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Raya-Sandino A, Lozada-Soto KM, Rajagopal N, Garcia-Hernandez V, Luissint AC, Brazil JC, Cui G, Koval M, Parkos CA, Nangia S, Nusrat A. Claudin-23 reshapes epithelial tight junction architecture to regulate barrier function. Nat Commun 2023; 14:6214. [PMID: 37798277 PMCID: PMC10556055 DOI: 10.1038/s41467-023-41999-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2022] [Accepted: 09/26/2023] [Indexed: 10/07/2023] Open
Abstract
Claudin family tight junction proteins form charge- and size-selective paracellular channels that regulate epithelial barrier function. In the gastrointestinal tract, barrier heterogeneity is attributed to differential claudin expression. Here, we show that claudin-23 (CLDN23) is enriched in luminal intestinal epithelial cells where it strengthens the epithelial barrier. Complementary approaches reveal that CLDN23 regulates paracellular ion and macromolecule permeability by associating with CLDN3 and CLDN4 and regulating their distribution in tight junctions. Computational modeling suggests that CLDN23 forms heteromeric and heterotypic complexes with CLDN3 and CLDN4 that have unique pore architecture and overall net charge. These computational simulation analyses further suggest that pore properties are interaction-dependent, since differently organized complexes with the same claudin stoichiometry form pores with unique architecture. Our findings provide insight into tight junction organization and propose a model whereby different claudins combine to form multiple distinct complexes that modify epithelial barrier function by altering tight junction structure.
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Affiliation(s)
- Arturo Raya-Sandino
- Department of Pathology, University of Michigan Medical School, Ann Arbor, MI, USA
| | | | - Nandhini Rajagopal
- Department of Biomedical and Chemical Engineering, Syracuse University, Syracuse, NY, USA
| | | | - Anny-Claude Luissint
- Department of Pathology, University of Michigan Medical School, Ann Arbor, MI, USA
| | - Jennifer C Brazil
- Department of Pathology, University of Michigan Medical School, Ann Arbor, MI, USA
| | - Guiying Cui
- Department of Pediatrics, Emory + Children's Center for Cystic Fibrosis and Airways Disease Research, Emory University School of Medicine, Atlanta, GA, USA
| | - Michael Koval
- Departments of Medicine and Cell Biology, Emory University School of Medicine, Atlanta, GA, USA
| | - Charles A Parkos
- Department of Pathology, University of Michigan Medical School, Ann Arbor, MI, USA
| | - Shikha Nangia
- Department of Biomedical and Chemical Engineering, Syracuse University, Syracuse, NY, USA.
| | - Asma Nusrat
- Department of Pathology, University of Michigan Medical School, Ann Arbor, MI, USA.
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2
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Kim S, Choi H, Kim B, Lim G, Kim T, Lee M, Ra H, Yeom J, Kim M, Kim E, Hwang J, Lee JS, Shim W. Extreme Ion-Transport Inorganic 2D Membranes for Nanofluidic Applications. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2023; 35:e2206354. [PMID: 36112951 DOI: 10.1002/adma.202206354] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/13/2022] [Revised: 08/28/2022] [Indexed: 06/15/2023]
Abstract
Inorganic 2D materials offer a new approach to controlling mass diffusion at the nanoscale. Controlling ion transport in nanofluidics is key to energy conversion, energy storage, water purification, and numerous other applications wherein persistent challenges for efficient separation must be addressed. The recent development of 2D membranes in the emerging field of energy harvesting, water desalination, and proton/Li-ion production in the context of green energy and environmental technology is herein discussed. The fundamental mechanisms, 2D membrane fabrication, and challenges toward practical applications are highlighted. Finally, the fundamental issues of thermodynamics and kinetics are outlined along with potential membrane designs that must be resolved to bridge the gap between lab-scale experiments and production levels.
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Affiliation(s)
- Sungsoon Kim
- Department of Materials Science and Engineering, Yonsei University, Seoul, 03722, Republic of Korea
- Center for Multi-Dimensional Materials, Yonsei University, Seoul, 03722, Republic of Korea
| | - Hong Choi
- Department of Materials Science and Engineering, Yonsei University, Seoul, 03722, Republic of Korea
- Center for Multi-Dimensional Materials, Yonsei University, Seoul, 03722, Republic of Korea
| | - Bokyeong Kim
- Department of Materials Science and Engineering, Yonsei University, Seoul, 03722, Republic of Korea
- Center for Multi-Dimensional Materials, Yonsei University, Seoul, 03722, Republic of Korea
| | - Geonwoo Lim
- Department of Materials Science and Engineering, Yonsei University, Seoul, 03722, Republic of Korea
- Center for Multi-Dimensional Materials, Yonsei University, Seoul, 03722, Republic of Korea
| | - Taehoon Kim
- Department of Materials Science and Engineering, Yonsei University, Seoul, 03722, Republic of Korea
- Center for Multi-Dimensional Materials, Yonsei University, Seoul, 03722, Republic of Korea
| | - Minwoo Lee
- Department of Materials Science and Engineering, Yonsei University, Seoul, 03722, Republic of Korea
- Center for Multi-Dimensional Materials, Yonsei University, Seoul, 03722, Republic of Korea
| | - Hansol Ra
- Department of Materials Science and Engineering, Yonsei University, Seoul, 03722, Republic of Korea
- Center for Multi-Dimensional Materials, Yonsei University, Seoul, 03722, Republic of Korea
| | - Jihun Yeom
- Department of Materials Science and Engineering, Yonsei University, Seoul, 03722, Republic of Korea
- Center for Multi-Dimensional Materials, Yonsei University, Seoul, 03722, Republic of Korea
| | - Minjun Kim
- Department of Materials Science and Engineering, Yonsei University, Seoul, 03722, Republic of Korea
- Center for Multi-Dimensional Materials, Yonsei University, Seoul, 03722, Republic of Korea
| | - Eohjin Kim
- Department of Materials Science and Engineering, Yonsei University, Seoul, 03722, Republic of Korea
- Center for Multi-Dimensional Materials, Yonsei University, Seoul, 03722, Republic of Korea
| | - Jiyoung Hwang
- Department of Materials Science and Engineering, Yonsei University, Seoul, 03722, Republic of Korea
- IT Materials Division, Advanced Materials Company, LG Chem R&D Campus, Daejeon, 34122, Republic of Korea
| | - Joo Sung Lee
- Separator Division, Advanced Materials Company, LG Chem R&D Campus, Daejeon, 34122, Republic of Korea
| | - Wooyoung Shim
- Department of Materials Science and Engineering, Yonsei University, Seoul, 03722, Republic of Korea
- Center for Multi-Dimensional Materials, Yonsei University, Seoul, 03722, Republic of Korea
- Center for NanoMedicine, Institute for Basic Science (IBS), Seoul, 03722, Republic of Korea
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3
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Park J, Bhoyate S, Kim YH, Kim YM, Lee YH, Conlin P, Cho K, Choi W. Unusually High Ion Conductivity in Large-Scale Patternable Two-Dimensional MoS 2 Film. ACS NANO 2021; 15:12267-12275. [PMID: 34184878 DOI: 10.1021/acsnano.1c04054] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
The advancement of ion transport applications will require the development of functional materials with a high ionic conductivity that is stable, scalable, and micro-patternable. We report unusually high ionic conductivity of Li+, Na+, and K+ in 2D MoS2 nanofilm exceeding 1 S/cm, which is more than 2 orders of magnitude higher when compared to that of conventional solid ionic materials. The high ion conductivity of different cations can be explained by the mitigated activation energy via percolative ion channels in 2H-MoS2, including the 1D ion channel at the grain boundary, as confirmed by modeling and analysis. We obtain field-effect modulation of ion transport with a high on/off ratio. The ion channel is large-scale patternable by conventional lithography, and the thickness can be tuned down to a single atomic layer. The findings yield insight into the ion transport mechanism of van der Waals solid materials and guide the development of future ionic devices owing to the facile and scalable device fabrication with superionic conductivity.
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Affiliation(s)
- Juhong Park
- Department of Materials Science and Engineering, University of North Texas, Denton, Texas 76203, United States
| | - Sanket Bhoyate
- Department of Materials Science and Engineering, University of North Texas, Denton, Texas 76203, United States
| | - Young-Hoon Kim
- Department of Energy Science, Sungkyunkwan University, Suwon 16419, Republic of Korea
| | - Young-Min Kim
- Department of Energy Science, Sungkyunkwan University, Suwon 16419, Republic of Korea
- Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Suwon 16419, Republic of Korea
| | - Young Hee Lee
- Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Suwon 16419, Republic of Korea
| | - Patrick Conlin
- Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75080, United States
| | - Kyeongjae Cho
- Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75080, United States
| | - Wonbong Choi
- Department of Materials Science and Engineering, University of North Texas, Denton, Texas 76203, United States
- Department of Mechanical and Energy Engineering, University of North Texas, Denton, Texas 76203, United States
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4
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Atobe M. Activation of Transient Receptor Potential Vanilloid (TRPV) 4 as a Therapeutic Strategy in Osteoarthritis. Curr Top Med Chem 2019; 19:2254-2267. [DOI: 10.2174/1568026619666191010162850] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2019] [Revised: 08/21/2019] [Accepted: 09/13/2019] [Indexed: 01/29/2023]
Abstract
Transient receptor potential vanilloid (TRPV) 4 belongs to the TRPV subfamily of TRP ion
channels. TRPV4 channels play a critical role in chondrocytes and thus TRPV4 is an attractive target of
Disease-Modifying Osteoarthritis Drugs (DMOADs). Initial investigations of small molecules by Glaxo
Smith Klein (GSK) as both agonists and antagonists via oral/intravenous administration have led to the
use of existing agonists as lead compounds for biological studies. Our recent results suggest that local
injection of a TRPV4 agonist is a potential treatment for osteoarthritis (OA). This review briefly summarizes
updates regarding TRPV4 agonists based on recent advances in drug discovery, and particularly
the local administration of TRPV4 agonists.
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Affiliation(s)
- Masakazu Atobe
- Laboratory for Medicinal Chemistry, Pharmaceutical Research Center, Asahi Kasei Pharma Corporation, 632-1 Mifuku, Izunokuni, Shizuoka 410-2321, Japan
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Luo Y, Marets N, Kato T. Selective lithium ion recognition in self-assembled columnar liquid crystals based on a lithium receptor. Chem Sci 2017; 9:608-616. [PMID: 29629125 PMCID: PMC5868304 DOI: 10.1039/c7sc03652c] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2017] [Accepted: 11/01/2017] [Indexed: 11/21/2022] Open
Abstract
Lithium is recognized as being significantly important due to its various applications in different areas especially in energy technology. In the present study, self-assembled nanostructured liquid-crystalline (LC) materials, that selectively bind lithium cations, have been developed for the first time. Wedge-shaped crown ether derivatives bearing dibenzo-14-crown-4 (DB14C4) or 12-crown-4 moieties are able to act as LC lithium-selective receptors. We have found that complexation of these receptors with lithium perchlorate induces liquid-crystalline columnar phases, while sodium perchlorate is immiscible with both receptors. Remarkably, a receptor consisting of DB14C4 as an effective lithium-selective ligand exhibits high selectivity for LiCl over NaCl, KCl, RbCl and CsCl. The lithium selectivity was demonstrated and investigated by 1H NMR, 1H COSY and FT-IR spectroscopic measurements. The preferred coordination number of four and the ideal cavity geometry of the DB14C4 moiety of the receptor are shown to be key factors for the high lithium selectivity. This new design of LC lithium-selective receptors opens unexplored paths for the development of methods to fabricate nanostructured materials for efficient selective lithium recognition.
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Affiliation(s)
- Yuan Luo
- Department of Chemistry and Biotechnology , School of Engineering , The University of Tokyo , Hongo, Bunkyo-ku , Tokyo 113-8656 , Japan .
| | - Nicolas Marets
- Department of Chemistry and Biotechnology , School of Engineering , The University of Tokyo , Hongo, Bunkyo-ku , Tokyo 113-8656 , Japan .
| | - Takashi Kato
- Department of Chemistry and Biotechnology , School of Engineering , The University of Tokyo , Hongo, Bunkyo-ku , Tokyo 113-8656 , Japan .
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6
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Kaufman IK, Fedorenko OA, Luchinsky DG, Gibby WA, Roberts SK, McClintock PV, Eisenberg RS. Ionic Coulomb blockade and anomalous mole fraction effect in the NaChBac bacterial ion channel and its charge-varied mutants. ACTA ACUST UNITED AC 2017. [DOI: 10.1051/epjnbp/2017003] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
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7
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Near-membrane electric field calcium ion dehydration. Cell Calcium 2016; 60:415-422. [DOI: 10.1016/j.ceca.2016.09.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2016] [Revised: 06/14/2016] [Accepted: 09/22/2016] [Indexed: 11/18/2022]
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8
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Voltage-gated calcium channels: Determinants of channel function and modulation by inorganic cations. Prog Neurobiol 2015; 129:1-36. [PMID: 25817891 DOI: 10.1016/j.pneurobio.2014.12.003] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2014] [Revised: 12/15/2014] [Accepted: 12/27/2014] [Indexed: 11/20/2022]
Abstract
Voltage-gated calcium channels (VGCCs) represent a key link between electrical signals and non-electrical processes, such as contraction, secretion and transcription. Evolved to achieve high rates of Ca(2+)-selective flux, they possess an elaborate mechanism for selection of Ca(2+) over foreign ions. It has been convincingly linked to competitive binding in the pore, but the fundamental question of how this is reconcilable with high rates of Ca(2+) transfer remains unanswered. By virtue of their similarity to Ca(2+), polyvalent cations can interfere with the function of VGCCs and have proven instrumental in probing the mechanisms underlying selective permeation. Recent emergence of crystallographic data on a set of Ca(2+)-selective model channels provides a structural framework for permeation in VGCCs, and warrants a reconsideration of their diverse modulation by polyvalent cations, which can be roughly separated into three general mechanisms: (I) long-range interactions with charged regions on the surface, affecting the local potential sensed by the channel or influencing voltage-sensor movement by repulsive forces (electrostatic effects), (II) short-range interactions with sites in the ion-conducting pathway, leading to physical obstruction of the channel (pore block), and in some cases (III) short-range interactions with extracellular binding sites, leading to non-electrostatic modifications of channel gating (allosteric effects). These effects, together with the underlying molecular modifications, provide valuable insights into the function of VGCCs, and have important physiological and pathophysiological implications. Allosteric suppression of some of the pore-forming Cavα1-subunits (Cav2.3, Cav3.2) by Zn(2+) and Cu(2+) may play a major role for the regulation of excitability by endogenous transition metal ions. The fact that these ions can often traverse VGCCs can contribute to the detrimental intracellular accumulation of metal ions following excessive release of endogenous Cu(2+) and Zn(2+) or exposure to non-physiological toxic metal ions.
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9
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Gillespie D, Xu L, Meissner G. Selecting ions by size in a calcium channel: the ryanodine receptor case study. Biophys J 2014; 107:2263-73. [PMID: 25418295 PMCID: PMC4241444 DOI: 10.1016/j.bpj.2014.09.031] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2014] [Revised: 09/25/2014] [Accepted: 09/30/2014] [Indexed: 10/24/2022] Open
Abstract
Many calcium channels can distinguish between ions of the same charge but different size. For example, when cations are in direct competition with each other, the ryanodine receptor (RyR) calcium channel preferentially conducts smaller cations such as Li(+) and Na(+) over larger ones such as K(+) and Cs(+). Here, we analyze the physical basis for this preference using a previously established model of RyR permeation and selectivity. Like other calcium channels, RyR has four aspartate residues in its GGGIGDE selectivity filter. These aspartates have their terminal carboxyl group in the pore lumen, which take up much of the available space for permeating ions. We find that small ions are preferred by RyR because they can fit into this crowded environment more easily.
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Affiliation(s)
- Dirk Gillespie
- Department of Molecular Biophysics and Physiology, Rush University Medical Center, Chicago, Illinois.
| | - Le Xu
- Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina
| | - Gerhard Meissner
- Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina
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10
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Wang XS, He D, Wylie JJ, Huang H. Singular perturbation solutions of steady-state Poisson-Nernst-Planck systems. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2014; 89:022722. [PMID: 25353523 DOI: 10.1103/physreve.89.022722] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/06/2013] [Indexed: 06/04/2023]
Abstract
We study the Poisson-Nernst-Planck (PNP) system with an arbitrary number of ion species with arbitrary valences in the absence of fixed charges. Assuming point charges and that the Debye length is small relative to the domain size, we derive an asymptotic formula for the steady-state solution by matching outer and boundary layer solutions. The case of two ionic species has been extensively studied, the uniqueness of the solution has been proved, and an explicit expression for the solution has been obtained. However, the case of three or more ions has received significantly less attention. Previous work has indicated that the solution may be nonunique and that even obtaining numerical solutions is a difficult task since one must solve complicated systems of nonlinear equations. By adopting a methodology that preserves the symmetries of the PNP system, we show that determining the outer solution effectively reduces to solving a single scalar transcendental equation. Due to the simple form of the transcendental equation, it can be solved numerically in a straightforward manner. Our methodology thus provides a standard procedure for solving the PNP system and we illustrate this by solving some practical examples. Despite the fact that for three ions, previous studies have indicated that multiple solutions may exist, we show that all except for one of these solutions are unphysical and thereby prove the existence and uniqueness for the three-ion case.
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Affiliation(s)
- Xiang-Sheng Wang
- Department of Mathematics, Southeast Missouri State University, Cape Girardeau, Missouri 63701, USA
| | - Dongdong He
- School of Aerospace Engineering and Applied Mechanics, Tongji University, Shanghai 200092, China
| | - Jonathan J Wylie
- Department of Mathematics, City University of Hong Kong, Tat Chee Avenue, Hong Kong
| | - Huaxiong Huang
- Department of Mathematics and Statistics, York University, Toronto, Ontario, Canada M3J 1P3
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11
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Finol-Urdaneta RK, Wang Y, Al-Sabi A, Zhao C, Noskov SY, French RJ. Sodium channel selectivity and conduction: prokaryotes have devised their own molecular strategy. ACTA ACUST UNITED AC 2014; 143:157-71. [PMID: 24420772 PMCID: PMC4001777 DOI: 10.1085/jgp.201311037] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The molecular strategy for alkali cation selectivity by a bacterial sodium channel resembles those of eukaryotic calcium and potassium channels, rather than those of eukaryotic sodium channels. Striking structural differences between voltage-gated sodium (Nav) channels from prokaryotes (homotetramers) and eukaryotes (asymmetric, four-domain proteins) suggest the likelihood of different molecular mechanisms for common functions. For these two channel families, our data show similar selectivity sequences among alkali cations (relative permeability, Pion/PNa) and asymmetric, bi-ionic reversal potentials when the Na/K gradient is reversed. We performed coordinated experimental and computational studies, respectively, on the prokaryotic Nav channels NaChBac and NavAb. NaChBac shows an “anomalous,” nonmonotonic mole-fraction dependence in the presence of certain sodium–potassium mixtures; to our knowledge, no comparable observation has been reported for eukaryotic Nav channels. NaChBac’s preferential selectivity for sodium is reduced either by partial titration of its highly charged selectivity filter, when extracellular pH is lowered from 7.4 to 5.8, or by perturbation—likely steric—associated with a nominally electro-neutral substitution in the selectivity filter (E191D). Although no single molecular feature or energetic parameter appears to dominate, our atomistic simulations, based on the published NavAb crystal structure, revealed factors that may contribute to the normally observed selectivity for Na over K. These include: (a) a thermodynamic penalty to exchange one K+ for one Na+ in the wild-type (WT) channel, increasing the relative likelihood of Na+ occupying the binding site; (b) a small tendency toward weaker ion binding to the selectivity filter in Na–K mixtures, consistent with the higher conductance observed with both sodium and potassium present; and (c) integrated 1-D potentials of mean force for sodium or potassium movement that show less separation for the less selective E/D mutant than for WT. Overall, tight binding of a single favored ion to the selectivity filter, together with crucial inter-ion interactions within the pore, suggests that prokaryotic Nav channels use a selective strategy more akin to those of eukaryotic calcium and potassium channels than that of eukaryotic Nav channels.
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Affiliation(s)
- Rocio K Finol-Urdaneta
- Department of Physiology and Pharmacology, 2 Hotchkiss Brain Institute, and 3 Department of Biological Sciences, Institute for Biocomplexity and Informatics, University of Calgary, Calgary, Alberta T2N 4N1, Canada
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12
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Liu JL, Eisenberg B. Correlated Ions in a Calcium Channel Model: A Poisson–Fermi Theory. J Phys Chem B 2013; 117:12051-8. [DOI: 10.1021/jp408330f] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Jinn-Liang Liu
- Department of Applied Mathematics, National Hsinchu University of Education, Hsinchu 300, Taiwan
| | - Bob Eisenberg
- Department of Molecular Biophysics
and Physiology, Rush University, 1653 West Congress Parkway, Chicago, Illinois 60612, United States
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13
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Eisenberg B. Interacting ions in biophysics: real is not ideal. Biophys J 2013; 104:1849-66. [PMID: 23663828 PMCID: PMC3647150 DOI: 10.1016/j.bpj.2013.03.049] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2012] [Revised: 03/03/2013] [Accepted: 03/27/2013] [Indexed: 11/28/2022] Open
Abstract
Ions in water are important throughout biology, from molecules to organs. Classically, ions in water were treated as ideal noninteracting particles in a perfect gas. Excess free energy of each ion was zero. Mathematics was not available to deal consistently with flows, or interactions with other ions or boundaries. Nonclassical approaches are needed because ions in biological conditions flow and interact. The concentration gradient of one ion can drive the flow of another, even in a bulk solution. A variational multiscale approach is needed to deal with interactions and flow. The recently developed energetic variational approach to dissipative systems allows mathematically consistent treatment of the bio-ions Na(+), K(+), Ca(2+), and Cl(-) as they interact and flow. Interactions produce large excess free energy that dominate the properties of the high concentration of ions in and near protein active sites, ion channels, and nucleic acids: the number density of ions is often >10 M. Ions in such crowded quarters interact strongly with each other as well as with the surrounding protein. Nonideal behavior found in many experiments has classically been ascribed to allosteric interactions mediated by the protein and its conformation changes. The ion-ion interactions present in crowded solutions-independent of conformation changes of the protein-are likely to change the interpretation of many allosteric phenomena. Computation of all atoms is a popular alternative to the multiscale approach. Such computations involve formidable challenges. Biological systems exist on very different scales from atomic motion. Biological systems exist in ionic mixtures (like extracellular and intracellular solutions), and usually involve flow and trace concentrations of messenger ions (e.g., 10(-7) M Ca(2+)). Energetic variational methods can deal with these characteristic properties of biological systems as we await the maturation and calibration of all-atom simulations of ionic mixtures and divalents.
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Affiliation(s)
- Bob Eisenberg
- Department of Molecular Biophysics Rush University, Chicago Illinois, USA.
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14
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Abstract
Ionic solutions are dominated by interactions because they must be electrically neutral, but classical theory assumes no interactions. Biological solutions are rather like seawater, concentrated enough so that the diameter of ions also produces important interactions. In my view, the theory of complex fluids is needed to deal with the interacting reality of biological solutions.
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Affiliation(s)
- Bob Eisenberg
- Department of Molecular Biophysics and Physiology, Rush University, Chicago, Illinois
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15
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Eisenberg B. Ionic interactions in biological and physical systems: a variational treatment. Faraday Discuss 2013; 160:279-96; discussion 311-27. [DOI: 10.1039/c2fd20066j] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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16
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Finnerty JJ, Eisenberg R, Carloni P. Localizing the Charged Side Chains of Ion Channels within the Crowded Charge Models. J Chem Theory Comput 2012; 9:766-73. [DOI: 10.1021/ct300768j] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Justin J. Finnerty
- Computational Biophysics, German
Research School for Simulation Sciences, 52425 Jülich, Germany
| | - Robert Eisenberg
- Department of Molecular Biophysics
and Physiology, Rush University, Chicago, Illinois 60612, United States
| | - Paolo Carloni
- Computational Biophysics, German
Research School for Simulation Sciences, 52425 Jülich, Germany
and Institute for Advanced Simulation IAS-5, Computational Biomedicine,
Forschungszentrum Jülich, 52425 Jülich, Germany
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17
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Horng TL, Lin TC, Liu C, Eisenberg B. PNP Equations with Steric Effects: A Model of Ion Flow through Channels. J Phys Chem B 2012; 116:11422-41. [DOI: 10.1021/jp305273n] [Citation(s) in RCA: 118] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Affiliation(s)
- Tzyy-Leng Horng
- Department of Applied Mathematics, Feng Chia University, 100 Wen-Hwa Road, Taichung, Taiwan
40724
| | - Tai-Chia Lin
- Department of Mathematics, Taida Institute for Mathematical
Sciences (TIMS), No. 1, Sec. 4, National Taiwan University, Roosevelt Road, Taipei 106, Taiwan
| | - Chun Liu
- Department of Mathematics, Pennsylvania State University University Park, Pennsylvania 16802,
United States
| | - Bob Eisenberg
- Department of Molecular Biophysics and Physiology, Rush University, 1653 West Congress Parkway, Chicago,
Illinois 60612, United States
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18
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Dudev T, Lim C. Competition among Ca2+, Mg2+, and Na+ for model ion channel selectivity filters: determinants of ion selectivity. J Phys Chem B 2012; 116:10703-14. [PMID: 22889116 DOI: 10.1021/jp304925a] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Because voltage-gated ion channels play critical biological roles, understanding how they can discriminate the native metal ion from rival cations in the milieu is of great interest. Although Ca(2+), Mg(2+), and Na(+) are present in comparable concentrations outside the cell, the factors governing the competition among these cations for the selectivity filter of voltage-gated Ca(2+) ion channel remain unclear. Using density functional theory combined with continuum dielectric methods, we evaluate the effect of (1) the number, chemical type, and charge of the ligands lining the pore, (2) the pore's rigidity, size, symmetry, and solvent accessibility, and (3) the Ca(2+) hydration number outside the selectivity filter on the competition among Ca(2+), Mg(2+), and Na(+) in model selectivity filters. The calculations show how the outcome of this competition depends on the interplay between electronic and solvation effects. Selectivity for monovalent Na(+) over divalent Ca(2+)/Mg(2+) is achieved when solvation effects outweigh electrostatic effects; thus filters comprising a few weak charge-donating groups such as Ser/Thr side chains, where electrostatic effects are relatively weak and are easily overcome by solvation effects, are Na(+)-selective. In contrast, selectivity for divalent Ca(2+)/Mg(2+) over monovalent Na(+) is achieved when metal-ligand electrostatic effects outweigh solvation effects. The key differences in selectivity between Mg(2+) and Ca(2+) lie in the pore size, oligomericity, and solvent accessibility. The results, which are consistent with available experimental data, reveal how the structure and composition of the ion channel selectivity pore had adapted to the specific physicochemical properties of the native metal ion to enhance the competitiveness of the native metal toward rival cations.
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Affiliation(s)
- Todor Dudev
- Institute of Biomedical Sciences, Academia Sinica, Taipei 115, Taiwan
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Reimold FR, Heneghan JF, Stewart AK, Zelikovic I, Vandorpe DH, Shmukler BE, Alper SL. Pendrin function and regulation in Xenopus oocytes. Cell Physiol Biochem 2011; 28:435-50. [PMID: 22116357 DOI: 10.1159/000335106] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/19/2011] [Indexed: 01/24/2023] Open
Abstract
SLC26A4/PDS mutations cause Pendred Syndrome and non-syndromic deafness. but some aspects of function and regulation of the SLC26A4 polypeptide gene product, pendrin, remain controversial or incompletely understood. We have therefore extended the functional analysis of wildtype and mutant pendrin in Xenopus oocytes, with studies of isotopic flux, electrophysiology, and protein localization. Pendrin mediated electroneutral, pH-insensitive, DIDS-insensitive anion exchange, with extracellular K((1/2)) (in mM) of 1.9 (Cl(-)), 1.8 (I(-)), and 0.9 (Br(-)). The unusual phenotype of Pendred Syndrome mutation E303Q (loss-of-function with normal surface expression) prompted systematic mutagenesis at position 303. Only mutant E303K exhibited loss-of-function unrescued by forced overexpression. Mutant E303C was insensitive to charge modification by methanethiosulfonates. The corresponding mutants SLC26A2 E336Q, SLC26A3 E293Q, and SLC26A6 E298Q exhibited similar loss-of-function phenotypes, with wildtype surface expression also documented for SLC26A2 E336Q. The strong inhibition of wildtype SLC26A2, SLC26A3, and SLC26A6 by phorbol ester contrasts with its modest inhibition of pendrin. Phorbol ester inhibition of SLC26A2, SLC26A3, and SLC26A6 was blocked by coexpressed kinase-dead PKCδ but was without effect on pendrin. Mutation of SLC26A2 serine residues conserved in PKCδ -sensitive SLC26 proteins but absent from pendrin failed to reduce PKCδ sensitivity of SLC26A2 (190).
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Affiliation(s)
- Fabian R Reimold
- Renal Division and Molecular and Vascular Medicine Unit, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA
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Csányi E, Boda D, Gillespie D, Kristóf T. Current and selectivity in a model sodium channel under physiological conditions: Dynamic Monte Carlo simulations. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1818:592-600. [PMID: 22080102 DOI: 10.1016/j.bbamem.2011.10.029] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/02/2011] [Revised: 10/06/2011] [Accepted: 10/26/2011] [Indexed: 11/15/2022]
Abstract
A reduced model of a sodium channel is analyzed using Dynamic Monte Carlo simulations. These include the first simulations of ionic current under approximately physiological ionic conditions through a model sodium channel and an analysis of how mutations of the sodium channel's DEKA selectivity filter motif transform the channel from being Na(+) selective to being Ca(2+) selective. Even though the model of the pore, amino acids, and permeant ions is simplified, the model reproduces the fundamental properties of a sodium channel (e.g., 10 to 1 Na(+) over K(+) selectivity, Ca(2+) exclusion, and Ca(2+) selectivity after several point mutations). In this model pore, ions move through the pore one at a time by simple diffusion and Na(+) versus K(+) selectivity is due to both the larger K(+) not fitting well into the selectivity filter that contains amino acid terminal groups and K(+) moving more slowly (compared to Na(+)) when it is in the selectivity filter.
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Affiliation(s)
- Eva Csányi
- Department of Physical Chemistry, University of Pannonia, Veszprém, Hungary
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