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Villanelo F, Minogue PJ, Maripillán J, Reyna-Jeldes M, Jensen-Flores J, García IE, Beyer EC, Pérez-Acle T, Berthoud VM, Martínez AD. Connexin channels and hemichannels are modulated differently by charge reversal at residues forming the intracellular pocket. Biol Res 2024; 57:31. [PMID: 38783330 PMCID: PMC11112876 DOI: 10.1186/s40659-024-00501-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2023] [Accepted: 04/16/2024] [Indexed: 05/25/2024] Open
Abstract
BACKGROUND Members of the β-subfamily of connexins contain an intracellular pocket surrounded by amino acid residues from the four transmembrane helices. The presence of this pocket has not previously been investigated in members of the α-, γ-, δ-, and ε-subfamilies. We studied connexin50 (Cx50) as a representative of the α-subfamily, because its structure has been determined and mutations of Cx50 are among the most common genetic causes of congenital cataracts. METHODS To investigate the presence and function of the intracellular pocket in Cx50 we used molecular dynamics simulation, site-directed mutagenesis, gap junction tracer intercellular transfer, and hemichannel activity detected by electrophysiology and by permeation of charged molecules. RESULTS Employing molecular dynamics, we determined the presence of the intracellular pocket in Cx50 hemichannels and identified the amino acids participating in its formation. We utilized site-directed mutagenesis to alter a salt-bridge interaction that supports the intracellular pocket and occurs between two residues highly conserved in the connexin family, R33 and E162. Substitution of opposite charges at either position decreased formation of gap junctional plaques and cell-cell communication and modestly reduced hemichannel currents. Simultaneous charge reversal at these positions produced plaque-forming non-functional gap junction channels with highly active hemichannels. CONCLUSIONS These results show that interactions within the intracellular pocket influence both gap junction channel and hemichannel functions. Disruption of these interactions may be responsible for diseases associated with mutations at these positions.
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Affiliation(s)
- Felipe Villanelo
- Computational Biology Lab, Centro Basal Ciencia & Vida, Santiago, 8580702, Chile
- Facultad de Ingeniería, Arquitectura y Diseño, Universidad San Sebastián, Bellavista 7, Recoleta, Santiago, Chile
| | - Peter J Minogue
- Department of Pediatrics, University of Chicago, Chicago, IL, 60637, USA
| | - Jaime Maripillán
- Facultad de Ciencias, Centro Interdisciplinario de Neurociencias de Valparaíso, Instituto de Neurociencia, Universidad de Valparaíso, Valparaíso, Chile
| | - Mauricio Reyna-Jeldes
- Facultad de Ciencias, Centro Interdisciplinario de Neurociencias de Valparaíso, Instituto de Neurociencia, Universidad de Valparaíso, Valparaíso, Chile
| | - Joaquin Jensen-Flores
- Computational Biology Lab, Centro Basal Ciencia & Vida, Santiago, 8580702, Chile
- Facultad de Ingeniería, Arquitectura y Diseño, Universidad San Sebastián, Bellavista 7, Recoleta, Santiago, Chile
| | - Isaac E García
- Facultad de Ciencias, Centro Interdisciplinario de Neurociencias de Valparaíso, Instituto de Neurociencia, Universidad de Valparaíso, Valparaíso, Chile
- Laboratorio de Fisiología Molecular y Biofísica, Facultad de Odontología, Universidad de Valparaíso, Valparaíso, Chile
- Centro de Investigación en Ciencias Odontológicas y Médicas, Universidad de Valparaíso, Valparaíso, Chile
| | - Eric C Beyer
- Department of Pediatrics, University of Chicago, Chicago, IL, 60637, USA
| | - Tomás Pérez-Acle
- Computational Biology Lab, Centro Basal Ciencia & Vida, Santiago, 8580702, Chile
- Facultad de Ingeniería, Arquitectura y Diseño, Universidad San Sebastián, Bellavista 7, Recoleta, Santiago, Chile
| | - Viviana M Berthoud
- Department of Pediatrics, University of Chicago, Chicago, IL, 60637, USA.
| | - Agustín D Martínez
- Facultad de Ciencias, Centro Interdisciplinario de Neurociencias de Valparaíso, Instituto de Neurociencia, Universidad de Valparaíso, Valparaíso, Chile.
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Dixit M, Hajari T, Meti MD, Srivastava S, Srivastava A, Daniel J. Ionic Pairing and Selective Solvation of Butylmethylimidazolium Chloride Ion Pairs in DMSO-Water Mixtures: A Comprehensive Examination via Molecular Dynamics Simulations and Potentials of Mean Force Analysis. J Phys Chem B 2024; 128:2168-2180. [PMID: 38415290 DOI: 10.1021/acs.jpcb.3c06876] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/29/2024]
Abstract
Ionic liquids (ILs) with dimethyl sulfoxide (DMSO) and water act as a promising solvent medium for the dissolution of cellulose in an efficient manner. To develop a proper solvent system, it is really important to understand the thermodynamics of the molecular solutions consisting of ILs, DMSO, and water. The ion-pairing propensity of the ILs in the presence of DMSO and water plays a crucial role in governing the property of the solvent mixtures. Employing all-atom molecular dynamics simulations, we estimate the potentials of mean force between BMIM+ and Cl- ions in DMSO-water mixtures. Analysis reveals a significant increase in the thermodynamic stability of both contact ion pair (CIP) and solvent-assisted ion pair (SAIP) states with a rising DMSO mole fraction. Thermodynamic assessments highlight the entropic stabilization of CIP states and SAIP states in pure water, in DMSO-water mixtures, and in pure DMSO. The structural analysis reveals that in comparison to the DMSO local density, the local water density is relatively very high around ion pairs, more specifically in the solvation shell of a chloride ion. Preferential binding coefficients also consistently indicate exclusion of DMSO from the ion pair in DMSO-water mixtures. To enhance our understanding regarding the solvent molecules kinetics around the ion pairs, the survival probabilities of DMSO and water are computed. The calculations reveal that the water molecules prefer a prolonged stay in the solvation shell of Cl- ions.
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Affiliation(s)
- Mayank Dixit
- Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan
| | - Timir Hajari
- Department of Chemistry, City College, 102/1, Raja Rammohan Sarani, Kolkata - 700009, India
| | - Manjunath D Meti
- Bio-physical Laboratory, Department of Plant Sciences, School of Life Sciences, University of Hyderabad, Hyderabad, Telangana 500046, India
| | - Srishti Srivastava
- Department of Zoology, Allahabad University, Prayagraj, Uttar Pradesh 211002, India
| | - Amar Srivastava
- Chemistry Department, Har Sahai (PG) College, Kanpur, Uttar Pradesh 208012, India
| | - Joseph Daniel
- Department of Chemistry, Christ Church College, Kanpur 208001, India
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3
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Dixit M, Taniguchi T. Role of Terminal Groups of cis-1,4-Polyisoprene Chains in the Formation of Physical Junction Points in Natural Rubber. Biomacromolecules 2023; 24:3589-3602. [PMID: 37527033 DOI: 10.1021/acs.biomac.3c00355] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/03/2023]
Abstract
The terminal structures of cis-1,4-polyisoprene (PI) chains play a vital role in the excellent comprehensive performance of Hevea natural rubber (NR) with properties such as high toughness, tear-resistance, and wet skid resistance. The cis-1,4-polyisoprene chain constituting NR exhibits a distinct composition of terminal groups comprising two distinct types, namely, the ω and α terminal groups. The structures of the ω terminal [dimethyl allyl (DMA)-(trans-1,4-isoprene)2] and six kinds of α end groups of the polymer chain of NR have been explored by utilizing a newly developed 2D NMR method. In the present work, we examine different kinds of PI melt systems, and we choose various combinations of terminal groups: Hydrogen, one DMA unit with two trans isoprene units as ω end groups and ester-terminated isopentene (α1), hydroxy-terminated isopentene (α2), ester-terminated isobutane (α3), hydroxy-terminated isobutane (α4), ester-terminated 1,4-cis-isoprene (α5), and hydroxy-terminated 1,4-cis-isoprene (α6), i.e., HPIH (PI0)-pure PI (Hydrogen terminal), ωPIα1 (PII), ωPIα2 (PIII), ωPIα3 (PIIII), ωPIα4 (PIIV), ωPIα5 (PIV), and ωPIα6 (PIVI). We evaluated dynamic and static properties of PI chains such as the end-to-end vector autocorrelation function (C(t)), its average relaxation time (τ), end-to-end distance (Ree), and radius of gyration (Rg). We also estimated the diffusion coefficients of polyisoprene chains and pair correlation functions [radial distribution functions (RDFs)], potentials of mean force (PMFs) in between end residues, and survival probability (P(τ)) of end groups around the end group by analyzing the equilibrated trajectories of full-atom MD simulations. As per the examination of C(t), rotational relaxation time τ, and RDFs, we discovered that the existence of a strong hydrogen bond in α2-α2, α4-α4, and α6-α6 residues makes the dynamics of hydroxy-terminated polyisoprene chains in ωPIα2,α4,α6 melt systems slower. From the analyses of RDFs and PMFs (W(r)), the association between [α2]-[α2], [α4]-[α4], and [α6]-[α6] terminals in ωPIα2,α4,α6 melt systems is significantly stronger than in [ISO]-[ISO] [Hydrogen terminated 1,4-cis-isoprene:(ISO)] in HPIH and ω-ω, [α1]-[α1], [α3]-[α3], and [α5]-[α5] in ωPIα1,α3,α5 systems. We quantified the fraction of cluster formation of terminal groups of a given size in the seven PI melt systems by employing the criteria of PMFs. It is revealed that no stable cluster exists in the HPIH, ωPIα1, ωPIα3, and ωPIα5 melt systems. Conversely, in the ωPIα2, ωPIα4, and ωPIα6 systems, we perceived stable clusters of [(α2)p] [(α4)p] and [(α6)p] end groups where p (2 ≤ x ≤ 6). These stable clusters validate the presence of physical junction points in between hydroxy-terminated polyisoprene chains through their α2, α4, and α6 terminals. These physical junction points might be crucial for superior properties of NR such as high toughness, crack growth resistance, and strain-induced crystallization.
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Affiliation(s)
- Mayank Dixit
- Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan
| | - Takashi Taniguchi
- Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan
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Dixit M, Taniguchi T. Substantial Effect of Terminal Groups in cis-Polyisoprene: A Multiscale Molecular Dynamics Simulation Study. Macromolecules 2022. [DOI: 10.1021/acs.macromol.2c01414] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Mayank Dixit
- Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan
| | - Takashi Taniguchi
- Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan
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5
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Ghasemi M, Shafiei A, Foroozesh J. A systematic and critical review of application of molecular dynamics simulation in low salinity water injection. Adv Colloid Interface Sci 2022; 300:102594. [PMID: 34971915 DOI: 10.1016/j.cis.2021.102594] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2021] [Revised: 11/24/2021] [Accepted: 12/20/2021] [Indexed: 01/29/2023]
Abstract
Low Salinity Water Injection (LSWI) has been a well-researched EOR method, with several experimental and theoretical scientific papers reported in the literature over the past few decades. Despite this, there is still an ongoing debate on dominant mechanisms behind this complex EOR process, and some issues remain elusive. Part of the complexity arises from the scale of investigation, which spans from sub-pore scale (atomic and electronic scale) to pore scale, core scale, and reservoir scale. Molecular Dynamics (MD) simulation has been used as a research tool in the past decade to investigate the nano-scale interactions among reservoir rock (e.g., calcite, silica), crude oil, and brine systems in presence of some impurities (e.g., clay minerals) and additives (e.g., nanoparticles). In this paper, fundamental concepts of MD simulation and common analyses driven by MD are briefly reviewed. Then, an overview of molecular models of the most common minerals encountered in petroleum reservoirs: quartz, calcite, and clay, with their most common types of potential function, is provided. Next, a critical review and in depth analysis of application of MD simulations in LSWI process in both sandstone and carbonate reservoirs in terms of sub-pore scale mechanisms, namely electrical double layer (EDL) expansion, multi-ion exchange (MIE), and cation hydration, is presented to scrutinize role of salinity, ionic composition, and rock surface chemistry from an atomic level. Some inconsistencies observed in the literature are also highlighted and the reasons behind them are explained. Finally, a future research guide is provided after critically discussing the challenges and potential of the MD in LSWI to shed more light on governing mechanisms behind LSWI by enhancing the reliability of MD outcomes in future researches. Such insights can be used for design of new MD researches with complementary experimental studies at core scale to capture the main mechanisms behind LSWI.
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Affiliation(s)
- Mehdi Ghasemi
- Petroleum Engineering Program, School of Mining & Geosciences, Nazarbayev University, Nur-Sultan, 010000, Kazakhstan
| | - Ali Shafiei
- Petroleum Engineering Program, School of Mining & Geosciences, Nazarbayev University, Nur-Sultan, 010000, Kazakhstan.
| | - Jalal Foroozesh
- Senior Lecturer, School of Energy and Electronic Engineering, University of Portsmouth, Portsmouth, UK
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6
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Leo L, Bridelli MG, Polverini E. Reversible processes in collagen dehydration: A molecular dynamics study. Arch Biochem Biophys 2021; 714:109079. [PMID: 34748734 DOI: 10.1016/j.abb.2021.109079] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2021] [Revised: 10/11/2021] [Accepted: 11/01/2021] [Indexed: 11/18/2022]
Abstract
Collagen dehydration is an unavoidable damaging process that causes the lack of fibers' physical properties and it is usually irreversible. However, the identification of low hydration conditions that permit a recovering of initial collagen features after a rehydration treatment is particularly of interest. Monitoring structural changes by means of MD simulations, we investigated the hydration-dehydration-rehydration cycle of two microfibril models built on different fragments of the sequence of rat tail collagen type I. The microfibrils have different hydropathic features, to investigate the influence of amino acid composition on the whole process. We showed that with low hydration at a level corresponding to the first shell, microfibril gains in compactness and tubularity. Crucially, some water molecules remain trapped inside the fibrils, allowing, by rehydrating, a recovery of the initial collagen structural features. Water rearranges in cluster around the protein, and its first layer is more anchored to the surface. However, these changes in distribution and mobility in low hydration conditions get back with rehydration.
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Affiliation(s)
- Ludovica Leo
- Department of Mathematical, Physical and Computer Science, University of Parma, Parco Area Delle Scienze, 7/A, 43124, Parma, Italy.
| | - Maria Grazia Bridelli
- Department of Mathematical, Physical and Computer Science, University of Parma, Parco Area Delle Scienze, 7/A, 43124, Parma, Italy.
| | - Eugenia Polverini
- Department of Mathematical, Physical and Computer Science, University of Parma, Parco Area Delle Scienze, 7/A, 43124, Parma, Italy.
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7
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Rustam S, Intan NN, Pfaendtner J. Effect of graphitic anode surface functionalization on the structure and dynamics of electrolytes at the interface. J Chem Phys 2021; 155:134702. [PMID: 34624985 DOI: 10.1063/5.0066268] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Surface termination on a graphitic surface and the type of electrolytes in lithium-ion batteries (LIBs) play an important part in determining the structure, composition, and thus, the quality of the emergent solid electrolyte interphase. In this paper, we analyze the structure and dynamics of electrolyte molecules in multi-component electrolyte with varying species compositions combinatorially paired with four different graphitic surfaces terminated with hydrogen, hydroxyl, carbonyl, and carboxyl to explore the interplay between surface chemistry and electrolyte dynamics at electrode/electrolyte interfaces. Addition of dimethyl carbonate and fluoroethylene carbonate brought substantial changes in the ethylene carbonate (EC) and LiPF6 surface population density for hydroxyl and carbonyl surfaces. Strong density oscillation and drastic slowing of the dynamics of the electrolyte molecules at the interface are reported for all the systems. While these observations are universal, carboxyl surfaces have the strongest local and long-range effects. Characterization of the average dipole direction at the interface shows strong orientational preferences of ethylene carbonate molecules. EC molecules are preferred to be oriented either almost parallel or perpendicular to the hydroxyl surface, are tilted between parallel and perpendicular with a higher angle of incidence of the dipole vs surface normal on the carbonyl surface than on the hydroxyl surface, and are oriented perpendicularly against the carboxyl surface. These differences highlight the significant effect of graphite surface termination on the dynamics of the electrolytes and provide insight into the complex interplays between electrolyte species and graphite anode in LIBs.
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Affiliation(s)
- Sabiha Rustam
- Department of Chemical Engineering, University of Washington, Seattle, Washington 98195, USA
| | - Nadia N Intan
- Department of Chemical Engineering, University of Washington, Seattle, Washington 98195, USA
| | - Jim Pfaendtner
- Department of Chemical Engineering, University of Washington, Seattle, Washington 98195, USA
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8
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Villanelo F, Carrasco J, Jensen-Flores J, Garate JA, Perez-Acle T. Simulations on Simple Models of Connexin Hemichannels Indicate That Ca 2+ Blocking Is Not a Pure Electrostatic Effect. MEMBRANES 2021; 11:372. [PMID: 34065259 PMCID: PMC8161212 DOI: 10.3390/membranes11050372] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/09/2021] [Revised: 03/30/2021] [Accepted: 04/05/2021] [Indexed: 11/16/2022]
Abstract
Connexin hemichannels allow the unspecific but regulated interchange of molecules from ions to second messenger and ATP, between the eukariotic cell and its extracellular space. The transport of ions and water through hemichannels is important for physiological functions and also in the progression of several pathological conditions. Extracellular Ca2+ concentration is one of the regulators that drives the channel to a closed state. However the relation between their functional and structural states is far for being totally understood. In this work, we modelled connexin hemichannels using simple systems based on a fixed array of carbon atoms and assess the Ca2+ regulation using molecular dynamics simulations. The two proposed mechanism described so far for calcium action were studied combined, e.g., an electrostatic effect and a pore stretching. Our results show that the addition of positive charge density inside the channel cannot stop the flow of potassium, chloride nor water. Only a pore stretching at the center of the pore can explain the channel blocking.
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Affiliation(s)
- Felipe Villanelo
- Computational Biology Laboratory, Fundación Ciencia & Vida, Zañartu 1482, Ñuñoa, Santiago 7780132, Chile; (F.V.); (J.C.); (J.J.-F.)
- Facultad de Ingeniería y Tecnología, Universidad San Sebastián, Santiago 8420524, Chile
| | - Jorge Carrasco
- Computational Biology Laboratory, Fundación Ciencia & Vida, Zañartu 1482, Ñuñoa, Santiago 7780132, Chile; (F.V.); (J.C.); (J.J.-F.)
- Facultad de Ingeniería y Tecnología, Universidad San Sebastián, Santiago 8420524, Chile
| | - Joaquin Jensen-Flores
- Computational Biology Laboratory, Fundación Ciencia & Vida, Zañartu 1482, Ñuñoa, Santiago 7780132, Chile; (F.V.); (J.C.); (J.J.-F.)
- Facultad de Ingeniería y Tecnología, Universidad San Sebastián, Santiago 8420524, Chile
| | - Jose Antonio Garate
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Valparaíso 2360102, Chile;
| | - Tomas Perez-Acle
- Computational Biology Laboratory, Fundación Ciencia & Vida, Zañartu 1482, Ñuñoa, Santiago 7780132, Chile; (F.V.); (J.C.); (J.J.-F.)
- Facultad de Ingeniería y Tecnología, Universidad San Sebastián, Santiago 8420524, Chile
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Valparaíso 2360102, Chile;
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9
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Ahmadi D, Ledder R, Mahmoudi N, Li P, Tellam J, Robinson D, Heenan RK, Smith P, Lorenz CD, Barlow DJ, Lawrence MJ. Supramolecular architecture of a multi-component biomimetic lipid barrier formulation. J Colloid Interface Sci 2021; 587:597-612. [DOI: 10.1016/j.jcis.2020.11.017] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2020] [Revised: 10/05/2020] [Accepted: 11/04/2020] [Indexed: 10/23/2022]
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Tiwari S, Gogoi A, Anki Reddy K. Effect of an ionic environment on membrane fouling: a molecular dynamics study. Phys Chem Chem Phys 2021; 23:5001-5011. [PMID: 33624656 DOI: 10.1039/d0cp05268j] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The effect of the ionic environment on membrane fouling was investigated for polyamide (PA) and graphene oxide (GO) membranes using equilibrium molecular dynamics (MD) simulations. For each of these membranes, bovine serum albumin (BSA) was considered as the model foulant. The effect of the foulant on the membranes is investigated at seawater concentration and also in a normal aqueous environment. We investigated the translational and rotational motion of the protein relative to the membrane, interaction energy between the protein and the membrane surface, structural changes in the protein, and ion distribution around the protein and the membrane surface for all the systems. We found that the effects of ions were very different on both the membranes. Specifically, with an increase in ionic strength, the repulsion between the protein and membrane was observed in the case of GO, while for PA, no significant changes were observed for the same. Also, the ion distribution around the protein and the membrane surface were found to be different. In particular, for GO, there were more number of chloride ions around the protein and the membrane than that of sodium ions, which was probably the reason for the repulsion in the case of GO. However, in the case of PA, the membrane surface did not exhibit any affinity towards a specific ion, and the protein in the case of PA was surrounded by more number of sodium ions than chloride ions.
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Affiliation(s)
- Shivam Tiwari
- Department of Chemical Engineering, Indian Institute of Technology Guwahati, Assam 781039, India.
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11
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Zhao Y, Choi S, Yu J. In Situ Generated Silver Nanodot Förster Resonance Energy Transfer Pair Reveals Nanocage Sizes. J Phys Chem Lett 2020; 11:6867-6872. [PMID: 32787207 DOI: 10.1021/acs.jpclett.0c01950] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
Characterizing nanocages in macromolecules is one of the keys to understanding various biological activities and further utilizing nanocages for novel materials synthesis. However, fast and straightforward detection of the nanocage size remains challenging. Here, we present a new approach to detect the diameter of a nanocage by Förster resonance energy transfer (FRET) of luminescent silver nanodot pairs with reverse micelles as a model. Silver nanodot FRET pairs can be generated in situ from a single silver nanodot species with critical energy transfer distances, R0, of 4.8-6.5 nm. We have applied this approach to clarify the size variation of the water nanocage in nonionic surfactant Triton X-100-based reverse micelles. FRET efficiency decreases as more water is added, indicating that the size of the reverse micelles continuously expands with water content. The silver element in the nanocage also enhances the visualization of the nanocage under cryo-TEM imaging. The diameter of the water nanocage measured with the above approach is consistent with that obtained by cryo-TEM, demonstrating that the FRET measurement of silver nanodots can be a fast and accurate tool to detect nanocage dimensions. The above demonstration allows us to apply our strategy to other protein-based nanocages.
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Affiliation(s)
- Yanlu Zhao
- Department of Chemistry Education, Seoul National University, Seoul 08826, Republic of Korea
| | - Sungmoon Choi
- Department of Chemistry Education, Seoul National University, Seoul 08826, Republic of Korea
| | - Junhua Yu
- Department of Chemistry Education, Seoul National University, Seoul 08826, Republic of Korea
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12
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Lee HJ, Jeong H, Hyun J, Ryu B, Park K, Lim HH, Yoo J, Woo JS. Cryo-EM structure of human Cx31.3/GJC3 connexin hemichannel. SCIENCE ADVANCES 2020; 6:eaba4996. [PMID: 32923625 PMCID: PMC7455182 DOI: 10.1126/sciadv.aba4996] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2019] [Accepted: 07/15/2020] [Indexed: 05/28/2023]
Abstract
Connexin family proteins assemble into hexameric channels called hemichannels/connexons, which function as transmembrane channels or dock together to form gap junction intercellular channels (GJIChs). We determined the cryo-electron microscopy structures of human connexin 31.3 (Cx31.3)/GJC3 hemichannels in the presence and absence of calcium ions and with a hearing-loss mutation R15G at 2.3-, 2.5-, and 2.6-Å resolutions, respectively. Compared with available structures of GJICh in open conformation, Cx31.3 hemichannel shows substantial structural changes of highly conserved regions in the connexin family, including opening of calcium ion-binding tunnels, reorganization of salt-bridge networks, exposure of lipid-binding sites, and collocation of amino-terminal helices at the cytoplasmic entrance. We also found that the hemichannel has a pore with a diameter of ~8 Å and selectively transports chloride ions. Our study provides structural insights into the permeant selectivity of Cx31.3 hemichannel.
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Affiliation(s)
- Hyuk-Joon Lee
- Department of Life Sciences, Korea University, Seoul 02841, Republic of Korea
| | - Hyeongseop Jeong
- Department of Life Sciences, Korea University, Seoul 02841, Republic of Korea
- Korea Basic Science Institute, Chungcheongbuk-do 28119, Republic of Korea
| | - Jaekyung Hyun
- Korea Basic Science Institute, Chungcheongbuk-do 28119, Republic of Korea
- Molecular Cryo-electron Microscopy Unit, Okinawa Institute of Science and Technology Graduate University, Okinawa 904-0496, Japan
| | - Bumhan Ryu
- Department of Life Sciences, Korea University, Seoul 02841, Republic of Korea
| | - Kunwoong Park
- Neurovascular Unit Research Group, Korea Brain Research Institute (KBRI), 41062 Daegu, Republic of Korea
| | - Hyun-Ho Lim
- Neurovascular Unit Research Group, Korea Brain Research Institute (KBRI), 41062 Daegu, Republic of Korea
| | - Jejoong Yoo
- Department of Physics, Sungkyunkwan University, Suwon, Republic of Korea
- Center for Self-assembly and Complexity (CSC), Institute for Basic Science (IBS), Pohang 37673, Republic of Korea
| | - Jae-Sung Woo
- Department of Life Sciences, Korea University, Seoul 02841, Republic of Korea
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13
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Xu S, Kennedy MA. Structural dynamics of pentapeptide repeat proteins. Proteins 2020; 88:1493-1512. [PMID: 32548861 DOI: 10.1002/prot.25969] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2020] [Revised: 03/19/2020] [Accepted: 06/06/2020] [Indexed: 12/14/2022]
Abstract
Pentapeptide repeat proteins (PRPs) represent a large superfamily with more than 38 000 sequences in nearly 3500 species, the majority belonging to cyanobacteria but represented among all branches of life. PRPs contain at least eight consecutive pentapeptide repeats with the consensus (A/C/S/V/T/L/I)(D/N/S/K/E/I/R)(L/F)(S/T/R/E/Q/K/V/D)(G/D/E/N/R/Q/K). PRPs fold into right-handed quadrilateral β helices, also known as repeat-five-residue (Rfr)-folds, with four consecutive pentapeptide repeats comprising a single coil, the ~90° change in polypeptide direction in square-shaped coils achieved by type I, II and IV β turns, and hydrogen bonds between coils establishing β ladders on each Rfr-fold face. PRPs are broadly categorized into group 1 and 2 involved in antibiotic resistance and group 3 currently having unknown functions. Motivated by their intriguing structures, we are investigating PRP biophysical characteristics, including Rfr-fold thermal stability, β turn and β ladder hydrogen bond amide exchange rates and backbone dynamics. Here, we present analysis of 20 ns molecular dynamics (MD) simulations and all atom normal mode analysis (aaNMA) calculations for four group 1 and group 2 and four group 3 PRPs whose structures have been determined by X-ray crystallography. The MD cross-correlation matrices and aaNMA indicated strong correlated motion between adjacent coils and weak coupled motion between coils separated by one or more intervening coils. Slow anticorrelated motions were detected between adjacent coils in aaNMA modes that we hypothesize are requisite to access exchange-competent states necessary to permit solvent exchange of amide hydrogens involved in β-ladder and β-turns hydrogen bonds, which can have lifetimes on the order of months.
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Affiliation(s)
- Shenyuan Xu
- Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio, USA
| | - Michael A Kennedy
- Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio, USA
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14
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Abstract
This protocol was developed to assess communication in tumor cells and to provide a dependable and standardized assay for the in vitro determination of gap junction function. The method is noninvasive; in this method, the cell population under study is divided such that 1 fraction is loaded with a lipophilic cell plasma membrane permeable dye, calcein acetoxymethyl ester, that is hydrolyzed upon cellular uptake by cytoplasmic esterases to yield calcein, a fluorescent and membrane-impermeable molecule. The other fraction is loaded with 1,1'-dioctadecyl-3,3,3',3' tetramethylindodicarbocyanine perchlorate (DiD)/1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate [Dil; DilC18(3)], which is a lipophilic membrane dye that diffuses laterally to stain the entire cell membrane, is impermeable, and attains an orange-red fluorescence upon incorporation into membranes. The 2 fractions are mixed and incubated under coculture conditions. Calcein with MW 890 kD is transferred to the DiD/DiI-stained cells through gap junctions. The assessment of this uptake is made with confocal imaging and quantitated using flow cytometry. Cell lines representing cancer of the breast as well as a nontransformed cell line developed from the buccal mucosa were analyzed for gap junction competency. Confocal imaging with acquisition at specific time points during the in vitro treatment and flow cytometry gave a qualitative and quantitative analysis of the passage of molecules through the gap junctions. Here, the method has been combined to obtain images as well as quantitation and is a simple and effective approach in assessing the functional competency of gap junction in epithelial cells.
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Affiliation(s)
- Ujjwala M Warawdekar
- Cancer Research Institute (CRI) Lab, Advanced Centre for Treatment, Research and Education in Cancer, Tata Memorial Centre, Navi Mumbai 410210, India.,Homi Bhabha National Institute, Anushakti Nagar, Mumbai 400085, India
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15
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Park MS, Araya-Secchi R, Brackbill JA, Phan HD, Kehling AC, Abd El-Wahab EW, Dayeh DM, Sotomayor M, Nakanishi K. Multidomain Convergence of Argonaute during RISC Assembly Correlates with the Formation of Internal Water Clusters. Mol Cell 2019; 75:725-740.e6. [PMID: 31324450 DOI: 10.1016/j.molcel.2019.06.011] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2018] [Revised: 04/30/2019] [Accepted: 06/07/2019] [Indexed: 11/17/2022]
Abstract
Despite the relevance of Argonaute proteins in RNA silencing, little is known about the structural steps of small RNA loading to form RNA-induced silencing complexes (RISCs). We report the 1.9 Å crystal structure of human Argonaute4 with guide RNA. Comparison with the previously determined apo structure of Neurospora crassa QDE2 revealed that the PIWI domain has two subdomains. Binding of guide RNA fastens the subdomains, thereby rearranging the active-site residues and increasing the affinity for TNRC6 proteins. We also identified two water pockets beneath the nucleic acid-binding channel that appeared to stabilize the mature RISC. Indeed, mutating the water-pocket residues of Argonaute2 and Argonaute4 compromised RISC assembly. Simulations predict that internal water molecules are exchangeable with the bulk solvent but always occupy specific positions at the domain interfaces. These results suggest that after guide RNA-driven conformational changes, water-mediated hydrogen-bonding networks tie together the converged domains to complete the functional RISC structure.
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Affiliation(s)
- Mi Seul Park
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; Center for RNA Biology, The Ohio State University, Columbus, OH 43210, USA
| | - Raul Araya-Secchi
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA
| | - James A Brackbill
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; Center for RNA Biology, The Ohio State University, Columbus, OH 43210, USA
| | - Hong-Duc Phan
- Center for RNA Biology, The Ohio State University, Columbus, OH 43210, USA; Ohio State Biochemistry Program, The Ohio State University, Columbus, OH 43210, USA
| | - Audrey C Kehling
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; Center for RNA Biology, The Ohio State University, Columbus, OH 43210, USA
| | - Ekram W Abd El-Wahab
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; Center for RNA Biology, The Ohio State University, Columbus, OH 43210, USA
| | - Daniel M Dayeh
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; Center for RNA Biology, The Ohio State University, Columbus, OH 43210, USA; Ohio State Biochemistry Program, The Ohio State University, Columbus, OH 43210, USA
| | - Marcos Sotomayor
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; Ohio State Biochemistry Program, The Ohio State University, Columbus, OH 43210, USA; Biophysics Graduate Program, The Ohio State University, Columbus, OH 43210, USA
| | - Kotaro Nakanishi
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; Center for RNA Biology, The Ohio State University, Columbus, OH 43210, USA; Ohio State Biochemistry Program, The Ohio State University, Columbus, OH 43210, USA.
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16
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Poch A, Villanelo F, Henriquez S, Kohen P, Muñoz A, Strauss JF, Devoto L. Molecular modelling predicts that 2-methoxyestradiol disrupts HIF function by binding to the PAS-B domain. Steroids 2019; 144:21-29. [PMID: 30738071 DOI: 10.1016/j.steroids.2019.02.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/10/2018] [Revised: 01/17/2019] [Accepted: 02/04/2019] [Indexed: 01/28/2023]
Abstract
An estradiol metabolite, 2-methoxyestradiol (2ME), has emerged as an important regulator of ovarian physiology. 2ME is recognized as a potent anti-angiogenic agent in clinical trials and laboratory studies. However, little is known about its molecular actions and its endogenous targets. 2ME is produced by human ovarian cells during the normal menstrual cycle, being higher during regression of the corpus luteum, and is postulated to be involved in the anti-angiogenic process that plays out during luteolysis. We utilized cell biology techniques to understand the molecular mechanism of 2ME anti-angiogenic effects on human granulosa luteal cells. The principal effect of 2ME was to alter Hypoxia Inducible Factor 1A (HIF1A) sub-cellular localization. Molecular modelling and multiple bioinformatics tools indicated that 2ME impairs Hypoxia Inducible Factor complex (HIF) nuclear translocation by binding to a buried pocket in the HIF1A Per Arnt Sim (PAS)-B domain. Binding of 2ME to HIF1A protein is predicted to perturb HIF1A-Hypoxia Inducible Factor B (HIFB) interaction, a key step in HIF nuclear translocation, preventing the transcriptional actions of HIF, including Vascular Endotelial Growth Factor (VEGF) gene activation. To our knowledge, 2ME is the first putative HIF endogenous ligand characterized with anti-angiogenic activity. This postulate has important implications for reproduction, because angiogenic processes are critical for ovarian follicular development, ovulation and corpus luteum regression. The present research could contribute to the development of novel pharmacological approaches for controlling HIF activity in human reproductive diseases.
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Affiliation(s)
- Andrea Poch
- Institute for Maternal and Child Research (IDIMI), School of Medicine, University of Chile, Avenida Santa Rosa 1234, 8360160 Santiago-Centro, Santiago, Chile
| | - Felipe Villanelo
- Computational Biology Lab (DLab), Fundación Ciencia & Vida. Avenida Zañartu 1482, 7780272 Ñuñoa, Santiago, Chile; Centro Interdisciplinario de Neurociencias de Valparaíso, Universidad de Valparaíso, Harrington 287, Valparaíso, Chile
| | - Soledad Henriquez
- Institute for Maternal and Child Research (IDIMI), School of Medicine, University of Chile, Avenida Santa Rosa 1234, 8360160 Santiago-Centro, Santiago, Chile
| | - Paulina Kohen
- Institute for Maternal and Child Research (IDIMI), School of Medicine, University of Chile, Avenida Santa Rosa 1234, 8360160 Santiago-Centro, Santiago, Chile
| | - Alex Muñoz
- Institute for Maternal and Child Research (IDIMI), School of Medicine, University of Chile, Avenida Santa Rosa 1234, 8360160 Santiago-Centro, Santiago, Chile
| | - Jerome F Strauss
- Department of Obstetrics and Gynecology, School of Medicine, Virginia Commonwealth University, Sanger Hall, 1101 E Marshall St., 980565 Richmond, VA, USA
| | - Luigi Devoto
- Institute for Maternal and Child Research (IDIMI), School of Medicine, University of Chile, Avenida Santa Rosa 1234, 8360160 Santiago-Centro, Santiago, Chile; Department of Obstetrics and Gynecology, School of Medicine, San Borja-Arriaran Clinical Hospital, University of Chile, Avenida Santa Rosa 1234, 8360160 Santiago-Centro, Santiago, Chile.
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17
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Contreras-Riquelme S, Garate JA, Perez-Acle T, Martin AJM. RIP-MD: a tool to study residue interaction networks in protein molecular dynamics. PeerJ 2018; 6:e5998. [PMID: 30568854 PMCID: PMC6287582 DOI: 10.7717/peerj.5998] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2018] [Accepted: 10/25/2018] [Indexed: 11/20/2022] Open
Abstract
Protein structure is not static; residues undergo conformational rearrangements and, in doing so, create, stabilize or break non-covalent interactions. Molecular dynamics (MD) is a technique used to simulate these movements with atomic resolution. However, given the data-intensive nature of the technique, gathering relevant information from MD simulations is a complex and time consuming process requiring several computational tools to perform these analyses. Among different approaches, the study of residue interaction networks (RINs) has proven to facilitate the study of protein structures. In a RIN, nodes represent amino-acid residues and the connections between them depict non-covalent interactions. Here, we describe residue interaction networks in protein molecular dynamics (RIP-MD), a visual molecular dynamics (VMD) plugin to facilitate the study of RINs using trajectories obtained from MD simulations of proteins. Our software generates RINs from MD trajectory files. The non-covalent interactions defined by RIP-MD include H-bonds, salt bridges, VdWs, cation-π, π–π, Arginine–Arginine, and Coulomb interactions. In addition, RIP-MD also computes interactions based on distances between Cαs and disulfide bridges. The results of the analysis are shown in an user friendly interface. Moreover, the user can take advantage of the VMD visualization capacities, whereby through some effortless steps, it is possible to select and visualize interactions described for a single, several or all residues in a MD trajectory. Network and descriptive table files are also generated, allowing their further study in other specialized platforms. Our method was written in python in a parallelized fashion. This characteristic allows the analysis of large systems impossible to handle otherwise. RIP-MD is available at http://www.dlab.cl/ripmd.
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Affiliation(s)
- Sebastián Contreras-Riquelme
- Computational Biology Laboratory (DLab), Fundacion Ciencia & Vida, Santiago, Chile.,Facultad de Ciencias de la Vida, Universidad Andrés Bello, Santiago, Chile.,Network Biology Laboratory, Centro de Genómica y Bioinformática, Facultad de Ciencias, Universidad Mayor, Santiago, Chile
| | | | - Tomas Perez-Acle
- Computational Biology Laboratory (DLab), Fundacion Ciencia & Vida, Santiago, Chile.,Centro Interdisciplinario de Neurociencia de Valparaíso, Valparaíso, Chile
| | - Alberto J M Martin
- Network Biology Laboratory, Centro de Genómica y Bioinformática, Facultad de Ciencias, Universidad Mayor, Santiago, Chile
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18
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Albano JMR, Mussini N, Toriano R, Facelli JC, Ferraro MB, Pickholz M. Calcium interactions with Cx26 hemmichannel: Spatial association between MD simulations biding sites and variant pathogenicity. Comput Biol Chem 2018; 77:331-342. [PMID: 30466042 DOI: 10.1016/j.compbiolchem.2018.11.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2018] [Revised: 07/08/2018] [Accepted: 11/08/2018] [Indexed: 01/23/2023]
Abstract
Connexinophaties are a collective of diseases related to connexin channels and hemichannels. In particular many Cx26 alterations are strongly associated to human deafness. Calcium plays an important role on this structures regulation. Here, using calcium as a probe, extensive atomistic Molecular Dynamics simulations were performed on the Cx26 hemichannel embedded in a lipid bilayer. Exploring different initial conditions and calcium concentration, simulation reached ∼4 μs. Several analysis were carried out in order to reveal the calcium distribution and localization, such as electron density profiles, density maps and distance time evolution, which is directly associated to the interaction energy. Specific amino acid interactions with calcium and their stability were capture within this context. Few of these sites such as, GLU42, GLU47, GLY45 and ASP50, were already suggested in the literature. Besides, we identified novel calcium biding sites: ASP2, ASP117, ASP159, GLU114, GLU119, GLU120 and VAL226. To the best of our knowledge, this is the first time that these sites are reported within this context. Furthermore, since various pathologies involving the Cx26 hemichannel are associated with pathogenic variants in the corresponding CJB2 gene, using ClinVar, we were able to spatially associate the 3D positions of the identified calcium binding sites within the framework of this work with reported pathogenic variants in the CJB2 gene. This study presents a first step on finding associations between molecular features and pathological variants of the Cx26 hemichannel.
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Affiliation(s)
- Juan M R Albano
- Facultad de Ciencias Exactas y Naturales, Departamento de Física, Universidad de Buenos Aires, Argentina; CONICET- Universidad de Buenos Aires, IFIBA, Buenos Aires, Argentina
| | - Nahuel Mussini
- Facultad de Ciencias Exactas y Naturales, Departamento de Física, Universidad de Buenos Aires, Argentina; CONICET- Universidad de Buenos Aires, IFIBA, Buenos Aires, Argentina
| | - Roxana Toriano
- Facultad de Medicina, Departamento de Ciencias Fisiológicas, Laboratorio de Biomembranas, Buenos Aires, Argentina; CONICET - Universidad de Buenos Aires, IFIBIO Houssay, Buenos Aires, Argentina
| | - Julio C Facelli
- Department of Biomedical Informatics, The University of Utah, 421 Wakara Way, Suite 140, Salt Lake City, UT 84108, USA.
| | - Marta B Ferraro
- Facultad de Ciencias Exactas y Naturales, Departamento de Física, Universidad de Buenos Aires, Argentina; CONICET- Universidad de Buenos Aires, IFIBA, Buenos Aires, Argentina
| | - Mónica Pickholz
- Facultad de Ciencias Exactas y Naturales, Departamento de Física, Universidad de Buenos Aires, Argentina; CONICET- Universidad de Buenos Aires, IFIBA, Buenos Aires, Argentina
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19
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Frischauf I, Litviňuková M, Schober R, Zayats V, Svobodová B, Bonhenry D, Lunz V, Cappello S, Tociu L, Reha D, Stallinger A, Hochreiter A, Pammer T, Butorac C, Muik M, Groschner K, Bogeski I, Ettrich RH, Romanin C, Schindl R. Transmembrane helix connectivity in Orai1 controls two gates for calcium-dependent transcription. Sci Signal 2017; 10:eaao0358. [PMID: 29184031 PMCID: PMC6433236 DOI: 10.1126/scisignal.aao0358] [Citation(s) in RCA: 59] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The channel Orai1 requires Ca2+ store depletion in the endoplasmic reticulum and an interaction with the Ca2+ sensor STIM1 to mediate Ca2+ signaling. Alterations in Orai1-mediated Ca2+ influx have been linked to several pathological conditions including immunodeficiency, tubular myopathy, and cancer. We screened large-scale cancer genomics data sets for dysfunctional Orai1 mutants. Five of the identified Orai1 mutations resulted in constitutively active gating and transcriptional activation. Our analysis showed that certain Orai1 mutations were clustered in the transmembrane 2 helix surrounding the pore, which is a trigger site for Orai1 channel gating. Analysis of the constitutively open Orai1 mutant channels revealed two fundamental gates that enabled Ca2+ influx: Arginine side chains were displaced so they no longer blocked the pore, and a chain of water molecules formed in the hydrophobic pore region. Together, these results enabled us to identify a cluster of Orai1 mutations that trigger Ca2+ permeation associated with gene transcription and provide a gating mechanism for Orai1.
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Affiliation(s)
- Irene Frischauf
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Linz A-4020, Austria
| | - Monika Litviňuková
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Linz A-4020, Austria
- Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Cardiovascular and Metabolic Sciences, Berlin D-13125, Germany
| | - Romana Schober
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Linz A-4020, Austria
| | - Vasilina Zayats
- Center for Nanobiology and Structural Biology, Institute of Microbiology, Academy of Sciences of the Czech Republic, Nové Hrady CZ-373 33, Czech Republic
- Center of New Technologies, University of Warsaw, Warsaw 02-097, Poland
| | - Barbora Svobodová
- Institute for Biophysics, Medical University of Graz, Graz A-8010, Austria
| | - Daniel Bonhenry
- Center for Nanobiology and Structural Biology, Institute of Microbiology, Academy of Sciences of the Czech Republic, Nové Hrady CZ-373 33, Czech Republic
| | - Victoria Lunz
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Linz A-4020, Austria
| | - Sabrina Cappello
- Molecular Physiology, Institute of Cardiovascular Physiology, University Medical Center, Georg August University Göttingen, Göttingen, Niedersachsen 37073, Germany
- Department of Biophysics, Center for Integrative Physiology and Molecular Medicine, Medical Faculty, Saarland University, Homburg D-66421, Germany
| | - Laura Tociu
- Center for Nanobiology and Structural Biology, Institute of Microbiology, Academy of Sciences of the Czech Republic, Nové Hrady CZ-373 33, Czech Republic
- University of Chicago, Chicago, IL 60637, USA
| | - David Reha
- Center for Nanobiology and Structural Biology, Institute of Microbiology, Academy of Sciences of the Czech Republic, Nové Hrady CZ-373 33, Czech Republic
- Faculty of Sciences, University of South Bohemia, Nové Hrady CZ-373 33, Czech Republic
| | - Amrutha Stallinger
- Institute for Molecular Biosciences, Karl-Franzens-University Graz, Graz A-8010, Austria
| | - Anna Hochreiter
- Institute for Experimental and Clinical Cell Therapy, Paracelsus Medical University, Salzburg A-5020, Austria
| | - Teresa Pammer
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Linz A-4020, Austria
| | - Carmen Butorac
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Linz A-4020, Austria
| | - Martin Muik
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Linz A-4020, Austria
| | - Klaus Groschner
- Institute for Biophysics, Medical University of Graz, Graz A-8010, Austria
| | - Ivan Bogeski
- Molecular Physiology, Institute of Cardiovascular Physiology, University Medical Center, Georg August University Göttingen, Göttingen, Niedersachsen 37073, Germany
| | - Rüdiger H Ettrich
- Center for Nanobiology and Structural Biology, Institute of Microbiology, Academy of Sciences of the Czech Republic, Nové Hrady CZ-373 33, Czech Republic
- Faculty of Sciences, University of South Bohemia, Nové Hrady CZ-373 33, Czech Republic
| | - Christoph Romanin
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Linz A-4020, Austria
| | - Rainer Schindl
- Institute for Biophysics, Medical University of Graz, Graz A-8010, Austria.
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20
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Escalona Y, Garate JA, Araya-Secchi R, Huynh T, Zhou R, Perez-Acle T. Exploring the Membrane Potential of Simple Dual-Membrane Systems as Models for Gap-Junction Channels. Biophys J 2017; 110:2678-2688. [PMID: 27332126 DOI: 10.1016/j.bpj.2016.05.005] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2015] [Revised: 05/02/2016] [Accepted: 05/03/2016] [Indexed: 11/26/2022] Open
Abstract
The conductance of ion channels can be modulated by a transmembrane potential difference, due to alterations on ion-mobility and also by changes in the pore structure. Despite the vast knowledge regarding the influence of voltage on transport properties of ion channels, little attention has been paid to describe, with atomic detail, the modulation of ionic transport in gap-junction channels (GJCs). Hence, molecular dynamics simulations were performed to explore the conductance of simple dual-membrane systems that account for the very basic features of GJCs. In doing so, we studied the influence of different charge distributions in the channel surface on these idealized systems under external electric fields, paying attention to the behavior of the electrostatic potential, ion density, ion currents, and equilibrium properties. Our results demonstrate that the incorporation of a charge distribution akin GJCs decreased anionic currents, favoring the transport of cationic species. Moreover, a thermodynamic characterization of ionic transport in these systems demonstrate the existence of a kinetic barrier that hinders anionic currents, reinforcing the role played by the internal arrangement of charges in GJCs. Overall, our results provide insights at the atomic scale on the effects of charge distributions over ionic transport, constituting a step forward into a better understanding of GJCs.
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Affiliation(s)
- Yerko Escalona
- Computational Biology Lab (DLab), Fundación Ciencia & Vida, Santiago, Chile
| | - Jose A Garate
- Computational Biology Lab (DLab), Fundación Ciencia & Vida, Santiago, Chile; Centro Interdisciplinario de Neurociencia de Valparaíso (CINV), Universidad de Valparaíso, Valparaíso, Chile
| | - Raul Araya-Secchi
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio
| | - Tien Huynh
- Computational Biology Center, IBM Thomas J. Watson Research Center, Yorktown Heights, New York
| | - Ruhong Zhou
- Computational Biology Center, IBM Thomas J. Watson Research Center, Yorktown Heights, New York
| | - Tomas Perez-Acle
- Computational Biology Lab (DLab), Fundación Ciencia & Vida, Santiago, Chile; Centro Interdisciplinario de Neurociencia de Valparaíso (CINV), Universidad de Valparaíso, Valparaíso, Chile.
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21
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Skerrett IM, Williams JB. A structural and functional comparison of gap junction channels composed of connexins and innexins. Dev Neurobiol 2017; 77:522-547. [PMID: 27582044 PMCID: PMC5412853 DOI: 10.1002/dneu.22447] [Citation(s) in RCA: 55] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2016] [Revised: 08/12/2016] [Accepted: 08/30/2016] [Indexed: 02/03/2023]
Abstract
Methods such as electron microscopy and electrophysiology led to the understanding that gap junctions were dense arrays of channels connecting the intracellular environments within almost all animal tissues. The characteristics of gap junctions were remarkably similar in preparations from phylogenetically diverse animals such as cnidarians and chordates. Although few studies directly compared them, minor differences were noted between gap junctions of vertebrates and invertebrates. For instance, a slightly wider gap was noted between cells of invertebrates and the spacing between invertebrate channels was generally greater. Connexins were identified as the structural component of vertebrate junctions in the 1980s and innexins as the structural component of pre-chordate junctions in the 1990s. Despite a lack of similarity in gene sequence, connexins and innexins are remarkably similar. Innexins and connexins have the same membrane topology and form intercellular channels that play a variety of tissue- and temporally specific roles. Both protein types oligomerize to form large aqueous channels that allow the passage of ions and small metabolites and are regulated by factors such as pH, calcium, and voltage. Much more is currently known about the structure, function, and structure-function relationships of connexins. However, the innexin field is expanding. Greater knowledge of innexin channels will permit more detailed comparisons with their connexin-based counterparts, and provide insight into the ubiquitous yet specific roles of gap junctions. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 522-547, 2017.
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Affiliation(s)
- I Martha Skerrett
- Biology Department, SUNY Buffalo State, 1300 Elmwood Ave, Buffalo, New York, 14222
| | - Jamal B Williams
- Biology Department, SUNY Buffalo State, 1300 Elmwood Ave, Buffalo, New York, 14222
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22
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Abstract
Gap junction channels facilitate the intercellular exchange of ions and small molecules, a process that is critical for the function of many different kinds of cells and tissues. Recent crystal structures of channels formed by one connexin isoform (connexin26) have been determined, and they have been subjected to molecular modeling. These studies have provided high-resolution models to gain insights into the mechanisms of channel conductance, molecular permeability, and gating. The models share similarities, but there are some differences in the conclusions reached by these studies. Many unanswered questions remain to allow an atomic-level understanding of intercellular communication mediated by connexin26. Because some domains of the connexin polypeptides are highly conserved (like the transmembrane regions), it is likely that some features of the connexin26 structure will apply to other members of the family of gap junction proteins. However, determination of high-resolution structures and modeling of other connexin channels will be required to account for the diverse biophysical properties and regulation conferred by the differences in their sequences.
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Affiliation(s)
- Eric C Beyer
- Department of Pediatrics, University of Chicago, Chicago, IL, 60637, USA
| | - Viviana M Berthoud
- Department of Pediatrics, University of Chicago, Chicago, IL, 60637, USA
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23
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Alizadeh H, Davoodi J, Rafii-Tabar H. Deconstruction of the human connexin 26 hemichannel due to an applied electric field; A molecular dynamics simulation study. J Mol Graph Model 2017; 73:108-114. [PMID: 28259639 DOI: 10.1016/j.jmgm.2017.02.006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2016] [Revised: 02/12/2017] [Accepted: 02/13/2017] [Indexed: 10/20/2022]
Abstract
Connexins are a 21-member membrane protein family constituting channels evolved in direct communication between adjacent cells by passaging cytoplasmic molecules and ions. Hexametrical assembly of connexin proteins in plasma membrane forms a wide aqueous pore known as connexin hemichannel. These hemichannels mediate cytoplasm and extracellular milieu communication both in many external tissues and in the central nervous system. In this study, a series of molecular dynamics simulations has been performed to investigate the effect of applied static and alternating electric fields on the stability and conformation of human connexin26 hemichannel. The root mean square deviations of C-alpha atoms, the dipole moment distribution, the number of inter-protein hydrogen bonds and the number of water-protein hydrogen bonds were used to assess connexin26 hemichannel stability. In the static field case, our results show that although the lowest field used in this study (0.1V/nm) does not lead to the hemichannel deconstruction, stronger fields (>0.1V/nm), however, disrupt the protein structure during the simulations time period. Furthermore, in the alternating case, compared to static field case, field effects on the connexin26 hemichannel conformation are reduced and consequently the protein maintains its native structure for longer times. Specifically, for the highest frequency used in this study (50GHz), the hemichannel keeps its structure even under the effect of the strongest field (0.4V/nm). According to our results, the protein secondary structure is preserved in the characteristic times determined for the protein deconstruction. Consequently, we suggest that the protein deconstruction is due to the tertiary and quaternary structure loss.
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Affiliation(s)
- Hadi Alizadeh
- Department of Physics, Faculty of Sciences, University of Zanjan, Zanajn, Iran
| | - Jamal Davoodi
- Department of Physics, Faculty of Sciences, University of Zanjan, Zanajn, Iran
| | - Hashem Rafii-Tabar
- Department of Medical Physics and Biomedical Engineering, School of Medicine, Shahid Beheshti University of Medical Science, Tehran, Iran.
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24
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Pereira A. Astroglial hydro-ionic waves guided by the extracellular matrix: An exploratory model. J Integr Neurosci 2017; 16:57-72. [DOI: 10.3233/jin-160003] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Affiliation(s)
- Alfredo Pereira
- Institute of Biosciences, São Paulo State University, Brazil. E-mail:
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25
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Vargas AA, Cisterna BA, Saavedra-Leiva F, Urrutia C, Cea LA, Vielma AH, Gutierrez-Maldonado SE, Martin AJM, Pareja-Barrueto C, Escalona Y, Schmachtenberg O, Lagos CF, Perez-Acle T, Sáez JC. On Biophysical Properties and Sensitivity to Gap Junction Blockers of Connexin 39 Hemichannels Expressed in HeLa Cells. Front Physiol 2017; 8:38. [PMID: 28232803 PMCID: PMC5298994 DOI: 10.3389/fphys.2017.00038] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2016] [Accepted: 01/13/2017] [Indexed: 02/02/2023] Open
Abstract
Although connexins (Cxs) are broadly expressed by cells of mammalian organisms, Cx39 has a very restricted pattern of expression and the biophysical properties of Cx39-based channels [hemichannels (HCs) and gap junction channels (GJCs)] remain largely unknown. Here, we used HeLa cells transfected with Cx39 (HeLa-Cx39 cells) in which intercellular electrical coupling was not detected, indicating the absence of GJCs. However, functional HCs were found on the surface of cells exposed to conditions known to increase the open probability of other Cx HCs (e.g., extracellular divalent cationic-free solution (DCFS), extracellular alkaline pH, mechanical stimulus and depolarization to positive membrane potentials). Cx39 HCs were blocked by some traditional Cx HC blockers, but not by others or a pannexin1 channel blocker. HeLa-Cx39 cells showed similar resting membrane potentials (RMPs) to those of parental cells, and exposure to DCFS reduced RMPs in Cx39 transfectants, but not in parental cells. Under these conditions, unitary events of ~75 pS were frequent in HeLa-Cx39 cells and absent in parental cells. Real-time cellular uptake experiments of dyes with different physicochemical features, as well as the application of a machine-learning approach revealed that Cx39 HCs are preferentially permeable to molecules characterized by six categories of descriptors, namely: (1) electronegativity, (2) ionization potential, (3) polarizability, (4) size and geometry, (5) topological flexibility and (6) valence. However, Cx39 HCs opened by mechanical stimulation or alkaline pH were impermeable to Ca2+. Molecular modeling of Cx39-based channels suggest that a constriction present at the intracellular portion of the para helix region co-localizes with an electronegative patch, imposing an energetic and steric barrier, which in the case of GJCs may hinder channel function. Results reported here demonstrate that Cx39 form HCs and add to our understanding of the functional roles of Cx39 HCs under physiological and pathological conditions in cells that express them.
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Affiliation(s)
- Anibal A Vargas
- Departamento de Fisiología, Pontificia Universidad Católica de Chile Santiago, Chile
| | - Bruno A Cisterna
- Departamento de Fisiología, Pontificia Universidad Católica de ChileSantiago, Chile; Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de ValparaísoValparaíso, Chile
| | - Fujiko Saavedra-Leiva
- Departamento de Fisiología, Pontificia Universidad Católica de Chile Santiago, Chile
| | - Carolina Urrutia
- Departamento de Fisiología, Pontificia Universidad Católica de Chile Santiago, Chile
| | - Luis A Cea
- Institute of Biomedical Sciences, Faculty of Medicine, Universidad de Chile Santiago, Chile
| | - Alex H Vielma
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso Valparaíso, Chile
| | - Sebastian E Gutierrez-Maldonado
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de ValparaísoValparaíso, Chile; Computational Biology Lab (DLab), Fundación Ciencia & VidaSantiago, Chile
| | - Alberto J M Martin
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de ValparaísoValparaíso, Chile; Computational Biology Lab (DLab), Fundación Ciencia & VidaSantiago, Chile
| | | | - Yerko Escalona
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de ValparaísoValparaíso, Chile; Computational Biology Lab (DLab), Fundación Ciencia & VidaSantiago, Chile
| | - Oliver Schmachtenberg
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso Valparaíso, Chile
| | - Carlos F Lagos
- Department of Endocrinology, School of Medicine, Pontificia Universidad Católica de ChileSantiago, Chile; Facultad de Ciencia, Universidad San SebastiánSantiago, Chile
| | - Tomas Perez-Acle
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de ValparaísoValparaíso, Chile; Computational Biology Lab (DLab), Fundación Ciencia & VidaSantiago, Chile
| | - Juan C Sáez
- Departamento de Fisiología, Pontificia Universidad Católica de ChileSantiago, Chile; Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de ValparaísoValparaíso, Chile
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Villanelo F, Escalona Y, Pareja-Barrueto C, Garate JA, Skerrett IM, Perez-Acle T. Accessing gap-junction channel structure-function relationships through molecular modeling and simulations. BMC Cell Biol 2017; 18:5. [PMID: 28124624 PMCID: PMC5267332 DOI: 10.1186/s12860-016-0121-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Background Gap junction channels (GJCs) are massive protein channels connecting the cytoplasm of adjacent cells. These channels allow intercellular transfer of molecules up to ~1 kDa, including water, ions and other metabolites. Unveiling structure-function relationships coded into the molecular architecture of these channels is necessary to gain insight on their vast biological function including electrical synapse, inflammation, development and tissular homeostasis. From early works, computational methods have been critical to analyze and interpret experimental observations. Upon the availability of crystallographic structures, molecular modeling and simulations have become a valuable tool to assess structure-function relationships in GJCs. Modeling different connexin isoforms, simulating the transport process, and exploring molecular variants, have provided new hypotheses and out-of-the-box approaches to the study of these important channels. Methods Here, we review foundational structural studies and recent developments on GJCs using molecular modeling and simulation techniques, highlighting the methods and the cross-talk with experimental evidence. Results and discussion By comparing results obtained by molecular modeling and simulations techniques with structural and functional information obtained from both recent literature and structural databases, we provide a critical assesment of structure-function relationships that can be obtained from the junction between theoretical and experimental evidence.
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Affiliation(s)
- F Villanelo
- Computational Biology Lab. Fundación Ciencia & Vida, Santiago, Chile
| | - Y Escalona
- Computational Biology Lab. Fundación Ciencia & Vida, Santiago, Chile
| | - C Pareja-Barrueto
- Computational Biology Lab. Fundación Ciencia & Vida, Santiago, Chile
| | - J A Garate
- Computational Biology Lab. Fundación Ciencia & Vida, Santiago, Chile.,Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Playa Ancha, Valparaíso, Chile
| | - I M Skerrett
- State University of New York (SUNY) Buffalo State, Buffalo, NY, 14222, USA
| | - T Perez-Acle
- Computational Biology Lab. Fundación Ciencia & Vida, Santiago, Chile. .,Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Playa Ancha, Valparaíso, Chile.
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Brennan MJ, Karcz J, Vaughn NR, Woolwine-Cunningham Y, DePriest AD, Escalona Y, Perez-Acle T, Skerrett IM. Tryptophan Scanning Reveals Dense Packing of Connexin Transmembrane Domains in Gap Junction Channels Composed of Connexin32. J Biol Chem 2015; 290:17074-84. [PMID: 25969535 PMCID: PMC4498046 DOI: 10.1074/jbc.m115.650747] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2015] [Revised: 04/29/2015] [Indexed: 11/06/2022] Open
Abstract
Tryptophan was substituted for residues in all four transmembrane domains of connexin32. Function was assayed using dual cell two-electrode voltage clamp after expression in Xenopus oocytes. Tryptophan substitution was poorly tolerated in all domains, with the greatest impact in TM1 and TM4. For instance, in TM1, 15 substitutions were made, six abolished coupling and five others significantly reduced function. Only TM2 and TM3 included a distinct helical face that lacked sensitivity to tryptophan substitution. Results were visualized on a comparative model of Cx32 hemichannel. In this model, a region midway through the membrane appears highly sensitive to tryptophan substitution and includes residues Arg-32, Ile-33, Met-34, and Val-35. In the modeled channel, pore-facing regions of TM1 and TM2 were highly sensitive to tryptophan substitution, whereas the lipid-facing regions of TM3 and TM4 were variably tolerant. Residues facing a putative intracellular water pocket (the IC pocket) were also highly sensitive to tryptophan substitution. Although future studies will be required to separate trafficking-defective mutants from those that alter channel function, a subset of interactions important for voltage gating was identified. Interactions important for voltage gating occurred mainly in the mid-region of the channel and focused on TM1. To determine whether results could be extrapolated to other connexins, TM1 of Cx43 was scanned revealing similar but not identical sensitivity to TM1 of Cx32.
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Affiliation(s)
- Matthew J Brennan
- From the Biology Department, State University of New York Buffalo State, Buffalo, New York 14222
| | - Jennifer Karcz
- From the Biology Department, State University of New York Buffalo State, Buffalo, New York 14222
| | - Nicholas R Vaughn
- From the Biology Department, State University of New York Buffalo State, Buffalo, New York 14222
| | - Yvonne Woolwine-Cunningham
- the Clinical and Translational Research Center, State University of New York at Buffalo, Buffalo, New York 14214
| | - Adam D DePriest
- the Department of Cancer Genetics, Roswell Park Cancer Institute, Buffalo, New York 14263
| | - Yerko Escalona
- the Computational Biology Lab, Fundación Ciencia and Vida, 7780344 Santiago, Chile, and the Centro Interdisciplinario de Neurociencias de Valparaíso, Universidad de Valparaíso, 2360102 Valparaíso, Chile
| | - Tomas Perez-Acle
- the Computational Biology Lab, Fundación Ciencia and Vida, 7780344 Santiago, Chile, and the Centro Interdisciplinario de Neurociencias de Valparaíso, Universidad de Valparaíso, 2360102 Valparaíso, Chile
| | - I Martha Skerrett
- From the Biology Department, State University of New York Buffalo State, Buffalo, New York 14222,
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Connexins and skin disease: insights into the role of beta connexins in skin homeostasis. Cell Tissue Res 2015; 360:645-58. [PMID: 25616557 DOI: 10.1007/s00441-014-2094-3] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2014] [Accepted: 12/08/2014] [Indexed: 12/20/2022]
Abstract
Cell-to-cell communication triggered by connexin channels plays a central role in maintaining epidermal homeostasis. Here, we discuss the role of the beta connexin subgroup, where site-specific mutations in at least 4 of these proteins lead to distinctive non-inflammatory and inflammatory hyperproliferative epidermal disorders. Recent advances in the molecular pathways evoked and correlation with clinical outcome are discussed. The latest data provide increasing evidence that connexins in the epidermis are sensors to environmental stress and that targeting aberrant hemichannel activity holds significant therapeutic potential for inflammatory skin disorders.
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29
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Abstract
Voltage is an important parameter that regulates the conductance of both intercellular and plasma membrane channels (undocked hemichannels) formed by the 21 members of the mammalian connexin gene family. Connexin channels display two forms of voltage-dependence, rectification of ionic currents and voltage-dependent gating. Ionic rectification results either from asymmetries in the distribution of fixed charges due to heterotypic pairing of different hemichannels, or by channel block, arising from differences in the concentrations of divalent cations on opposite sides of the junctional plaque. This rectification likely underpins the electrical rectification observed in some electrical synapses. Both intercellular and undocked hemichannels also display two distinct forms of voltage-dependent gating, termed Vj (fast)-gating and loop (slow)-gating. This review summarizes our current understanding of the molecular determinants and mechanisms underlying these conformational changes derived from experimental, molecular-genetic, structural, and computational approaches.
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Affiliation(s)
- Seunghoon Oh
- Department of Physiology, College of Medicine, Dankook University, Cheonan, Korea
| | - Thaddeus A Bargiello
- Dominic P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY, USA.
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