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Das A, Bysack A, Raghuraman H. Cholesterol modulates the structural dynamics of the paddle motif loop of KvAP voltage sensor. Curr Res Struct Biol 2024; 7:100137. [PMID: 38500801 PMCID: PMC10945132 DOI: 10.1016/j.crstbi.2024.100137] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2023] [Revised: 02/29/2024] [Accepted: 03/03/2024] [Indexed: 03/20/2024] Open
Abstract
KvAP is a prokaryotic Kv channel, which has been widely used as a model system to understand voltage- and lipid-dependent gating mechanisms. In phospholipid membranes, the KvAP-VSD adopts the activated/'Up' conformation, whereas the presence of non-phospholipids in membranes favours the structural transition to resting/'Down' state. The S3b-S4 paddle motif loop of KvAP-VSD is functionally important as this participates in protein-protein interactions and is the target for animal toxins. In this study, we have monitored the modulatory role of cholesterol - the physiologically-relevant non-phospholipid - on the organization and dynamics of the S3b-S4 loop of the isolated KvAP-VSD in membranes by site-directed fluorescence approaches using the environmental sensitivity of 7-nitrobenz-2-oxa-1,3-diazol-4-yl-ethylenediamine (NBD) fluorescence. Our results show that cholesterol alters the dynamic nature (rotational and hydration dynamics) of S3b-S4 loop in a segmental fashion, i.e., the residues 110 to 114 and 115 to 117 behave differently in the presence of cholesterol, which is accompanied by considerable change in conformational heterogeneity. Further, quantitative depth measurements using the parallax quenching method reveal that the sensor loop is located at the shallow interfacial region of cholesterol-containing membranes, suggesting that the sensor loop organization is not directly correlated with S4 helix movement. Our results clearly show that cholesterol-induced changes in bilayer properties may not be the predominant factor for the sensor loop's altered structural dynamics, but can be attributed to the conformational change of the KvAP-VSD in cholesterol-containing membranes. Overall, these results are relevant for gating mechanisms, particularly the lipid-dependent gating, of Kv channels in membranes.
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Affiliation(s)
- Anindita Das
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata, India
- Homi Bhabha National Institute, Training School Complex, Anushaktinagar, Mumbai, 400 094, India
| | - Arpan Bysack
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata, India
- Homi Bhabha National Institute, Training School Complex, Anushaktinagar, Mumbai, 400 094, India
| | - H. Raghuraman
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata, India
- Homi Bhabha National Institute, Training School Complex, Anushaktinagar, Mumbai, 400 094, India
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2
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Mahato DR, Andersson M. Dynamic lipid interactions in the plasma membrane Na +,K +-ATPase. BIOCHIMICA ET BIOPHYSICA ACTA. MOLECULAR CELL RESEARCH 2023; 1870:119545. [PMID: 37481079 DOI: 10.1016/j.bbamcr.2023.119545] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/16/2023] [Revised: 06/12/2023] [Accepted: 07/13/2023] [Indexed: 07/24/2023]
Abstract
The function of ion-transporting Na+,K+-ATPases depends on the surrounding lipid environment in biological membranes. Two established lipid-interaction sites A and B within the transmembrane domain have been observed to induce protein activation and stabilization, respectively. In addition, lipid-mediated inhibition has been assigned to a site C, but with the exact location not experimentally confirmed. Also, possible effects on lipid interactions by disease mutants dwelling in the membrane-protein interface remain relatively uncharacterized. We simulated human Na+,K+-ATPase α1β1FXYD homology models in E1 and E2 states in an asymmetric, multicomponent plasma membrane to determine both wild-type and disease mutant lipid-protein interactions. The simulated wild-type lipid interactions at the established sites A and B were in agreement with experimental results thereby confirming the membrane-protein model system. The less well-characterized, proposed inhibitory site C was dominated by lipids lacking inhibitory properties. Instead, two sites hosting inhibitory lipids were identified at the extracellular side and also a cytoplasmic CHL-binding site that provide putative alternative locations of Na+,K+-ATPase inhibition. Three disease mutations, Leu302Arg, Glu840Arg and Met859Arg resided in the lipid-protein interface and caused drastic changes in the lipid interactions. The simulation results show that lipid interactions to the human Na+,K+-ATPase α1β1FXYD protein in the plasma membrane are highly state-dependent and can be disturbed by disease mutations located in the lipid interface, which can open up for new venues to understand genetic disorders.
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Affiliation(s)
- Dhani Ram Mahato
- Department of Chemistry, Umeå University, Umeå, Sweden; Institut de Química Computacional i Catàlisi, Universitat de Girona, Girona, 17003, Spain
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3
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Mihailescu M, Worcester DL, Carroll CL, Chamberlin AR, White SH. DOTAP: Structure, hydration, and the counterion effect. Biophys J 2023; 122:1086-1093. [PMID: 36703558 PMCID: PMC10111261 DOI: 10.1016/j.bpj.2023.01.031] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2022] [Revised: 01/04/2023] [Accepted: 01/23/2023] [Indexed: 01/27/2023] Open
Abstract
The cationic lipid 1,2-dioleoyl-3-trimethylammonium propane (DOTAP) is one of the original synthetic cationic lipids used for the liposomal transfection of oligonucleotides in gene therapy. The key structural element of DOTAP is its quaternary ammonium headgroup that is responsible for interactions with both nucleic acids and target cell membranes. Because these interactions are fundamental to the design of a major class of transfection lipids, it is important to understand the structure of DOTAP and how it interacts with halide counterions. Here, we use x-ray and neutron diffraction techniques to examine the structure of DOTAP and how chloride (Cl-) and iodide (I-) counterions alter the hydration properties of the DOTAP headgroup. A problem of particular interest is the poor solubility of DOTAP/I- in water solutions. Our results show that the poor solubility results from very tight binding of the I- counterion to the headgroup and the consequent expulsion of water. The structural principles we report here are important for assessing the suitability of DOTAP and its quaternary ammonium derivatives for transfection.
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Affiliation(s)
- Mihaela Mihailescu
- Institute for Bioscience and Biotechnology Research, Rockville, Maryland.
| | - David L Worcester
- Biology Division, University of Missouri, Columbia, Missouri; NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland; Department of Physiology and Biophysics, University of California at Irvine, Irvine, California
| | | | - A Richard Chamberlin
- Department of Chemistry, University of California at Irvine, Irvine, California; Department of Pharmaceutical Sciences, University of California at Irvine, Irvine, California
| | - Stephen H White
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland; Department of Physiology and Biophysics, University of California at Irvine, Irvine, California
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4
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Knaus LS, Basilico B, Malzl D, Gerykova Bujalkova M, Smogavec M, Schwarz LA, Gorkiewicz S, Amberg N, Pauler FM, Knittl-Frank C, Tassinari M, Maulide N, Rülicke T, Menche J, Hippenmeyer S, Novarino G. Large neutral amino acid levels tune perinatal neuronal excitability and survival. Cell 2023; 186:1950-1967.e25. [PMID: 36996814 DOI: 10.1016/j.cell.2023.02.037] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2022] [Revised: 02/03/2023] [Accepted: 02/23/2023] [Indexed: 03/31/2023]
Abstract
Little is known about the critical metabolic changes that neural cells have to undergo during development and how temporary shifts in this program can influence brain circuitries and behavior. Inspired by the discovery that mutations in SLC7A5, a transporter of metabolically essential large neutral amino acids (LNAAs), lead to autism, we employed metabolomic profiling to study the metabolic states of the cerebral cortex across different developmental stages. We found that the forebrain undergoes significant metabolic remodeling throughout development, with certain groups of metabolites showing stage-specific changes, but what are the consequences of perturbing this metabolic program? By manipulating Slc7a5 expression in neural cells, we found that the metabolism of LNAAs and lipids are interconnected in the cortex. Deletion of Slc7a5 in neurons affects the postnatal metabolic state, leading to a shift in lipid metabolism. Additionally, it causes stage- and cell-type-specific alterations in neuronal activity patterns, resulting in a long-term circuit dysfunction.
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Affiliation(s)
- Lisa S Knaus
- Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria
| | - Bernadette Basilico
- Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria
| | - Daniel Malzl
- Max Perutz Labs, Dr.-Bohr-Gasse 9, 1030 Vienna, Austria
| | - Maria Gerykova Bujalkova
- Institute of Medical Genetics, Medical University of Vienna, Währinger Straße 10, 1090 Vienna, Austria
| | - Mateja Smogavec
- Institute of Medical Genetics, Medical University of Vienna, Währinger Straße 10, 1090 Vienna, Austria
| | - Lena A Schwarz
- Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria
| | - Sarah Gorkiewicz
- Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria
| | - Nicole Amberg
- Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria
| | - Florian M Pauler
- Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria
| | - Christian Knittl-Frank
- Institute of Organic Chemistry, University of Vienna, Währinger Strasse 38, 1090 Vienna, Austria
| | - Marianna Tassinari
- Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria
| | - Nuno Maulide
- Institute of Organic Chemistry, University of Vienna, Währinger Strasse 38, 1090 Vienna, Austria; University of Vienna, Research Platform NeGeMac, Währinger Strasse 38, 1090 Vienna, Austria
| | - Thomas Rülicke
- University of Veterinary Medicine Vienna, Veterinärplatz 1, 1210 Vienna, Austria
| | - Jörg Menche
- Max Perutz Labs, Dr.-Bohr-Gasse 9, 1030 Vienna, Austria
| | - Simon Hippenmeyer
- Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria
| | - Gaia Novarino
- Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria.
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Malik C, Ghosh S. A mutation in the S6 segment of the KvAP channel changes the secondary structure and alters ion channel activity in a lipid bilayer membrane. Amino Acids 2022; 54:1461-1475. [PMID: 35896819 DOI: 10.1007/s00726-022-03188-8] [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: 05/04/2021] [Accepted: 07/04/2022] [Indexed: 11/01/2022]
Abstract
The peptide segment S6 is known to form the inner lining of the voltage-gated K+ channel KvAP (potassium channel of archaea-bacterium, Aeropyrum pernix). In our previous work, it has been demonstrated that S6 itself can form an ion channel on a bilayer lipid membrane (BLM). In the present work, the role of a specific amino acid sequence 'LIG' in determining the secondary structure of S6 has been investigated. For this purpose, 22-residue synthetic peptides named S6-Wild (S6W) and S6-Mutant (S6M) were used. Sequences of these peptides are similar except that the two amino acids isoleucine and glycine of the wild peptide interchanged in the mutant peptide. Channel forming capabilities of both the peptides were checked electro-physiologically on BLM composed of DPhPC and cholesterol. Bilayer electrophysiological experiments showed that the conductance of S6M is higher than that of S6W. Significant differences in the current versus voltage (I-V) plot, open probability, and gating characteristics were observed. Interestingly, two sub-types of channels, S6M Type 1 and Type 2, were identified in S6M differing in conductances and open probability patterns. Circular dichroism (CD) spectroscopy indicated that the secondary structures of the two peptides are different in phosphatidyl choline/asolectin liposomes and 1% SDS detergent. Reduced helicity of S6M was also noticed in membrane mimetic liposomes and 1% SDS detergent micelles. These results are interpreted in view of the difference in hydrophobicity of the two amino acids, isoleucine and glycine. It is concluded that the 'LIG' stretch regulates the structure and pore-forming ability of the S6 peptide.
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Affiliation(s)
- Chetan Malik
- Department of Biophysics, University of Delhi South Campus, Benito Juarez Road, New Delhi, 110021, India
| | - Subhendu Ghosh
- Department of Biophysics, University of Delhi South Campus, Benito Juarez Road, New Delhi, 110021, India.
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6
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Sridhar A, Lummis SCR, Pasini D, Mehregan A, Brams M, Kambara K, Bertrand D, Lindahl E, Howard RJ, Ulens C. Regulation of a pentameric ligand-gated ion channel by a semiconserved cationic lipid-binding site. J Biol Chem 2021; 297:100899. [PMID: 34157288 PMCID: PMC8327344 DOI: 10.1016/j.jbc.2021.100899] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2021] [Revised: 06/10/2021] [Accepted: 06/18/2021] [Indexed: 02/08/2023] Open
Abstract
Pentameric ligand-gated ion channels (pLGICs) are crucial mediators of electrochemical signal transduction in various organisms from bacteria to humans. Lipids play an important role in regulating pLGIC function, yet the structural bases for specific pLGIC-lipid interactions remain poorly understood. The bacterial channel ELIC recapitulates several properties of eukaryotic pLGICs, including activation by the neurotransmitter GABA and binding and modulation by lipids, offering a simplified model system for structure-function relationship studies. In this study, functional effects of noncanonical amino acid substitution of a potential lipid-interacting residue (W206) at the top of the M1-helix, combined with detergent interactions observed in recent X-ray structures, are consistent with this region being the location of a lipid-binding site on the outward face of the ELIC transmembrane domain. Coarse-grained and atomistic molecular dynamics simulations revealed preferential binding of lipids containing a positive charge, particularly involving interactions with residue W206, consistent with cation-π binding. Polar contacts from other regions of the protein, particularly M3 residue Q264, further support lipid binding via headgroup ester linkages. Aromatic residues were identified at analogous sites in a handful of eukaryotic family members, including the human GABAA receptor ε subunit, suggesting conservation of relevant interactions in other evolutionary branches. Further mutagenesis experiments indicated that mutations at this site in ε-containing GABAA receptors can change the apparent affinity of the agonist response to GABA, suggesting a potential role of this site in channel gating. In conclusion, this work details type-specific lipid interactions, which adds to our growing understanding of how lipids modulate pLGICs.
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Affiliation(s)
- Akshay Sridhar
- Department of Applied Physics, Science for Life Laboratory, KTH Royal Institute of Technology, Solna, Sweden
| | - Sarah C R Lummis
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
| | - Diletta Pasini
- Laboratory of Structural Neurobiology, Department of Cellular and Molecular Medicine, Faculty of Medicine, KU Leuven, Leuven, Belgium
| | - Aujan Mehregan
- Laboratory of Structural Neurobiology, Department of Cellular and Molecular Medicine, Faculty of Medicine, KU Leuven, Leuven, Belgium
| | - Marijke Brams
- Laboratory of Structural Neurobiology, Department of Cellular and Molecular Medicine, Faculty of Medicine, KU Leuven, Leuven, Belgium
| | | | | | - Erik Lindahl
- Department of Applied Physics, Science for Life Laboratory, KTH Royal Institute of Technology, Solna, Sweden; Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, Solna, Sweden
| | - Rebecca J Howard
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, Solna, Sweden.
| | - Chris Ulens
- Laboratory of Structural Neurobiology, Department of Cellular and Molecular Medicine, Faculty of Medicine, KU Leuven, Leuven, Belgium.
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Saikia C, Dym O, Altman-Gueta H, Gordon D, Reuveny E, Karbat I. A Molecular Lid Mechanism of K + Channel Blocker Action Revealed by a Cone Peptide. J Mol Biol 2021; 433:166957. [PMID: 33771569 DOI: 10.1016/j.jmb.2021.166957] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2020] [Revised: 03/08/2021] [Accepted: 03/16/2021] [Indexed: 12/15/2022]
Abstract
Many venomous organisms carry in their arsenal short polypeptides that block K+ channels in a highly selective manner. These toxins may compete with the permeating ions directly via a "plug" mechanism or indirectly via a "pore-collapse" mechanism. An alternative "lid" mechanism was proposed but remained poorly defined. Here we study the Drosophila Shaker channel block by Conkunitzin-S1 and Conkunitzin-C3, two highly similar toxins derived from cone venom. Despite their similarity, the two peptides exhibited differences in their binding poses and biophysical assays, implying discrete action modes. We show that while Conkunitzin-S1 binds tightly to the channel turret and acts via a "pore-collapse" mechanism, Conkunitzin-C3 does not contact this region. Instead, Conk-C3 uses a non-conserved Arg to divert the permeant ions and trap them in off-axis cryptic sites above the SF, a mechanism we term a "molecular-lid". Our study provides an atomic description of the "lid" K+ blocking mode and offers valuable insights for the design of therapeutics based on venom peptides.
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Affiliation(s)
- Chandamita Saikia
- Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Orly Dym
- Structural Proteomic Unit, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Hagit Altman-Gueta
- Department of Plant Molecular Biology and Ecology, Tel-Aviv University, Tel-Aviv 69978, Israel
| | - Dalia Gordon
- Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Eitan Reuveny
- Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot 76100, Israel.
| | - Izhar Karbat
- Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot 76100, Israel.
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8
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Das A, Raghuraman H. Conformational heterogeneity of the voltage sensor loop of KvAP in micelles and membranes: A fluorescence approach. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2021; 1863:183568. [PMID: 33529577 DOI: 10.1016/j.bbamem.2021.183568] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Received: 09/01/2020] [Revised: 01/06/2021] [Accepted: 01/27/2021] [Indexed: 12/14/2022]
Abstract
KvAP is a tetrameric voltage-gated potassium channel that is composed of a pore domain and a voltage-sensing domain (VSD). The VSD is crucial for sensing transmembrane potential and gating. At 0 mV, the VSD adopts an activated conformation in both n-octylglucoside (OG) micelles and phospholipid membranes. Importantly, gating-modifier toxins that bind at S3b-S4 loop of KvAP-VSD exhibit pronounced differences in binding affinity in these membrane-mimetic systems. However, the conformational heterogeneity of this functionally-important sensor loop in membrane mimetics is poorly understood, and is the focus of this work. In this paper, we establish, using intrinsic fluorescence of the uniquely positioned W70 in KvAP-VSD and environment-sensitive NBD (7-nitrobenz-2-oxa-1,3-diazol-4-yl-ethylenediamine) fluorescence of the labelled S3b-S4 loop, that the surface charge of the membrane does not significantly affect the topology and structural dynamics of the sensor loop in membranes. Importantly, the dynamic variability of the sensor loop is preserved in both zwitterionic (POPC) and anionic (POPC/POPG) membranes. Further, the lifetime distribution analysis for the NBD-labelled residues by maximum entropy method (MEM) demonstrates that, in contrast to micelles, the membrane environment not only reduces the relative discrete population of sensor loop conformations, but also broadens the lifetime distribution peaks. Overall, our results strongly suggest that the conformational heterogeneity of the sensor loop is significantly altered in membranes and this correlates well with its environmental heterogeneity. This constitutes the first report demonstrating that MEM-lifetime distribution could be a powerful tool to distinguish changes in conformational heterogeneity in potassium channels with similar architecture and topology.
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Affiliation(s)
- Anindita Das
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, Homi Bhabha National Institute, 1/AF Bidhannagar, Kolkata, India
| | - H Raghuraman
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, Homi Bhabha National Institute, 1/AF Bidhannagar, Kolkata, India.
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9
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Abstract
Potassium channels are present in every living cell and essential to setting up a stable, non-zero transmembrane electrostatic potential which manifests the off-equilibrium livelihood of the cell. They are involved in other cellular activities and regulation, such as the controlled release of hormones, the activation of T-cells for immune response, the firing of action potential in muscle cells and neurons, etc. Pharmacological reagents targeting potassium channels are important for treating various human diseases linked to dysfunction of the channels. High-resolution structures of these channels are very useful tools for delineating the detailed chemical basis underlying channel functions and for structure-based design and optimization of their pharmacological and pharmaceutical agents. Structural studies of potassium channels have revolutionized biophysical understandings of key concepts in the field - ion selectivity, conduction, channel gating, and modulation, making them multi-modality targets of pharmacological regulation. In this chapter, I will select a few high-resolution structures to illustrate key structural insights, proposed allostery behind channel functions, disagreements still open to debate, and channel-lipid interactions and co-evolution. The known structural consensus allows the inference of conserved molecular mechanisms shared among subfamilies of K+ channels and makes it possible to develop channel-specific pharmaceutical agents.
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Affiliation(s)
- Qiu-Xing Jiang
- Laboratory of Molecular Physiology and Biophysics and the Cryo-EM Center, Hauptmann-Woodward Medical Research Institute, Buffalo, NY, USA.
- Department of Medicinal Chemistry, University of Florida, Gainesville, FL, USA.
- Departments of Materials Design and Invention and Physiology and Biophysics, University of Buffalo (SUNY), Buffalo, NY, USA.
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10
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Liu Y, Xu X, Gao J, Naffaa MM, Liang H, Shi J, Wang HZ, Yang ND, Hou P, Zhao W, White KM, Kong W, Dou A, Cui A, Zhang G, Cohen IS, Zou X, Cui J. A PIP 2 substitute mediates voltage sensor-pore coupling in KCNQ activation. Commun Biol 2020; 3:385. [PMID: 32678288 PMCID: PMC7367283 DOI: 10.1038/s42003-020-1104-0] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2020] [Accepted: 06/22/2020] [Indexed: 12/25/2022] Open
Abstract
KCNQ family K+ channels (KCNQ1-5) in the heart, nerve, epithelium and ear require phosphatidylinositol 4,5-bisphosphate (PIP2) for voltage dependent activation. While membrane lipids are known to regulate voltage sensor domain (VSD) activation and pore opening in voltage dependent gating, PIP2 was found to interact with KCNQ1 and mediate VSD-pore coupling. Here, we show that a compound CP1, identified in silico based on the structures of both KCNQ1 and PIP2, can substitute for PIP2 to mediate VSD-pore coupling. Both PIP2 and CP1 interact with residues amongst a cluster of amino acids critical for VSD-pore coupling. CP1 alters KCNQ channel function due to different interactions with KCNQ compared with PIP2. We also found that CP1 returned drug-induced action potential prolongation in ventricular myocytes to normal durations. These results reveal the structural basis of PIP2 regulation of KCNQ channels and indicate a potential approach for the development of anti-arrhythmic therapy.
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Affiliation(s)
- Yongfeng Liu
- grid.4367.60000 0001 2355 7002Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University in Saint Louis, Saint Louis, MO 63130 USA
| | - Xianjin Xu
- grid.134936.a0000 0001 2162 3504Dalton Cardiovascular Research Center, Department of Physics and Astronomy, Department of Biochemistry, Institute for Data Science & Informatics, University of Missouri, Columbia, MO 65211 USA
| | - Junyuan Gao
- grid.36425.360000 0001 2216 9681Department of Physiology and Biophysics, and Institute for Molecular Cardiology, Stony Brook University, Stony Brook, NY 11794 USA
| | - Moawiah M. Naffaa
- grid.4367.60000 0001 2355 7002Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University in Saint Louis, Saint Louis, MO 63130 USA
| | - Hongwu Liang
- grid.4367.60000 0001 2355 7002Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University in Saint Louis, Saint Louis, MO 63130 USA
| | - Jingyi Shi
- grid.4367.60000 0001 2355 7002Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University in Saint Louis, Saint Louis, MO 63130 USA
| | - Hong Zhan Wang
- grid.36425.360000 0001 2216 9681Department of Physiology and Biophysics, and Institute for Molecular Cardiology, Stony Brook University, Stony Brook, NY 11794 USA
| | - Nien-Du Yang
- grid.4367.60000 0001 2355 7002Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University in Saint Louis, Saint Louis, MO 63130 USA
| | - Panpan Hou
- grid.4367.60000 0001 2355 7002Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University in Saint Louis, Saint Louis, MO 63130 USA
| | - Wenshan Zhao
- grid.4367.60000 0001 2355 7002Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University in Saint Louis, Saint Louis, MO 63130 USA
| | - Kelli McFarland White
- grid.4367.60000 0001 2355 7002Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University in Saint Louis, Saint Louis, MO 63130 USA
| | - Wenjuan Kong
- grid.4367.60000 0001 2355 7002Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University in Saint Louis, Saint Louis, MO 63130 USA
| | - Alex Dou
- grid.4367.60000 0001 2355 7002Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University in Saint Louis, Saint Louis, MO 63130 USA
| | - Amy Cui
- grid.4367.60000 0001 2355 7002Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University in Saint Louis, Saint Louis, MO 63130 USA
| | - Guohui Zhang
- grid.4367.60000 0001 2355 7002Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University in Saint Louis, Saint Louis, MO 63130 USA
| | - Ira S. Cohen
- grid.36425.360000 0001 2216 9681Department of Physiology and Biophysics, and Institute for Molecular Cardiology, Stony Brook University, Stony Brook, NY 11794 USA
| | - Xiaoqin Zou
- grid.134936.a0000 0001 2162 3504Dalton Cardiovascular Research Center, Department of Physics and Astronomy, Department of Biochemistry, Institute for Data Science & Informatics, University of Missouri, Columbia, MO 65211 USA
| | - Jianmin Cui
- grid.4367.60000 0001 2355 7002Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University in Saint Louis, Saint Louis, MO 63130 USA
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11
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Lipinski K, McKay MJ, Afrose F, Martfeld AN, Koeppe RE, Greathouse DV. Influence of Lipid Saturation, Hydrophobic Length and Cholesterol on Double-Arginine-Containing Helical Peptides in Bilayer Membranes. Chembiochem 2019; 20:2784-2792. [PMID: 31150136 DOI: 10.1002/cbic.201900282] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2019] [Indexed: 12/12/2022]
Abstract
Membrane proteins are essential for many cell processes yet are more difficult to investigate than soluble proteins. Charged residues often contribute significantly to membrane protein function. Model peptides such as GWALP23 (acetyl-GGALW5 LAL8 LALALAL16 ALW19 LAGA-amide) can be used to characterize the influence of specific residues on transmembrane protein domains. We have substituted R8 and R16 in GWALP23 in place of L8 and L16, equidistant from the peptide center, and incorporated specific 2 H-labeled alanine residues within the central sequence for detection by solid-state 2 H NMR spectroscopy. The resulting pattern of [2 H]Ala quadrupolar splitting (Δνq ) magnitudes indicates the core helix for R8,16 GWALP23 is significantly tilted to give a similar transmembrane orientation in thinner bilayers with either saturated C12:0 or C14:0 acyl chains (1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC) or 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC)) or unsaturated C16:1 Δ9 cis acyl chains. In bilayers of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC; C18:1 Δ9 cis) multiple orientations are indicated, whereas in longer, unsaturated 1,2-dieicosenoyl-sn-glycero-3-phosphocholine (DEiPC; C20:1 Δ11 cis) bilayers, the R8,16 GWALP23 helix adopts primarily a surface orientation. The inclusion of 10-20 mol % cholesterol in DOPC bilayers drives more of the R8,16 GWALP23 helix population to the membrane surface, thereby allowing both charged arginines access to the interfacial lipid head groups. The results suggest that hydrophobic thickness and cholesterol content are more important than lipid saturation for the arginine peptide dynamics and helix orientation in lipid membranes.
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Affiliation(s)
- Karli Lipinski
- Department of Chemistry and Biochemistry, University of Arkansas, 119 Chemistry Building, Fayetteville, AR, 72701, USA
| | - Matthew J McKay
- Department of Chemistry and Biochemistry, University of Arkansas, 119 Chemistry Building, Fayetteville, AR, 72701, USA
| | - Fahmida Afrose
- Department of Chemistry and Biochemistry, University of Arkansas, 119 Chemistry Building, Fayetteville, AR, 72701, USA
| | - Ashley N Martfeld
- Department of Chemistry and Biochemistry, University of Arkansas, 119 Chemistry Building, Fayetteville, AR, 72701, USA.,Present address: Department Department of Neurobiology, Duke University Medical Center, 311 Research Drive, Durham, NC, 27710, USA
| | - Roger E Koeppe
- Department of Chemistry and Biochemistry, University of Arkansas, 119 Chemistry Building, Fayetteville, AR, 72701, USA
| | - Denise V Greathouse
- Department of Chemistry and Biochemistry, University of Arkansas, 119 Chemistry Building, Fayetteville, AR, 72701, USA
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12
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Duncan AL, Song W, Sansom MSP. Lipid-Dependent Regulation of Ion Channels and G Protein-Coupled Receptors: Insights from Structures and Simulations. Annu Rev Pharmacol Toxicol 2019; 60:31-50. [PMID: 31506010 DOI: 10.1146/annurev-pharmtox-010919-023411] [Citation(s) in RCA: 96] [Impact Index Per Article: 19.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Ion channels and G protein-coupled receptors (GPCRs) are regulated by lipids in their membrane environment. Structural studies combined with biophysical and molecular simulation investigations reveal interaction sites for specific lipids on membrane protein structures. For K channels, PIP2 plays a key role in regulating Kv and Kir channels. Likewise, several recent cryo-EM structures of TRP channels have revealed bound lipids, including PIP2 and cholesterol. Among the pentameric ligand-gated ion channel family, structural and biophysical studies suggest the M4 TM helix may act as a lipid sensor, e.g., forming part of the binding sites for neurosteroids on the GABAA receptor. Structures of GPCRs have revealed multiple cholesterol sites, which may modulate both receptor dynamics and receptor oligomerization. PIP2 also interacts with GPCRs and may modulate their interactions with G proteins. Overall, it is evident that multiple lipid binding sites exist on channels and receptors that modulate their function allosterically and are potential druggable sites.
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Affiliation(s)
- Anna L Duncan
- Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom;
| | - Wanling Song
- Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom;
| | - Mark S P Sansom
- Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom;
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13
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Das A, Chatterjee S, Raghuraman H. Structural Dynamics of the Paddle Motif Loop in the Activated Conformation of KvAP Voltage Sensor. Biophys J 2019; 118:873-884. [PMID: 31547975 DOI: 10.1016/j.bpj.2019.08.017] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2019] [Revised: 07/31/2019] [Accepted: 08/06/2019] [Indexed: 02/07/2023] Open
Abstract
Voltage-dependent potassium (Kv) channels play a fundamental role in neuronal and cardiac excitability and are potential therapeutic targets. They assemble as tetramers with a centrally located pore domain surrounded by a voltage-sensing domain (VSD), which is critical for sensing transmembrane potential and subsequent gating. Although the sensor is supposed to be in "Up" conformation in both n-octylglucoside (OG) micelles and phospholipid membranes in the absence of membrane potential, toxins that bind VSD and modulate the gating behavior of Kv channels exhibit dramatic affinity differences in these membrane-mimetic systems. In this study, we have monitored the structural dynamics of the S3b-S4 loop of the paddle motif in activated conformation of KvAP-VSD by site-directed fluorescence approaches, using the environment-sensitive fluorescent probe 7-nitrobenz-2-oxa-1,3-diazol-4-yl-ethylenediamine (NBD). Emission maximum of NBD-labeled loop region of KvAP-VSD (residues 110-117) suggests a significant change in the polarity of local environment in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine/1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) membranes compared to OG micelles. This indicates that S3b-S4 loop residues might be partitioning to membrane interface, which is supported by an overall increased mean fluorescence lifetimes and significantly reduced water accessibility in membranes. Further, the magnitude of red edge excitation shift (REES) supports the presence of restricted/bound water molecules in the loop region of the VSD in micelles and membranes. Quantitative analysis of REES data using Gaussian probability distribution function clearly indicates that the sensor loop has fewer discrete equilibrium conformational states when reconstituted in membranes. Interestingly, this reduced molecular heterogeneity is consistent with the site-specific NBD polarization results, which suggest that the membrane environment offers a relaxed/dynamic organization for most of the S3b-S4 loop residues of the sensor. Overall, our results are relevant for understanding toxin-VSD interaction and gating mechanisms of Kv channels in membranes.
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Affiliation(s)
- Anindita Das
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, Homi Bhabha National Institute, 1/AF Bidhannagar, Kolkata, India
| | - Satyaki Chatterjee
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, Homi Bhabha National Institute, 1/AF Bidhannagar, Kolkata, India
| | - H Raghuraman
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, Homi Bhabha National Institute, 1/AF Bidhannagar, Kolkata, India.
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14
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Sawatani T, Kaneko YK, Ishikawa T. Dual effect of reduced type I diacylglycerol kinase activity on insulin secretion from MIN6 β-cells. J Pharmacol Sci 2019; 140:178-186. [PMID: 31279581 DOI: 10.1016/j.jphs.2019.06.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2019] [Revised: 05/03/2019] [Accepted: 06/11/2019] [Indexed: 02/07/2023] Open
Abstract
The role of type I diacylglycerol kinases (DGKs) in the regulation of insulin secretion was investigated in MIN6 β-cells. In intracellular Ca2+ concentration ([Ca2+]i) measurement experiments, 1 μM R59949, a type I DGK inhibitor, and 10 μM DiC8, a diacylglycerol (DAG) analog, amplified 22.2 mM glucose-induced [Ca2+]i oscillations in a protein kinase C (PKC)-dependent manner, whereas 10 μM R59949 and 100 μM DiC8 decreased [Ca2+]i independent of PKC. High concentrations of R59949 and DiC8 attenuated voltage-dependent Ca2+ channel currents. According to these results, 22.2 mM glucose-stimulated insulin secretion (GSIS) was potentiated by 1 μM R59949 but suppressed by 10 μM of the same. The DGKα inhibitor R59022 showed a similar dual effect. Conversely, DiC8 at 10 and 100 μM potentiated GSIS, although 100 μM DiC8 decreased [Ca2+]i. These results suggest that DAG accumulated through declined type I DGK activity shows a dual effect on insulin secretion depending on the degree of accumulation; a mild DAG accumulation induces a PKC-dependent stimulatory effect on insulin secretion, whereas an excessive DAG accumulation suppresses it in a PKC-independent manner, possibly via attenuation of VDCC activity.
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Affiliation(s)
- Toshiaki Sawatani
- Department of Pharmacology, School of Pharmaceutical Sciences, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka City, Shizuoka, 422-8526, Japan
| | - Yukiko K Kaneko
- Department of Pharmacology, School of Pharmaceutical Sciences, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka City, Shizuoka, 422-8526, Japan.
| | - Tomohisa Ishikawa
- Department of Pharmacology, School of Pharmaceutical Sciences, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka City, Shizuoka, 422-8526, Japan
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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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Startek JB, Boonen B, López-Requena A, Talavera A, Alpizar YA, Ghosh D, Van Ranst N, Nilius B, Voets T, Talavera K. Mouse TRPA1 function and membrane localization are modulated by direct interactions with cholesterol. eLife 2019; 8:e46084. [PMID: 31184584 PMCID: PMC6590989 DOI: 10.7554/elife.46084] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2019] [Accepted: 06/10/2019] [Indexed: 01/04/2023] Open
Abstract
The cation channel TRPA1 transduces a myriad of noxious chemical stimuli into nociceptor electrical excitation and neuropeptide release, leading to pain and neurogenic inflammation. Despite emergent evidence that TRPA1 is regulated by the membrane environment, it remains unknown whether this channel localizes in membrane microdomains or whether it interacts with cholesterol. Using total internal reflection fluorescence microscopy and density gradient centrifugation we found that mouse TRPA1 localizes preferably into cholesterol-rich domains and functional experiments revealed that cholesterol depletion decreases channel sensitivity to chemical agonists. Moreover, we identified two structural motifs in transmembrane segments 2 and 4 involved in mTRPA1-cholesterol interactions that are necessary for normal agonist sensitivity and plasma membrane localization. We discuss the impact of such interactions on TRPA1 gating mechanisms, regulation by the lipid environment, and role of this channel in sensory membrane microdomains, all of which helps to understand the puzzling pharmacology and pathophysiology of this channel.
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Affiliation(s)
- Justyna B Startek
- Laboratory of Ion Channel Research and TRP Research Platform Leuven (TRPLe), Department of Cellular and Molecular MedicineKU LeuvenLeuvenBelgium
- VIB Center for Brain & Disease ResearchLeuvenBelgium
| | - Brett Boonen
- Laboratory of Ion Channel Research and TRP Research Platform Leuven (TRPLe), Department of Cellular and Molecular MedicineKU LeuvenLeuvenBelgium
- VIB Center for Brain & Disease ResearchLeuvenBelgium
| | - Alejandro López-Requena
- Laboratory of Ion Channel Research and TRP Research Platform Leuven (TRPLe), Department of Cellular and Molecular MedicineKU LeuvenLeuvenBelgium
- VIB Center for Brain & Disease ResearchLeuvenBelgium
| | - Ariel Talavera
- Center for Microscopy and Molecular Imaging (CMMI), Laboratory of MicroscopyUniversité Libre de BruxellesGosseliesBelgium
| | - Yeranddy A Alpizar
- Laboratory of Ion Channel Research and TRP Research Platform Leuven (TRPLe), Department of Cellular and Molecular MedicineKU LeuvenLeuvenBelgium
- VIB Center for Brain & Disease ResearchLeuvenBelgium
| | - Debapriya Ghosh
- Laboratory of Ion Channel Research and TRP Research Platform Leuven (TRPLe), Department of Cellular and Molecular MedicineKU LeuvenLeuvenBelgium
- VIB Center for Brain & Disease ResearchLeuvenBelgium
| | - Nele Van Ranst
- Laboratory of Ion Channel Research and TRP Research Platform Leuven (TRPLe), Department of Cellular and Molecular MedicineKU LeuvenLeuvenBelgium
- VIB Center for Brain & Disease ResearchLeuvenBelgium
| | - Bernd Nilius
- Laboratory of Ion Channel Research and TRP Research Platform Leuven (TRPLe), Department of Cellular and Molecular MedicineKU LeuvenLeuvenBelgium
- VIB Center for Brain & Disease ResearchLeuvenBelgium
| | - Thomas Voets
- Laboratory of Ion Channel Research and TRP Research Platform Leuven (TRPLe), Department of Cellular and Molecular MedicineKU LeuvenLeuvenBelgium
- VIB Center for Brain & Disease ResearchLeuvenBelgium
| | - Karel Talavera
- Laboratory of Ion Channel Research and TRP Research Platform Leuven (TRPLe), Department of Cellular and Molecular MedicineKU LeuvenLeuvenBelgium
- VIB Center for Brain & Disease ResearchLeuvenBelgium
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17
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Cholesterol-Dependent Gating Effects on Ion Channels. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2019; 1115:167-190. [PMID: 30649760 DOI: 10.1007/978-3-030-04278-3_8] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Biomembranes separate a live cell from its environment and keep it in an off-equilibrium, steady state. They contain both phospholipids and nonphospholipids, depending on whether there are phosphate groups in the headgroup regions. Cholesterol (CHOL) is one type of nonphospholipids, and one of the most abundant lipid molecules in humans. Its content in plasma membranes and intracellular membranes varies and is tightly regulated. Voltage-gated ion channels are universally present in every cell and are fairly diversified in the eukaryotic domain of life. Our lipid-dependent gating hypothesis postulates that the controlled switch of the voltage-sensor domains (VSDs) in a voltage-gated potassium (Kv) channel between the "down" and the "up" state (gating) is sensitive to the ratio of phospholipids:nonphospholipids in the annular layer around the channel. High CHOL content is found to exert strong inhibitory effects on Kv channels. Such effects have been observed in in vitro membranes, cultured cells, and animal models for cholesterol metabolic defects. Thermodynamic analysis of the CHOL-dependent gating suggests that the inhibitory effects of CHOL result from collective interactions between annular CHOL molecules and the channel, which appear to be a more generic principle behind the CHOL effects on other ion channels and transporters. We will review the recent progress in the CHOL-dependent gating of voltage-gated ion channels, discuss the current technical limitations, and then expand briefly the learned principles to other ion channels that are known to be sensitive to the CHOL-channel interactions.
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18
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Babakhanian M, Yang L, Nowroozi B, Saddik G, Boodaghians L, Blount P, Grundfest W. Effects of Low Intensity Focused Ultrasound on Liposomes Containing Channel proteins. Sci Rep 2018; 8:17250. [PMID: 30467339 PMCID: PMC6250712 DOI: 10.1038/s41598-018-35486-1] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2018] [Accepted: 10/06/2018] [Indexed: 02/08/2023] Open
Abstract
The ability to reversibly and non-invasively modulate region-specific brain activity in vivo suggests Low Intensity Focused Ultrasound (LIFU) as potential therapeutics for neurological dysfunctions such as epilepsy and Parkinson's disease. While in vivo studies provide evidence of the bioeffects of LIFU on neuronal activity, they merely hint at potential mechanisms but do not fully explain how this technology achieves these effects. One potential hypothesis is that LIFU produces local membrane depolarization by mechanically perturbing the neuronal cell membrane, or activating channels or other proteins embedded in the membrane. Proteins that sense mechanical perturbations of the membrane, such as those gated by membrane tension, are prime candidates for activating in response to LIFU and thus leading to the neurological responses that have been measured. Here we use the bacterial mechanosensitive channel MscL, which has been purified and reconstituted in liposomes, to determine how LIFU may affect the activation of this membrane-tension gated channel. Two bacterial voltage-gated channels, KvAP and NaK2K F92A channels were also studied. Surprisingly, the results suggest that ultrasound modulation and membrane perturbation does not induce channel gating, but rather induces pore formation at the membrane protein-lipid interface. However, in vesicles with high MscL mechanosensitive channel concentrations, apparent decreases in pore formation are observed, suggesting that this membrane-tension-sensitive protein may serve to increase the elasticity of the membrane, presumably because of expansion of the channel in the plane of the membrane independent of channel gating.
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Affiliation(s)
- Meghedi Babakhanian
- Department of Bioengineering, University of California, Los Angeles, CA, 90095, USA
- Center for Advanced Surgical and Interventional Technology (CASIT), University of California, Los Angeles, CA, 90095, USA
| | - Limin Yang
- Department of Physiology, UT Southwestern Medical Center, Dallas, TX, 75390-9040, USA
| | - Bryan Nowroozi
- Department of Bioengineering, University of California, Los Angeles, CA, 90095, USA
- Center for Advanced Surgical and Interventional Technology (CASIT), University of California, Los Angeles, CA, 90095, USA
| | - George Saddik
- Department of Bioengineering, University of California, Los Angeles, CA, 90095, USA
- Center for Advanced Surgical and Interventional Technology (CASIT), University of California, Los Angeles, CA, 90095, USA
| | - Lilian Boodaghians
- Department of Bioengineering, University of California, Los Angeles, CA, 90095, USA
- Center for Advanced Surgical and Interventional Technology (CASIT), University of California, Los Angeles, CA, 90095, USA
| | - Paul Blount
- Department of Physiology, UT Southwestern Medical Center, Dallas, TX, 75390-9040, USA.
| | - Warren Grundfest
- Department of Bioengineering, University of California, Los Angeles, CA, 90095, USA.
- Center for Advanced Surgical and Interventional Technology (CASIT), University of California, Los Angeles, CA, 90095, USA.
- Department of Electrical Engineering, University of California, Los Angeles, CA, 90095, USA.
- David Geffen School of Medicine, University of California, Los Angeles, USA.
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19
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Yadav GP, Zheng H, Yang Q, Douma LG, Bloom LB, Jiang QX. Secretory granule protein chromogranin B (CHGB) forms an anion channel in membranes. Life Sci Alliance 2018; 1:e201800139. [PMID: 30456382 PMCID: PMC6238609 DOI: 10.26508/lsa.201800139] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2018] [Revised: 08/29/2018] [Accepted: 09/11/2018] [Indexed: 12/14/2022] Open
Abstract
The CHGB subfamily of secretory granule proteins forms a new family of anion-selective channels by interacting with membranes via two amphipathic α-helices. The channel exhibits higher anion selectivity, larger conductance, higher DIDS-binding affinity, and higher Cl− sensitivity than other known anion channels. Regulated secretion is an intracellular pathway that is highly conserved from protists to humans. Granin family proteins were proposed to participate in the biogenesis, maturation and release of secretory granules in this pathway. However, the exact molecular mechanisms underlying the intracellular functions of the granin family proteins remain unclear. Here, we show that chromogranin B (CHGB), a secretory granule protein, inserts itself into membrane and forms a chloride-conducting channel. CHGB interacts strongly with phospholipid membranes through two amphipathic α helices. At a high local concentration, CHGB insertion in membrane causes significant bilayer remodeling, producing protein-coated nanoparticles and nanotubules. Fast kinetics and high cooperativity for anion efflux from CHGB vesicles suggest that CHGB tetramerizes to form a functional channel with a single-channel conductance of ∼125 pS (150/150 mM Cl−). The CHGB channel is sensitive to an anion channel blocker and exhibits higher anion selectivity than the other six known families of Cl− channels. Our data suggest that the CHGB subfamily of granin proteins forms a new family of organelle chloride channels.
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Affiliation(s)
- Gaya P Yadav
- Department of Microbiology and Cell Science, University of Florida, Gainesville, FL, USA
| | - Hui Zheng
- Department of Physiology, University of Texas Southwestern Medical Center at Dallas, Dallas, TX, USA
| | - Qing Yang
- Crop Designing Center, Henan Academy of Agricultural Sciences, Zhengzhou, PR China
| | - Lauren G Douma
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, FL, USA
| | - Linda B Bloom
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, FL, USA
| | - Qiu-Xing Jiang
- Department of Microbiology and Cell Science, University of Florida, Gainesville, FL, USA
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20
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Chatterjee S, Vyas R, Chalamalasetti SV, Sahu ID, Clatot J, Wan X, Lorigan GA, Deschênes I, Chakrapani S. The voltage-gated sodium channel pore exhibits conformational flexibility during slow inactivation. J Gen Physiol 2018; 150:1333-1347. [PMID: 30082431 PMCID: PMC6122925 DOI: 10.1085/jgp.201812118] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2018] [Accepted: 07/06/2018] [Indexed: 01/02/2023] Open
Abstract
Voltage-gated sodium channels undergo slow inactivation during prolonged depolarization by means of a mechanism that is poorly understood. Chatterjee et al. study this process spectroscopically and reveal conformational flexibility of the pore region in the slow-inactivated state. Slow inactivation in voltage-gated sodium channels (NaVs) directly regulates the excitability of neurons, cardiac myocytes, and skeletal muscles. Although NaV slow inactivation appears to be conserved across phylogenies—from bacteria to humans—the structural basis for this mechanism remains unclear. Here, using site-directed labeling and EPR spectroscopic measurements of membrane-reconstituted prokaryotic NaV homologues, we characterize the conformational dynamics of the selectivity filter region in the conductive and slow-inactivated states to determine the molecular events underlying NaV gating. Our findings reveal profound conformational flexibility of the pore in the slow-inactivated state. We find that the P1 and P2 pore helices undergo opposing movements with respect to the pore axis. These movements result in changes in volume of both the central and intersubunit cavities, which form pathways for lipophilic drugs that modulate slow inactivation. Our findings therefore provide novel insight into the molecular basis for state-dependent effects of lipophilic drugs on channel function.
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Affiliation(s)
- Soumili Chatterjee
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH
| | - Rajan Vyas
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH
| | | | - Indra D Sahu
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH
| | - Jérôme Clatot
- Heart and Vascular Research Center, Department of Medicine, Case Western Reserve University, Cleveland, OH
| | - Xiaoping Wan
- Heart and Vascular Research Center, Department of Medicine, Case Western Reserve University, Cleveland, OH
| | - Gary A Lorigan
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH
| | - Isabelle Deschênes
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH.,Heart and Vascular Research Center, Department of Medicine, Case Western Reserve University, Cleveland, OH
| | - Sudha Chakrapani
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH
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21
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Lee J, Pothula KR, Kleinekathöfer U, Im W. Simulation Study of Occk5 Functional Properties in Pseudomonas aeruginosa Outer Membranes. J Phys Chem B 2018; 122:8185-8192. [DOI: 10.1021/acs.jpcb.8b07109] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Affiliation(s)
- Joonseong Lee
- Departments of Biological Sciences and Bioengineering, Lehigh University, Bethlehem, Pennsylvania 18015, United States
| | - Karunakar R. Pothula
- Department of Physics and Earth Sciences, Jacobs University Bremen, Campus Ring 1, 28759 Bremen, Germany
| | - Ulrich Kleinekathöfer
- Department of Physics and Earth Sciences, Jacobs University Bremen, Campus Ring 1, 28759 Bremen, Germany
| | - Wonpil Im
- Departments of Biological Sciences and Bioengineering, Lehigh University, Bethlehem, Pennsylvania 18015, United States
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22
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A complicated complex: Ion channels, voltage sensing, cell membranes and peptide inhibitors. Neurosci Lett 2018; 679:35-47. [DOI: 10.1016/j.neulet.2018.04.030] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2018] [Revised: 04/11/2018] [Accepted: 04/17/2018] [Indexed: 01/04/2023]
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23
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Imbrici P, Altamura C, Gualandi F, Mangiatordi GF, Neri M, De Maria G, Ferlini A, Padovani A, D'Adamo MC, Nicolotti O, Pessia M, Conte D, Filosto M, Desaphy JF. A novel KCNA1 mutation in a patient with paroxysmal ataxia, myokymia, painful contractures and metabolic dysfunctions. Mol Cell Neurosci 2017; 83:6-12. [PMID: 28666963 DOI: 10.1016/j.mcn.2017.06.006] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2016] [Revised: 04/05/2017] [Accepted: 06/25/2017] [Indexed: 11/26/2022] Open
Abstract
Episodic ataxia type 1 (EA1) is a human dominant neurological syndrome characterized by continuous myokymia, episodic attacks of ataxic gait and spastic contractions of skeletal muscles that can be triggered by emotional stress and fatigue. This rare disease is caused by missense mutations in the KCNA1 gene coding for the neuronal voltage gated potassium channel Kv1.1, which contributes to nerve cell excitability in the cerebellum, hippocampus, cortex and peripheral nervous system. We identified a novel KCNA1 mutation, E283K, in an Italian proband presenting with paroxysmal ataxia and myokymia aggravated by painful contractures and metabolic dysfunctions. The E283K mutation is located in the S3-S4 extracellular linker belonging to the voltage sensor domain of Kv channels. In order to test whether the E283K mutation affects Kv1.1 biophysical properties we transfected HEK293 cells with WT or mutant cDNAs alone or in a 1:1 combination, and recorded relative potassium currents in the whole-cell configuration of patch-clamp. Mutant E283K channels display voltage-dependent activation shifted by 10mV toward positive potentials and kinetics of activation slowed by ~2 fold compared to WT channels. Potassium currents resulting from heteromeric WT/E283K channels show voltage-dependent gating and kinetics of activation intermediate between WT and mutant homomeric channels. Based on homology modeling studies of the mutant E283K, we propose a molecular explanation for the reduced voltage sensitivity and slow channel opening. Overall, our results suggest that the replacement of a negatively charged residue with a positively charged lysine at position 283 in Kv1.1 causes a drop of potassium current that likely accounts for EA-1 symptoms in the heterozygous carrier.
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Affiliation(s)
- Paola Imbrici
- Department of Pharmacy - Drug Sciences, University of Bari Aldo Moro, Bari, Italy.
| | - Concetta Altamura
- Department of Pharmacy - Drug Sciences, University of Bari Aldo Moro, Bari, Italy
| | - Francesca Gualandi
- Logistic Unit of Medical Genetics, Department of Medical Sciences, University-Hospital of Ferrara, Italy
| | | | - Marcella Neri
- Logistic Unit of Medical Genetics, Department of Medical Sciences, University-Hospital of Ferrara, Italy
| | | | - Alessandra Ferlini
- Logistic Unit of Medical Genetics, Department of Medical Sciences, University-Hospital of Ferrara, Italy
| | - Alessandro Padovani
- Center for Neuromuscular Diseases and Neuropathies, Unit of Neurology, ASST "Spedali Civili", and University of Brescia, Brescia, Italy
| | - Maria Cristina D'Adamo
- Faculty of Medicine, Department of Physiology and Biochemistry, University of Malta, MSD-2080 Msida, Malta
| | - Orazio Nicolotti
- Department of Pharmacy - Drug Sciences, University of Bari Aldo Moro, Bari, Italy
| | - Mauro Pessia
- Faculty of Medicine, Department of Physiology and Biochemistry, University of Malta, MSD-2080 Msida, Malta; Department of Experimental Medicine, Section of Physiology & Biochemistry, University of Perugia School of Medicine, Perugia, Italy
| | - Diana Conte
- Department of Pharmacy - Drug Sciences, University of Bari Aldo Moro, Bari, Italy
| | - Massimiliano Filosto
- Center for Neuromuscular Diseases and Neuropathies, Unit of Neurology, ASST "Spedali Civili", and University of Brescia, Brescia, Italy
| | - Jean-Francois Desaphy
- Department of Biomedical Sciences and Human Oncology, University of Bari Aldo Moro, Bari, Italy
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24
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Mlayeh L, Krammer EM, Léonetti M, Prévost M, Homblé F. The mitochondrial VDAC of bean seeds recruits phosphatidylethanolamine lipids for its proper functioning. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2017; 1858:786-794. [PMID: 28666835 DOI: 10.1016/j.bbabio.2017.06.005] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2017] [Revised: 05/28/2017] [Accepted: 06/24/2017] [Indexed: 12/31/2022]
Abstract
The voltage-dependent anion-selective channel (VDAC) is the main pathway for inorganic ions and metabolites through the mitochondrial outer membrane. Studies recently demonstrated that membrane lipids regulate its function. It remains, however, unclear how this regulation takes place. In this study, we show that phospholipids are key regulators of Phaseolus VDAC function and, furthermore, that the salt concentration modulates this regulation. Both selectivity and voltage dependence of Phaseolus VDAC are very sensitive to a change in the lipid polar head from PC to PE. Interestingly enough, this dependence is observed only at low salt concentration. Furthermore, significant changes in VDAC functional properties also occur with the gradual methylation of the PE group pointing to the role of subtle chemical variations in the lipid head group. The dependence of PcVDAC gating upon the introduction of a small mole fraction of PE in a PC bilayer has prompted us to propose the existence of a specific interaction site for PE on the outer surface of PcVDAC. Eventually, comparative modeling and molecular dynamics simulations suggest a potential mechanism to get insight into the anion selectivity enhancement of PcVDAC observed in PE relative to PC.
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Affiliation(s)
- Lamia Mlayeh
- Structure et Fonction des Membranes Biologiques, Université Libre de Bruxelles (ULB), Boulevard du Triomphe CP 206/2, B-1050 Brussels, Belgium
| | - Eva-Maria Krammer
- Structure et Fonction des Membranes Biologiques, Université Libre de Bruxelles (ULB), Boulevard du Triomphe CP 206/2, B-1050 Brussels, Belgium.
| | - Marc Léonetti
- I.R.P.H.E., Aix-Marseille Université, CNRS, Technopôle de Château-Gombert, F-13384, Marseille Cedex 13, France.
| | - Martine Prévost
- Structure et Fonction des Membranes Biologiques, Université Libre de Bruxelles (ULB), Boulevard du Triomphe CP 206/2, B-1050 Brussels, Belgium.
| | - Fabrice Homblé
- Structure et Fonction des Membranes Biologiques, Université Libre de Bruxelles (ULB), Boulevard du Triomphe CP 206/2, B-1050 Brussels, Belgium.
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25
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Chen L, Li Z, Zhang Q, Wei S, Li B, Zhang X, Zhang L, Li Q, Xu H, Xu Z. Silencing of AQP3 induces apoptosis of gastric cancer cells via downregulation of glycerol intake and downstream inhibition of lipogenesis and autophagy. Onco Targets Ther 2017; 10:2791-2804. [PMID: 28620264 PMCID: PMC5466363 DOI: 10.2147/ott.s134016] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Gastric cancer (GC) has a poor prognosis and is a leading cause of cancer-related death. Optimal therapeutic targets have not been identified. AQP3 is capable of transporting glycerol across the cytomembrane. Previous studies have shown that AQP3 is involved in proliferation, invasion and migration by regulating glycerol and lipid metabolism in diverse cancer cell types. However, the potential roles of glycerol and lipid metabolism in AQP3-related cell apoptosis in GC remain unclear. In this study, we observed that AQP3 expression was upregulated in tumor tissues, and positively correlated with tumor size, lymph node metastasis and glycerol concentration in human GC samples. Silencing of AQP3 resulted in decreased glycerol intake and impaired lipid synthesis, which contributed to increased cell apoptosis. Furthermore, inhibition of autophagy induced by AQP3 knockdown promoted cell apoptosis. Administration of either glycerol or rapamycin restored cell viability, and overexpression of AQP3 increased cell viability by upregulating cellular glycerol metabolism and autophagy. Our study demonstrates that the increase in cell apoptosis of AQP3-deficient GC cells is a consequence of reduced glycerol uptake and lipogenesis and is associated with autophagy inhibition induced by AQP3 deficiency.
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Affiliation(s)
- Liang Chen
- Department of General Surgery, The First Affiliated Hospital of Nanjing Medical University, Nanjing, People's Republic of China
| | - Zheng Li
- Department of General Surgery, The First Affiliated Hospital of Nanjing Medical University, Nanjing, People's Republic of China
| | - Qiang Zhang
- Department of General Surgery, The First Affiliated Hospital of Nanjing Medical University, Nanjing, People's Republic of China
| | - Song Wei
- Department of General Surgery, The First Affiliated Hospital of Nanjing Medical University, Nanjing, People's Republic of China
| | - Bowen Li
- Department of General Surgery, The First Affiliated Hospital of Nanjing Medical University, Nanjing, People's Republic of China
| | - Xuan Zhang
- Department of General Surgery, The First Affiliated Hospital of Nanjing Medical University, Nanjing, People's Republic of China
| | - Lei Zhang
- Department of General Surgery, The First Affiliated Hospital of Nanjing Medical University, Nanjing, People's Republic of China
| | - Qing Li
- Department of General Surgery, The First Affiliated Hospital of Nanjing Medical University, Nanjing, People's Republic of China
| | - Hao Xu
- Department of General Surgery, The First Affiliated Hospital of Nanjing Medical University, Nanjing, People's Republic of China
| | - Zekuan Xu
- Department of General Surgery, The First Affiliated Hospital of Nanjing Medical University, Nanjing, People's Republic of China
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26
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Poveda JA, Marcela Giudici A, Lourdes Renart M, Morales A, González-Ros JM. Towards understanding the molecular basis of ion channel modulation by lipids: Mechanistic models and current paradigms. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1859:1507-1516. [PMID: 28408206 DOI: 10.1016/j.bbamem.2017.04.003] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/31/2016] [Revised: 03/27/2017] [Accepted: 04/09/2017] [Indexed: 10/19/2022]
Abstract
Research on ion channel modulation has become a hot topic because of the key roles these membrane proteins play in both prokaryotic and eukaryotic organisms. In this respect, lipid modulation adds to the overall modulatory mechanisms as a potential via to find new pharmacological targets for drug design based on interfering with lipid/channel interactions. However, our knowledge in this field is scarce and often circumscribed to the sites where lipids bind and/or its final functional consequences. To fully understand this process it is necessary to improve our knowledge on its molecular basis, from the binding sites to the signalling pathways that derive in structural and functional effects on the ion channel. In this review, we have compiled information about such mechanisms and established a classification into four different modes of action. Afterwards, we have revised in more detail the lipid modulation of Cys-loop receptors and of the potassium channel KcsA, which were chosen as model channels modulated by specific lipids. This article is part of a Special Issue entitled: Membrane Lipid Therapy: Drugs Targeting Biomembranes edited by Pablo V. Escribá.
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Affiliation(s)
- José A Poveda
- Instituto de Biología Molecular y Celular, Universidad Miguel Hernández, Elche, 03202 Alicante, Spain.
| | - A Marcela Giudici
- Instituto de Biología Molecular y Celular, Universidad Miguel Hernández, Elche, 03202 Alicante, Spain
| | - M Lourdes Renart
- Instituto de Biología Molecular y Celular, Universidad Miguel Hernández, Elche, 03202 Alicante, Spain
| | - Andrés Morales
- Departamento de Fisiología, Genética y Microbiología, Universidad de Alicante, 03080 Alicante, Spain
| | - José M González-Ros
- Instituto de Biología Molecular y Celular, Universidad Miguel Hernández, Elche, 03202 Alicante, Spain.
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27
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Disulfide mapping the voltage-sensing mechanism of a voltage-dependent potassium channel. Sci Rep 2016; 6:37303. [PMID: 27853286 PMCID: PMC5112519 DOI: 10.1038/srep37303] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2016] [Accepted: 10/27/2016] [Indexed: 11/08/2022] Open
Abstract
Voltage-dependent potassium (Kv) channels allow for the selective permeability of potassium ions in a membrane potential dependent manner, playing crucial roles in neurotransmission and muscle contraction. Kv channel is a tetramer, in which each subunit possesses a voltage-sensing domain (VSD) and a pore domain (PD). Although several lines of evidence indicated that membrane depolarization is sensed as the movement of helix S4 of the VSD, the detailed voltage-sensing mechanism remained elusive, due to the difficulty of structural analyses at resting potential. In this study, we conducted a comprehensive disulfide locking analysis of the VSD using 36 double Cys mutants, in order to identify the proximal residue pairs of the VSD in the presence or absence of a membrane potential. An intramolecular SS-bond was formed between 6 Cys pairs under both polarized and depolarized environment, and one pair only under depolarized environment. The multiple conformations captured by the SS-bond can be divided by two states, up and down, where S4 lies on the extracellular and intracellular sides of the membrane, respectively, with axial rotation of 180°. The transition between these two states is caused by the S4 translocation of 12 Å, enabling allosteric regulation of the gating at the PD.
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28
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Genetically Encoded Voltage Indicators: Opportunities and Challenges. J Neurosci 2016; 36:9977-89. [PMID: 27683896 DOI: 10.1523/jneurosci.1095-16.2016] [Citation(s) in RCA: 99] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2016] [Accepted: 07/25/2016] [Indexed: 11/21/2022] Open
Abstract
UNLABELLED A longstanding goal in neuroscience is to understand how spatiotemporal patterns of neuronal electrical activity underlie brain function, from sensory representations to decision making. An emerging technology for monitoring electrical dynamics, voltage imaging using genetically encoded voltage indicators (GEVIs), couples the power of genetics with the advantages of light. Here, we review the properties that determine indicator performance and applicability, discussing both recent progress and technical limitations. We then consider GEVI applications, highlighting studies that have already deployed GEVIs for biological discovery. We also examine which classes of biological questions GEVIs are primed to address and which ones are beyond their current capabilities. As GEVIs are further developed, we anticipate that they will become more broadly used by the neuroscience community to eavesdrop on brain activity with unprecedented spatiotemporal resolution. SIGNIFICANCE STATEMENT Genetically encoded voltage indicators are engineered light-emitting protein sensors that typically report neuronal voltage dynamics as changes in brightness. In this review, we systematically discuss the current state of this emerging method, considering both its advantages and limitations for imaging neural activity. We also present recent applications of this technology and discuss what is feasible now and what we anticipate will become possible with future indicator development. This review will inform neuroscientists of recent progress in the field and help potential users critically evaluate the suitability of genetically encoded voltage indicator imaging to answer their specific biological questions.
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29
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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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30
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Huang Y, Hemmer E, Rosei F, Vetrone F. Multifunctional Liposome Nanocarriers Combining Upconverting Nanoparticles and Anticancer Drugs. J Phys Chem B 2016; 120:4992-5001. [DOI: 10.1021/acs.jpcb.6b02013] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Yue Huang
- Institut
National de la Recherche Scientifique - Énergie, Matériaux
et Télécommunications, Université du Québec, Varennes, Québec J3X 1S2, Canada
| | - Eva Hemmer
- Institut
National de la Recherche Scientifique - Énergie, Matériaux
et Télécommunications, Université du Québec, Varennes, Québec J3X 1S2, Canada
| | - Federico Rosei
- Institut
National de la Recherche Scientifique - Énergie, Matériaux
et Télécommunications, Université du Québec, Varennes, Québec J3X 1S2, Canada
- Institute
for Fundamental and Frontier Science, University of Electronic Science and Technology of China, Chengdu, PR China
- Centre
for Self-Assembled Chemical Structures, McGill University, Montreal, Québec H3A 2K6, Canada
| | - Fiorenzo Vetrone
- Institut
National de la Recherche Scientifique - Énergie, Matériaux
et Télécommunications, Université du Québec, Varennes, Québec J3X 1S2, Canada
- Institute
for Fundamental and Frontier Science, University of Electronic Science and Technology of China, Chengdu, PR China
- Centre
for Self-Assembled Chemical Structures, McGill University, Montreal, Québec H3A 2K6, Canada
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31
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Kim DM, Nimigean CM. Voltage-Gated Potassium Channels: A Structural Examination of Selectivity and Gating. Cold Spring Harb Perspect Biol 2016; 8:a029231. [PMID: 27141052 PMCID: PMC4852806 DOI: 10.1101/cshperspect.a029231] [Citation(s) in RCA: 76] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Voltage-gated potassium channels play a fundamental role in the generation and propagation of the action potential. The discovery of these channels began with predictions made by early pioneers, and has culminated in their extensive functional and structural characterization by electrophysiological, spectroscopic, and crystallographic studies. With the aid of a variety of crystal structures of these channels, a highly detailed picture emerges of how the voltage-sensing domain reports changes in the membrane electric field and couples this to conformational changes in the activation gate. In addition, high-resolution structural and functional studies of K(+) channel pores, such as KcsA and MthK, offer a comprehensive picture on how selectivity is achieved in K(+) channels. Here, we illustrate the remarkable features of voltage-gated potassium channels and explain the mechanisms used by these machines with experimental data.
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Affiliation(s)
- Dorothy M Kim
- Department of Anesthesiology, Weill Cornell Medical College, New York, New York 10065
| | - Crina M Nimigean
- Department of Anesthesiology, Weill Cornell Medical College, New York, New York 10065
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32
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Eich C, Manzo C, de Keijzer S, Bakker GJ, Reinieren-Beeren I, García-Parajo MF, Cambi A. Changes in membrane sphingolipid composition modulate dynamics and adhesion of integrin nanoclusters. Sci Rep 2016; 6:20693. [PMID: 26869100 PMCID: PMC4751618 DOI: 10.1038/srep20693] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2015] [Accepted: 01/11/2016] [Indexed: 12/14/2022] Open
Abstract
Sphingolipids are essential constituents of the plasma membrane (PM) and play an important role in signal transduction by modulating clustering and dynamics of membrane receptors. Changes in lipid composition are therefore likely to influence receptor organisation and function, but how this precisely occurs is difficult to address given the intricacy of the PM lipid-network. Here, we combined biochemical assays and single molecule dynamic approaches to demonstrate that the local lipid environment regulates adhesion of integrin receptors by impacting on their lateral mobility. Induction of sphingomyelinase (SMase) activity reduced sphingomyelin (SM) levels by conversion to ceramide (Cer), resulting in impaired integrin adhesion and reduced integrin mobility. Dual-colour imaging of cortical actin in combination with single molecule tracking of integrins showed that this reduced mobility results from increased coupling to the actin cytoskeleton brought about by Cer formation. As such, our data emphasizes a critical role for the PM local lipid composition in regulating the lateral mobility of integrins and their ability to dynamically increase receptor density for efficient ligand binding in the process of cell adhesion.
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Affiliation(s)
- Christina Eich
- Department of Tumor Immunology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Postbox 9101, 6500 HB Nijmegen, The Netherlands
| | - Carlo Manzo
- ICFO-Institut de Ciencies Fotoniques, Mediterranean Technology Park, 08860 Castelldefels (Barcelona), Spain
| | - Sandra de Keijzer
- Department of Tumor Immunology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Postbox 9101, 6500 HB Nijmegen, The Netherlands
| | - Gert-Jan Bakker
- Department of Cell Biology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Postbox 9101, 6500 HB Nijmegen, The Netherlands
| | - Inge Reinieren-Beeren
- Department of Tumor Immunology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Postbox 9101, 6500 HB Nijmegen, The Netherlands
| | - Maria F García-Parajo
- ICFO-Institut de Ciencies Fotoniques, Mediterranean Technology Park, 08860 Castelldefels (Barcelona), Spain.,ICREA-Institució Catalana de Recerca i Estudis Avançats, 08010 Barcelona, Spain
| | - Alessandra Cambi
- Department of Tumor Immunology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Postbox 9101, 6500 HB Nijmegen, The Netherlands
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33
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Li Z, Li B, Zhang L, Chen L, Sun G, Zhang Q, Wang J, Zhi X, Wang L, Xu Z, Xu H. The proliferation impairment induced by AQP3 deficiency is the result of glycerol uptake and metabolism inhibition in gastric cancer cells. Tumour Biol 2016; 37:9169-79. [PMID: 26768614 DOI: 10.1007/s13277-015-4753-8] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2015] [Accepted: 12/29/2015] [Indexed: 12/16/2022] Open
Abstract
Gastric cancer is a big threat to human health. Effective therapeutic cancer target remains to be discovered. Aquaporin 3 (AQP3) belongs to a family of transmembrane channels that are important in transporting water, glycerol, and other small molecules across the cell membrane. Glycerol that is transported by AQP3 is necessary for cell energy generation and lipid synthesis which fulfill the cell biological processes. Previous studies have shown that AQP3 is implicated in disease progression in several cancer types. However, whether AQP3-regulated glycerol uptake and metabolism were involved in cancer progression remains to be further studied. Our study demonstrated that the expression of AQP3 was positively correlated with glycerol level in human gastric cancer tissues. AQP3 inhibition induced proliferation impairment in gastric cancer cells both in vitro and in vivo. AQP3 inhibition that induced glycerol uptake reduction and glycerol administration would rehabilitate the cell proliferation. The energy and lipid production decreased when AQP3 was knocked down since the cellular glycerol level and several lipogenesis enzymes were downregulated. PI3K/Akt signaling pathway, which was involved in the impaired lipid and ATP production, was also inhibited after AQP3 knockdown. Our study indicated that the energy and lipid production inhibition, which were responsible for gastric cancer cell proliferation impairment, were induced by glycerol uptake reduction after AQP3 knockdown.
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Affiliation(s)
- Zheng Li
- Department of General Surgery, The First Affiliated Hospital of Nanjing Medical University, Nanjing, China
| | - Bowen Li
- Department of General Surgery, The First Affiliated Hospital of Nanjing Medical University, Nanjing, China
| | - Lei Zhang
- Department of General Surgery, The First Affiliated Hospital of Nanjing Medical University, Nanjing, China
| | - Liang Chen
- Department of General Surgery, The First Affiliated Hospital of Nanjing Medical University, Nanjing, China
| | - Guangli Sun
- Department of General Surgery, The First Affiliated Hospital of Nanjing Medical University, Nanjing, China
| | - Qun Zhang
- Department of General Surgery, The First Affiliated Hospital of Nanjing Medical University, Nanjing, China
| | - Jiwei Wang
- Department of General Surgery, The First Affiliated Hospital of Nanjing Medical University, Nanjing, China
| | - Xiaofei Zhi
- Department of General Surgery, The Affiliated Hospital of Nantong University, Nantong, China
| | - Linjun Wang
- Department of General Surgery, The First Affiliated Hospital of Nanjing Medical University, Nanjing, China.,Department of General Surgery, The People's Hospital of Taizhou, Taizhou, China
| | - Zekuan Xu
- Department of General Surgery, The First Affiliated Hospital of Nanjing Medical University, Nanjing, China
| | - Hao Xu
- Department of General Surgery, The First Affiliated Hospital of Nanjing Medical University, Nanjing, China.
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34
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Yonkunas M, Kurnikova M. The Hydrophobic Effect Contributes to the Closed State of a Simplified Ion Channel through a Conserved Hydrophobic Patch at the Pore-Helix Crossing. Front Pharmacol 2015; 6:284. [PMID: 26640439 PMCID: PMC4661268 DOI: 10.3389/fphar.2015.00284] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2015] [Accepted: 11/10/2015] [Indexed: 11/13/2022] Open
Abstract
Ion selectivity-filter structures are strikingly similar throughout the large family of K++ channels and other p-loop-like receptors (i.e., glutamate receptors). At the same time, the triggers for opening these channels, or gating, are diverse. Two questions that remain unanswered regarding these channels are: (1) what force(s) stabilize the closed non-conducting channel-pore conformation? And (2) what is the free energy associated with transitioning from a closed (non-conducting) to an open (conducting) channel-pore conformation? The effects of charge and hydrophobicity on the conformational states of a model tetrameric biological ion channel are shown utilizing the amino acid sequence from the K+ channel KcsA as the model “channel”. Its widely conserved hydrophobic bundle crossing located adjacent to the lipid head-groups at the intracellular side of the membrane was calculated to have a 5 kcal/mol free energy difference between modeled open and closed conformations. Simulated mutants of amino acids within the hydrophobic region significantly contribute to the size of this difference. Specifically for KcsA, these residues are part of the pH sensor important for channel gating and our results are in agreement with published electrophysiology data. Our simulations support the idea that the hydrophobic effect contributes significantly to the stability of the closed conformation in tetrameric ion channels with a hydrophobic bundle crossing positioned in proximity to the lipid head groups of the biological membrane.
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Affiliation(s)
- Michael Yonkunas
- Department of Chemistry, Carnegie Mellon University, Pittsburgh PA, USA
| | - Maria Kurnikova
- Department of Chemistry, Carnegie Mellon University, Pittsburgh PA, USA
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35
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Ozawa SI, Kimura T, Nozaki T, Harada H, Shimada I, Osawa M. Structural basis for the inhibition of voltage-dependent K+ channel by gating modifier toxin. Sci Rep 2015; 5:14226. [PMID: 26382304 PMCID: PMC4585561 DOI: 10.1038/srep14226] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2015] [Accepted: 08/20/2015] [Indexed: 01/24/2023] Open
Abstract
Voltage-dependent K+ (Kv) channels play crucial roles in nerve and muscle action potentials. Voltage-sensing domains (VSDs) of Kv channels sense changes in the transmembrane potential, regulating the K+-permeability across the membrane. Gating modifier toxins, which have been used for the functional analyses of Kv channels, inhibit Kv channels by binding to VSD. However, the structural basis for the inhibition remains elusive. Here, fluorescence and NMR analyses of the interaction between VSD derived from KvAP channel and its gating modifier toxin, VSTx1, indicate that VSTx1 recognizes VSD under depolarized condition. We identified the VSD-binding residues of VSTx1 and their proximal residues of VSD by the cross-saturation (CS) and amino acid selective CS experiments, which enabled to build a docking model of the complex. These results provide structural basis for the specific binding and inhibition of Kv channels by gating modifier toxins.
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Affiliation(s)
- Shin-ichiro Ozawa
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
| | - Tomomi Kimura
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
| | - Tomohiro Nozaki
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
| | - Hitomi Harada
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
| | - Ichio Shimada
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
| | - Masanori Osawa
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.,Keio University Faculty of Pharmacy, Shibakoen, Minato-ku, Tokyo 105-8512, Japan
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36
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Galati F, Galati A, Massari S. Lack of Atorvastatin Protective Effect Against Atrial Fibrillation in CETP TaqIB2B2 Genotype. J Atr Fibrillation 2015; 8:1210. [PMID: 27957173 DOI: 10.4022/jafib.1210] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2015] [Revised: 05/23/2015] [Accepted: 05/25/2015] [Indexed: 11/10/2022]
Abstract
There has been some evidence for a role of statins in reducing the risk of atrial fibrillation, but the response to statin treatment varies considerably due to environmental and genetic factors. One of these is related to CETP expression. So we assessed whether CETP TaqIB polymorphism influences atrial fibrillation occurrence after treatment with statins. 200 unrelated dyslipidemic Caucasian patients (146 men and 54 women; mean age 75±8) from Salento (Southern Italy), assigned to atorvastatin treatment, and 158 normolipidemic subjects (119 men and 39 women; mean age 75±11), selected from the same ward, were enrolled. All patients were followed at six-month intervals. CETP TaqIB polymorphism was genotyped by RFLP-PCR. During a mean follow-up time of 71±6 months, 64 patients (32%) of the group treated with atorvastatin and 70 subjects (44%) of the group without atorvastatin experienced at least one episode of AF, with a statistically significant difference (p = 0,0208) between the two groups. No significant differences were observed between the two groups with regard to demographic and echocardiographic data, to clinical history and pharmacological treatment. While in patients not assuming atorvastatin there was no significant difference (p = 1) between TaqIB genotype and atrial fibrillation occurence, in subjects treated with atorvastatin B2B2 genotype was more frequent in patients with atrial fibrillation (p = 0,0001). According to these data the subjects with the B2B2 genotype seem to be more susceptible to atrial fibrillation development (RR 2,74; IC 95% 1,92-3,90; p<0.025). Our data seem to provide a further evidence for the hypothesis that statins may have adverse effect in subjects with genetically low CETP levels. Because statins reduce CETP activity up to 30%, we hypothesize that such CETP activity reduction by statins, in patients with low CETP levels induced by polymorphism, may counteract the beneficial effect of statins on atrial fibrillation.
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Affiliation(s)
- Francesca Galati
- Department of Biological and Environmental Sciences and Technologies - University of Salento, Lecce, Italy
| | - Antonio Galati
- Department of Cardiology - "Card. G. Panico" Hospital, Tricase, Lecce, Italy
| | - Serafina Massari
- Department of Biological and Environmental Sciences and Technologies - University of Salento, Lecce, Italy
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37
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Kuang Q, Purhonen P, Hebert H. Structure of potassium channels. Cell Mol Life Sci 2015; 72:3677-93. [PMID: 26070303 PMCID: PMC4565861 DOI: 10.1007/s00018-015-1948-5] [Citation(s) in RCA: 167] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2015] [Revised: 05/09/2015] [Accepted: 06/03/2015] [Indexed: 12/25/2022]
Abstract
Potassium channels ubiquitously exist in nearly all kingdoms of life and perform diverse but important functions. Since the first atomic structure of a prokaryotic potassium channel (KcsA, a channel from Streptomyces lividans) was determined, tremendous progress has been made in understanding the mechanism of potassium channels and channels conducting other ions. In this review, we discuss the structure of various kinds of potassium channels, including the potassium channel with the pore-forming domain only (KcsA), voltage-gated, inwardly rectifying, tandem pore domain, and ligand-gated ones. The general properties shared by all potassium channels are introduced first, followed by specific features in each class. Our purpose is to help readers to grasp the basic concepts, to be familiar with the property of the different domains, and to understand the structure and function of the potassium channels better.
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Affiliation(s)
- Qie Kuang
- Department of Biosciences and Nutrition, Karolinska Institutet, Novum, 14183, Huddinge, Sweden.
- School of Technology and Health, KTH Royal Institute of Technology, Novum, 14183, Huddinge, Sweden.
| | - Pasi Purhonen
- Department of Biosciences and Nutrition, Karolinska Institutet, Novum, 14183, Huddinge, Sweden
| | - Hans Hebert
- Department of Biosciences and Nutrition, Karolinska Institutet, Novum, 14183, Huddinge, Sweden
- School of Technology and Health, KTH Royal Institute of Technology, Novum, 14183, Huddinge, Sweden
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38
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Kitjaruwankul S, Boonamnaj P, Fuklang S, Supunyabut C, Sompornpisut P. Shaping the Water Crevice To Accommodate the Voltage Sensor in a Down Conformation: A Molecular Dynamics Simulation Study. J Phys Chem B 2015; 119:6516-24. [DOI: 10.1021/acs.jpcb.5b00787] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Sunan Kitjaruwankul
- Graduate
School of Nanoscience and Technology, Chulalongkorn University, Bangkok 10330, Thailand
| | - Panisak Boonamnaj
- Department
of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand
| | - Sunit Fuklang
- Department
of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand
| | - Chirayut Supunyabut
- Department
of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand
| | - Pornthep Sompornpisut
- Department
of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand
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39
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Adhya L, Mapder T, Adhya S. Effect of dielectric interface on charge aggregation in the voltage-gated K(+) ion channel. J Nat Sci Biol Med 2015; 6:188-97. [PMID: 25810659 PMCID: PMC4367034 DOI: 10.4103/0976-9668.149120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Background: There is experimental evidence of many cases of stable macromolecular conformations with charged amino-acids facing lipid, an arrangement thought to be energetically unfavourable. Methods and Objectives: Employing classical electrostatics, we show that, this is not necessarily the case and studied the physical basis of the specific role of proximity of charges to the dielectric interface between two different environments. We illustrate how self and induced energies due to the dielectric medium polarization, on either side of the interface, contribute differentially to the stability of a pair of charges and hence the mutual conformation of the S3b-S4 α-helix pair of the voltage-gated K+ channel. Results and Conclusion: We show that (1) a pair of opposite charges on either side of lipid-protein interface confers significant stability; (2) hydrophobic media has an important role in holding together two similar repelling charges; (3) dielectric interface has stabilizing effect on a pair of charges, when an ion is closer to its interface than its neighboring charge; (4) in spite of the presence of dielectric interface, there is a nonexistence of any dielectric effect, when an ion is equidistant from its image and neighboring charge. We also demonstrate that, variation in dielectric media of the surrounding environment confers new mutual conformations to S3b-S4 α-helices of voltage sensor domain at zero potential, especially lipid environment on the helix side, which improved stability to the configuration by lowering the potential energy. Our results provide an answer to the long standing question of why charges face hydrophobic lipid membranes in the stable conformation of a protein.
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Affiliation(s)
- Lipika Adhya
- Department of Engineering Physics, B. P. Poddar Institute of Management and Technology, Kolkata, West Bengal, India
| | - Tarunendu Mapder
- Department of Engineering Physics, B. P. Poddar Institute of Management and Technology, Kolkata, West Bengal, India
| | - Samit Adhya
- Department of Engineering Physics, B. P. Poddar Institute of Management and Technology, Kolkata, West Bengal, India
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40
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Abstract
Ion channels open and close in response to diverse stimuli, and the molecular events underlying these processes are extensively modulated by ligands of both endogenous and exogenous origin. In the past decade, high-resolution structures of several channel types have been solved, providing unprecedented details of the molecular architecture of these membrane proteins. Intrinsic conformational flexibility of ion channels critically governs their functions. However, the dynamics underlying gating mechanisms and modulations are obscured in the information from crystal structures. While nuclear magnetic resonance spectroscopic methods allow direct measurements of protein dynamics, they are limited by the large size of these membrane protein assemblies in detergent micelles or lipid membranes. Electron paramagnetic resonance (EPR) spectroscopy has emerged as a key biophysical tool to characterize structural dynamics of ion channels and to determine stimulus-driven conformational transition between functional states in a physiological environment. This review will provide an overview of the recent advances in the field of voltage- and ligand-gated channels and highlight some of the challenges and controversies surrounding the structural information available. It will discuss general methods used in site-directed spin labeling and EPR spectroscopy and illustrate how findings from these studies have narrowed the gap between high-resolution structures and gating mechanisms in membranes, and have thereby helped reconcile seemingly disparate models of ion channel function.
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41
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Assmann MA, Lenz P. Membrane tension influences the spike propagation between voltage-gated ion channel clusters of excitable membranes. Phys Biol 2014; 11:046006. [PMID: 25051247 DOI: 10.1088/1478-3975/11/4/046006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Ion channels of excitable membranes are known to be sensitive to various kinds of stimuli, but the case of simultaneous occurrence of different stimuli is poorly understood. Here, we theoretically analyze the influence of membrane tension on the dynamics of voltage-gated ion channels of excitable membranes. To do so, we develop a modification of the well-known Hodgkin-Huxley model to study numerically the spike generation and propagation in a single and two coupled excitable cells. We find that these cells can use membrane tension to trigger sub-threshold spike propagation, to suppress spike propagation and to alter the intensity of the signal transmission. These effects indicate that cells could use membrane tension to regulate cell-to-cell communication.
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Affiliation(s)
- Marcus-Alexander Assmann
- Department of Physics, Philipps-Universität Marburg, D-35032 Marburg, Germany. Center for Synthetic Microbiology, Philipps-Universität Marburg, D-35032 Marburg, Germany
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42
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Poveda J, Giudici A, Renart M, Molina M, Montoya E, Fernández-Carvajal A, Fernández-Ballester G, Encinar J, González-Ros J. Lipid modulation of ion channels through specific binding sites. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1838:1560-7. [DOI: 10.1016/j.bbamem.2013.10.023] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/19/2013] [Revised: 10/24/2013] [Accepted: 10/30/2013] [Indexed: 01/08/2023]
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43
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Zaydman MA, Cui J. PIP2 regulation of KCNQ channels: biophysical and molecular mechanisms for lipid modulation of voltage-dependent gating. Front Physiol 2014; 5:195. [PMID: 24904429 PMCID: PMC4034418 DOI: 10.3389/fphys.2014.00195] [Citation(s) in RCA: 93] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2014] [Accepted: 05/08/2014] [Indexed: 12/28/2022] Open
Abstract
Voltage-gated potassium (Kv) channels contain voltage-sensing (VSD) and pore-gate (PGD) structural domains. During voltage-dependent gating, conformational changes in the two domains are coupled giving rise to voltage-dependent opening of the channel. In addition to membrane voltage, KCNQ (Kv7) channel opening requires the membrane lipid phosphatidylinositol 4,5-bisphosphate (PIP2). Recent studies suggest that PIP2 serves as a cofactor to mediate VSD-PGD coupling in KCNQ1 channels. In this review, we put these findings in the context of the current understanding of voltage-dependent gating, lipid modulation of Kv channel activation, and PIP2-regulation of KCNQ channels. We suggest that lipid-mediated coupling of functional domains is a common mechanism among KCNQ channels that may be applicable to other Kv channels and membrane proteins.
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Affiliation(s)
- Mark A Zaydman
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Diseases, Cardiac Bioelectricity and Arrhythmia Center, Washington University in St. Louis St. Louis, MO, USA
| | - Jianmin Cui
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Diseases, Cardiac Bioelectricity and Arrhythmia Center, Washington University in St. Louis St. Louis, MO, USA
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44
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Galati F, Colonna P, Galati A, Ciardiello C, Bozzetti MP, Massari S. CETP TaqIB Polymorphism, Serum Lipid Levels And Risk Of Atrial Fibrillation: A Case-Control Study. J Atr Fibrillation 2014; 6:964. [PMID: 27957053 DOI: 10.4022/jafib.964] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2013] [Revised: 02/19/2014] [Accepted: 02/19/2014] [Indexed: 11/10/2022]
Abstract
The cholesteryl ester transfer protein (CETP) mediates the transfer of cholesteryl esters from high-density lipoproteins (HDL) to triglyceride (TG)-rich lipoproteins. A consistent number of investigations has suggested an association between the TaqIB polymorphism of the CETP gene, plasma HDL-C levels and the risk of cardiovascular disease, but the results are controversial. The aim of this study was to determine if the TaqIB polymorphism might be related to the presence of atrial fibrillation (AF). We conducted a case-control study, enrolling 109 Caucasian unrelated patients coming from Salento (Southern Italy) with documented AF and 109 controls selected from the same ward. The CETP TaqIB genotypes were determined by RFLP-PCR. The subjects with the B2B2 genotype seem to be more susceptible to AF development (OR=2.28, 95% CI 1.06-4.89, p=0.032). The AF incidence is higher if we consider only the female subgroup (OR=5.14, 95% CI 1.57-16.82, p=0.0061). In the AF female subgroup the B2B2 patients had a statistically significant decrease of HDL-C levels (1.50 ± 0.35 vs 2.07 ± 0.42; p=0.012) and statistically higher TG levels (1.34 ± 0.46 vs 0.77 ± 0.14; p=0.027) and TG/HDL-C ratio (2.14 ± 0.80 vs 0.88 ± 0.23; p=0.007) when compared to B2B2 female control subjects. When we analyzed the linkage between the TaqIB polymorphism and the promoter variant (-629C/A), we found that 100% of the B2 alleles of the TaqIB polymorphism were associated with the A alleles of the -629 promoter polymorphism in our subjects. This study suggests that in post-menopausal women atrial fibrillation could be promoted by the association of CETP B2B2/AA genotype with higher triglycerides values.
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Affiliation(s)
- Francesca Galati
- Department of Biological and Environmental Sciences and Technologies - University of Salento, Lecce, Italy
| | - Paolo Colonna
- Department of Cardiology - Policlinic Hospital, Bari, Italy
| | - Antonio Galati
- Department of Cardiology - "Card. G. Panico" Hospital, Tricase, Lecce, Italy
| | | | - Maria P Bozzetti
- Department of Biological and Environmental Sciences and Technologies - University of Salento, Lecce, Italy
| | - Serafina Massari
- Department of Biological and Environmental Sciences and Technologies - University of Salento, Lecce, Italy
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45
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Faure É, Thompson C, Blunck R. Do lipids show state-dependent affinity to the voltage-gated potassium channel KvAP? J Biol Chem 2014; 289:16452-61. [PMID: 24742679 DOI: 10.1074/jbc.m113.537134] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
As all integral membrane proteins, voltage-gated ion channels are embedded in a lipid matrix that regulates their channel behavior either by physicochemical properties or by direct binding. Because manipulation of the lipid composition in cells is difficult, we investigated the influence of different lipids on purified KvAP channels reconstituted in planar lipid bilayers of known composition. Lipids developed two distinct and independent effects on the KvAP channels; lipids interacting with the pore lowered the energy barriers for the final transitions, whereas voltage sensor-bound lipids shifted the midpoint of activation dependent on their electrostatic charge. Above all, the midpoint of activation was determined only by those lipids the channels came in contact with first after purification and can seemingly only be exchanged if the channel resides in the open state. The high affinity of the bound lipids to the binding site has implications not only on our understanding of the gating mechanism but also on the general experimental design of any lipid dependence study.
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Affiliation(s)
- Élise Faure
- Groupe d'étude des protéines membranaires (GÉPROM), Université de Montréal, Montréal CH3C 3J7, Canada Physiology
| | - Christine Thompson
- Groupe d'étude des protéines membranaires (GÉPROM), Université de Montréal, Montréal CH3C 3J7, CanadaFrom the Departments of Physics and
| | - Rikard Blunck
- Groupe d'étude des protéines membranaires (GÉPROM), Université de Montréal, Montréal CH3C 3J7, Canada Physiology, From the Departments of Physics and
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46
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Li Q, Wanderling S, Paduch M, Medovoy D, Singharoy A, McGreevy R, Villalba-Galea C, Hulse RE, Roux B, Schulten K, Kossiakoff A, Perozo E. Structural mechanism of voltage-dependent gating in an isolated voltage-sensing domain. Nat Struct Mol Biol 2014; 21:244-52. [PMID: 24487958 PMCID: PMC4116111 DOI: 10.1038/nsmb.2768] [Citation(s) in RCA: 191] [Impact Index Per Article: 19.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2013] [Accepted: 01/10/2014] [Indexed: 01/26/2023]
Abstract
The transduction of transmembrane electric fields into protein motion has an essential role in the generation and propagation of cellular signals. Voltage-sensing domains (VSDs) carry out these functions through reorientations of positive charges in the S4 helix. Here, we determined crystal structures of the Ciona intestinalis VSD (Ci-VSD) in putatively active and resting conformations. S4 undergoes an ~5-Å displacement along its main axis, accompanied by an ~60° rotation. This movement is stabilized by an exchange in countercharge partners in helices S1 and S3 that generates an estimated net charge transfer of ~1 eo. Gating charges move relative to a ''hydrophobic gasket' that electrically divides intra- and extracellular compartments. EPR spectroscopy confirms the limited nature of S4 movement in a membrane environment. These results provide an explicit mechanism for voltage sensing and set the basis for electromechanical coupling in voltage-dependent enzymes and ion channels.
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Affiliation(s)
- Qufei Li
- Department of Biochemistry and Molecular Biology, The University
of Chicago, Chicago, IL 60637, USA
| | - Sherry Wanderling
- Department of Biochemistry and Molecular Biology, The University
of Chicago, Chicago, IL 60637, USA
| | - Marcin Paduch
- Department of Biochemistry and Molecular Biology, The University
of Chicago, Chicago, IL 60637, USA
| | - David Medovoy
- Department of Biochemistry and Molecular Biology, The University
of Chicago, Chicago, IL 60637, USA
| | - Abhishek Singharoy
- Department of Physics and Beckman Institute, University of
Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Ryan McGreevy
- Department of Physics and Beckman Institute, University of
Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Carlos Villalba-Galea
- Department of Physiology and Biophysics, Virginia Commonwealth
University School of Medicine, Richmond, VA 23298, USA
| | - Raymond E. Hulse
- Department of Biochemistry and Molecular Biology, The University
of Chicago, Chicago, IL 60637, USA
| | - Benoit Roux
- Department of Biochemistry and Molecular Biology, The University
of Chicago, Chicago, IL 60637, USA
| | - Klaus Schulten
- Department of Physics and Beckman Institute, University of
Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Anthony Kossiakoff
- Department of Biochemistry and Molecular Biology, The University
of Chicago, Chicago, IL 60637, USA
| | - Eduardo Perozo
- Department of Biochemistry and Molecular Biology, The University
of Chicago, Chicago, IL 60637, USA
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47
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Zheng X, Dong S, Zheng J, Li D, Li F, Luo Z. Expression, stabilization and purification of membrane proteins via diverse protein synthesis systems and detergents involving cell-free associated with self-assembly peptide surfactants. Biotechnol Adv 2014; 32:564-74. [PMID: 24566241 DOI: 10.1016/j.biotechadv.2014.02.003] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2013] [Revised: 06/13/2013] [Accepted: 02/17/2014] [Indexed: 12/21/2022]
Abstract
G-protein coupled receptors (GPCRs) are involved in regulating most of physiological actions and metabolism in the bodies, which have become most frequently addressed therapeutic targets for various disorders and diseases. Purified GPCR-based drug discoveries have become routine that approaches to structural study, novel biophysical and biochemical function analyses. However, several bottlenecks that GPCR-directed drugs need to conquer the problems including overexpression, solubilization, and purification as well as stabilization. The breakthroughs are to obtain efficient protein yield and stabilize their functional conformation which are both urgently requiring of effective protein synthesis system methods and optimal surfactants. Cell-free protein synthesis system is superior to the high yields and post-translation modifications, and early signs of self-assembly peptide detergents also emerged to superiority in purification of membrane proteins. We herein focus several predominant protein synthesis systems and surfactants involving the novel peptide detergents, and uncover the advantages of cell-free protein synthesis system with self-assembling peptide detergents in purification of functional GPCRs. This review is useful to further study in membrane proteins as well as the new drug exploration.
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Affiliation(s)
- Xuan Zheng
- College of Basic Medical Sciences, Molecular Medicine and Cancer Research Center, Chongqing Medical University, Chongqing, China
| | - Shuangshuang Dong
- College of Basic Medical Sciences, Molecular Medicine and Cancer Research Center, Chongqing Medical University, Chongqing, China
| | - Jie Zheng
- College of laboratory Medicine, Chongqing Medical University, Chongqing, China
| | - Duanhua Li
- Sichuan Industrial Institute of Antibiotics, Chengdu University, Chengdu, China
| | - Feng Li
- China Tobacco Gene Research Center, Zhengzhou Tobacco Research Institute, Zhengzhou, China
| | - Zhongli Luo
- College of Basic Medical Sciences, Molecular Medicine and Cancer Research Center, Chongqing Medical University, Chongqing, China.
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48
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Li Q, Wanderling S, Sompornpisut P, Perozo E. Structural basis of lipid-driven conformational transitions in the KvAP voltage-sensing domain. Nat Struct Mol Biol 2014; 21:160-6. [PMID: 24413055 PMCID: PMC3946318 DOI: 10.1038/nsmb.2747] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2013] [Accepted: 11/14/2013] [Indexed: 11/30/2022]
Abstract
Voltage-gated ion channels respond to transmembrane electric fields through reorientations of the positively charged S4 helix within the voltage-sensing domain (VSD). Despite a wealth of structural and functional data, the details of this conformational change remain controversial. Recent electrophysiological evidence showed that equilibrium between the resting ('down') and activated ('up') conformations of the KvAP VSD from Aeropyrum pernix can be biased through reconstitution in lipids with or without phosphate groups. We investigated the structural transition between these functional states, using site-directed spin-labeling and EPR spectroscopic methods. Solvent accessibility and interhelical distance determinations suggest that KvAP gates through S4 movements involving an ∼3-Å upward tilt and simultaneous ∼2-Å axial shift. This motion leads to large accessibly changes in the intracellular water-filled crevice and supports a new model of gating that combines structural rearrangements and electric-field remodeling.
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Affiliation(s)
- Qufei Li
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois, USA
| | - Sherry Wanderling
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois, USA
| | - Pornthep Sompornpisut
- Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok, Thailand
| | - Eduardo Perozo
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois, USA
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49
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Vornanen M, Haverinen J, Egginton S. Acute heat tolerance of cardiac excitation in the brown trout (Salmo trutta fario). ACTA ACUST UNITED AC 2013; 217:299-309. [PMID: 24072804 DOI: 10.1242/jeb.091272] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The upper thermal tolerance and mechanisms of heat-induced cardiac failure in the brown trout (Salmo trutta fario) was examined. The point above which ion channel function and sinoatrial contractility in vitro, and electrocardiogram (ECG) in vivo, started to fail (break point temperature, BPT) was determined by acute temperature increases. In general, electrical excitation of the heart was most sensitive to heat in the intact animal (electrocardiogram, ECG) and least sensitive in isolated cardiac myocytes (ion currents). BPTs of Ca(2+) and K(+) currents of cardiac myocytes were much higher (>28°C) than BPT of in vivo heart rate (23.5 ± 0.6°C) (P<0.05). A striking exception among sarcolemmal ion conductances was the Na(+) current (INa), which was the most heat-sensitive molecular function, with a BPT of 20.9 ± 0.5°C. The low heat tolerance of INa was reflected as a low BPT for the rate of action potential upstroke in vitro (21.7 ± 1.2°C) and the velocity of impulse transmission in vivo (21.9 ± 2.2°C). These findings from different levels of biological organization strongly suggest that heat-dependent deterioration of Na(+) channel function disturbs normal spread of electrical excitation over the heart, leading to progressive variability of cardiac rhythmicity (missed beats, bursts of fast beating), reduction of heart rate and finally cessation of the normal heartbeat. Among the cardiac ion currents INa is 'the weakest link' and possibly a limiting factor for upper thermal tolerance of electrical excitation in the brown trout heart. Heat sensitivity of INa may result from functional requirements for very high flux rates and fast gating kinetics of the Na(+) channels, i.e. a trade-off between high catalytic activity and thermal stability.
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Affiliation(s)
- Matti Vornanen
- University of Eastern Finland, Department of Biology, PO Box 111, 80101 Joensuu, Finland
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Combs DJ, Shin HG, Xu Y, Ramu Y, Lu Z. Tuning voltage-gated channel activity and cellular excitability with a sphingomyelinase. ACTA ACUST UNITED AC 2013; 142:367-80. [PMID: 24043861 PMCID: PMC3787777 DOI: 10.1085/jgp.201310986] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Voltage-gated ion channels generate action potentials in excitable cells and help set the resting membrane potential in nonexcitable cells like lymphocytes. It has been difficult to investigate what kinds of phospholipids interact with these membrane proteins in their native environments and what functional impacts such interactions create. This problem might be circumvented if we could modify specific lipid types in situ. Using certain voltage-gated K(+) (KV) channels heterologously expressed in Xenopus laevis oocytes as a model, our group has shown previously that sphingomyelinase (SMase) D may serve this purpose. SMase D is known to remove the choline group from sphingomyelin, a phospholipid primarily present in the outer leaflet of plasma membranes. This SMase D action lowers the energy required for voltage sensors of a KV channel to enter the activated state, causing a hyperpolarizing shift of the Q-V and G-V curves and thus activating them at more hyperpolarized potentials. Here, we find that this SMase D effect vanishes after removing most of the voltage-sensor paddle sequence, a finding supporting the notion that SMase D modification of sphingomyelin molecules alters these lipids' interactions with voltage sensors. Then, using SMase D to probe lipid-channel interactions, we find that SMase D not only similarly stimulates voltage-gated Na(+) (Na(V)) and Ca(2+) channels but also markedly slows Na(V) channel inactivation. However, the latter effect is not observed in tested mammalian cells, an observation highlighting the profound impact of the membrane environment on channel function. Finally, we directly demonstrate that SMase D stimulates both native K(V)1.3 in nonexcitable human T lymphocytes at their typical resting membrane potential and native Na(V) channels in excitable cells, such that it shifts the action potential threshold in the hyperpolarized direction. These proof-of-concept studies illustrate that the voltage-gated channel activity in both excitable and nonexcitable cells can be tuned by enzymatically modifying lipid head groups.
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Affiliation(s)
- David J Combs
- Department of Physiology, Howard Hughes Medical Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104
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