, 35 residues). Hui1 is potent, blocking single KcsA channels in planar lipid bilayers half-maximally (Ki) at 1 nM. Hui1 is also specific, inhibiting KcsA-Shaker channels in Xenopus oocytes with a Ki of 0.5 nM whereas Shaker, Kv1.2, and Kv1.3 channels are blocked over 200-fold less well. HmK is potent but promiscuous, blocking KcsA-Shaker, Shaker, Kv1.2, and Kv1.3 channels with Ki of 1-4 nM. As anticipated, one Hui1 blocks the KcsA pore and two conserved toxin residues, Lys21 and Tyr22, are essential for high-affinity binding. Unexpectedly, potassium ions traversing the channel from the inside confer voltage sensitivity to the Hui1 off-rate via Arg23, indicating that Lys21 is not in the pore. The 3D structure of Hui1 reveals a SAK1 fold, rationalizes KcsA inhibition, and validates the scaffold-based approach for isolation of high-affinity toxins for orphan receptors.
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31
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Lockless SW. Determinants of cation transport selectivity: Equilibrium binding and transport kinetics. J Gen Physiol 2015; 146:3-13. [PMID: 26078056 PMCID: PMC4485025 DOI: 10.1085/jgp.201511371] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2015] [Accepted: 05/11/2015] [Indexed: 01/13/2023] Open
Abstract
The crystal structures of channels and transporters reveal the chemical nature of ion-binding sites and, thereby, constrain mechanistic models for their transport processes. However, these structures, in and of themselves, do not reveal equilibrium selectivity or transport preferences, which can be discerned only from various functional assays. In this Review, I explore the relationship between cation transport protein structures, equilibrium binding measurements, and ion transport selectivity. The primary focus is on K(+)-selective channels and nonselective cation channels because they have been extensively studied both functionally and structurally, but the principles discussed are relevant to other transport proteins and molecules.
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Affiliation(s)
- Steve W Lockless
- Department of Biology, Texas A&M University, College Station, TX 77843
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32
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Abstract
The hydration structure of Ba(2+) ion is important for understanding blocking mechanisms in potassium ion channels. Here, we combine statistical mechanical theory, ab initio molecular dynamics simulations, and electronic structure methods to calculate the hydration free energy and local hydration structure of Ba(2+)(aq). The predicted hydration free energy (-304 ± 1 kcal/mol) agrees with the experimental value (-303 kcal/mol) when a maximally occupied, unimodal inner solvation shell is treated. In the local environment defined by the first shell of hydrating waters, Ba(2+) is directly and stably coordinated by eight (8) waters. Octa-coordination resembles the crystal structure of Ba(2+) and K(+) bound in potassium ion channels, but differs from the local hydration structure of K(+)(aq) determined earlier.
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Affiliation(s)
- Mangesh I Chaudhari
- †Center for Biological and Engineering Sciences, Sandia National Laboratories, Albuquerque, New Mexico 87185, United States
| | - Marielle Soniat
- ‡Department of Chemistry, University of New Orleans, New Orleans, Louisiana 70148, United States
| | - Susan B Rempe
- †Center for Biological and Engineering Sciences, Sandia National Laboratories, Albuquerque, New Mexico 87185, United States
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Abstract
The Fluc family is a set of small membrane proteins forming F(-)-specific electrodiffusive ion channels that rescue microorganisms from F(-) toxicity during exposure to weakly acidic environments. The functional channel is built as a dual-topology homodimer with twofold symmetry parallel to the membrane plane. Fluc channels are blocked by nanomolar-affinity fibronectin-domain monobodies originally selected from phage-display libraries. The unusual symmetrical antiparallel dimeric architecture of Flucs demands that the two chemically equivalent monobody-binding epitopes reside on opposite ends of the channel, a double-sided blocking situation that has never before presented itself in ion channel biophysics. However, it is not known if both sites can be simultaneously occupied, and if so, whether monobodies bind independently or cooperatively to their transmembrane epitopes. Here, we use direct monobody-binding assays and single-channel recordings of a Fluc channel homolog to reveal a novel trimolecular blocking behavior that reveals a doubly occupied blocked state. Kinetic analysis of single-channel recordings made with monobody on both sides of the membrane shows substantial negative cooperativity between the two blocking sites.
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34
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Stockbridge RB, Tsai MF. Lipid Reconstitution and Recording of Recombinant Ion Channels. Methods Enzymol 2015; 556:385-404. [DOI: 10.1016/bs.mie.2014.12.028] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
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Horn R, Roux B, Åqvist J. Permeation redux: thermodynamics and kinetics of ion movement through potassium channels. Biophys J 2014; 106:1859-63. [PMID: 24806917 DOI: 10.1016/j.bpj.2014.03.039] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2014] [Revised: 03/14/2014] [Accepted: 03/27/2014] [Indexed: 10/25/2022] Open
Abstract
The fundamental biophysics underlying the selective movement of ions through ion channels was launched by George Eisenman in the 1960s, using glass electrodes. This minireview examines the insights from these early studies and the explosive progress made since then.
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Affiliation(s)
- Richard Horn
- Department of Molecular Physiology and Biophysics, Jefferson Medical College, Philadelphia, Pennsylvania.
| | - Benoît Roux
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, Illinois
| | - Johan Åqvist
- Department of Cell & Molecular Biology, Uppsala University, Biomedical Center, Uppsala, Sweden
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36
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Dondapati SK, Kreir M, Quast RB, Wüstenhagen DA, Brüggemann A, Fertig N, Kubick S. Membrane assembly of the functional KcsA potassium channel in a vesicle-based eukaryotic cell-free translation system. Biosens Bioelectron 2014; 59:174-83. [DOI: 10.1016/j.bios.2014.03.004] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2013] [Revised: 02/27/2014] [Accepted: 03/03/2014] [Indexed: 10/25/2022]
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37
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Guo R, Zeng W, Cui H, Chen L, Ye S. Ionic interactions of Ba2+ blockades in the MthK K+ channel. ACTA ACUST UNITED AC 2014; 144:193-200. [PMID: 25024268 PMCID: PMC4113901 DOI: 10.1085/jgp.201411192] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The movement and interaction of multiple ions passing through in single file underlie various fundamental K(+) channel properties, from the effective conduction of K(+) ions to channel blockade by Ba(2+) ions. In this study, we used single-channel electrophysiology and x-ray crystallography to probe the interactions of Ba(2+) with permeant ions within the ion conduction pathway of the MthK K(+) channel. We found that, as typical of K(+) channels, the MthK channel was blocked by Ba(2+) at the internal side, and the Ba(2+)-blocking effect was enhanced by external K(+). We also obtained crystal structures of the MthK K(+) channel pore in both Ba(2+)-Na(+) and Ba(2+)-K(+) environments. In the Ba(2+)-Na(+) environment, we found that a single Ba(2+) ion remained bound in the selectivity filter, preferably at site 2, whereas in the Ba(2+)-K(+) environment, Ba(2+) ions were predominantly distributed between sites 3 and 4. These ionic configurations are remarkably consistent with the functional studies and identify a molecular basis for Ba(2+) blockade of K(+) channels.
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Affiliation(s)
- Rui Guo
- Life Sciences Institute and Innovation Center for Cell Biology, Zhejiang University, Hangzhou 310058, China
| | - Weizhong Zeng
- Howard Hughes Medical Institute, Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX 75390
| | - Hengjun Cui
- Life Sciences Institute and Innovation Center for Cell Biology, Zhejiang University, Hangzhou 310058, China
| | - Liping Chen
- Howard Hughes Medical Institute, Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX 75390
| | - Sheng Ye
- Life Sciences Institute and Innovation Center for Cell Biology, Zhejiang University, Hangzhou 310058, China
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38
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Lam YL, Zeng W, Sauer DB, Jiang Y. The conserved potassium channel filter can have distinct ion binding profiles: structural analysis of rubidium, cesium, and barium binding in NaK2K. ACTA ACUST UNITED AC 2014; 144:181-92. [PMID: 25024267 PMCID: PMC4113894 DOI: 10.1085/jgp.201411191] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The ion-binding profile in NaK2K is distinct from that in KcsA, even though the selectivity filter has been conserved. Potassium channels are highly selective for K+ over the smaller Na+. Intriguingly, they are permeable to larger monovalent cations such as Rb+ and Cs+ but are specifically blocked by the similarly sized Ba2+. In this study, we used structural analysis to determine the binding profiles for these permeant and blocking ions in the selectivity filter of the potassium-selective NaK channel mutant NaK2K and also performed permeation experiments using single-channel recordings. Our data revealed that some ion binding properties of NaK2K are distinct from those of the canonical K+ channels KcsA and MthK. Rb+ bound at sites 1, 3, and 4 in NaK2K, as it does in KcsA. Cs+, however, bound predominantly at sites 1 and 3 in NaK2K, whereas it binds at sites 1, 3, and 4 in KcsA. Moreover, Ba2+ binding in NaK2K was distinct from that which has been observed in KcsA and MthK, even though all of these channels show similar Ba2+ block. In the presence of K+, Ba2+ bound to the NaK2K channel at site 3 in conjunction with a K+ at site 1; this led to a prolonged block of the channel (the external K+-dependent Ba2+ lock-in state). In the absence of K+, however, Ba2+ acts as a permeating blocker. We found that, under these conditions, Ba2+ bound at sites 1 or 0 as well as site 3, allowing it to enter the filter from the intracellular side and exit from the extracellular side. The difference in the Ba2+ binding profile in the presence and absence of K+ thus provides a structural explanation for the short and prolonged Ba2+ block observed in NaK2K.
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Affiliation(s)
- Yee Ling Lam
- Department of Physiology and Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, TX 75390
| | - Weizhong Zeng
- Department of Physiology and Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, TX 75390Department of Physiology and Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, TX 75390
| | - David Bryant Sauer
- Department of Physiology and Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, TX 75390
| | - Youxing Jiang
- Department of Physiology and Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, TX 75390Department of Physiology and Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, TX 75390
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39
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Equilibrium selectivity alone does not create K+-selective ion conduction in K+ channels. Nat Commun 2014; 4:2746. [PMID: 24217508 DOI: 10.1038/ncomms3746] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2013] [Accepted: 10/10/2013] [Indexed: 02/03/2023] Open
Abstract
Potassium (K(+)) channels are selective for K(+) over Na(+) ions during their transport across membranes. We and others have previously shown that tetrameric K(+) channels are primarily occupied by K(+) ions in their selectivity filters under physiological conditions, demonstrating the channel's intrinsic equilibrium preference for K(+) ions. Based on this observation, we hypothesize that the preference for K(+) ions over Na(+) ions in the filter determines its selectivity during ion conduction. Here, we ask whether non-selective cation channels, which share an overall structure and similar individual ion-binding sites with K(+) channels, have an ion preference at equilibrium. The variants of the non-selective Bacillus cereus NaK cation channel we examine are all selective for K(+) over Na(+) ions at equilibrium. Thus, the detailed architecture of the K(+) channel selectivity filter, and not only its equilibrium ion preference, is fundamental to the generation of selectivity during ion conduction.
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40
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Yang F, Ma L, Cao X, Wang K, Zheng J. Divalent cations activate TRPV1 through promoting conformational change of the extracellular region. ACTA ACUST UNITED AC 2013; 143:91-103. [PMID: 24344245 PMCID: PMC3874565 DOI: 10.1085/jgp.201311024] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Divalent cations Mg2+ and Ba2+ selectively and directly potentiate transient receptor potential vanilloid type 1 heat activation by lowering the activation threshold into the room temperature range. We found that Mg2+ potentiates channel activation only from the extracellular side; on the intracellular side, Mg2+ inhibits channel current. By dividing the extracellularly accessible region of the channel protein into small segments and perturbing the structure of each segment with sequence replacement mutations, we observed that the S1–S2 linker, the S3–S4 linker, and the pore turret are all required for Mg2+ potentiation. Sequence replacements at these regions substantially reduced or eliminated Mg2+-induced activation at room temperature while sparing capsaicin activation. Heat activation was affected by many, but not all, of these structural alternations. These observations indicate that extracellular linkers and the turret may interact with each other. Site-directed fluorescence resonance energy transfer measurements further revealed that, like heat, Mg2+ also induces structural changes in the pore turret. Interestingly, turret movement induced by Mg2+ precedes channel activation, suggesting that Mg2+-induced conformational change in the extracellular region most likely serves as the cause of channel activation instead of a coincidental or accommodating structural adjustment.
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Affiliation(s)
- Fan Yang
- Department of Physiology and Membrane Biology, University of California School of Medicine, Davis, Davis, CA 95616
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41
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Rowley CN, Roux B. A computational study of barium blockades in the KcsA potassium channel based on multi-ion potential of mean force calculations and free energy perturbation. J Gen Physiol 2013; 142:451-63. [PMID: 24043859 PMCID: PMC3787775 DOI: 10.1085/jgp.201311049] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2013] [Accepted: 08/16/2013] [Indexed: 11/20/2022] Open
Abstract
Electrophysiological studies have established that the permeation of Ba(2+) ions through the KcsA K(+)-channel is impeded by the presence of K(+) ions in the external solution, while no effect is observed for external Na(+) ions. This Ba(2+) "lock-in" effect suggests that at least one of the external binding sites of the KcsA channel is thermodynamically selective for K(+). We used molecular dynamics simulations to interpret these lock-in experiments in the context of the crystallographic structure of KcsA. Assuming that the Ba(2+) is bound in site S(2) in the dominant blocked state, we examine the conditions that could impede its translocation and cause the observed "lock-in" effect. Although the binding of a K(+) ion to site S(1) when site S(2) is occupied by Ba(2+) is prohibitively high in energy (>10 kcal/mol), binding to site S0 appears to be more plausible (ΔG > 4 kcal/mol). The 2D potential of mean force (PMF) for the simultaneous translocation of Ba(2+) from site S(2) to site S(1) and of a K(+) ion on the extracellular side shows a barrier that is consistent with the concept of external lock-in. The barrier opposing the movement of Ba(2+) is very high when a cation is in site S(0), and considerably smaller when the site is unoccupied. Furthermore, free energy perturbation calculations show that site S(0) is selective for K(+) by 1.8 kcal/mol when S(2) is occupied by Ba(2+). However, the same site S(0) is nonselective when site S(2) is occupied by K(+), which shows that the presence of Ba(2+) affects the selectivity of the pore. A theoretical framework within classical rate theory is presented to incorporate the concentration dependence of the external ions on the lock-in effect.
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Affiliation(s)
- Christopher N. Rowley
- Department of Chemistry, Memorial University of Newfoundland, St. John’s, NL A1b 3X9, Canada
| | - Benoît Roux
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL 60637
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42
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Filter gate closure inhibits ion but not water transport through potassium channels. Proc Natl Acad Sci U S A 2013; 110:10842-7. [PMID: 23754382 DOI: 10.1073/pnas.1304714110] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The selectivity filter of K(+) channels is conserved throughout all kingdoms of life. Carbonyl groups of highly conserved amino acids point toward the lumen to act as surrogates for the water molecules of K(+) hydration. Ion conductivity is abrogated if some of these carbonyl groups flip out of the lumen, which happens (i) in the process of C-type inactivation or (ii) during filter collapse in the absence of K(+). Here, we show that K(+) channels remain permeable to water, even after entering such an electrically silent conformation. We reconstituted fluorescently labeled and constitutively open mutants of the bacterial K(+) channel KcsA into lipid vesicles that were either C-type inactivating or noninactivating. Fluorescence correlation spectroscopy allowed us to count both the number of proteoliposomes and the number of protein-containing micelles after solubilization, providing the number of reconstituted channels per proteoliposome. Quantification of the per-channel increment in proteoliposome water permeability with the aid of stopped-flow experiments yielded a unitary water permeability pf of (6.9 ± 0.6) × 10(-13) cm(3)⋅s(-1) for both mutants. "Collapse" of the selectivity filter upon K(+) removal did not alter pf and was fully reversible, as demonstrated by current measurements through planar bilayers in a K(+)-containing medium to which K(+)-free proteoliposomes were fused. Water flow through KcsA is halved by 200 mM K(+) in the aqueous solution, which indicates an effective K(+) dissociation constant in that range for a singly occupied channel. This questions the widely accepted hypothesis that multiple K(+) ions in the selectivity filter act to mutually destabilize binding.
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43
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Moscoso C, Vergara-Jaque A, Márquez-Miranda V, Sepúlveda RV, Valencia I, Díaz-Franulic I, González-Nilo F, Naranjo D. K⁺ conduction and Mg²⁺ blockade in a shaker Kv-channel single point mutant with an unusually high conductance. Biophys J 2013; 103:1198-207. [PMID: 22995492 DOI: 10.1016/j.bpj.2012.08.015] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2012] [Revised: 07/30/2012] [Accepted: 08/01/2012] [Indexed: 12/27/2022] Open
Abstract
Potassium channels exhibit a large diversity of single-channel conductances. Shaker is a low-conductance K-channel in which Pro475→Asp, a single-point mutation near the internal pore entrance, promotes 6- to 8-fold higher unitary current. To assess the mechanism for this higher conductance, we measured Shaker-P475D single-channel current in a wide range of symmetrical K(+) concentrations and voltages. Below 300 mM K(+), the current-to-voltage relations (i-V) showed inward rectification that disappeared at 1000 mM K(+). Single-channel conductance reached a maximum of ∼190 pS at saturating [K(+)], a value 4- to 5-fold larger than that estimated for the native channel. Intracellular Mg(2+) blocked this variant with ∼100-fold higher affinity. Near zero voltage, blockade was competitively antagonized by K(+); however, at voltages >100 mV, it was enhanced by K(+). This result is consistent with a lock-in effect in a single-file diffusion regime of Mg(2+) and K(+) along the pore. Molecular-dynamics simulations revealed higher K(+) density in the pore, especially near the Asp-475 side chains, as in the high-conductance MthK bacterial channel. The molecular dynamics also showed that K(+) ions bound distally can coexist with other K(+) or Mg(2+) in the cavity, supporting a lock-in mechanism. The maximal K(+) transport rate and higher occupancy could be due to a decrease in the electrostatic energy profile for K(+) throughout the pore, reducing the energy wells and barriers differentially by ∼0.7 and ∼2 kT, respectively.
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Affiliation(s)
- Cristian Moscoso
- Centro Interdisciplinario de Neurociencias de Valparaíso, Universidad de Valparaíso, Valparaíso, Chile
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44
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Zaydman MA, Silva JR, Cui J. Ion channel associated diseases: overview of molecular mechanisms. Chem Rev 2012; 112:6319-33. [PMID: 23151230 DOI: 10.1021/cr300360k] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- Mark A Zaydman
- Department of Biomedical Engineering, Washington University, Saint Louis, Missouri 63130, United States
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Liu S, Bian X, Lockless SW. Preferential binding of K+ ions in the selectivity filter at equilibrium explains high selectivity of K+ channels. ACTA ACUST UNITED AC 2012; 140:671-9. [PMID: 23148260 PMCID: PMC3514730 DOI: 10.1085/jgp.201210855] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
K+ channels exhibit strong selectivity for K+ ions over Na+ ions based on electrophysiology experiments that measure ions competing for passage through the channel. During this conduction process, multiple ions interact within the region of the channel called the selectivity filter. Ion selectivity may arise from an equilibrium preference for K+ ions within the selectivity filter or from a kinetic mechanism whereby Na+ ions are precluded from entering the selectivity filter. Here, we measure the equilibrium affinity and selectivity of K+ and Na+ ions binding to two different K+ channels, KcsA and MthK, using isothermal titration calorimetry. Both channels exhibit a large preference for K+ over Na+ ions at equilibrium, in line with electrophysiology recordings of reversal potentials and Ba2+ block experiments used to measure the selectivity of the external-most ion-binding sites. These results suggest that the high selectivity observed during ion conduction can originate from a strong equilibrium preference for K+ ions in the selectivity filter, and that K+ selectivity is an intrinsic property of the filter. We hypothesize that the equilibrium preference for K+ ions originates in part through the optimal spacing between sites to accommodate multiple K+ ions within the selectivity filter.
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Affiliation(s)
- Shian Liu
- Department of Biology, Texas A&M University, College Station, TX 77843, USA
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Protonation state of E71 in KcsA and its role for channel collapse and inactivation. Proc Natl Acad Sci U S A 2012; 109:15265-70. [PMID: 22942391 DOI: 10.1073/pnas.1211900109] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The prototypical prokaryotic potassium channel KcsA alters its pore depending on the ambient potassium; at high potassium, it exists in a conductive form, and at low potassium, it collapses into a nonconductive structure with reduced ion occupancy. We present solid-state NMR studies of KcsA in which we test the hypothesis that an important channel-inactivation process, known as C-type inactivation, proceeds via a state similar to this collapsed state. We test this using an inactivation-resistant mutant E71A, and show that E71A is unable to collapse its pore at both low potassium and low pH, suggesting that the collapsed state is structurally similar to the inactivated state. We also show that E71A has a disordered selectivity filter. Using site-specific K(+) titrations, we detect a local change at E71 that is coupled to channel collapse at low K(+). To gain more insight into this change, we site specifically measure the chemical shift tensors of the side-chain carboxyls of E71 and its hydrogen bond partner D80, and use the tensors to assign protonation states to E71 and D80 at high K(+) and neutral pH. Our measurements show that E71 is protonated at pH 7.5 and must have an unusually perturbed pK(a) (> 7.5) suggesting that the change at E71 is a structural rearrangement rather than a protonation event. The results offer new mechanistic insights into why the widely used mutant KcsA-E71A does not inactivate and establish the ambient K(+) level as a means to populate the inactivated state of KcsA in a controlled way.
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