1
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Hitchhiking into a cell: flavonoids may produce complexes with transition metals for transmembrane translocation. Biometals 2022; 35:1299-1306. [PMID: 36161545 DOI: 10.1007/s10534-022-00445-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2022] [Accepted: 09/12/2022] [Indexed: 12/14/2022]
Abstract
Flavonoids are a group of food polyphenols that are delivered to the human body with plant foods. In recent years, these substances have attracted the attention of researchers due to their effectiveness in preventing a wide variety of diseases, including neurodegenerative, oncological, autoimmune, and cardiovascular. Similar pathologies may also occur with a lack of some first-row transition metals, including Cu(II), Zn(II), Mn(II), Fe(II/III). It is noteworthy that flavonoids are known as transition metal chelators. When a complex with these metals is formed, the therapeutic effect of flavonoids can be enhanced, assuming the possibility of synergy. Molecular models have shown that the lipophilicity of flavonoid-metal complexes can vary significantly depending on their binding stoichiometry. Therefore, a unique process of translocation of flavonoid-metal complexes of various lipophilicity through cell membranes is assumed, based on the possibility of their sequential association and dissociation, called "hitchhiking". It is expected that studies of the interaction of flavonoids with metals will improve the effectiveness of drugs based on flavonoids.
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2
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Okuno Y, Schwieters CD, Yang Z, Clore GM. Theory and Applications of Nitroxide-based Paramagnetic Cosolutes for Probing Intermolecular and Electrostatic Interactions on Protein Surfaces. J Am Chem Soc 2022; 144:21371-21388. [DOI: 10.1021/jacs.2c10035] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Yusuke Okuno
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0520, United States
| | - Charles D. Schwieters
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0520, United States
- Computational Biomolecular Magnetic Resonance Core, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0520, United States
| | - Zhilin Yang
- Laboratory of Cell Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, United States
| | - G. Marius Clore
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0520, United States
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3
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Mechanisms of Co, Ni, and Mn toxicity: From exposure and homeostasis to their interactions with and impact on lipids and biomembranes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2020; 1862:183250. [DOI: 10.1016/j.bbamem.2020.183250] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/26/2019] [Revised: 02/12/2020] [Accepted: 02/24/2020] [Indexed: 01/21/2023]
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4
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Nguyen DM, Chen LS, Jeng G, Yu WP, Chen TY. Cobalt ion interaction with TMEM16A calcium-activated chloride channel: Inhibition and potentiation. PLoS One 2020; 15:e0231812. [PMID: 32302365 PMCID: PMC7164836 DOI: 10.1371/journal.pone.0231812] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2020] [Accepted: 04/01/2020] [Indexed: 11/22/2022] Open
Abstract
TMEM16A, a Ca2+-sensitive Cl- channel, plays key roles in many physiological functions related to Cl- transport across lipid membranes. Activation of this channel is mediated via binding intracellular Ca2+ to the channel with a relatively high apparent affinity, roughly in the sub-μM to low μM concentration range. Recently available high-resolution structures of TMEM16 molecules reveal that the high-affinity Ca2+ activation sites are formed by several acidic amino acids, using their negatively charged sidechain carboxylates to coordinate the bound Ca2+. In this study, we examine the interaction of TMEM16A with a divalent cation, Co2+, which by itself cannot activate current in TMEM16A. This divalent cation, however, has two effects when applied intracellularly. It inhibits the Ca2+-induced TMEM16A current by competing with Ca2+ for the aforementioned high-affinity activation sites. In addition, Co2+ also potentiates the Ca2+-induced current with a low affinity. This potentiation effect requires high concentration (mM) of Co2+, similar to our previous findings that high concentrations (mM) of intracellular Ca2+ ([Ca2+]i) can induce more TMEM16A current after the Ca2+-activation sites are saturated by tens of μM [Ca2+]i. The degrees of potentiation by Co2+ and Ca2+ also roughly correlate with each other. Interestingly, mutating a pore residue of TMEM16A, Y589, alters the degree of potentiation in that the smaller the sidechain of the replaced residue, the larger the potentiation induced by divalent cations. We suggest that the Co2+ potentiation and the Ca2+ potentiation share a similar mechanism by increasing Cl- flux through the channel pore, perhaps due to an increase of positive pore potential after the binding of divalent cations to phospholipids in the pore. A smaller sidechain of a pore residue may allow the pore to accommodate more phospholipids, thus enhancing the current potentiation caused by high concentrations of divalent cations.
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Affiliation(s)
- Dung M. Nguyen
- Center for Neuroscience, University of California, Davis, California, United States of America
| | - Louisa S. Chen
- Center for Neuroscience, University of California, Davis, California, United States of America
| | - Grace Jeng
- Center for Neuroscience, University of California, Davis, California, United States of America
| | - Wei-Ping Yu
- Center for Neuroscience, University of California, Davis, California, United States of America
| | - Tsung-Yu Chen
- Center for Neuroscience, University of California, Davis, California, United States of America
- Department of Neurology, University of California, Davis, California, United States of America
- * E-mail:
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5
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Vasquez-Montes V, Gerhart J, Thévenin D, Ladokhin AS. Divalent Cations and Lipid Composition Modulate Membrane Insertion and Cancer-Targeting Action of pHLIP. J Mol Biol 2019; 431:5004-5018. [PMID: 31689432 PMCID: PMC6920566 DOI: 10.1016/j.jmb.2019.10.016] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2019] [Revised: 10/24/2019] [Accepted: 10/24/2019] [Indexed: 02/06/2023]
Abstract
The pH-Low Insertion Peptide (pHLIP) has emerged as an important tool for targeting cancer cells; it has been assumed that its targeting mechanism depends solely on the mild acidic environment surrounding tumors. Here, we examine the role of Ca2+ and Mg2+ on pHLIP's insertion, cellular targeting, and drug delivery. We demonstrate that physiologically relevant concentrations of either cation can shift the protonation-dependent transition by up to several pH units toward basic pH and induce substantial protonation-independent transmembrane insertion of pHLIP at pH as high as 10. Consistent with these results, the ability of pHLIP to deliver the cytotoxic compound monomethyl-auristatin-F to HeLa cells is increased several fold in presence of Ca2+. Complementary measurements with model membranes confirmed this Ca2+/Mg2+-dependent membrane-insertion mechanism. The magnitude of this alternative Ca2+/Mg2+-dependent effect is also modulated by lipid composition-specifically by the presence of phosphatidylserine-providing new clues to pHLIP's unique tumor-targeting ability in vivo. These results exemplify the complex coupling between protonation of anionic residues and lipid-selective targeting by divalent cations, which is relevant to the general signaling on membrane interfaces.
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Affiliation(s)
- Victor Vasquez-Montes
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, KS, 66160, USA
| | - Janessa Gerhart
- Department of Chemistry, Lehigh University, 6 East Packer Avenue, Bethlehem, PA, 18015, USA
| | - Damien Thévenin
- Department of Chemistry, Lehigh University, 6 East Packer Avenue, Bethlehem, PA, 18015, USA
| | - Alexey S Ladokhin
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, KS, 66160, USA.
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6
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Pannwitt S, Slama K, Depoix F, Helm M, Schneider D. Against Expectations: Unassisted RNA Adsorption onto Negatively Charged Lipid Bilayers. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:14704-14711. [PMID: 31626734 DOI: 10.1021/acs.langmuir.9b02830] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The composition and physicochemical properties of biological membranes can be altered by diverse membrane integral and peripheral proteins as well as by small molecules, natural and synthetic. Diverse oligonucleotides have been shown to electrostatically interact with cationic and bivalent ion loaded zwitterionic liposomes, leading to the formation of oligonucleotide-liposome aggregates. However, interaction of RNAs with other membrane surfaces remains ill understood. We used the nonnatural RNA10 to investigate RNA binding to anionic and net-uncharged membrane surfaces. RNA10 had initially been selected in a screen for nonnatural RNA motives that bind to phosphatidylcholine liposomes in the presence of Mg2+. Here we show that interaction of defined RNA molecules with membrane surfaces crucially depends on electrostatic surface properties. Furthermore, RNA10 electrostatically binds to anionic lipid bilayers in the absence of Mg2+ or other bivalent cations, and this interaction leads to measurably changed physicochemical properties of the bilayer and the oligonucleotide. Thus, the structure of polyanionic RNA can be modulated via contact with negatively charged membrane surfaces and vice versa.
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Affiliation(s)
- Stefanie Pannwitt
- Institute of Pharmacy and Biochemistry , Johannes Gutenberg University , Johann-Joachim-Becherweg 30 , 55128 Mainz , Germany
| | - Kaouthar Slama
- Institute of Pharmacy and Biochemistry , Johannes Gutenberg University , Staudinger Weg 5 , 55128 Mainz , Germany
| | - Frank Depoix
- Institute of Molecular Physiology , Johannes Gutenberg University , Johann-Joachim-Becherweg 9-11 , 55128 Mainz , Germany
| | - Mark Helm
- Institute of Pharmacy and Biochemistry , Johannes Gutenberg University , Staudinger Weg 5 , 55128 Mainz , Germany
| | - Dirk Schneider
- Institute of Pharmacy and Biochemistry , Johannes Gutenberg University , Johann-Joachim-Becherweg 30 , 55128 Mainz , Germany
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7
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Baxter AJ, Santiago-Ruiz AN, Yang T, Cremer PS. Modulation of Cu 2+ Binding to Sphingosine-1-Phosphate by Lipid Charge. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:824-830. [PMID: 30638371 DOI: 10.1021/acs.langmuir.8b03718] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Sphingosine-1-phosphate (S1P) is a sphingolipid metabolite that is thought to participate in the regulation of many physiological processes and may play a key role in several diseases. Herein, we found that Cu2+ binds tightly to supported lipid bilayers (SLBs) containing S1P. Specifically, we demonstrated via fluorescence assays that Cu2+-S1P binding was bivalent and sensitive to the concentration of S1P in the SLB. In fact, the apparent equilibrium dissociation constant, KDApp, tightened by a factor of 132 from 4.5 μM to 34 nM as the S1P density was increased from 5.0 to 20 mol %. A major driving force for this apparent tightening was the more negative surface potential with increasing S1P concentration. This potential remained unaltered upon Cu2+ binding at pH 7.4 because two protons were released for every Cu2+ that bound. At pH 5.4, however, Cu2+ could not outcompete protons for the amine and no binding occurred. Moreover, at pH 9.4, the amine was partially deprotonated before Cu2+ binding and the surface potential became more positive on binding. The results for Cu2+-S1P binding were reminiscent of those for Cu2+-phosphatidylserine binding, where a carboxylate group helped to deprotonate the amine. In the case of S1P, however, the phosphate needed to bear two negative charges to facilitate amine deprotonation in the presence of Cu2+.
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Affiliation(s)
| | - Adriana N Santiago-Ruiz
- Department of Chemistry , The University of Puerto Rico , Cayey , Puerto Rico 00736 , United States
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8
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Cámara C, Lurgo FE, Fanani ML, Wilke N. Mechanical Stability of Lipid Membranes Decorated with Dextran Sulfate. ACS OMEGA 2018; 3:11673-11683. [PMID: 31459263 PMCID: PMC6645315 DOI: 10.1021/acsomega.8b01537] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/04/2018] [Accepted: 09/10/2018] [Indexed: 06/10/2023]
Abstract
Lipid vesicles decorated with polysaccharides have been proposed as vehicles for drug delivery because the polymers confer to the vesicles an enhanced stability, increasing the probability of the drug for reaching the target cell. Here, we first test the affinity of dextran sulfate (DS) for two different vesicle composition, and afterward, we study the effect of DS on the liposome mechanical properties. We found that DS binds to both tested membrane compositions. The interaction of DS with the anionic membranes studied here is mediated by the metal ions present in the aqueous solution (Na+ and Ca2+), being higher in the presence of Ca2+. Binding occurs preferentially in regions of closely packed lipids. Strikingly, DS did not affect the stability against detergent and the membrane rigidity of none of the vesicles. Thus, the proposed stability increase induced by this kind of polymers in drug delivery systems is not related with a modulation of the membrane thermodynamic properties but to other biochemical factors.
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Affiliation(s)
- Candelaria
I. Cámara
- Facultad
de Ciencias Químicas, Departamento de Química Biológica
Ranwel Caputto, Ciudad Universitaria, Universidad
Nacional de Córdoba, X5000HUA Córdoba, Argentina
- Centro
de Investigaciones en Química Biológica de Córdoba
(CIQUIBIC), Ciudad Universitaria, CONICET,
Universidad Nacional de Córdoba, X5000HUA Córdoba, Argentina
| | - Florencia E. Lurgo
- Facultad
de Ciencias Químicas, Departamento de Química Biológica
Ranwel Caputto, Ciudad Universitaria, Universidad
Nacional de Córdoba, X5000HUA Córdoba, Argentina
- Centro
de Investigaciones en Química Biológica de Córdoba
(CIQUIBIC), Ciudad Universitaria, CONICET,
Universidad Nacional de Córdoba, X5000HUA Córdoba, Argentina
| | - Maria Laura Fanani
- Facultad
de Ciencias Químicas, Departamento de Química Biológica
Ranwel Caputto, Ciudad Universitaria, Universidad
Nacional de Córdoba, X5000HUA Córdoba, Argentina
- Centro
de Investigaciones en Química Biológica de Córdoba
(CIQUIBIC), Ciudad Universitaria, CONICET,
Universidad Nacional de Córdoba, X5000HUA Córdoba, Argentina
| | - Natalia Wilke
- Facultad
de Ciencias Químicas, Departamento de Química Biológica
Ranwel Caputto, Ciudad Universitaria, Universidad
Nacional de Córdoba, X5000HUA Córdoba, Argentina
- Centro
de Investigaciones en Química Biológica de Córdoba
(CIQUIBIC), Ciudad Universitaria, CONICET,
Universidad Nacional de Córdoba, X5000HUA Córdoba, Argentina
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9
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Cobalt and nickel affect the fluidity of negatively-charged biomimetic membranes. Chem Phys Lipids 2018; 210:28-37. [DOI: 10.1016/j.chemphyslip.2017.11.016] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2017] [Revised: 11/02/2017] [Accepted: 11/24/2017] [Indexed: 01/28/2023]
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10
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Graber ZT, Shi Z, Baumgart T. Cations induce shape remodeling of negatively charged phospholipid membranes. Phys Chem Chem Phys 2017; 19:15285-15295. [PMID: 28569910 PMCID: PMC5562360 DOI: 10.1039/c7cp00718c] [Citation(s) in RCA: 64] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
The divalent cation Ca2+ is a key component in many cell signaling and membrane trafficking pathways. Ca2+ signal transduction commonly occurs through interaction with protein partners. However, in this study we show a novel mechanism by which Ca2+ may impact membrane structure. We find an asymmetric concentration of Ca2+ across the membrane triggers deformation of membranes containing negatively charged lipids such as phosphatidylserine (PS) and phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2). Membrane invaginations in vesicles were observed forming away from the leaflet with higher Ca2+ concentration, showing that Ca2+ induces negative curvature. We hypothesize that the negative curvature is produced by Ca2+-induced clustering of PS and PI(4,5)P2. In support of this notion, we find that Ca2+-induced membrane deformation is stronger for membranes containing PI(4,5)P2, which is known to more readily cluster in the presence of Ca2+. The observed Ca2+-induced membrane deformation is strongly influenced by Na+ ions. A high symmetric [Na+] across the membrane reduces Ca2+ binding by electrostatic shielding, inhibiting Ca2+-induced membrane deformation. An asymmetric [Na+] across the membrane, however, can either oppose or support Ca2+-induced deformation, depending on the direction of the gradient in [Na+]. At a sufficiently high asymmetric Na+ concentration it can impact membrane structure in the absence of Ca2+. We propose that Ca2+ works in concert with curvature generating proteins to modulate membrane curvature and shape transitions. This novel structural impact of Ca2+ could be important for Ca2+-dependent cellular processes that involve the creation of membrane curvature, including exocytosis, invadopodia, and cell motility.
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Affiliation(s)
- Z T Graber
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA, USA.
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11
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Cesium and Strontium Retentions Governed by Aluminosilicate Gel in Alkali-Activated Cements. MATERIALS 2017; 10:ma10040447. [PMID: 28772803 PMCID: PMC5506979 DOI: 10.3390/ma10040447] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/28/2017] [Revised: 04/07/2017] [Accepted: 04/13/2017] [Indexed: 11/16/2022]
Abstract
The present study investigates the retention mechanisms of cesium and strontium for alkali-activated cements. Retention mechanisms such as adsorption and precipitation were examined in light of chemical interactions. Batch adsorption experiments and multi-technical characterizations by using X-ray diffraction, zeta potential measurements, and the N₂ gas adsorption/desorption methods were conducted for this purpose. Strontium was found to crystalize in alkali-activated cements, while no cesium-bearing crystalline phases were detected. The adsorption kinetics of alkali-activated cements having relatively high adsorption capacities were compatible with pseudo-second-order kinetic model, thereby suggesting that it is governed by complex multistep adsorption. The results provide new insight, demonstrating that characteristics of aluminosilicate gel with a highly negatively charged surface and high micropore surface area facilitated more effective immobilization of cesium and strontium in comparison with calcium silicate hydrates.
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12
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Furse S. Is phosphatidylglycerol essential for terrestrial life? J Chem Biol 2016; 10:1-9. [PMID: 28101250 DOI: 10.1007/s12154-016-0159-3] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2016] [Accepted: 08/29/2016] [Indexed: 01/11/2023] Open
Abstract
Lipids are of increasing importance in understanding biological systems. Lipids carrying an anionic charge are noted in particular for their electrostatic interactions with both proteins and divalent cations. However, the biological, analytical, chemical and biophysical data of such species are rarely considered together, limiting our ability to assess the true role of such lipids in vivo. In this review, evidence from a range of studies about the lipid phosphatidylglycerol is considered. This evidence supports the conclusions that this lipid is ubiquitous in living systems and generally of low abundance but probably fundamental for terrestrial life. Possible reasons for this are discussed and further questions posed.
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Affiliation(s)
- Samuel Furse
- Molekylærbiologisk institutt, Unversitetet i Bergen, Thormøhlens gate 55, 5006 Bergen, Norway
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13
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Turek AB, Tirrell DA. Competitive Adsorption of Divalent Cations and Cationic Polyelectrolytes on Phosphatidylglycerol Bilayer Membranes. J BIOACT COMPAT POL 2016. [DOI: 10.1177/088391158600100303] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Affiliation(s)
- Anne B. Turek
- Department of Chemistry Carnegie-Mellon University Pittsburgh, PA 15213
| | - David A. Tirrell
- Department of Polymer Science and Engineering University of Massachusetts Amherst, MA 01003
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14
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Potvin-Fournier K, Lefèvre T, Picard-Lafond A, Marcotte C, Dufresne C, Cantin L, Salesse C, Auger M. Discriminating Lipid– from Protein–Calcium Binding To Understand the Interaction between Recoverin and Phosphatidylglycerol Model Membranes. Biochemistry 2016; 55:3481-91. [DOI: 10.1021/acs.biochem.6b00408] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Affiliation(s)
- Kim Potvin-Fournier
- Département
de chimie, Regroupement québécois de recherche sur la
fonction, l’ingénierie et les applications des protéines
(PROTEO), Centre de recherche sur les matériaux avancés
(CERMA), Centre québécois sur les matériaux fonctionnels
(CQMF), Université Laval, Pavillon Alexandre-Vachon, 1045
avenue de la médecine, Québec, Québec G1V 0A6, Canada
- CUO-recherche,
Centre de recherche du CHU de Québec, Hôpital du Saint-Sacrement,
Département d’ophtalmologie, Faculté de médecine,
PROTEO, Université Laval, Québec, Québec G1S 4L8, Canada
| | - Thierry Lefèvre
- Département
de chimie, Regroupement québécois de recherche sur la
fonction, l’ingénierie et les applications des protéines
(PROTEO), Centre de recherche sur les matériaux avancés
(CERMA), Centre québécois sur les matériaux fonctionnels
(CQMF), Université Laval, Pavillon Alexandre-Vachon, 1045
avenue de la médecine, Québec, Québec G1V 0A6, Canada
| | - Audrey Picard-Lafond
- Département
de chimie, Regroupement québécois de recherche sur la
fonction, l’ingénierie et les applications des protéines
(PROTEO), Centre de recherche sur les matériaux avancés
(CERMA), Centre québécois sur les matériaux fonctionnels
(CQMF), Université Laval, Pavillon Alexandre-Vachon, 1045
avenue de la médecine, Québec, Québec G1V 0A6, Canada
| | - Catherine Marcotte
- Département
de chimie, Regroupement québécois de recherche sur la
fonction, l’ingénierie et les applications des protéines
(PROTEO), Centre de recherche sur les matériaux avancés
(CERMA), Centre québécois sur les matériaux fonctionnels
(CQMF), Université Laval, Pavillon Alexandre-Vachon, 1045
avenue de la médecine, Québec, Québec G1V 0A6, Canada
| | - Caroline Dufresne
- Département
de chimie, Regroupement québécois de recherche sur la
fonction, l’ingénierie et les applications des protéines
(PROTEO), Centre de recherche sur les matériaux avancés
(CERMA), Centre québécois sur les matériaux fonctionnels
(CQMF), Université Laval, Pavillon Alexandre-Vachon, 1045
avenue de la médecine, Québec, Québec G1V 0A6, Canada
| | - Line Cantin
- CUO-recherche,
Centre de recherche du CHU de Québec, Hôpital du Saint-Sacrement,
Département d’ophtalmologie, Faculté de médecine,
PROTEO, Université Laval, Québec, Québec G1S 4L8, Canada
| | - Christian Salesse
- CUO-recherche,
Centre de recherche du CHU de Québec, Hôpital du Saint-Sacrement,
Département d’ophtalmologie, Faculté de médecine,
PROTEO, Université Laval, Québec, Québec G1S 4L8, Canada
| | - Michèle Auger
- Département
de chimie, Regroupement québécois de recherche sur la
fonction, l’ingénierie et les applications des protéines
(PROTEO), Centre de recherche sur les matériaux avancés
(CERMA), Centre québécois sur les matériaux fonctionnels
(CQMF), Université Laval, Pavillon Alexandre-Vachon, 1045
avenue de la médecine, Québec, Québec G1V 0A6, Canada
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15
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Surface Electrical Potentials of Root Cell Plasma Membranes: Implications for Ion Interactions, Rhizotoxicity, and Uptake. Int J Mol Sci 2014; 15:22661-22677. [PMID: 25493475 PMCID: PMC4284729 DOI: 10.3390/ijms151222661] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2014] [Revised: 11/28/2014] [Accepted: 12/01/2014] [Indexed: 11/25/2022] Open
Abstract
Many crop plants are exposed to heavy metals and other metals that may intoxicate the crop plants themselves or consumers of the plants. The rhizotoxicity of heavy metals is influenced strongly by the root cell plasma membrane (PM) surface’s electrical potential (ψ0). The usually negative ψ0 is created by negatively charged constituents of the PM. Cations in the rooting medium are attracted to the PM surface and anions are repelled. Addition of ameliorating cations (e.g., Ca2+ and Mg2+) to the rooting medium reduces the effectiveness of cationic toxicants (e.g., Cu2+ and Pb2+) and increases the effectiveness of anionic toxicants (e.g., SeO42− and H2AsO4−). Root growth responses to ions are better correlated with ion activities at PM surfaces ({IZ}0) than with activities in the bulk-phase medium ({IZ}b) (IZ denotes an ion with charge Z). Therefore, electrostatic effects play a role in heavy metal toxicity that may exceed the role of site-specific competition between toxicants and ameliorants. Furthermore, ψ0 controls the transport of ions across the PM by influencing both {IZ}0 and the electrical potential difference across the PM from the outer surface to the inner surface (Em,surf). Em,surf is a component of the driving force for ion fluxes across the PM and controls ion-channel voltage gating. Incorporation of {IZ}0 and Em,surf into quantitative models for root metal toxicity and uptake improves risk assessments of toxic metals in the environment. These risk assessments will improve further with future research on the application of electrostatic theory to heavy metal phytotoxicity in natural soils and aquatic environments.
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16
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Bahreman A, Rabe M, Kros A, Bruylants G, Bonnet S. Binding of a ruthenium complex to a thioether ligand embedded in a negatively charged lipid bilayer: a two-step mechanism. Chemistry 2014; 20:7429-38. [PMID: 24782232 DOI: 10.1002/chem.201400377] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2014] [Indexed: 01/14/2023]
Abstract
The interaction between the ruthenium polypyridyl complex [Ru(terpy)(dcbpy)(H2O)](2+) (terpy = 2,2';6',2"-terpyridine, dcbpy = 6,6'-dichloro-2,2'-bipyridine) and phospholipid membranes containing either thioether ligands or cholesterol were investigated using UV-visible spectroscopy, Langmuir-Blodgett monolayer surface pressure measurements, and isothermal titration calorimety (ITC). When embedded in a membrane, the thioether ligand coordinated to the dicationic metal complex only when the phospholipids of the membrane were negatively charged, that is, in the presence of attractive electrostatic interaction. In such a case coordination is much faster than in homogeneous conditions. A two-step model for the coordination of the metal complex to the membrane-embedded sulfur ligand is proposed, in which adsorption of the complex to the negative surface of the monolayers or bilayers occurs within minutes, whereas formation of the coordination bond between the surface-bound metal complex and ligand takes hours. Finally, adsorption of the aqua complex to the membrane is driven by entropy. It does not involve insertion of the metal complex into the hydrophobic lipid layer, but rather simple electrostatic adsorption at the water-bilayer interface.
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Affiliation(s)
- Azadeh Bahreman
- Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, P.O. Box 9502, Leiden, 2300 RA (The Netherlands)
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17
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Abstract
Control and modulation of electrical signaling is vital to normal physiology, particularly in neurons, cardiac myocytes, and skeletal muscle. The orchestrated activities of variable sets of ion channels and transporters, including voltage-gated ion channels (VGICs), are responsible for initiation, conduction, and termination of the action potential (AP) in excitable cells. Slight changes in VGIC activity can lead to severe pathologies including arrhythmias, epilepsies, and paralyses, while normal excitability depends on the precise tuning of the AP waveform. VGICs are heavily posttranslationally modified, with upward of 30% of the mature channel mass consisting of N- and O-glycans. These glycans are terminated typically by negatively charged sialic acid residues that modulate voltage-dependent channel gating directly. The data indicate that sialic acids alter VGIC activity in isoform-specific manners, dependent in part, on the number/location of channel sialic acids attached to the pore-forming alpha and/or auxiliary subunits that often act through saturating electrostatic mechanisms. Additionally, cell-specific regulation of sialylation can affect VGIC gating distinctly. Thus, channel sialylation is likely regulated through two mechanisms that together contribute to a dynamic spectrum of possible gating motifs: a subunit-specific mechanism and regulated (aberrant) changes in the ability of the cell to glycosylate. Recent studies showed that neuronal and cardiac excitability is modulated through regulated changes in voltage-gated Na(+) channel sialylation, suggesting that both mechanisms of differential VGIC sialylation contribute to electrical signaling in the brain and heart. Together, the data provide insight into an important and novel paradigm involved in the control and modulation of electrical signaling.
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Affiliation(s)
- Andrew R Ednie
- Programs in Cardiovascular Research and Neuroscience, Department of Molecular Pharmacology & Physiology, College of Medicine, University of South Florida, Tampa, Florida, USA
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18
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Chieng YY, Chen SB. Complexation of cationic polyelectrolyte with anionic phospholipid vesicles: Concentration, molecular weight and salt effects. J Colloid Interface Sci 2011; 354:226-33. [DOI: 10.1016/j.jcis.2010.10.045] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2010] [Revised: 10/20/2010] [Accepted: 10/21/2010] [Indexed: 11/16/2022]
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19
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Vesicles with charged domains. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1798:1338-47. [DOI: 10.1016/j.bbamem.2009.12.023] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/17/2009] [Revised: 12/15/2009] [Accepted: 12/22/2009] [Indexed: 01/29/2023]
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20
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Ausili A, de Godos A, Torrecillas A, Corbalán-García S, Gómez-Fernández JC. The interaction of the Bax C-terminal domain with membranes is influenced by the presence of negatively charged phospholipids. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2009; 1788:1924-32. [DOI: 10.1016/j.bbamem.2009.06.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/13/2009] [Revised: 06/02/2009] [Accepted: 06/08/2009] [Indexed: 11/17/2022]
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21
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Pavani C, Uchoa AF, Oliveira CS, Iamamoto Y, Baptista MS. Effect of zinc insertion and hydrophobicity on the membrane interactions and PDT activity of porphyrin photosensitizers. Photochem Photobiol Sci 2008; 8:233-40. [PMID: 19247516 DOI: 10.1039/b810313e] [Citation(s) in RCA: 106] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A series of photosensitizers (PS), which are meso-substituted tetra-cationic porphyrins, was synthesized in order to study the role of amphiphilicity and zinc insertion in photodynamic therapy (PDT) efficacy. Several properties of the PS were evaluated and compared within the series including photophysical properties (absorption spectra, fluorescence quantum yield Phif, and singlet oxygen quantum yield PhiDelta), uptake by vesicles, mitochondria and HeLa cells, dark and phototoxicity in HeLa cells. The photophysical properties of all compounds are quite similar (Phif<or=0.02; PhiDelta approximately 0.8). An increase in lipophilicity and the presence of zinc in the porphyrin ring result in higher vesicle and cell uptake. Binding in mitochondria is dependent on the PS lipophilicity and on the electrochemical membrane potential, i.e., in uncoupled mitochondria PS binding decreases by up to 53%. The porphyrin substituted with octyl groups (TC8PyP) is the compound that is most enriched in mitochondria, and its zinc derivative (ZnTC8PyP) has the highest global uptake. The stronger membrane interaction of the zinc-substituted porphyrins is attributed to a complexing effect with phosphate groups of the phospholipids. Zinc insertion was also shown to decrease the interaction with isolated mitochondria and with the mitochondria of HeLa cells, an effect that has been explained by the particular characteristics of the mitochondrial internal membrane. Phototoxicity was shown to increase proportionally with membrane binding efficiency, which is attributed to favorable membrane interactions which allow more efficient membrane photooxidation. For this series of compounds, photodynamic efficiency is directly proportional to the membrane binding and cell uptake, but it is not totally related to mitochondrial targeting.
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Affiliation(s)
- Christiane Pavani
- Departamento de Química, FFCLRP, Universidade de São Paulo, Ribeirão Preto, Brazil
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22
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Sou K, Tsuchida E. Electrostatic interactions and complement activation on the surface of phospholipid vesicle containing acidic lipids: Effect of the structure of acidic groups. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2008; 1778:1035-41. [DOI: 10.1016/j.bbamem.2008.01.006] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/05/2007] [Revised: 11/22/2007] [Accepted: 01/07/2008] [Indexed: 10/22/2022]
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23
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Pashkovskaya AA, Sokolenko EA, Sokolov VS, Kotova EA, Antonenko YN. Photodynamic activity and binding of sulfonated metallophthalocyanines to phospholipid membranes: Contribution of metal-phosphate coordination. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2007; 1768:2459-65. [PMID: 17662238 DOI: 10.1016/j.bbamem.2007.05.018] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/29/2007] [Revised: 05/08/2007] [Accepted: 05/18/2007] [Indexed: 10/23/2022]
Abstract
Photosensitized efficacy of tetrasulfonated phthalocyanines of zinc, aluminum and nickel (ZnPcS(4), AlPcS(4) and NiPcS(4), respectively) as studied by gramicidin channel (gA) photoinactivation was compared with adsorption of the dyes on the surface of a bilayer lipid membrane as measured by the inner field compensation method. The adsorption of the negatively charged phthalocyanines on diphytanoylphosphatidylcholine (DPhPC) membranes led to formation of a negative boundary potential difference between the membrane/water interfaces. Good correlation was shown between the photodynamic activity and the membrane binding of the three metallophthalocyanines. ZnPcS(4) appeared to be the most potent of these photosensitizers, while NiPcS(4) was completely ineffective. All of these phthalocyanines displayed no binding and negligible gA photoinactivation with membranes formed of glycerol monooleate (GMO), whereas Rose Bengal exhibited significant binding and photodynamic efficacy with GMO membranes. Gramicidin photoinactivation in the presence of AlPcS(4), being insensitive to the ionic strength of the bathing solution, was inhibited by fluoride and attenuated by phosphate ions. A blue shift of the fluorescence peak position of ZnPcS(4) dissolved in ethanol was elicited by phosphate, similarly to fluoride, which was indicative of the coordination interaction of these ions with the central metal atom of the phthalocyanine macrocycle. This interaction was enhanced in the medium modeling the water-membrane interface. The results obtained imply that binding of tetrasulfonated metallophthalocyanines to phospholipid membranes is determined primarily by metal-phosphate coordination.
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Affiliation(s)
- Alina A Pashkovskaya
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow 119992, Russia
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24
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Zhou Y, Raphael RM. Solution pH alters mechanical and electrical properties of phosphatidylcholine membranes: relation between interfacial electrostatics, intramembrane potential, and bending elasticity. Biophys J 2006; 92:2451-62. [PMID: 17172308 PMCID: PMC1864824 DOI: 10.1529/biophysj.106.096362] [Citation(s) in RCA: 106] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Solution pH affects numerous biological processes and some biological membranes are exposed to extreme pH environments. We utilized micropipette aspiration of giant unilamellar vesicles composed of 1-stearoyl-2-oleoyl-phosphatidylcholine to characterize the effect of solution pH (2-9) on membrane mechanical properties. The elastic area compressibility modulus was unaffected between pH 3 and 9 but was reduced by approximately 30% at pH 2. Fluorescence experiments utilizing the phase-sensitive probe Laurdan confirmed gel-phase characteristics at pH 2, explaining the reduction of membrane elasticity. The membrane bending stiffness, kc, increased by approximately 40% at pH 4 and pH 9 over the control value at pH 6.5. Electrophoretic mobility measurements indicate that these changes are qualitatively consistent with theoretical models that predict the effect of membrane surface charge density and Debye length on kc, substantiating a coupling between the mechanical and interfacial electrical properties of the membrane. The effect of pH on intramembrane electrical properties was examined by studying the spectral shifts of the potentiometric probe di-8 ANEPPS. The intramembrane (dipole) potential (Psid) increased linearly as the solution pH decreased in a manner consistent with the partitioning of hydroxide ions into the membrane. However, changes in Psid did not correlate with changes in kc. These mechanical and electrical studies lead to the conclusion that the effect of pH on membrane bending stiffness results from alterations in interfacial, as opposed to intramembrane, electrostatics.
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Affiliation(s)
- Yong Zhou
- Department of Biochemistry and Cell Biology, Rice University, Houston, Texas, USA
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25
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Sinn CG, Antonietti M, Dimova R. Binding of calcium to phosphatidylcholine–phosphatidylserine membranes. Colloids Surf A Physicochem Eng Asp 2006. [DOI: 10.1016/j.colsurfa.2005.10.014] [Citation(s) in RCA: 119] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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26
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Arseneault M, Lafleur M. Isothermal titration calorimetric study of calcium association to lipid bilayers: influence of the vesicle preparation and composition. Chem Phys Lipids 2006; 142:84-93. [PMID: 16620798 DOI: 10.1016/j.chemphyslip.2006.03.003] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2005] [Revised: 03/02/2006] [Accepted: 03/15/2006] [Indexed: 11/19/2022]
Abstract
The association of Ca2+ ions with phospholipid bilayers was investigated using isothermal titration calorimetry. The study reveals that the binding enthalpy of these cations to bilayers formed with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG) depends strongly on the method of preparation of the unilamellar vesicles. Extruded vesicles lead to an exothermic association, whereas sonicated ones lead to an endothermic association. In the later case, the calorimetric signal is sensitive to the length of the sonication period. It is proposed that a reorganization of the lipid bilayers under stress, obtained with sonicated small unilamellar vesicles, contributes to the calorimetric signal upon the titration with Ca2+. The analysis of the titrations indicates that, as expected, the nature of the association of Ca2+ with negatively charged phospholipid bilayers is essentially of electrostatic nature. Using a Scatchard approach, it is found that bilayers become saturated in Ca2+ approximately when the electroneutrality of the bilayer interface is reached. Moreover, the affinity constant was reduced by the increase of the ionic strength of the aqueous buffer. It was found that the intrinsic binding constant of Ca2+ to membranes containing 30 and 50 mol% of POPG was about 11 mM-1, in a MES buffer containing 10 mM NaCl, at pH 5.6.
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Affiliation(s)
- Marjolaine Arseneault
- Department of Chemistry, Université de Montréal, C.P. 6128, Succ. Centre Ville, Montréal, Que., H3C3J7 Canada
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27
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Flunitrazepam effect on distearoylphosphatidylglycerol, cholesterol and distearoylphosphatidylglycerol+cholesterol mixed monolayers structure at a DCE/water interface. Electrochim Acta 2006. [DOI: 10.1016/j.electacta.2005.12.036] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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28
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Liu X, Shang L, Jiang X, Dong S, Wang E. Conformational changes of beta-lactoglobulin induced by anionic phospholipid. Biophys Chem 2006; 121:218-23. [PMID: 16494994 DOI: 10.1016/j.bpc.2005.12.015] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2005] [Revised: 12/25/2005] [Accepted: 12/26/2005] [Indexed: 11/23/2022]
Abstract
Conformational changes of beta-lactoglobulin (beta-LG) induced by anionic phospholipid (dimyristoylphosphatidylglycerol, DMPG) at physiological conditions (pH 7.0) have been investigated by UV-VIS, circular dichroism (CD) and fluorescence spectra. The experimental results suggest that beta-LG-DMPG interactions cause beta-LG a structural reorganization of the secondary structure elements accompanied by an increase in alpha-helical content, and a loosening of the protein tertiary structure. The interaction forces between beta-LG and DMPG are further evaluated by fluorescence spectra. The fluorescence spectral data show that conformational changes in the protein are driven by electrostatic interaction at first, then by hydrophobic interaction between a protein with a negative net charge and a negatively charged phospholipid.
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Affiliation(s)
- Xiaohua Liu
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Renmin Street 5625, Changchun, Jilin 130022, China
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29
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Shoemaker SD, Vanderlick TK. Calcium modulates the mechanical properties of anionic phospholipid membranes. J Colloid Interface Sci 2004; 266:314-21. [PMID: 14527454 DOI: 10.1016/s0021-9797(03)00582-4] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Using micropipette aspiration and fluorescence techniques, we have studied the material properties of charged lipid vesicles in calcium solutions. Vesicles were composed of phosphatidylglycerol (PG)/phosphatidylcholine (PC) or phosphatidic acid (PA)/PC mixtures. For the case of PG/PC membranes, we measure no effect of anionic lipid fraction on elasticity but a monotonic decrease up to 20% for tension required to induce membrane failure. Both of these observations are rationalized by a model we have developed to describe membrane electrostatic interactions in a two-component salt solution and the resulting changes in membrane properties. Critical tensions measured for PA/PC membranes, on the other hand, did not depend on anionic lipid fraction and were uniformly approximately 35% lower than PG/PC vesicles. This is likely due to a lateral phase separation in the membrane. By combining mechanical properties with fluorescence observations we propose that the PA-rich phase separates into small unconnected domains.
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Affiliation(s)
- Scott D Shoemaker
- Department of Chemical Engineering, Princeton University, Princeton, NJ 08544, USA
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30
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Binder H, Lindblom G. Charge-dependent translocation of the Trojan peptide penetratin across lipid membranes. Biophys J 2003; 85:982-95. [PMID: 12885645 PMCID: PMC1303219 DOI: 10.1016/s0006-3495(03)74537-8] [Citation(s) in RCA: 157] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We studied the interaction of the cell-penetrating peptide penetratin with mixed dioleoylphosphatidylcholine/dioleoylphoshatidylglycerol (DOPC/DOPG) unilamellar vesicles as a function of the molar fraction of anionic lipid, X(PG), by means of isothermal titration calorimetry. The work was aimed at getting a better understanding of factors that affect the peptide binding to lipid membranes and its permeation through the bilayer. The binding was well described by a surface partitioning equilibrium using an effective charge of the peptide of z(P) approximately 5.1 +/- 0.5. The peptide first binds to the outer surface of the vesicles, the effective binding capacity of which increases with X(PG). At X(PG) approximately 0.5 and a molar ratio of bound peptide-to-lipid of approximately 1/20 the membranes become permeable and penetratin binds also to the inner monolayer after internalization. The results were rationalized in terms of an "electroporation-like" mechanism, according to which the asymmetrical distribution of the peptide between the outer and inner surfaces of the charged bilayer causes a transmembrane electrical field, which alters the lateral and the curvature stress acting within the membrane. At a threshold value these effects induce internalization of penetratin presumably via inversely curved transient structures.
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Affiliation(s)
- Hans Binder
- Department of Biophysical Chemistry, Umeå University, SE-90187 Umeå, Sweden.
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31
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Ruso JM, Besada L, Martínez-Landeira P, Seoane L, Prieto G, Sarmiento F. Interactions between liposomes and cations in aqueous solution. J Liposome Res 2003; 13:131-45. [PMID: 12855108 DOI: 10.1081/lpr-120020316] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
An investigation on the dependence of electrophoretic mobilities of unilamellar vesicles of phosphatidylcholine-cholesterol-phosphatidylinositol (PC-Chol-PI) on the concentration of several cations with variations in the relation charge/radius in the range Na+, K+, Cs+, Mg2+, Ca2+, Ba2+, Al3+, and La3+ has been realized. Plots of zeta potential against ion concentration exhibit a maximum for all the cations under study, the position of the maximum is greatly affected by the charge of the ion. From the feature of these plots two phenomenon were observed: an initial binding of cations into the slipping plane for ion concentration below the maximum and a phenomenon of vesicle association for concentration above the maximum. To confirm these observations measurements on dynamic light scattering were performed to obtain the corresponding size distribution of the liposomes at different ion concentrations. Finally the ability of the Stern isotherm to describe the adsorption of the cations to vesicles was tested by two methods. The two main parameters of the theory: the total number of adsorption sites per unit area, N1, and the equilibrium constant, K; (and consequently the free energy of adsorption, deltaG0ads) were calculated for the different ions, showing good agreement. The equilibrium constants of adsorption have been found to obey a linear relationship with ion radius the slope of which decreases with the ion charge.
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Affiliation(s)
- Juan M Ruso
- Biophysics and Interfaces Group, Department of Applied Physics, Faculty of Physics, University of Santiago de Compostela, Santiago de Compostela, Spain
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32
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Binder H, Lindblom G. Interaction of the Trojan peptide penetratin with anionic lipid membranes–a calorimetric study. Phys Chem Chem Phys 2003. [DOI: 10.1039/b309667j] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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33
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Takeda Y, Kasamo K. In vitro fusion of plant Golgi membranes can be influenced by divalent cations. J Biol Chem 2002; 277:47756-64. [PMID: 12368278 DOI: 10.1074/jbc.m209199200] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The fusogenic activity of plant Golgi membranes was studied in a cell-free system by assaying lipid mixing and content leakages of fluorescence probes. Golgi membranes from mung bean (Vigna radiata L.) hypocotyl cells fused to liposomes in the absence of any cytosolic proteins and nucleotides. It was demonstrated that the fusion was mediated by integral membrane protein(s), and was influenced by divalent cations (mm). Mg(2+), Ca(2+), and Mn(2+) ions enhanced the lipid mixing by reducing repulsive forces between membranes. In the content leakage assay, Mg(2+) ions also showed a stimulative effect. However, other divalent cations were inhibitory. It is suggested that the fusion system of Golgi membranes comprises at least two components: one that mediates the formation of fusion intermediates prior to pore opening, and one that mediates the subsequent processes. The latter must be sensitive to divalent cations at millimolar concentrations. The fusion of Golgi and biological membranes was induced by divalent cations. We speculated about the biological role of the fusion system studied here.
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Affiliation(s)
- Yuichi Takeda
- Research Institute for Bioresources, Okayama University, 1-20-2 Chuo, Kurashiki 710-0046, Japan.
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34
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Abstract
Results of atomistic molecular dynamics simulations of dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylglycerol monolayers at the air/water interface are presented. Dipalmitoylphosphatidylcholine is zwitterionic and dipalmitoylphosphatidylglycerol is anionic at physiological pH. NaCl and CaCl2 water subphases are simulated. The simulations are carried out at different surface densities, and a simulation cell geometry is chosen that greatly facilitates the investigation of phospholipid monolayer properties. Ensemble average monolayer properties calculated from simulation are in agreement with experimental measurements. The dependence of the properties of the monolayers on the surface density, the type of the headgroup, and the ionic environment are explained in terms of atomistically detailed pair distribution functions and electron density profiles, demonstrating the strength of simulations in investigating complex, multicomponent systems of biological importance.
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Affiliation(s)
- Yiannis N Kaznessis
- Department of Chemical Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136, USA
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35
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Olivares-Rivas W, Fillous L, Villegas JC. A Revised Stern Equation for Ion Exchange at Charged Membranes. J Colloid Interface Sci 2001; 233:313-319. [PMID: 11121281 DOI: 10.1006/jcis.2000.7217] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We revised the classical Stern equation for ion exchange at charged membranes using the statistical mechanics concept of chemical potential and ion activity in nonhomogeneous systems. Our proposed equation does not require an iterative procedure to obtain the self-regulated surface charge at the membranes. We predict significant differences with the classical results. When compared with experimental results, our approach not only gives a better fit but also predicts dissociation constants that are physically more reasonable than those from the classical approach. Copyright 2001 Academic Press.
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Affiliation(s)
- W Olivares-Rivas
- Grupo de Química Teórica Quimicofísica de Fluidos y Fenómenos Interfaciales (QUIFFIS), Departamento de Química Facultad de Ciencias, Universidad de los Andes, Mérida, Venezuela
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36
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Vikström S, Li L, Wieslander A. The nonbilayer/bilayer lipid balance in membranes. Regulatory enzyme in Acholeplasma laidlawii is stimulated by metabolic phosphates, activator phospholipids, and double-stranded DNA. J Biol Chem 2000; 275:9296-302. [PMID: 10734070 DOI: 10.1074/jbc.275.13.9296] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In membranes of Acholeplasma laidlawii a single glucosyltransferase step between the major, nonbilayer-prone monoglucosyl-diacylglycerol (MGlcDAG) and the bilayer-forming diglucosyl-diacylglycerol (DGlcDAG) is important for maintenance of lipid phase equilibria and curvature packing stress. This DGlcDAG synthase is activated in a cooperative fashion by phosphatidylglycerol (PG), but in vivo PG amounts are not enough for efficient DGlcDAG synthesis. In vitro, phospholipids with an sn-glycero-3-phosphate backbone, and no positive head group charge, functioned as activators. Different metabolic, soluble phosphates could supplement PG for activation, depending on type, amount, and valency. Especially efficient were the glycolytic intermediates fructose 1,6-bisphosphate and ATP, active at cellular concentrations on the DGlcDAG but not on the preceding MGlcDAG synthase. Potencies of different phosphatidylinositol (foreign lipid) derivatives differed with numbers and positions of their phosphate moieties. A selective stimulation of the DGlcDAG, but not the MGlcDAG synthase, by minor amounts of double-stranded DNA was additive to the best phospholipid activators. These results support two types of activator sites on the enzyme: (i) lipid-phosphate ones close to the membrane interphase, and (ii) soluble (or particulate)-phosphate ones further out from the surface. Thereby, the nonbilayer (MGlcDAG) to bilayer (DGlcDAG) lipid balance may be integrated with the metabolic status of the cell and potentially also to membrane and cell division.
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Affiliation(s)
- S Vikström
- Department of Biochemistry, Umeå University, 901 87 Umeå, Sweden.
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37
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Banerjee S, Bennouna M, Ferreira-Marques J, Ruysschaert JM, Caspers J. Lipid-Drug Interaction and Colligative Properties in Phospholipid Vesicles. J Colloid Interface Sci 1999; 219:168-177. [PMID: 10527584 DOI: 10.1006/jcis.1999.6442] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Imipramine penetration into the lipid core of a membrane was demonstrated through measurements on lipid monolayers (surface pressure and surface potential). The surface pressure measurements allow us to calculate the intrinsic binding constant (partition coefficient) for the lipid-Imipramine interaction. This latter value is in correct agreement with the results obtained by electrophoretic mobility measurements on liposomes. In addition, it was observed that the same mole fraction of "lipid-soluble drug" (Chlorpromazine or Imipramine) incorporated in a given lipidic phase (DPPC) induced the same shift in the transition temperature. Copyright 1999 Academic Press.
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Affiliation(s)
- S Banerjee
- Laboratoire de Chimie Physique des Macromolécules aux Interfaces, Université Libre de Bruxelles, Bd du Triomphe, Bruxelles, B-1050, Belgium
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38
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The Effect of Membrane Charge on Gold Nanoparticle Synthesis via Surfactant Membranes. J Colloid Interface Sci 1999; 210:73-85. [PMID: 9924109 DOI: 10.1006/jcis.1998.5932] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The effect of vesicle membrane structure and charge on the synthesis of gold nanoparticles was investigated. The vesicle membranes were comprised of either negatively charged soy lipids or mixtures of charge neutral and negatively charged soy lipids. Palladium ions bound to the membranes served as the catalyst for metal particle synthesis using an electroless metallization procedure. The size range of particles synthesized using membranes comprised of only negatively charged lipids (5-15 nm) was significantly smaller than those synthesized using mixtures of negatively charged and charge-neutral lipids (2-180 nm). X-ray diffraction revealed that the average crystallite size decreased with increasing palladium ion content of the membranes. It also showed that the average crystallite size was smaller for particles synthesized using vesicles comprised of only soy phoshohydroxyethanol lipids than for particles synthesized using vesicles comprised of only soy phosphatidic acid lipids. Particles synthesized with membranes comprised of only negatively charged lipids were encapsulated within the resulting lipid membrane matrix. FT-IR of the lipid matrix indicated that the matrix was formed as the result of ionic bridging of the lipid phosphate headgroups with gold ions. Copyright 1999 Academic Press.
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Kinraide TB, Yermiyahu U, Rytwo G. Computation of surface electrical potentials of plant cell membranes . Correspondence To published zeta potentials from diverse plant sources. PLANT PHYSIOLOGY 1998; 118:505-512. [PMID: 9765535 PMCID: PMC34825 DOI: 10.1104/pp.118.2.505] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/1998] [Accepted: 06/24/1998] [Indexed: 05/22/2023]
Abstract
A Gouy-Chapman-Stern model has been developed for the computation of surface electrical potential (psi0) of plant cell membranes in response to ionic solutes. The present model is a modification of an earlier version developed to compute the sorption of ions by wheat (Triticum aestivum L. cv Scout 66) root plasma membranes. A single set of model parameters generates values for psi0 that correlate highly with published zeta potentials of protoplasts and plasma membrane vesicles from diverse plant sources. The model assumes ion binding to a negatively charged site (R- = 0.3074 &mgr;mol m-2) and to a neutral site (P0 = 2.4 &mgr;mol m-2) according to the reactions R- + IZ &rlharr; RIZ-1 and P0 + IZ &rlharr; PIZ, where IZ represents an ion of charge Z. Binding constants for the negative site are 21, 500 M-1 for H+, 20,000 M-1 for Al3+, 2,200 M-1 for La3+, 30 M-1 for Ca2+ and Mg2+, and 1 M-1 for Na+ and K+. Binding constants for the neutral site are 1/180 the value for binding to the negative site. Ion activities at the membrane surface, computed on the basis of psi0, appear to determine many aspects of plant-mineral interactions, including mineral nutrition and the induction and alleviation of mineral toxicities, according to previous and ongoing studies. A computer program with instructions for the computation of psi0, ion binding, ion concentrations, and ion activities at membrane surfaces may be requested from the authors.
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Affiliation(s)
- TB Kinraide
- Appalachian Soil and Water Conservation Research Laboratory, Agricultural Research Service, United States Department of Agriculture, Beaver, West Virginia 25813-0400 (T.B.K.)
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Akashi K, Miyata H, Itoh H, Kinosita K. Formation of giant liposomes promoted by divalent cations: critical role of electrostatic repulsion. Biophys J 1998; 74:2973-82. [PMID: 9635751 PMCID: PMC1299638 DOI: 10.1016/s0006-3495(98)78004-x] [Citation(s) in RCA: 99] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Spontaneous formation of giant unilamellar liposomes in a gentle hydration process, as well as the adhesion energy between liposomal membranes, has been found to be dependent on the concentration of divalent alkali cations, Ca2+ or Mg2+, in the medium. With electrically neutral phosphatidylcholine (PC), Ca2+ or Mg2+ at 1-30 mM greatly promoted liposome formation compared to low yields in nonelectrolyte or potassium chloride solutions. When negatively charged phosphatidylglycerol (PG) was mixed at 10%, the yield was high in nonelectrolytes but liposomes did not form at 3-10 mM CaCl2. In the adhesion test with micropipette manipulation, liposomal membranes adhered to each other only in a certain range of CaCl2 concentrations, which agreed with the range where liposome did not form. The adhesion range shifted to higher Ca2+ concentrations as the amount of PG was increased. These results indicate that the divalent cations bind to and add positive charges to the lipids, and that membranes are separated and stabilized in the form of unilamellar liposomes when net charges on the membranes produce large enough electrostatic repulsion. Under the assumption that the maximum of adhesion energy within an adhesive range corresponds to exact charge neutralization by added Ca2+, association constants of PC and PG for Ca2+ were estimated at 7.3 M(-1) and 86 M(-1), respectively, in good agreement with literature values.
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Affiliation(s)
- K Akashi
- Department of Physics, Faculty of Science and Technology, Keio University, Yokohama, Japan
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Soeller C, Cannell MB. Numerical simulation of local calcium movements during L-type calcium channel gating in the cardiac diad. Biophys J 1997; 73:97-111. [PMID: 9199775 PMCID: PMC1180912 DOI: 10.1016/s0006-3495(97)78051-2] [Citation(s) in RCA: 139] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Computer simulation was used to investigate the calcium levels after sarcolemmal calcium influx through L-type calcium channels (DHPRs) into the narrow diadic space of cardiac muscle. The effect of various cytosolic and membranebound buffers, diad geometry, DHPR properties (open time and current), and surface charge were examined. The simulations showed that phospholipid binding sites on the sarcolemmal membrane are the major buffer affecting free calcium ([Ca2+]) levels in the diad. The inclusion of surface charge effects calculated from Gouy-Chapman theory resulted in a marked decrease in [Ca2+] levels at all times and a faster decay of [Ca2+] after termination of DHPR influx. For a DHPR current of 200 fA, [Ca2+] at the center of the diad reached peak levels of approximately 73 microM. In larger diads (> or = 400 nm diameter), [Ca2+] decayed more slowly than in smaller diads (100-200 nm diameter), although peak [Ca2+] levels reached during typical DHPR open times were similar. For a wide range of DHPR single-channel current magnitudes (Ica = 25-200 fA), [Ca2+] levels in the diad were approximately proportional to ICa. The decrease in calculated [Ca2+] levels due to the effects of surface charge can be interpreted as resulting from an effective "volume expansion" of the diad space. Furthermore, the layer of increased [Ca2+] close to the sarcolemmal membrane can act as a fast buffer.
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Affiliation(s)
- C Soeller
- Department of Pharmacology and Clinical Pharmacology, St. George's Hospital Medical School, London, England
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Abstract
We have measured the distribution of the hexavalent ruthenium red cation (RuR) between water and phospholipid membranes, have shown the critical importance of membrane negative surface charge for RuR binding, and determined the association constant of RuR for different phospholipid bilayers. The studies were performed with liposomes made of mixtures of zwitterionic L-alpha-phosphatidylcholine (PC), and one of the negatively charged phospholipids: L-alpha-phosphatidylserine (PS), L-alpha-phosphatidylinositol (PI), or L-alpha-phosphatidylglycerol (PG). Lipid composition of PC:PX membranes was 1:0, 19:1, 9:1, and 4:1. Liposomes were processed using freeze-and-thaw treatment, and their size distribution was characterized by light scattering and electron microscopy. Experimental distribution isotherms of RuR obtained by ultracentrifugation and spectrophotometry can be reproduced with the Langmuir-Stern-Grahame model, assuming that RuR behaves in the diffuse double layer as an ion with effective valency < 6. In terms of this model, PC-PS, PC-PI, and PC-PG membranes were found to be electrostatically equivalent and the intrinsic association constants of RuR were obtained. RuR has highest affinity to PS-containing membranes; its association constant for PC-PI and PC-PG membranes is about 5 times smaller than that for PC-PS membranes. From the comparison of RuR binding to mixed negatively charged phospholipid membranes and RuR binding to sarcoplasmic reticulum (SR), we conclude that the low-affinity RuR binding sites may indeed be associated with the lipid bilayer of SR.
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Affiliation(s)
- D Voelker
- Department of Physics, Portland State University, Oregon 97207, USA
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Satoh K. Determination of binding constants of Ca2+, Na+, and Cl- ions to liposomal membranes of dipalmitoylphosphatidylcholine at gel phase by particle electrophoresis. BIOCHIMICA ET BIOPHYSICA ACTA 1995; 1239:239-48. [PMID: 7488629 DOI: 10.1016/0005-2736(95)00154-u] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The zeta potentials of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) liposomes were measured at a gel phase as a function of CaCl2 concentration (0-200 mM) in a solution containing different NaCl concentrations (0-200 mM). The data obtained were analyzed with the diffuse double layer theory including the Graham theory. The intrinsic binding constants of ions to DPPC membranes and the distance of the shear plane have been determined independent of both the concentration of CaCl2 and that of NaCl. The values of the constants were 37 M-1 for Ca2+, 0.28 M-1 for Cl, and 0.25 M-1 for Na+; the distance was 0.24 nm under the assumption of binding stoichiometry of Ca2+/DPPC = 1:1.
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Affiliation(s)
- K Satoh
- Department of Physics, Jikei University School of Medicine, Tokyo, Japan
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Yamaguchi T, Nishizaki K, Itai S, Nemoto M, Ohshima H. Adsorption of divalent cations onto the membrane surface of lipid emulsion. Colloids Surf B Biointerfaces 1995. [DOI: 10.1016/0927-7765(95)01204-v] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Taneva SG, Keough KM. Calcium ions and interactions of pulmonary surfactant proteins SP-B and SP-C with phospholipids in spread monolayers at the air/water interface. BIOCHIMICA ET BIOPHYSICA ACTA 1995; 1236:185-95. [PMID: 7794949 DOI: 10.1016/0005-2736(95)00046-6] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Spread monolayers containing hydrophobic pulmonary surfactant protein, SP-B or SP-C, or SP-B/SP-C (2:1, w/w), alone or mixed with dipalmitoylphosphatidylcholine (DPPC) or dipalmitoylphosphatidylglycerol (DPPG), were formed on saline subphases containing calcium ions. Surface pressure-area characteristics of the films of the proteins were not affected by the presence of Ca2+ in the subphase. Calcium ions did not alter the surface properties of the binary and ternary films of DPPC plus either SP-B, or SP-C, or SP-B/SP-C (2:1, w/w). Surface pressure-area isotherms for the spread films of DPPG plus hydrophobic surfactant protein were Ca(2+)-dependent. The exclusion pressures of SP-B, SP-C and SP-B/SP-C (2:1, w/w) from protein-DPPG films in the presence of calcium were lower than the exclusion pressures in the absence of Ca2+. The divalent cation appeared to suppress the ability of SP-C and SP-B/SP-C (2:1, w/w) to remove phospholipid during squeeze-out from their mixed films with DPPG. The effects of Ca2+ on the monolayers of DPPG plus hydrophobic surfactant proteins were consistent with calcium producing diminished lipid-protein interactions, possibly resulting from Ca(2+)-induced changes in the ionization state and molecular packing of DPPG.
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Affiliation(s)
- S G Taneva
- Department of Biochemistry, Memorial University of Newfoundland, St. John's, Canada
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Seelig J, Lehrmann R, Terzi E. Domain formation induced by lipid-ion and lipid-peptide interactions. Mol Membr Biol 1995; 12:51-7. [PMID: 7767383 DOI: 10.3109/09687689509038495] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
High sensitivity titration calorimetry was performed for metal ions such as calcium and lanthanum and for different types of Alzheimer peptides. Ca2+ adsorbs to mixed phosphatidylcholine (PC)/phosphatidylglycerol (PG) membranes with an endothermic reaction enthalpy of delta H approximately +0.1 kcal/mol. La3+ binds to sonified PC vesicles with a reaction enthalpy of delta H approximately + 1.8 kcal/mol. The binding constants are of the order of 10 M-1 for Ca2+ and 4 x 10(3) M-1 for La3+. The role of lipids in the random coil<-->beta-sheet equilibrium of different types of Alzheimer model peptides was investigated with circular dichroism (CD) and high sensitivity titration calorimetry. Alzheimer peptide beta AP(1-40)OH and several fragments of this peptide undergo a concentration-dependent, co-operative random coil<-->beta-sheet transition in solution which can be described by a linear association model with a nucleation parameter sigma approximately 0.2-0.01 and a growth parameter s approximately 10(4) M-1. Addition of sonified lipid vesicles containing negatively charged lipids shifts the equilibrium towards the beta-sheet conformation. This can be explained by an aggregation phenomenon at the lipid/water interphase. The cationic peptides are attracted to the negatively charged membrane surface causing a local increase in peptide concentration. The high peptide concentration, together with the ordering of the peptide molecules on the membrane surface, facilitates beta-sheet formation, constituting the first experimental evidence for the induction of beta-sheet formation via the membrane surface. The binding of Alzheimer peptide fragments to the lipid membrane is accompanied by an exothermic heat of reaction with delta H in the range -2 - -8 kcal/mol.
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Affiliation(s)
- J Seelig
- Biocenter, University of Basel, Switzerland
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Schendel SL, Cramer WA. On the nature of the unfolded intermediate in the in vitro transition of the colicin E1 channel domain from the aqueous to the membrane phase. Protein Sci 1994; 3:2272-9. [PMID: 7756984 PMCID: PMC2142766 DOI: 10.1002/pro.5560031212] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The transition of the colicin E1 channel polypeptide from a water-soluble to membrane-bound state occurs in vitro at acid pH values that are associated with an unfolded channel structure whose properties qualitatively resemble those of a "molten globule," or "compact unfolded," intermediate state. The role of such a state for activity was tested by comparing the pH dependence of channel-induced solute efflux and the amplitude of the near-UV CD spectrum. The requirement of a partly unfolded state for activity was shown by the coincidence of the onset of channel activity measured for 4 different lipid compositions with the decrease in near-UV CD amplitude as a function of pH. Tertiary constraints on the 3 tryptophans of the colicin channel, assayed by the amplitude of the near-UV CD spectrum, are retained over the pH range 3-4 where channel activity could be measured and, as well, at pH 2. In addition, the tryptophan fluorescence emission spectrum is virtually unchanged over the pH range 2-6. The temperature independence of the near-UV spectrum at pH 3-6 up to 70 degrees C implies that the colicin E1 channel polypeptide is more stable than that of colicin A. A transition between 53 and 58 degrees C in the amplitude of the near-UV CD is consistent with preservation of part of the hydrophobic core in a destabilized state at pH 2. Thus, the unfolded state associated with colicin activity at acidic pH has the properties of a "compact unfolded" state, having some, but not all of the properties of a "molten globule."(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- S L Schendel
- Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, USA
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Kwon KO, Abe M, Ogino K, Kim MJ, Ohshima H. Effects of calcium ions on phospholipid aggregates at subzero temperatures. Colloids Surf B Biointerfaces 1994. [DOI: 10.1016/0927-7765(93)01110-d] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
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49
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Activation of the membrane glucolipid synthesis in Acholeplasma laidlawii by phosphatidylglycerol and other anionic lipids. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)31542-9] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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Egorova EM. The validity of the Smoluchowski equation in electrophoretic studies of lipid membranes. Electrophoresis 1994; 15:1125-31. [PMID: 7859719 DOI: 10.1002/elps.11501501170] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The Helmholtz-Smoluchowski theory, widely used for the calculation of zeta potential from the measured electrophoretic mobility (EPM), is known to be invalid in the region where the mobility is affected by the surface conductivity and polarization of the electrical double layer. In this region, the zeta potential found according to the Smoluchowski equation (zeta sm) is not identical to the true electrostatic potential at the hydrodynamic plane of shear (zeta), which is considered in the Gouy-Chapman-Stern theory of the electrical double layer. As a result, zeta sm cannot be used for the subsequent calculation of surface potential and surface charge density of a membrane studied. here we suggest a simple way, allowing one to decide between the validity and nonvalidity of the Smoluchowski equation in various sets of experimental conditions used in electrophoretic measurements on lipid membranes. We calculated the dimensionless criterion Rel, accepted in the Dukhin theory of electrophoresis as a measure of the extent of the influence of surface conductivity and double layer polarization on EPM. The Rel changes, with membrane charge density, ionic strength and vesicle radius, were found to be helpful in finding the combinations of these three parameters, corresponding to the validity of the Smoluchowski equation.
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Affiliation(s)
- E M Egorova
- A. N. Frumkin Institute of Electrochemistry, Russian Academy of Sciences, Moscow
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