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Knyazev DG, Silverstein TP, Brescia S, Maznichenko A, Pohl P. A New Theory about Interfacial Proton Diffusion Revisited: The Commonly Accepted Laws of Electrostatics and Diffusion Prevail. Biomolecules 2023; 13:1641. [PMID: 38002323 PMCID: PMC10669390 DOI: 10.3390/biom13111641] [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: 09/26/2023] [Revised: 11/02/2023] [Accepted: 11/07/2023] [Indexed: 11/26/2023] Open
Abstract
The high propensity of protons to stay at interfaces has attracted much attention over the decades. It enables long-range interfacial proton diffusion without relying on titratable residues or electrostatic attraction. As a result, various phenomena manifest themselves, ranging from spillover in material sciences to local proton circuits between proton pumps and ATP synthases in bioenergetics. In an attempt to replace all existing theoretical and experimental insight into the origin of protons' preference for interfaces, TELP, the "Transmembrane Electrostatically-Localized Protons" hypothesis, has been proposed. The TELP hypothesis envisions static H+ and OH- layers on opposite sides of interfaces that are up to 75 µm thick. Yet, the separation at which the electrostatic interaction between two elementary charges is comparable in magnitude to the thermal energy is more than two orders of magnitude smaller and, as a result, the H+ and OH- layers cannot mutually stabilize each other, rendering proton accumulation at the interface energetically unfavorable. We show that (i) the law of electroneutrality, (ii) Fick's law of diffusion, and (iii) Coulomb's law prevail. Using them does not hinder but helps to interpret previously published experimental results, and also helps us understand the high entropy release barrier enabling long-range proton diffusion along the membrane surface.
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Affiliation(s)
- Denis G. Knyazev
- Institute of Biophysics, Johannes Kepler University, 4020 Linz, Austria; (D.G.K.); (S.B.); (A.M.)
| | | | - Stefania Brescia
- Institute of Biophysics, Johannes Kepler University, 4020 Linz, Austria; (D.G.K.); (S.B.); (A.M.)
| | - Anna Maznichenko
- Institute of Biophysics, Johannes Kepler University, 4020 Linz, Austria; (D.G.K.); (S.B.); (A.M.)
| | - Peter Pohl
- Institute of Biophysics, Johannes Kepler University, 4020 Linz, Austria; (D.G.K.); (S.B.); (A.M.)
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2
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Wang K, Geng TM, Guo C, Zhou XH, Zhu F. The syntheses of fluorescein-based conjugated microporous polymers by direct arylation polymerization and fluorescence sensing Fe 3+ in aqueous solutions. Anal Chim Acta 2023; 1279:341747. [PMID: 37827661 DOI: 10.1016/j.aca.2023.341747] [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: 06/02/2023] [Revised: 08/13/2023] [Accepted: 08/22/2023] [Indexed: 10/14/2023]
Abstract
Determination of ferri ions in environment and human bodies is very important for environmental protection and disease diagnosis. Recently, conjugated microporous polymers (CMPs) used for fluorescence sensing metal ions have attracted much attention, but this technique is done in organic solvents. In this study, the two new fluorescein-based CMPs named FLEDOT and FLBTh were synthesized by "greener method", direct arylation polymerization, with tetraiodofluorescein sodium salt (TIFS) and 3,4-ethylenedioxy thiophene or 2,2'-bithiophene. Pleasely, the prepared fluorescein-based CMPs can fluorescently sense for Fe3+ in water with high sensitivity and selectivity. The quenching constants (KSV) of FLEDOT and FLBTh are 1.51 × 104 and 1.09 × 104 L mol-1, and the limits of detection (LODs) as low as 1.99 × 10-10 and 2.75 × 10-10 mol L-1, which are comparable to the sensitivity found in organic solvents' dispersions such as N,N-dimethylformamide (DMF)' dispersions. UV-Vis absorption spectra show that the fluorescence quenching mechanisms of Fe3+ are absorption competition quenching process and energy transfer process.
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Affiliation(s)
- Kang Wang
- School of Chemistry and Chemical Engineering, Anqing Normal University, Anqing, 246011, China
| | - Tong-Mou Geng
- School of Chemistry and Chemical Engineering, Anqing Normal University, Anqing, 246011, China.
| | - Chang Guo
- School of Chemistry and Chemical Engineering, Anqing Normal University, Anqing, 246011, China
| | - Xue-Hua Zhou
- School of Chemistry and Chemical Engineering, Anqing Normal University, Anqing, 246011, China
| | - Feng Zhu
- School of Chemistry and Chemical Engineering, Anqing Normal University, Anqing, 246011, China
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3
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Sun Y, Wei J, Fu Z, Zhang M, Zhao S, Xu G, Li C, Zhang J, Zhou T. Bio-Inspired Synthetic Hydrogen-Bonded Organic Frameworks for Efficient Proton Conduction. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2023; 35:e2208625. [PMID: 36401823 DOI: 10.1002/adma.202208625] [Citation(s) in RCA: 21] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/20/2022] [Revised: 11/09/2022] [Indexed: 06/16/2023]
Abstract
Hydrogen-bonded organic frameworks (HOFs) are a rising class of promising proton-conducting materials. However, they always suffer from the inherent contradiction between chemical stability and proton conduction. Herein, inspired by the self-assembly of lipid bilayer membranes, a series of aminomethylphosphonic acid-derived single-component HOFs are successfully developed with different substituents attached to the phosphonate oxygen group. They remain highly stable in strong acid or alkaline water solutions for one month owing to the presence of charge-assisted hydrogen bonds. Interestingly, in the absence of external proton carriers, the methyl-substituted phosphonate-based HOF exhibits a very high proton conductivity of up to 4.2 × 10-3 S cm-1 under 80 °C and 98% relative humidity. This value is not only comparable to that of HOFs consisting of mixed ligands but also is the highest reported in single-component HOFs. A combination of single-crystal structure analysis and density functional theory calculations reveals that the high conductivity is attributed to the strengthened H-bonding interactions between positively charged amines and negatively charged phosphonate groups in the channel of bio-inspired HOFs. This finding demonstrates that the well-defined molecular structure of proton conductors is of great importance in the precise understanding of the relationship between structure and property.
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Affiliation(s)
- Yayong Sun
- State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, 350002, P. R. China
- University of Chinese Academy of Sciences, No. 19A Yuquan Road, Beijing, 100049, P. R. China
| | - Jing Wei
- State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, 350002, P. R. China
| | - Zhihua Fu
- State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, 350002, P. R. China
| | - Minyi Zhang
- State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, 350002, P. R. China
| | - Sangen Zhao
- State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, 350002, P. R. China
| | - Gang Xu
- State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, 350002, P. R. China
| | - Chunsen Li
- State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, 350002, P. R. China
| | - Jian Zhang
- State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, 350002, P. R. China
- University of Chinese Academy of Sciences, No. 19A Yuquan Road, Beijing, 100049, P. R. China
| | - Tianhua Zhou
- State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, 350002, P. R. China
- University of Chinese Academy of Sciences, No. 19A Yuquan Road, Beijing, 100049, P. R. China
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4
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Arslanov VV, Ermakova EV, Kutsybala DS, Raitman OA, Selektor SL. Planar Supramolecular Systems: Assembly and Functional Potential. COLLOID JOURNAL 2022. [DOI: 10.1134/s1061933x22700065] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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5
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Karathanou K, Bondar AN. Algorithm to catalogue topologies of dynamic lipid hydrogen-bond networks. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2022; 1864:183859. [PMID: 34999081 DOI: 10.1016/j.bbamem.2022.183859] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2021] [Revised: 12/21/2021] [Accepted: 12/31/2021] [Indexed: 06/14/2023]
Abstract
Lipid membrane interfaces host reactions essential for the functioning of cells. The hydrogen-bonding environment at the membrane interface is particularly important for binding of proteins, drug molecules, and ions. We present here the implementation and applications of a depth-first search algorithm that analyzes dynamic lipid interaction networks. Lipid hydrogen-bond networks sampled transiently during simulations of lipid bilayers are clustered according to main types of topologies that characterize three-dimensional arrangements of lipids connected to each other via short water bridges. We characterize the dynamics of hydrogen-bonded lipid clusters in simulations of model POPE and POPE:POPG membranes that are often used for bacterial membrane proteins, in a model of the Escherichia coli membrane with six different lipid types, and in POPS membranes. We find that all lipids sample dynamic hydrogen-bonded networks with linear, star, or circular arrangements of the lipid headgroups, and larger networks with combinations of these three types of topologies. Overall, linear lipid-water bridges tend to be short. Water-mediated lipid clusters in all membranes with PE lipids tend to be somewhat small, with about four lipids in all membranes studied here. POPS membranes allow circular arrangements of three POPS lipids to be sampled frequently, and complex arrangements of linear, star, and circular paths may also be sampled. These findings suggest a molecular picture of the membrane interface whereby lipid molecules transiently connect in clusters with somewhat small spatial extension.
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Affiliation(s)
- Konstantina Karathanou
- Freie Universität Berlin, Department of Physics, Theoretical Molecular Biophysics, Arnimallee 14, D-14195 Berlin, Germany
| | - Ana-Nicoleta Bondar
- Freie Universität Berlin, Department of Physics, Theoretical Molecular Biophysics, Arnimallee 14, D-14195 Berlin, Germany; University of Bucharest, Faculty of Physics, Str. Atomiştilor 405, Bucharest-Măgurele 077125, Romania; Institute for Neuroscience and Medicine and Institute for Advanced Simulations (IAS-5/INM-9), Computational Biomedicine, Forschungszentrum Jülich, 52425 Jülich, Germany.
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6
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Rice M, Wong B, Oja M, Samuels K, Williams AK, Fong J, Sapse AM, Maran U, Korobkova EA. A role of flavonoids in cytochrome c-cardiolipin interactions. Bioorg Med Chem 2021; 33:116043. [PMID: 33530021 DOI: 10.1016/j.bmc.2021.116043] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2020] [Revised: 01/13/2021] [Accepted: 01/20/2021] [Indexed: 11/26/2022]
Abstract
The processes preceding the detachment of cytochrome c (cyt c) from the inner mitochondrial membrane in intrinsic apoptosis involve peroxidation of cardiolipin (CL) catalyzed by cyt c-CL complex. In the present work, we studied the effect of 17 dietary flavonoids on the peroxidase activity of cyt c bound to liposomes. Specifically, we explored the relationship between peroxidase activity and flavonoids' (1) potential to modulate cyt c unfolding, (2) effect on the oxidation state of heme iron, (3) membrane permeability, (4) membrane binding energy, and (5) structure. The measurements revealed that flavones, flavonols, and flavanols were the strongest, while isoflavones were the weakest inhibitors of the oxidation. Flavonoids' peroxidase inhibition activity correlated positively with their potential to suppress Trp-59 fluorescence in cyt c as well as the number of OH groups. Hydrophilic flavonoids, such as catechin, having the lowest membrane permeability and the strongest binding with phosphocholine (PC) based on the quantum chemical calculations exhibited the strongest inhibition of Amplex Red (AR) peroxidation, suggesting a membrane-protective function of flavonoids at the surface. The results of the present research specify basic principles for the design of molecules that will control the catalytic oxidation of lipids in mitochondrial membranes. These principles take into account the number of hydroxyl groups and hydrophilicity of flavonoids.
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Affiliation(s)
- Malaysha Rice
- Department of Sciences, John Jay College of Criminal Justice, City University of New York, 524 W 59th St., NY 10019, USA
| | - Bokey Wong
- Department of Sciences, John Jay College of Criminal Justice, City University of New York, 524 W 59th St., NY 10019, USA
| | - Mare Oja
- Institute of Chemistry, University of Tartu, Ravila 14A, Tartu 50411, Estonia
| | - Kelley Samuels
- Department of Sciences, John Jay College of Criminal Justice, City University of New York, 524 W 59th St., NY 10019, USA
| | - Alicia K Williams
- Department of Sciences, John Jay College of Criminal Justice, City University of New York, 524 W 59th St., NY 10019, USA
| | - Jenny Fong
- Department of Sciences, John Jay College of Criminal Justice, City University of New York, 524 W 59th St., NY 10019, USA
| | - Anne-Marie Sapse
- Department of Sciences, John Jay College of Criminal Justice, City University of New York, 524 W 59th St., NY 10019, USA; The Graduate Center at the City University of New York, 365 5th Ave, New York, NY 10016, USA
| | - Uko Maran
- Institute of Chemistry, University of Tartu, Ravila 14A, Tartu 50411, Estonia
| | - Ekaterina A Korobkova
- Department of Sciences, John Jay College of Criminal Justice, City University of New York, 524 W 59th St., NY 10019, USA.
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7
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Pannwitt S, Kaltbeitzel J, Ahlers P, Spitzer D, Hellmann N, Depoix F, Besenius P, Schneider D. Lipid Bilayer Interactions of Peptidic Supramolecular Polymers and Their Impact on Membrane Permeability and Stability. Biochemistry 2020; 59:1845-1853. [PMID: 32320213 DOI: 10.1021/acs.biochem.0c00114] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The synthesis and physicochemical characterization of supramolecular polymers with tunable assembly profiles offer exciting opportunities, involving the development of new biomedical carriers. Because synthetic nanocarriers aim to transport substances across or toward cellular membranes, we evaluated the interactions of amphiphilic peptide-based supramolecular polymers with lipid bilayers. Here, we focused on nanorod-like supramolecular polymers, obtained from two C3-symmetric dendritic peptide amphiphiles with alternating Phe/His sequences, equipped with a peripheral tetraethylene glycol dendron (C3-PH) or charged ethylenediamine end groups (C3-PH+). Triggered by pH changes, these amphiphiles assemble reversibly. Our results show that the supramolecular polymers have an impact on the lipid order in model membranes. Changes in the lipid order were observed depending on the charge state of the amphiphilic building blocks, as well as the chemical composition and physical properties of the bilayer. Furthermore, we further performed cell viability assays with the C3-PH+ and C3-PH supramolecular polymers. For C3-PH, the cell viability and extent of proliferation were decreased and the membrane permeability was enhanced, indicating a strong interaction of the polymer with cellular membranes. The results have implications for the design of novel pH-switchable supramolecular drug carriers and delivery vehicles that can respond to an altered microenvironment of tumorous or inflamed tissue.
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Affiliation(s)
- Stefanie Pannwitt
- Department of Chemistry, Biochemistry, Johannes Gutenberg University Mainz, Johann-Joachim Becherweg 30, 55128 Mainz, Germany
| | - Jonas Kaltbeitzel
- Department of Chemistry, Biochemistry, Johannes Gutenberg University Mainz, Johann-Joachim Becherweg 30, 55128 Mainz, Germany
| | - Patrick Ahlers
- Department of Chemistry, Organic Chemistry, Johannes Gutenberg University Mainz, Duesbergweg 10-14, 55128 Mainz, Germany
| | - Daniel Spitzer
- Department of Chemistry, Organic Chemistry, Johannes Gutenberg University Mainz, Duesbergweg 10-14, 55128 Mainz, Germany
| | - Nadja Hellmann
- Department of Chemistry, Biochemistry, Johannes Gutenberg University Mainz, Johann-Joachim Becherweg 30, 55128 Mainz, Germany
| | - Frank Depoix
- Institute of Molecular Physiology, Johannes Gutenberg University, Johann-Joachim-Becher-Weg 9-11, 55128 Mainz, Germany
| | - Pol Besenius
- Department of Chemistry, Organic Chemistry, Johannes Gutenberg University Mainz, Duesbergweg 10-14, 55128 Mainz, Germany
| | - Dirk Schneider
- Department of Chemistry, Biochemistry, Johannes Gutenberg University Mainz, Johann-Joachim Becherweg 30, 55128 Mainz, Germany
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8
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Artemov VG, Uykur E, Kapralov PO, Kiselev A, Stevenson K, Ouerdane H, Dressel M. Anomalously High Proton Conduction of Interfacial Water. J Phys Chem Lett 2020; 11:3623-3628. [PMID: 32329348 DOI: 10.1021/acs.jpclett.0c00910] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Water at the solid-liquid interface exhibits an anomalous ionic conductivity and dielectric constant compared to bulk water. Both phenomena still lack a detailed understanding. Here, we report radio-frequency measurements and analyses of the electrodynamic properties of interfacial water confined in nanoporous matrices formed by diamond grains of various sizes, ranging from 5 nm to 0.5 μm in diameter. Contrary to bulk water, the charge-carrying protons/holes in interfacial water are not mutually screened, allowing for higher mobility in the external electric field. Thus, the protonic conductivity reaches a maximum value, which can be 5 orders of magnitude higher than that of bulk water. Our results aid in the understanding of physical and chemical properties of water confined in porous materials and pave the way to the development of new type of highly efficient proton-conductive materials for applications in electrochemical energy systems, membrane separations science, and nanofluidics.
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Affiliation(s)
- V G Artemov
- Center for Energy Science and Technology, Skolkovo Institute of Science and Technology, 121205 Moscow, Russia
| | - E Uykur
- 1. Physikalisches Institut, Universität Stuttgart, 70569 Stuttgart, Germany
| | | | - A Kiselev
- Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany
| | - K Stevenson
- Center for Energy Science and Technology, Skolkovo Institute of Science and Technology, 121205 Moscow, Russia
| | - H Ouerdane
- Center for Energy Science and Technology, Skolkovo Institute of Science and Technology, 121205 Moscow, Russia
| | - M Dressel
- 1. Physikalisches Institut, Universität Stuttgart, 70569 Stuttgart, Germany
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9
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Satake H, Sakata T. Interfacial pH Behavior at a Cell/Gate Insulator Nanogap Induced by Allergic Responses. ACS OMEGA 2019; 4:14255-14260. [PMID: 31508549 PMCID: PMC6733167 DOI: 10.1021/acsomega.9b01872] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/23/2019] [Accepted: 08/12/2019] [Indexed: 06/10/2023]
Abstract
In this paper, we clarify the interfacial pH behavior induced by allergic responses at a mast cell/gate insulator nanogap detected by laser scanning confocal fluorescence microscopy. In a previous work, the change in interfacial pH detected on the basis of allergic responses was monitored at a mast cell/gate insulator nanogap interface using a cell-cultured gate ion-sensitive field-effect transistor (ISFET), but the interfacial pH behavior at a mast cell/gate insulator nanogap has not been clarified using other methods. Here, the phospholipid fluorescein is employed as the extracellular pH indicator, which is fixed to the external side of the plasma membrane of mast cells cultured on a substrate. As a result, the interfacial pH at the mast cell/substrate nanogap increases after mast cells with IgE on their membrane are activated by the interaction between IgE and an allergen. This is due to the basicity of histamine molecules released from mast cells. Moreover, the change in the interfacial pH at the mast cell/substrate nanogap is larger than that at the mast cell/bulk solution interface. That is, molecules of substances secreted as a result of allergic responses are assumed to accumulate around the cell/substrate nanogap. The data obtained in this study support the idea that potentiometric ion sensors such as ISFETs can detect a cellular-function-induced change in pH at a cell/electrode nanogap in real time.
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10
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Tomášková N, Varhač R, Lysáková V, Musatov A, Sedlák E. Peroxidase activity of cytochrome c in its compact state depends on dynamics of the heme region. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2018; 1866:1073-1083. [DOI: 10.1016/j.bbapap.2018.09.003] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2018] [Revised: 09/06/2018] [Accepted: 09/10/2018] [Indexed: 10/28/2022]
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11
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Satake H, Saito A, Sakata T. Elucidation of interfacial pH behaviour at the cell/substrate nanogap for in situ monitoring of cellular respiration. NANOSCALE 2018; 10:10130-10136. [PMID: 29781490 DOI: 10.1039/c8nr02950d] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
In situ monitoring of cellular metabolism is useful for elucidating dynamic functions of living cells. In our previous studies, cellular respiration was continuously monitored as a change in pH at the cell/electrode nanoscale interface (i.e., interfacial pH) using an ion-sensitive field-effect transistor (ISFET). However, such interfacial pH behaviour on the nanoscale has not been confirmed using other methods such as fluorescence imaging. In this study, we have clarified the interfacial pH behaviour at a cell/substrate nanogap using a laser scanning confocal fluorescence microscope. The phospholipid fluorescein used as a pH indicator was fixed to the plasma membrane on the external side of a cell by inserting its lipophilic alkyl chain into the membrane, and used to observe the change in interfacial pH. As a result, hydrogen ions generated by cellular respiration were gradually accumulated at the cell/substrate nanogap, resulting in a decrease in pH. Moreover, the interfacial pH between the plasma membrane and the substrate became lower than the pH near the surface of cells not in contact with the substrate. The data obtained in this study support the idea that potentiometric ion sensors such as ISFETs can detect a cellular-metabolism-induced change in pH at a cell/electrode nanogap in real time.
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Affiliation(s)
- Hiroto Satake
- Department of Materials Engineering, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan 113-8656.
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12
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Sato T, Tsukamoto M, Yamamoto S, Mitsuishi M, Miyashita T, Nagano S, Matsui J. Acid-Group-Content-Dependent Proton Conductivity Mechanisms at the Interlayer of Poly(N-dodecylacrylamide-co-acrylic acid) Copolymer Multilayer Nanosheet Films. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2017; 33:12897-12902. [PMID: 29058441 DOI: 10.1021/acs.langmuir.7b03160] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The effect of the content of acid groups on the proton conductivity at the interlayer of polymer-nanosheet assemblies was investigated. For that purpose, amphiphilic poly(N-dodecylacrylamide-co-acrylic acid) copolymers [p(DDA/AA)] with varying contents of AA were synthesized by free radical polymerization. Surface pressure (π)-area (A) isotherms of these copolymers indicated that stable polymer monolayers are formed at the air/water interface for AA mole fraction (n) ≤ 0.49. In all cases, a uniform dispersion of the AA groups in the polymer monolayer was observed. Subsequently, polymer monolayers were transferred onto solid substrates using the Langmuir-Blodgett (LB) technique. X-ray diffraction (XRD) analyses of the multilayer films showed strong Bragg diffraction peaks, suggesting a highly uniform lamellar structure for the multilayer films. The proton conductivity of the multilayer films parallel to the direction of the layer planes were measured by impedance spectroscopy, which revealed that the conductivity increased with increasing values of n. Activation energies for proton conduction of ∼0.3 and 0.42 eV were observed for n ≥ 0.32 and n = 0.07, respectively. Interestingly, the proton conductivity of a multilayer film with n = 0.19 did not follow the Arrhenius equation. These results were interpreted in terms of the average distance between the AA groups (lAA), and it was concluded that, for n ≥ 0.32, an advanced 2D hydrogen bonding network was formed, while for n = 0.07, lAA is too long to form such hydrogen bonding networks. The lAA for n = 0.19 is intermediate to these extremes, resulting in the formation of hydrogen bonding networks at low temperatures, and disruption of these networks at high temperatures due to thermally induced motion. These results indicate that a high proton conductivity with low activation energy can be achieved, even under weakly acidic conditions, by arranging the acid groups at an optimal distance.
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Affiliation(s)
- Takuma Sato
- Graduate School of Science and Engineering, Yamagata University , 1-4-12 Kojirakawa-machi, Yamagata 990-8560, Japan
| | - Mayu Tsukamoto
- Graduate School of Science and Engineering, Yamagata University , 1-4-12 Kojirakawa-machi, Yamagata 990-8560, Japan
| | - Shunsuke Yamamoto
- Institute for Multidisciplinary Research for Advanced Materials, Tohoku University , 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
| | - Masaya Mitsuishi
- Institute for Multidisciplinary Research for Advanced Materials, Tohoku University , 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
| | - Tokuji Miyashita
- Institute for Multidisciplinary Research for Advanced Materials, Tohoku University , 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
| | - Shusaku Nagano
- Nagoya University Venture Business Laboratory, Nagoya University , Furo-cho, Chikusa, Nagoya 464-8603, Japan
| | - Jun Matsui
- Faculty of Science, Yamagata University , 1-4-12 Kojirakawa-machi, Yamagata 990-8560, Japan
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Speed of the bacterial flagellar motor near zero load depends on the number of stator units. Proc Natl Acad Sci U S A 2017; 114:11603-11608. [PMID: 29078322 DOI: 10.1073/pnas.1708054114] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
The bacterial flagellar motor (BFM) rotates hundreds of times per second to propel bacteria driven by an electrochemical ion gradient. The motor consists of a rotor 50 nm in diameter surrounded by up to 11 ion-conducting stator units, which exchange between motors and a membrane-bound pool. Measurements of the torque-speed relationship guide the development of models of the motor mechanism. In contrast to previous reports that speed near zero torque is independent of the number of stator units, we observe multiple speeds that we attribute to different numbers of units near zero torque in both Na+- and H+-driven motors. We measure the full torque-speed relationship of one and two H+ units in Escherichia coli by selecting the number of H+ units and controlling the number of Na+ units in hybrid motors. These experiments confirm that speed near zero torque in H+-driven motors increases with the stator number. We also measured 75 torque-speed curves for Na+-driven chimeric motors at different ion-motive force and stator number. Torque and speed were proportional to ion-motive force and number of stator units at all loads, allowing all 77 measured torque-speed curves to be collapsed onto a single curve by simple rescaling.
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14
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Jeong BS, Dyer RB. Proton Transport Mechanism of M2 Proton Channel Studied by Laser-Induced pH Jump. J Am Chem Soc 2017; 139:6621-6628. [PMID: 28467842 DOI: 10.1021/jacs.7b00617] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The M2 proton transport channel of the influenza virus A is an important model system because it conducts protons with high selectivity and unidirectionally when activated at low pH, despite the relative simplicity of its structure. Although it has been studied extensively, the molecular details of the pH-dependent gating and proton conductance mechanisms are incompletely understood. We report direct observation of the M2 proton channel activation process using a laser-induced pH jump coupled with tryptophan fluorescence as a probe. Biphasic kinetics is observed, with the fast phase corresponding to the His37 protonation, and the slow phase associated with the subsequent conformation change. Unusually fast His37 protonation was observed (2.0 × 1010 M-1 s-1), implying the existence of proton collecting antennae for expedited proton transport. The conformation change (4 × 103 s-1) was about 2 orders of magnitude slower than protonation at endosomal pH, suggesting that a transporter model is likely not feasible.
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Affiliation(s)
- Ban-Seok Jeong
- Department of Chemistry, Emory University , Atlanta, Georgia 30322, United States
| | - R Brian Dyer
- Department of Chemistry, Emory University , Atlanta, Georgia 30322, United States
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15
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Geng TM, Ye SN, Wang Y, Zhu H, Wang X, Liu X. Conjugated microporous polymers-based fluorescein for fluorescence detection of 2,4,6-trinitrophenol. Talanta 2017; 165:282-288. [DOI: 10.1016/j.talanta.2016.12.046] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2016] [Revised: 12/09/2016] [Accepted: 12/20/2016] [Indexed: 10/20/2022]
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16
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Yoshinaga MY, Kellermann MY, Valentine DL, Valentine RC. Phospholipids and glycolipids mediate proton containment and circulation along the surface of energy-transducing membranes. Prog Lipid Res 2016; 64:1-15. [PMID: 27448687 DOI: 10.1016/j.plipres.2016.07.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2015] [Revised: 05/29/2016] [Accepted: 07/13/2016] [Indexed: 01/06/2023]
Abstract
Proton bioenergetics provides the energy for growth and survival of most organisms in the biosphere ranging from unicellular marine phytoplankton to humans. Chloroplasts harvest light and generate a proton electrochemical gradient (proton motive force) that drives the production of ATP needed for carbon dioxide fixation and plant growth. Mitochondria, bacteria and archaea generate proton motive force to energize growth and other physiologies. Energy transducing membranes are at the heart of proton bioenergetics and are responsible for catalyzing the conversion of energy held in high-energy electrons→electron transport chain→proton motive force→ATP. Whereas the electron transport chain is understood in great detail there are major gaps in understanding mechanisms of proton transfer or circulation during proton bioenergetics. This paper is built on the proposition that phospho- and glyco-glycerolipids form proton transport circuitry at the membrane's surface. By this proposition, an emergent membrane property, termed the hyducton, confines active/unbound protons or hydronium ions to a region of low volume close to the membrane surface. In turn, a von Grotthuß mechanism rapidly moves proton substrate in accordance with nano-electrochemical poles on the membrane surface created by powerful proton pumps such as ATP synthase.
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Affiliation(s)
- Marcos Y Yoshinaga
- University of Bremen, MARUM - Center for Marine and Environmental Sciences, Germany.
| | - Matthias Y Kellermann
- University of California Santa Barbara - Department of Earth Science and Marine Science Institute, USA
| | - David L Valentine
- University of California Santa Barbara - Department of Earth Science and Marine Science Institute, USA
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17
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Scholkmann F. Long range physical cell-to-cell signalling via mitochondria inside membrane nanotubes: a hypothesis. Theor Biol Med Model 2016; 13:16. [PMID: 27267202 PMCID: PMC4896004 DOI: 10.1186/s12976-016-0042-5] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2016] [Accepted: 05/27/2016] [Indexed: 02/07/2023] Open
Abstract
Coordinated interaction of single cells by cell-to-cell communication (signalling) enables complex behaviour necessary for the functioning of multicellular organisms. A quite newly discovered cell-to-cell signalling mechanism relies on nanotubular cell-co-cell connections, termed "membrane nanotubes" (MNTs). The present paper presents the hypothesis that mitochondria inside MNTs can form a connected structure (mitochondrial network) which enables the exchange of energy and signals between cells. It is proposed that two modes of energy and signal transmission may occur: electrical/electrochemical and electromagnetic (optical). Experimental work supporting the hypothesis is reviewed, and suggestions for future research regarding the discussed topic are given.
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Affiliation(s)
- Felix Scholkmann
- Biomedical Optics Research Laboratory, Department of Neonatology, University Hospital Zurich, University of Zurich, Frauenklinikstr. 10, 8091, Zurich, Switzerland.
- Research Office for Complex Physical and Biological Systems (ROCoS), Mutschellenstr. 179, 8038, Zurich, Switzerland.
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Bychkova VE, Basova LV, Balobanov VA. How membrane surface affects protein structure. BIOCHEMISTRY (MOSCOW) 2015; 79:1483-514. [DOI: 10.1134/s0006297914130045] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
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19
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Membrane-induced changes in the holomyoglobin tertiary structure: interplay with function. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2014; 43:317-29. [DOI: 10.1007/s00249-014-0964-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/03/2014] [Revised: 04/04/2014] [Accepted: 04/25/2014] [Indexed: 11/26/2022]
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20
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Kundu A, Yamaguchi S, Tahara T. Evaluation of pH at Charged Lipid/Water Interfaces by Heterodyne-Detected Electronic Sum Frequency Generation. J Phys Chem Lett 2014; 5:762-766. [PMID: 26270850 DOI: 10.1021/jz500107e] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Although the interface pH at a biological membrane is important for biological processes at the membrane, there has been no systematic study to evaluate it. We apply novel interface-selective nonlinear spectroscopy to the evaluation of the pH at model biological membranes (lipid/water interfaces). It is clearly shown that the pH at the charged lipid/water interfaces is substantially deviated from the bulk pH. The pH at the lipid/water interface is higher than that in the bulk when the head group of the lipid is positively charged, whereas the pH at the lipid/water interface is lower when the lipid has a negatively charged head group.
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Affiliation(s)
- Achintya Kundu
- †Molecular Spectroscopy Laboratory, RIKEN, Wako, Saitama 351-0198, Japan
| | - Shoichi Yamaguchi
- †Molecular Spectroscopy Laboratory, RIKEN, Wako, Saitama 351-0198, Japan
| | - Tahei Tahara
- †Molecular Spectroscopy Laboratory, RIKEN, Wako, Saitama 351-0198, Japan
- ‡Ultrafast Spectroscopy Research Team, RIKEN Center for Advanced Photonics (RAP), Wako, Saitama 351-0198, Japan
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21
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Uversky VN. Hypothesis: The unfolding power of protein dielectricity. INTRINSICALLY DISORDERED PROTEINS 2013; 1:e25725. [PMID: 28516018 PMCID: PMC5424796 DOI: 10.4161/idp.25725] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/25/2013] [Revised: 07/02/2013] [Accepted: 07/11/2013] [Indexed: 01/25/2023]
Abstract
A hypothesis is proposed on a potential role of protein dielectricity as an unfolding factor in protein-protein interactions. It is suggested that large protein complexes and aggregation seeds can unfold target proteins by virtue of their effect on the dielectric properties of water at the protein-solvent interface. Here, similar to the effect of membrane surfaces, protein surface can cause decrease in the local dielectric constant of solvent and thereby induce structural changes in a target protein approaching this surface. Some potential implementations of this hypothetical mechanism are also discussed.
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Affiliation(s)
- Vladimir N Uversky
- Department of Molecular Medicine and USF Health Byrd Alzheimer's Research Institute; Morsani College of Medicine; University of South Florida; Tampa, FL USA.,Institute for Biological Instrumentation; Russian Academy of Sciences; Moscow Region, Russia
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Khan JM, Qadeer A, Ahmad E, Ashraf R, Bhushan B, Chaturvedi SK, Rabbani G, Khan RH. Monomeric banana lectin at acidic pH overrules conformational stability of its native dimeric form. PLoS One 2013; 8:e62428. [PMID: 23638080 PMCID: PMC3637162 DOI: 10.1371/journal.pone.0062428] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2013] [Accepted: 03/21/2013] [Indexed: 11/18/2022] Open
Abstract
Banana lectin (BL) is a homodimeric protein categorized among jacalin-related family of lectins. The effect of acidic pH was examined on conformational stability of BL by using circular dichroism, intrinsic fluorescence, 1-anilino-8-napthalene sulfonate (ANS) binding, size exclusion chromatography (SEC) and dynamic light scattering (DLS). During acid denaturation of BL, the monomerization of native dimeric protein was found at pH 2.0. The elution profile from SEC showed two different peaks (59.65 ml & 87.98 ml) at pH 2.0 while single peak (61.45 ml) at pH 7.4. The hydrodynamic radii (R h) of native BL was 2.9 nm while at pH 2.0 two species were found with R h of 1.7 and 3.7 nm. Furthermore at, pH 2.0 the secondary structures of BL remained unaltered while tertiary structure was significantly disrupted with the exposure of hydrophobic clusters confirming the existence of molten globule like state. The unfolding of BL with different subunit status was further evaluated by urea and temperature mediated denaturation to check their stability. As inferred from high Cm and ΔG values, the monomeric form of BL offers more resistance towards chemical denaturation than the native dimeric form. Besides, dimeric BL exhibited a Tm of 77°C while no loss in secondary structures was observed in monomers even up to 95°C. To the best of our knowledge, this is the first report on monomeric subunit of lectins showing more stability against denaturants than its native dimeric state.
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Affiliation(s)
- Javed M. Khan
- Interdisciplinary Biotechnology Unit, Aligarh Muslim University, Aligarh, India
| | - Atiyatul Qadeer
- Interdisciplinary Biotechnology Unit, Aligarh Muslim University, Aligarh, India
| | - Ejaz Ahmad
- Interdisciplinary Biotechnology Unit, Aligarh Muslim University, Aligarh, India
| | - Raghib Ashraf
- Interdisciplinary Biotechnology Unit, Aligarh Muslim University, Aligarh, India
| | - Bharat Bhushan
- Interdisciplinary Biotechnology Unit, Aligarh Muslim University, Aligarh, India
| | - Sumit K. Chaturvedi
- Interdisciplinary Biotechnology Unit, Aligarh Muslim University, Aligarh, India
| | - Gulam Rabbani
- Interdisciplinary Biotechnology Unit, Aligarh Muslim University, Aligarh, India
| | - Rizwan H. Khan
- Interdisciplinary Biotechnology Unit, Aligarh Muslim University, Aligarh, India
- * E-mail:
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Mashaghi S, Jadidi T, Koenderink G, Mashaghi A. Lipid nanotechnology. Int J Mol Sci 2013; 14:4242-82. [PMID: 23429269 PMCID: PMC3588097 DOI: 10.3390/ijms14024242] [Citation(s) in RCA: 150] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2012] [Revised: 01/29/2013] [Accepted: 01/30/2013] [Indexed: 01/14/2023] Open
Abstract
Nanotechnology is a multidisciplinary field that covers a vast and diverse array of devices and machines derived from engineering, physics, materials science, chemistry and biology. These devices have found applications in biomedical sciences, such as targeted drug delivery, bio-imaging, sensing and diagnosis of pathologies at early stages. In these applications, nano-devices typically interface with the plasma membrane of cells. On the other hand, naturally occurring nanostructures in biology have been a source of inspiration for new nanotechnological designs and hybrid nanostructures made of biological and non-biological, organic and inorganic building blocks. Lipids, with their amphiphilicity, diversity of head and tail chemistry, and antifouling properties that block nonspecific binding to lipid-coated surfaces, provide a powerful toolbox for nanotechnology. This review discusses the progress in the emerging field of lipid nanotechnology.
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Affiliation(s)
- Samaneh Mashaghi
- Zernike Institute for Advanced Materials, Centre for Synthetic Biology, Nijenborgh 4, 9747 AG Groningen, The Netherlands; E-Mail:
| | - Tayebeh Jadidi
- Department of Physics, University of Osnabrück, Barbarastraße 7, 49076 Osnabrück, Germany; E-Mail:
| | - Gijsje Koenderink
- FOM Institute AMOLF, Science Park 104, 1098XG Amsterdam, The Netherlands; E-Mail:
| | - Alireza Mashaghi
- FOM Institute AMOLF, Science Park 104, 1098XG Amsterdam, The Netherlands; E-Mail:
- Department of Bionanoscience, Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands
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24
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Balakrishnan G, Hu Y, Spiro TG. His26 protonation in cytochrome c triggers microsecond β-sheet formation and heme exposure: implications for apoptosis. J Am Chem Soc 2012; 134:19061-9. [PMID: 23094892 PMCID: PMC3529097 DOI: 10.1021/ja307100a] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Cytochrome c unfolds locally and reversibly upon heating at pH 3. UV resonance Raman (UVRR) spectra reveal that instead of producing unordered structure, unfolding converts turns and some helical elements to β-sheet. It also disrupts the Met80-heme bond, and has been previously shown to induce peroxidase activity. Aromatic residues that are H-bonded to a heme propionate (Trp59 and Tyr48) alter their orientation, indicating heme displacement. T-jump/UVRR measurements give time constants of 0.2, 3.9, and 67 μs for successive phases of β-sheet formation and concomitant reorientation of Trp59. UVRR spectra reveal protonation of histidines, and specifically of His26, whose H-bond to Pro44 anchors the 40s Ω loop; this loop is known to be the least stable 'foldon' in the protein. His26 protonation is proposed to disrupt its H-bond with Pro44, triggering the extension of a short β-sheet segment at the 'neck' of the 40s Ω loop into the loop itself and back into the 60s and 70s helices. The secondary structure change displaces the heme via H-bonds from residues in the growing β-sheet, thereby exposing it to exogenous ligands, and inducing peroxidase activity. This unfolding mechanism may play a role in cardiolipin peroxidation by cyt c during apoptosis.
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25
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26
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Raven JA, Hurd CL. Ecophysiology of photosynthesis in macroalgae. PHOTOSYNTHESIS RESEARCH 2012; 113:105-25. [PMID: 22843100 DOI: 10.1007/s11120-012-9768-z] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/12/2012] [Accepted: 07/04/2012] [Indexed: 05/07/2023]
Abstract
Macroalgae occur in the marine benthos from the upper intertidal to depths of more than 200 m, contributing up to 1 Pg C per year to global primary productivity. Freshwater macroalgae are mainly green (Chlorophyta) with some red (Rhodophyta) and a small contribution of brown (Phaeophyceae) algae, while in the ocean all three higher taxa are important. Attempts to relate the depth distribution of three higher taxa of marine macroalgae to their photosynthetic light use through their pigmentation in relation to variations in spectral quality of photosynthetically active radiation (PAR) with depth (complementary chromatic adaptation) and optical thickness (package effect) have been relatively unsuccessful. The presence (Chlorophyta, Phaeophyceae) or absence (Rhodophyta) of a xanthophyll cycle is also not well correlated with depth distribution of marine algae. The relative absence of freshwater brown algae does not seem to be related to their photosynthetic light use. Photosynthetic inorganic carbon acquisition in some red and a few green macroalgae involves entry of CO(2) by diffusion. Other red and green macroalgae, and brown macroalgae, have CO(2) concentrating mechanisms; these frequently involve acid and alkaline zones on the surface of the alga with CO(2) (produced from HCO(3) (-)) entering in the acid zones, while some macroalgae have CCMs based on active influx of HCO(3) (-). These various mechanisms of carbon acquisition have different responses to the thickness of the diffusion boundary layer, which is determined by macroalgal morphology and water velocity. Energetic predictions that macroalgae growing at or near the lower limit of PAR for growth should rely on diffusive CO(2) entry without acid and alkaline zones, and on NH(4) (+) rather than NO(3) (-) as nitrogen source, are only partially borne out by observation. The impact of global environmental change on marine macroalgae mainly relates to ocean acidification and warming with shoaling of the thermocline and decreased nutrient flux to the upper mixed layer. Predictions of the impact on macroalgae requires further experiments on interactions among increased inorganic carbon, increased temperature and decreased nitrogen and phosphorus supply, and, when possible, studies of genetic adaptation to environmental change.
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Affiliation(s)
- John A Raven
- Division of Plant Sciences, University of Dundee at the James Hutton Institute, Invergowrie, Dundee, DD2 5DA, Scotland, UK.
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Medvedev ES, Stuchebrukhov AA. Proton diffusion along biological membranes. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2011; 23:234103. [PMID: 21613715 DOI: 10.1088/0953-8984/23/23/234103] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Biological surfaces are known to be capable of retaining protons and facilitating their lateral diffusion. Since the surface dynamically exchanges protons with the bulk, the proton movement from a source to a target at the surface acquires a complicated pattern of coupled surface and bulk (2D + 3D) diffusion of which the main feature is that the surface acts as a proton-collecting antenna enhancing the proton flux from the bulk. A phenomenological model of this process is reviewed and its applications to recent experiments on lipid bilayers and small unilaminar vesicles are discussed. The model (i) introduces the important notions of the fast and slow regimes of proton exchange between the surface and the bulk, (ii) permits evaluation of the antenna radius and amplification coefficient in both regimes, (iii) explains the observed macroscopically large distances (in the micrometer range; Antonenko and Pohl 1998 FEBS Lett. 429 197) that the proton can travel along lipid membranes embedded into pure aqueous solutions, and (iv) predicts the dependence of the steady-state proton flux and the kinetics of the non-stationary diffusion upon the buffer concentration in buffered solutions. The surface diffusion coefficient for small unilaminar vesicles is calculated from experimental data (Sandén et al 2010 Proc. Natl Acad. Sci. USA 107 4129) to be 1 × 10(-5) cm(2) s(-1). The dependence of the shape of the kinetic curves representing protonation/deprotonation of a lipid-bound pH-sensitive dye attached to a planar bilayer lipid membrane upon the buffer concentration (Serowy et al 2003 Biophys. J. 84 1031) and the effect of changing the membrane composition (Antonenko and Pohl 2008 Eur. Biophys. J. 37 865) are explained.
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Affiliation(s)
- E S Medvedev
- Institute of Problems of Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka, Russian Federation
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Guan X, Lai S, Su Z. Facile preparation and potential application of water-soluble polymeric temperature/pH probes bearing fluorescein. J Appl Polym Sci 2011. [DOI: 10.1002/app.34038] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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29
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Wei-Guo J, Chang-Wei L, Ji-Lin T, Zheng-Yan W, Shao-Jun D, Er-Kang W. Electrochemical and Spectroscopic Study on the Interaction of Cytochrome c with Anionic Lipid Vesicles. CHINESE J CHEM 2010. [DOI: 10.1002/cjoc.20030210514] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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30
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Gasymov OK, Abduragimov AR, Glasgow BJ. Excited protein states of human tear lipocalin for low- and high-affinity ligand binding revealed by functional AB loop motion. Biophys Chem 2010; 149:47-57. [PMID: 20439130 DOI: 10.1016/j.bpc.2010.03.017] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2010] [Revised: 03/22/2010] [Accepted: 03/28/2010] [Indexed: 10/19/2022]
Abstract
Human tear lipocalin (TL), a prominent member of lipocalin family, exhibits functional and structural promiscuity. The plasticity of loop regions modulates entry to the ligand pocket at the "open" end of the eight-stranded beta-barrel. Site-directed multi-distance measurements using fluorescence resonance energy transfer between functional loops register two excited protein states for low- and high-affinity ligand binding. At low pH, the longest loop AB adopts the conformation of the low-affinity excited protein state that matches the crystal structure of holo-TL at pH 8. A "crankshaft" like movement is detected for the loop AB in a low pH transition. At pH 7.3 the holo-protein assumes a high-affinity excited protein state, in which the loop AB is more compact (RMS=3.1A). In the apo-holo transition, the reporter Trp 28 moves about 4.5A that reflects a decrease in distance between Glu27 and Lys108. This interaction fixes the loop AB conformation for the high-affinity mode. No such movement is detected at low pH, where Glu27 is protonated. Data strongly indicate that the protonation state of Glu27 modulates the conformation of the loop AB for high- and low-affinity binding.
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Affiliation(s)
- Oktay K Gasymov
- Department of Pathology, University of California at Los Angeles, USA.
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Gasymov OK, Abduragimov AR, Glasgow BJ. pH-Dependent conformational changes in tear lipocalin by site-directed tryptophan fluorescence. Biochemistry 2010; 49:582-90. [PMID: 20025287 DOI: 10.1021/bi901435q] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Tear lipocalin (TL), a major protein of human tears, binds a broad array of endogenous ligands. pH-dependent ligand binding in TL may have functional implications in tears. Previously, conformational selections of the AB and GH loops have been implicated in ligand binding by site-directed tryptophan fluorescence (SDTF). In this study, SDTF was applied to the AB and GH loops to investigate pH-driven conformational changes relevant to ligand binding. Both loops demonstrate significant but distinct conformational rearrangements over a wide pH range. In the low-pH transition, from 7.3 to 3.0, residues of the GH loop exhibit decreased solvent accessibilities. In acrylamide quenching experiments, the average quenching rate constant (k(q), accessibility parameter) of the residues in the GH loop is decreased approximately 38%, from 2.1 x 10(9) to 1.3 x 10(9) M(-1) s(-1). However, despite the significant changes in accessibilities for some residues in the AB loop, the average accessibility per residue remained unchanged (average k(q) = 1.2 M(-1) s(-1)). Accordingly, the low-pH transition induces conformational changes that reshuffle the accessibility profiles of the residues in the AB loop. A significant difference in the titration curves between the holo and apo forms of the W28 mutant suggests that the protonation states of the residues around position 28 modulate conformational switches of the AB loop relevant to ligand binding.
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Affiliation(s)
- Oktay K Gasymov
- Department of Pathology, UCLA School of Medicine, Jules Stein Eye Institute, 100 Stein Plaza, Los Angeles, California 90095, USA
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Dahlberg M, Marini A, Mennucci B, Maliniak A. Quantum Chemical Modeling of the Cardiolipin Headgroup. J Phys Chem A 2010; 114:4375-87. [DOI: 10.1021/jp9110019] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- Martin Dahlberg
- Division of Physical Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden, and Department of Chemistry, University of Pisa, Via Risorgimento 35, 56126 Pisa, Italy
| | - Alberto Marini
- Division of Physical Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden, and Department of Chemistry, University of Pisa, Via Risorgimento 35, 56126 Pisa, Italy
| | - Benedetta Mennucci
- Division of Physical Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden, and Department of Chemistry, University of Pisa, Via Risorgimento 35, 56126 Pisa, Italy
| | - Arnold Maliniak
- Division of Physical Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden, and Department of Chemistry, University of Pisa, Via Risorgimento 35, 56126 Pisa, Italy
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Motovilov KA, Yurkov VI, Volkov EM, Yaguzhinsky LS. Properties and new methods of non-equilibrium membrane bound proton fraction research under conditions of proton pump activation. BIOCHEMISTRY (MOSCOW) SUPPLEMENT SERIES A: MEMBRANE AND CELL BIOLOGY 2009. [DOI: 10.1134/s1990747809040163] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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35
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Xiong JW, Zhu L, Jiao X, Liu SS. Evidence for DeltapH surface component (DeltapH(S)) of proton motive force in ATP synthesis of mitochondria. Biochim Biophys Acta Gen Subj 2009; 1800:213-22. [PMID: 19695309 DOI: 10.1016/j.bbagen.2009.07.032] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2009] [Revised: 07/20/2009] [Accepted: 07/26/2009] [Indexed: 11/17/2022]
Abstract
BACKGROUND One of the central debates in membrane bioenergetics is whether proton-dependent energy coupling mechanisms are mediated exclusively by protonic transmembrane electrochemical potentials, as delocalized pmf, DeltamicroH(+), or by more localized membrane surface proton pathways, as interfacial pmf, DeltamicroH(S). METHODS We measure pH(S) in rat liver mitoplasts energized by respiration or ATP hydrolysis by inserting pH sensitive fluorescein-phosphatidyl-ethanolamine(F-PE) into mitoplast surface. RESULTS In the presence of rotenone and Ap5A, succinate oxidation induces a bi-phasic interfacial protonation on the mitoplast membranes, a fast phase followed by a slow one, and an interfacial pH decrease of 0.5 to 0.9 pH units of mitoplast with no simultaneous pH changes in the bulk. Antimycin A, other inhibitors or uncouplers of mitochondrial respiration prevent the decrease of mitoplast pH(S), supporting that DeltamicroH(S) is dependent and controlled by energization of mitoplast membranes. A quantitative assay of ATP synthesis coupled with pH(S) of mitoplasts oxidizing succinate with malonate titration shows a parallel correlation between ATP synthesis, State 4 respiration and pH(S), but not with Psi(E). GENERAL SIGNIFICANCE Our data substantiate pH(S) as the primary energy source of pmf for mitochondrial ATP synthesis. Evidence and discussion concerning the relative importance and interplay of pH(S) and Psi(E) in mitochondrial bioenergetics are also presented.
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Affiliation(s)
- Jing-Wei Xiong
- State Key Laboratory of Biomembrane and Membrane Biotechnology, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China
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36
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Tiktopulo EI, Kiseleva NV, Melnik BS, Vasiliev VD, Potekhin SA, Koretskaya NG. Structural changes in wild-type Cry3A δ-endotoxin and its mutant forms in ethanolic solutions at pH 2–2.5. Biophysics (Nagoya-shi) 2009. [DOI: 10.1134/s0006350909020043] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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37
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Harden J, Diorio N, Petrov AG, Jakli A. Chirality of lipids makes fluid lamellar phases piezoelectric. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2009; 79:011701. [PMID: 19257046 DOI: 10.1103/physreve.79.011701] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/14/2008] [Indexed: 05/27/2023]
Abstract
The role of chirality in membrane-forming lipids is not well appreciated at present. Here we demonstrate that the chirality of phospholipids makes fluid lipid bilayers piezoelectric. Thus, chiral lipids would play a central role in the functioning of cell membranes as active mechanotransducers. By periodically shearing and compressing nonaqueous lamellar phases of left ( L-alpha -phosphatidylcholine), right (D- alpha -phosphatidylcholine), and racemic (DL- alpha -phosphatidylcholine) lipids, we induced a tilt of the molecules with respect to the bilayer's normal and produced electric current perpendicular to the tilt plane, with the chiral lipids only. This effect is due to the Sm-A;{*} phase liquid crystal structure of the bilayers, which under molecular tilt becomes a ferroelectric Sm-C;{*} phase, where the polarization is normal to the tilt plane. This coupling allows for a wide variety of sensory possibilities of cell membranes such as mechanoreception, magnetosensitivity, as well as in-plane proton membrane transport and related phenomena such as adenosine triphosphate (ATP) synthesis, soft molecular machine performance, etc.
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Affiliation(s)
- John Harden
- Liquid Crystal Institute and Chemical Physics Interdisciplinary Program, Kent, Ohio 44242, USA
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38
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Fanucchi S, Adamson RJ, Dirr HW. Formation of an Unfolding Intermediate State of Soluble Chloride Intracellular Channel Protein CLIC1 at Acidic pH. Biochemistry 2008; 47:11674-81. [DOI: 10.1021/bi801147r] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Sylvia Fanucchi
- Protein Structure-Function Research Unit, School of Molecular and Cell Biology, University of the Witwatersrand, Johannesburg 2050, South Africa
| | - Roslin J. Adamson
- Protein Structure-Function Research Unit, School of Molecular and Cell Biology, University of the Witwatersrand, Johannesburg 2050, South Africa
| | - Heini W. Dirr
- Protein Structure-Function Research Unit, School of Molecular and Cell Biology, University of the Witwatersrand, Johannesburg 2050, South Africa
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39
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Literature Alerts. J Microencapsul 2008. [DOI: 10.3109/02652048709021811] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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40
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Antonenko YN, Pohl P. Microinjection in combination with microfluorimetry to study proton diffusion along phospholipid membranes. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2008; 37:865-70. [PMID: 18330554 DOI: 10.1007/s00249-008-0295-y] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/07/2008] [Revised: 02/15/2008] [Accepted: 02/26/2008] [Indexed: 10/22/2022]
Abstract
Proton diffusion along the surface of a planar bilayer lipid membrane was measured by means of acid/base injection with a micropipette and recording of the kinetics of fluorescence changes of fluorescein-labelled lipid on the surface. The dimensionality of the process was assayed by fitting the kinetic curves with two-dimensional (2D) or three-dimensional (3D) diffusion equations. In agreement with Serowy et al. (Biophys J 84:1031-1037, 2003), lateral proton diffusion proceeded via bulk phase by means of buffer molecules as proton carriers (D = 600 microm2/s) under the conditions of 1 mM buffer in the solution. Introduction of proton binding sites on the membrane surface led to the appearance of a considerable contribution of two-dimensional proton diffusion on the membrane surface with D = 1,100 mum(2)/s. The system described can be used to study the dependence of the proton diffusion rate on the phospholipid and protein composition of the membrane.
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Affiliation(s)
- Yuri N Antonenko
- A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow, 119992, Russia.
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41
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Basova LV, Tiktopulo EI, Kutyshenko VP, Mauk AG, Bychkova VE. Phospholipid membranes affect tertiary structure of the soluble cytochrome b5 heme-binding domain. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2008; 1778:1015-26. [PMID: 18275841 DOI: 10.1016/j.bbamem.2007.12.028] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/24/2007] [Revised: 12/21/2007] [Accepted: 12/28/2007] [Indexed: 11/30/2022]
Abstract
The influence of charged phospholipid membranes on the conformational state of the water-soluble fragment of cytochrome b5 has been investigated by a variety of techniques at neutral pH. The results of this work provide the first evidence that aqueous solutions with high phospholipid/protein molar ratios (pH 7.2) induce the cytochrome to undergo a structural transition from the native conformation to an intermediate state with molten-globule like properties that occur in the presence of an artificial membrane surface and that leads to binding of the protein to the membrane. At other phospholipid/protein ratios, equilibrium was observed between cytochrome free in solution and cytochrome bound to the surface of vesicles. Inhibition of protein binding to the vesicles with increasing ionic strength indicated for the most part an electrostatic contribution to the stability of cytochrome b5-vesicle interactions at pH 7.2. The possible physiological role of membrane-induced conformational change in the structure of cytochrome b5 upon the interaction with its redox partners is discussed.
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Affiliation(s)
- Liana V Basova
- Institute of Protein Research, Russian Academy of Sciences, Pushchino, Moscow Region, 142290 Russia
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42
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Teissie J. Biophysical effects of electric fields on membrane water interfaces: a mini review. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2007; 36:967-72. [PMID: 17492435 DOI: 10.1007/s00249-007-0168-9] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/15/2007] [Revised: 04/13/2007] [Accepted: 04/17/2007] [Indexed: 11/30/2022]
Abstract
Lipid-water interfaces are dielectric transition regions. Their local organizations are highly sophisticated. They are sensitive to electric field with dramatic consequences on the global membrane organization and function. The importance of using local values of parameters (e.g. dielectric constant) near water-solution interface due to hydration and different electrostatic effects is often neglected in the description of cellular functions. Structural changes in the lipid layer are induced by minute changes in the electric properties of the interface. They bring alterations in the structure and oligomerization of membrane proteins.
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Affiliation(s)
- Justin Teissie
- IPBS UMR 5089 UPS CNRS, 205 route de narbonne, 31077, Toulouse Cedex, France.
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43
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Guan X, Liu X, Su Z. Preparation and photophysical behaviors of fluorescent chitosan bearing fluorescein: Potential biomaterial as temperature/pH probes. J Appl Polym Sci 2007. [DOI: 10.1002/app.26200] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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44
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The preparation and photophysical behaviors of temperature/pH-sensitive polymer materials bearing fluorescein. REACT FUNCT POLYM 2006. [DOI: 10.1016/j.reactfunctpolym.2006.03.005] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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45
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Edwards MA, Martin S, Whitworth AL, Macpherson JV, Unwin PR. Scanning electrochemical microscopy: principles and applications to biophysical systems. Physiol Meas 2006; 27:R63-108. [PMID: 17135697 DOI: 10.1088/0967-3334/27/12/r01] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
This review highlights numerous and wide ranging biophysical and biochemical applications of scanning electrochemical microscopy (SECM). SECM instrumentation and theoretical modelling, necessary for experimental interpretation, are outlined, followed by a detailed discussion of the diverse applications of this technique. These include the measurement of flow through membranes, the determination of kinetic parameters of reactions, the investigation of the permeability of small molecules in tissues and monitoring biological processes, such as the production of oxygen or nitric oxide by cells. The significant impact of micro-electrochemical techniques on our understanding of basic physicochemical processes at biologically relevant interfaces is also considered. Studies reviewed include transport across and within bilayers and monolayers. Recent advances in SECM include the combination of SECM with other techniques, such as atomic force microscopy and optical microscopy. These developments are highlighted, along with prospects for the future.
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Affiliation(s)
- Martin A Edwards
- Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK
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46
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Li H, Frieden C. Fluorine-19 NMR studies on the acid state of the intestinal fatty acid binding protein. Biochemistry 2006; 45:6272-8. [PMID: 16700539 PMCID: PMC2501113 DOI: 10.1021/bi0602922] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The intestinal fatty acid binding protein (IFABP) is composed of two beta-sheets with a large hydrophobic cavity into which ligands bind. After eight 4-(19)F-phenylalanines were incorporated into the protein, the acid state of both apo- and holo-IFABP (at pH 2.8 and 2.3) was characterized by means of (1)H NMR diffusion measurements, circular dichroism, and (19)F NMR. Diffusion measurements show a moderately increased hydrodynamic radius while near- and far-UV CD measurements suggest that the acid state has substantial secondary structure as well as persistent tertiary interactions. At pH 2.8, these tertiary interactions have been further characterized by (19)F NMR and show an NOE cross-peak between residues that are located on different beta-strands. Side chain conformational heterogeneity on the millisecond time scale was captured by phase-sensitive (19)F-(19)F NOESY. At pH 2.3, native NMR peaks are mostly gone, but the protein can still bind fatty acid to form the holoprotein. An exchange cross-peak of one phenylalanine in the holoprotein is attributed to increased motional freedom of the fatty acid backbone caused by the slight opening of the binding pocket at pH 2.8. In the acid environment Phe128 and Phe17 show dramatic line broadening and chemical shift changes, reflecting greater degrees of motion around these residues. We propose that there is a separation of specific regions of the protein that gives rise to the larger radius of hydration. Temperature and urea unfolding studies indicate that persistent hydrophobic clusters are nativelike and may account for the ability of ligand to bind and induce nativelike structure, even at pH 2.3.
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Affiliation(s)
- Hua Li
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, 660 South Euclid Avenue, St. Louis, Missouri 63110, USA
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47
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Polverini E, Fornabaio M, Fasano A, Carlone G, Riccio P, Cavatorta P. The pH-dependent unfolding mechanism of P2 myelin protein: an experimental and computational study. J Struct Biol 2005; 153:253-63. [PMID: 16427315 DOI: 10.1016/j.jsb.2005.11.010] [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] [Received: 07/07/2005] [Revised: 11/04/2005] [Accepted: 11/10/2005] [Indexed: 10/25/2022]
Abstract
The P2 protein is a small, extrinsic protein of the myelin membrane in the peripheral nervous system that structurally belongs to the fatty acid binding proteins (FABPs) family, sharing with them a 10 strands beta-barrel structure. FABPs appear to be involved in cellular fatty acid transport, but very little is known about the role of P2 in the metabolism of peripheral myelin lipids. Study of protein conformation at different pHs is a useful tool for the characterization of the unfolding mechanisms and the intrinsic conformational properties of the protein, and may give insight into factors that guide protein folding pathways. In particular, low pH conditions have been shown to induce partially folded states in several proteins. In this paper, the acidic unfolding of purified P2 protein was studied with both spectroscopic techniques and molecular dynamics simulation. Both experimental and computational results indicate the presence of a partly folded state at low pH, which shows structural changes mainly involving the lid that is formed by the helix-turn-helix domain. The opening of the lid, together with a barrel relaxation, could regulate the ligand exchanges near the cell membrane, supporting the hypothesis that the P2 protein may transport fatty acids between Schwann cells and peripheral myelin.
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Affiliation(s)
- Eugenia Polverini
- Dipartimento di Fisica, CNR-INFM and CNISM, Università di Parma, Parco Area delle Scienze, 7/A, 43100 Parma, Italy.
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48
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Chenal A, Vernier G, Savarin P, Bushmarina NA, Gèze A, Guillain F, Gillet D, Forge V. Conformational states and thermodynamics of alpha-lactalbumin bound to membranes: a case study of the effects of pH, calcium, lipid membrane curvature and charge. J Mol Biol 2005; 349:890-905. [PMID: 15893324 DOI: 10.1016/j.jmb.2005.04.036] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2004] [Revised: 04/08/2005] [Accepted: 04/18/2005] [Indexed: 11/20/2022]
Abstract
The study of the conformational changes of bovine alpha-lactalbumin, switching from soluble states to membrane-bound states, deepens our knowledge of the behaviour of amphitropic proteins. The binding and the membrane-bound conformations of alpha-lactalbumin are highly sensitive to environmental factors, like calcium and proton concentrations, curvature and charge of the lipid membrane. The interactions between the protein and the membrane result from a combination of hydrophobic and electrostatic interactions and the respective weights of these interactions depend on the physicochemical conditions. As inferred by macroscopic as well as residue-level methods, the conformations of the membrane-bound protein range from native-like to molten globule-like states. However, the regions anchoring the protein to the membrane are similar and restricted to amphiphilic alpha-helices. H/(2)H-exchange experiments also yield residue-level data that constitute comprehensive information providing a new point of view on the thermodynamics of the interactions between the protein and the membrane.
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Affiliation(s)
- Alexandre Chenal
- Biophysique Moléculaire et Cellulaire, Unité Mixte de Recherche 5090, Département Réponse et Dynamique Cellulaires, CEA-Grenoble, 38054 Grenoble cedex 9, France.
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49
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Stock C, Gassner B, Hauck CR, Arnold H, Mally S, Eble JA, Dieterich P, Schwab A. Migration of human melanoma cells depends on extracellular pH and Na+/H+ exchange. J Physiol 2005; 567:225-38. [PMID: 15946960 PMCID: PMC1474168 DOI: 10.1113/jphysiol.2005.088344] [Citation(s) in RCA: 149] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Their glycolytic metabolism imposes an increased acid load upon tumour cells. The surplus protons are extruded by the Na+/H+ exchanger (NHE) which causes an extracellular acidification. It is not yet known by what mechanism extracellular pH (pHe) and NHE activity affect tumour cell migration and thus metastasis. We studied the impact of pHe and NHE activity on the motility of human melanoma (MV3) cells. Cells were seeded on/in collagen I matrices. Migration was monitored employing time lapse video microscopy and then quantified as the movement of the cell centre. Intracellular pH (pHi) was measured fluorometrically. Cell-matrix interactions were tested in cell adhesion assays and by the displacement of microbeads inside a collagen matrix. Migration depended on the integrin alpha2beta1. Cells reached their maximum motility at pHe approximately 7.0. They hardly migrated at pHe 6.6 or 7.5, when NHE was inhibited, or when NHE activity was stimulated by loading cells with propionic acid. These procedures also caused characteristic changes in cell morphology and pHi. The changes in pHi, however, did not account for the changes in morphology and migratory behaviour. Migration and morphology more likely correlate with the strength of cell-matrix interactions. Adhesion was the strongest at pHe 6.6. It weakened at basic pHe, upon NHE inhibition, or upon blockage of the integrin alpha2beta1. We propose that pHe and NHE activity affect migration of human melanoma cells by modulating cell-matrix interactions. Migration is hindered when the interaction is too strong (acidic pHe) or too weak (alkaline pHe or NHE inhibition).
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Affiliation(s)
- Christian Stock
- Institute of Physiology II, University of Münster, Robert-Koch-Str.27b, D-48149 Münster, Germany.
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50
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Vincent M, de Foresta B, Gallay J. Nanosecond dynamics of a mimicked membrane-water interface observed by time-resolved stokes shift of LAURDAN. Biophys J 2005; 88:4337-50. [PMID: 15778437 PMCID: PMC1305662 DOI: 10.1529/biophysj.104.057497] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We studied the dipolar relaxation of the surfactant-water interface in reverse micelles of AOT-water in isooctane in the nanosecond and subnanosecond time ranges by incorporating the amphipathic solvatochromic fluorescent probes LAURDAN and TOE. A negative component was observed in the fluorescence decays in the red edge of the emission spectrum-the signature of an excited state reaction-with LAURDAN but not for TOE. The deconvolution of the transient reconstructed spectra of LAURDAN based on a model constructed by adding together three log-normal Gaussian equations made it possible to separate the specific dynamic solvent response from the intramolecular excited state reactions of the probe. The deconvoluted spectrum of lowest energy displayed the largest Stokes shift. This spectral shift was described by unimodal kinetics on the nanosecond timescale, whereas the relaxation kinetics of water-soluble probes have been reported to be biphasic (on the subnanosecond and nanosecond timescales) due to the heterogeneous distribution of these probes in the water pool. Most of this spectral shift probably resulted from water relaxation as it was highly sensitive to the water to surfactant molar ratio (w(0)) (60-65 nm at w(0) = 20-30). A small part of this spectral shift (9 nm at w(0) = 0) probably resulted from dipolar interaction with the AOT polar headgroup. The measured relaxation time values were in the range of the rotational motion of the AOT polar headgroup region as assessed by LAURDAN and TOE fluorescence anisotropy decays.
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Affiliation(s)
- Michel Vincent
- LURE Laboratoire pour l'Utilisation du Rayonnement Electromagnétique, Université Paris-Sud, Bâtiment 209D, Orsay, France
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