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Rostovtseva TK, Weinrich M, Jacobs D, Rosencrans WM, Bezrukov SM. Dimeric Tubulin Modifies Mechanical Properties of Lipid Bilayer, as Probed Using Gramicidin A Channel. Int J Mol Sci 2024; 25:2204. [PMID: 38396879 PMCID: PMC10889239 DOI: 10.3390/ijms25042204] [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: 12/07/2023] [Revised: 01/31/2024] [Accepted: 02/05/2024] [Indexed: 02/25/2024] Open
Abstract
Using the gramicidin A channel as a molecular probe, we show that tubulin binding to planar lipid membranes changes the channel kinetics-seen as an increase in the lifetime of the channel dimer-and thus points towards modification of the membrane's mechanical properties. The effect is more pronounced in the presence of non-lamellar lipids in the lipid mixture used for membrane formation. To interpret these findings, we propose that tubulin binding redistributes the lateral pressure of lipid packing along the membrane depth, making it closer to the profile expected for lamellar lipids. This redistribution happens because tubulin perturbs the lipid headgroup spacing to reach the membrane's hydrophobic core via its amphiphilic α-helical domain. Specifically, it increases the forces of repulsion between the lipid headgroups and reduces such forces in the hydrophobic region. We suggest that the effect is reciprocal, meaning that alterations in lipid bilayer mechanics caused by membrane remodeling during cell proliferation in disease and development may also modulate tubulin membrane binding, thus exerting regulatory functions. One of those functions includes the regulation of protein-protein interactions at the membrane surface, as exemplified by VDAC complexation with tubulin.
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Affiliation(s)
- Tatiana K. Rostovtseva
- Program in Physical Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA (S.M.B.)
| | - Michael Weinrich
- Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
| | - Daniel Jacobs
- Program in Physical Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA (S.M.B.)
| | - William M. Rosencrans
- Program in Physical Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA (S.M.B.)
- Department of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Sergey M. Bezrukov
- Program in Physical Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA (S.M.B.)
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2
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Liu H, Lu J, Liu Z, Wang S, Yan H, Tian H. Proton conducting behavior of a microporous metal-organic framework assisted by ligand isomerization. J SOLID STATE CHEM 2020. [DOI: 10.1016/j.jssc.2020.121570] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
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3
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Branda MM, Guérin DMA. Alkalinization of Icosahedral Non-enveloped Viral Capsid Interior Through Proton Channeling. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2019; 1215:181-199. [DOI: 10.1007/978-3-030-14741-9_9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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4
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Tunuguntla RH, Allen FI, Kim K, Belliveau A, Noy A. Ultrafast proton transport in sub-1-nm diameter carbon nanotube porins. NATURE NANOTECHNOLOGY 2016; 11:639-44. [PMID: 27043198 DOI: 10.1038/nnano.2016.43] [Citation(s) in RCA: 122] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/09/2015] [Accepted: 02/18/2016] [Indexed: 05/06/2023]
Abstract
Proton transport plays an important role in many biological processes due to the ability of protons to rapidly translocate along chains of hydrogen-bonded water molecules. Molecular dynamics simulations have predicted that confinement in hydrophobic nanochannels should enhance the rate of proton transport. Here, we show that 0.8-nm-diameter carbon nanotube porins, which promote the formation of one-dimensional water wires, can support proton transport rates exceeding those of bulk water by an order of magnitude. The transport rates in these narrow nanotube pores also exceed those of biological channels and Nafion. With larger 1.5-nm-diameter nanotube porins, proton transport rates comparable to bulk water are observed. We also show that the proton conductance of these channels can be modulated by the presence of Ca(2+) ions. Our results illustrate the potential of small-diameter carbon nanotube porins as a proton conductor material and suggest that strong spatial confinement is a key factor in enabling efficient proton transport.
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Affiliation(s)
- Ramya H Tunuguntla
- Biosciences and Biotechnology Division, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550, USA
| | - Frances I Allen
- Department of Materials Science and Engineering, University of California, 210 Hearst Avenue, Berkeley, California 94720, USA
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, USA
| | - Kyunghoon Kim
- Biosciences and Biotechnology Division, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550, USA
| | - Allison Belliveau
- Biosciences and Biotechnology Division, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550, USA
| | - Aleksandr Noy
- Biosciences and Biotechnology Division, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550, USA
- School of Natural Sciences, University of California Merced, 5200 N. Lake Road, Merced, California 94343, USA
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5
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Titus S, Sreejalekshmi KG. Propeller-shaped molecules with a thiazole hub: structural landscape and hydrazone cap mediated tunable host behavior in 4-hydrazino-1,3-thiazoles. CrystEngComm 2015. [DOI: 10.1039/c5ce01042j] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Propeller-shaped molecules with 2,4,5-trisubstituted-1,3-thiazole as the hub and tunable blades (B1–B3) were synthesized as trivariant scaffolds.
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Affiliation(s)
- Sarah Titus
- Department of Chemistry
- Indian Institute of Space Science and Technology
- Thiruvananthapuram – 695 547, India
| | - Kumaran G. Sreejalekshmi
- Department of Chemistry
- Indian Institute of Space Science and Technology
- Thiruvananthapuram – 695 547, India
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6
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Peptide-induced membrane leakage by lysine derivatives of gramicidin A in liposomes, planar bilayers, and erythrocytes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1828:2428-35. [DOI: 10.1016/j.bbamem.2013.06.018] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/25/2013] [Revised: 06/10/2013] [Accepted: 06/13/2013] [Indexed: 11/21/2022]
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7
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Sorochkina AI, Plotnikov EY, Rokitskaya TI, Kovalchuk SI, Kotova EA, Sychev SV, Zorov DB, Antonenko YN. N-terminally glutamate-substituted analogue of gramicidin A as protonophore and selective mitochondrial uncoupler. PLoS One 2012; 7:e41919. [PMID: 22911866 PMCID: PMC3404012 DOI: 10.1371/journal.pone.0041919] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2012] [Accepted: 06/29/2012] [Indexed: 11/18/2022] Open
Abstract
Limited uncoupling of oxidative phosphorylation could be beneficial for cells by preventing excessive generation of reactive oxygen species. Typical uncouplers are weak organic acids capable of permeating across membranes with a narrow gap between efficacy and toxicity. Aimed at designing a nontoxic uncoupler, the protonatable amino acid residue Glu was substituted for Val at the N-terminus of the pentadecapeptide gramicidin A (gA). The modified peptide [Glu1]gA exhibited high uncoupling activity in isolated mitochondria, in particular, abolishing membrane potential at the inner mitochondrial membrane with the same or even larger efficacy as gA. With mitochondria in cell culture, the depolarizing activity of [Glu1]gA was observed at concentrations by an order of magnitude lower than those of gA. On the contrary, [Glu1]gA was much less potent in forming proton channels in planar lipid bilayers than gA. Remarkably, at uncoupling concentrations, [Glu1]gA did not alter cell morphology and was nontoxic in MTT test, in contrast to gA showing high toxicity. The difference in the behavior of [Glu1]gA and gA in natural and artificial membranes could be ascribed to increased capability of [Glu1]gA to permeate through membranes and/or redistribute between different membranes. Based on the protective role of mild uncoupling, [Glu1]gA and some other proton-conducting gA analogues may be considered as prototypes of prospective therapeutic agents.
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Affiliation(s)
- Alexandra I. Sorochkina
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russia
| | - Egor Y. Plotnikov
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russia
| | - Tatyana I. Rokitskaya
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russia
| | - Sergei I. Kovalchuk
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, Russia
| | - Elena A. Kotova
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russia
| | - Sergei V. Sychev
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, Russia
| | - Dmitry B. Zorov
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russia
| | - Yuri N. Antonenko
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russia
- * E-mail:
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8
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Rokitskaya TI, Sorochkina AI, Kovalchuk SI, Egorova NS, Kotova EA, Sychev SV, Antonenko YN. The pH-dependent induction of lipid membrane ionic permeability by N-terminally lysine-substituted analogs of gramicidin A. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2011; 41:129-38. [DOI: 10.1007/s00249-011-0764-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2011] [Revised: 09/30/2011] [Accepted: 10/11/2011] [Indexed: 11/29/2022]
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9
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Tripathi BP, Shahi VK. Organic–inorganic nanocomposite polymer electrolyte membranes for fuel cell applications. Prog Polym Sci 2011. [DOI: 10.1016/j.progpolymsci.2010.12.005] [Citation(s) in RCA: 447] [Impact Index Per Article: 34.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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10
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de Godoy CMG, Cukierman S. Membrane Phosphate Headgroups' Modulation of Permeation of Alkaline Cations in Gramicidin Channels. J Phys Chem B 2011; 115:5026-31. [DOI: 10.1021/jp2010716] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Affiliation(s)
- Carlos Marcelo G. de Godoy
- Department of Cell and Molecular Physiology, Loyola University Medical Center, 2160 South First Avenue, Maywood, Illinois 60153, United States, and Centro de Engenharia Biomédica, Universidade Camilo Castelo Branco, Parque Tecnológico, Rodovia Presidente Dutra km 138, São Jose dos Campos, São Paulo 12247-047, Brasil
| | - Samuel Cukierman
- Department of Cell and Molecular Physiology, Loyola University Medical Center, 2160 South First Avenue, Maywood, Illinois 60153, United States, and Centro de Engenharia Biomédica, Universidade Camilo Castelo Branco, Parque Tecnológico, Rodovia Presidente Dutra km 138, São Jose dos Campos, São Paulo 12247-047, Brasil
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11
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Wyatt DL, de Godoy CMG, Cukierman S. Enhancement of proton transfer in ion channels by membrane phosphate headgroups. J Phys Chem B 2009; 113:6725-31. [PMID: 19368364 DOI: 10.1021/jp900087g] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The transfer of protons (H+) in gramicidin (gA) channels is markedly distinct in monoglyceride and phospholipid membranes. In this study, the molecular groups that account for those differences were investigated using a new methodology. The rates of H+ transfer were measured in single gA channels reconstituted in membranes made of plain ceramides or sphingomyelins and compared to those in monoglyceride and phospholipid bilayers. Single-channel conductances to protons (gH) were significantly larger in sphingomyelin than in ceramide membranes. A novel and unsuspected finding was that H+ transfer was heavily attenuated or completely blocked in ceramide (but not in sphingomyelin) membranes in low-ionic-strength solutions. It is reasoned that H-bond dynamics at low ionic strengths between membrane ceramides and gA makes channels dysfunctional. The rate of H+ transfer in gA channels in ceramide membranes is significantly higher than that in monoglyceride bilayers. This suggests that solvation of the hydrophobic surface of gA channels by two acyl chains in ceramides stabilizes the gA channels and the water wire inside the pore, leading to an enhancement of H+ transfer in relation to that occurring in monoglyceride membranes. gH values in gA channels are similar in ceramide and monoglyceride bilayers and in sphingomyelin and phospholipid membranes. It is concluded that phospho headgroups in membranes have significant effects on the rate of H+ transfer at the membrane gA channel/solution interfaces, enhancing the entry and exit rates of protons in channels.
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Affiliation(s)
- Debra L Wyatt
- Department of Cell and Molecular Physiology, Loyola University Medical Center, 2160 South First Avenue, Maywood, Illinois 60153, USA
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12
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Honma I, Yamada M. Bio-Inspired Membranes for Advanced Polymer Electrolyte Fuel Cells. Anhydrous Proton-Conducting Membrane via Molecular Self-Assembly. BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 2007. [DOI: 10.1246/bcsj.80.2110] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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13
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Qin Z, Tepper HL, Voth GA. Effect of Membrane Environment on Proton Permeation through Gramicidin A Channels. J Phys Chem B 2007; 111:9931-9. [PMID: 17672487 DOI: 10.1021/jp0708998] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Multistate empirical valence bond simulations were employed to study proton transport through gramicidin A channels embedded in two different lipid bilayers, glycerol 1-monooleate (GMO) and diphytanolphosphatidylcholine (DiPhPC). Free energy barriers to proton permeation were derived using a new internal reaction coordinate describing the proton permeation process. The large quantitative and qualitative differences between the two systems are discussed in terms of local bilayer structures, ordering of interfacial water, and channel flexibility in the two environments.
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Affiliation(s)
- Zhen Qin
- Center for Biophysical Modeling and Simulation and Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, USA
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14
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Blood PD, Ayton GS, Voth GA. Probing the molecular-scale lipid bilayer response to shear flow using nonequilibrium molecular dynamics. J Phys Chem B 2007; 109:18673-9. [PMID: 16853402 DOI: 10.1021/jp0530449] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A nonequilibrium molecular dynamics simulation of the response of dimyristoylphosphatidylcholine (DMPC) bilayers to a solvent shear flow is presented. Application of shear flow to planar, stationary DMPC bilayers results in a redistribution of the membrane density profile along the bilayer normal due to the alignment of the lipids in the direction of flow and an increase in average lipid chain length. An increase in the intermolecular and intramolecular order of the lipids in response to the shear flow is also observed. This study provides groundwork for understanding the mechanism of the full response of lipid bilayers to externally imposed solvent shear flows, beginning with the response in the absence of collective lipid motions such as undulations and bilayer flow.
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Affiliation(s)
- Philip D Blood
- Center for Biophysical Modeling and Simulation and Department of Bioengineering, University of Utah, 315 S. 1400 E. Rm 2020, Salt Lake City, Utah 84112-0850, USA
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15
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Dutseva EA, Antonenko YN, Kotova EA, Pfeifer JR, Koert U. Sensitized photoinactivation of minigramicidin channels in bilayer lipid membranes. BIOCHIMICA ET BIOPHYSICA ACTA 2007; 1768:1230-7. [PMID: 17306219 DOI: 10.1016/j.bbamem.2007.01.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/05/2006] [Revised: 12/26/2006] [Accepted: 01/10/2007] [Indexed: 11/15/2022]
Abstract
The method of sensitized photoinactivation based on the photosensitized damage of gramicidin A (gA) molecules was applied here to study ionic channels formed by minigramicidin (the 11-residue analogue of gramicidin A) in a planar bilayer lipid membrane (BLM) of different thickness. Irradiation of BLM with a single flash of visible light in the presence of a photosensitizer (aluminum phthalocyanine or Rose Bengal) generating singlet oxygen provoked a decrease in the minigramicidin-induced electric current across BLM, the kinetics of which had the characteristic time of several seconds, as observed with gA. For gA, there is good correlation between the characteristic time of photoinactivation and the single-channel lifetime. In contrast to the covalent dimer of gA characterized by extremely long single-channel lifetime and the absence of current relaxation upon flash excitation, the covalent head-to-head dimer of minigramicidin displayed the flash-induced current decrease with the kinetics being strongly dependent on the membrane thickness. The current decrease became slower both upon increasing the concentration of the minigramicidin covalent dimer and upon including cholesterol in the membrane composition. These data in combination with the quadratic dependence of the current on the peptide concentration can be rationalized by hypothesizing that the macroscopic current across BLM measured at high concentrations of the peptide is provided by dimers of minigramicidin covalent dimers in the double beta(5.7)-helical conformation having the lifetime of about 0.4 s, while single channels with the lifetime of 0.01 s, observed at a very low peptide concentration, correspond to the single-stranded beta(6.3)-helical conformation. Alternatively the results can be explained by clustering of channels at high concentrations of the minigramicidin covalent dimer.
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Affiliation(s)
- Elena A Dutseva
- Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow 119992, Russia
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16
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Sobko AA, Kotova EA, Antonenko YN, Zakharov SD, Cramer WA. Lipid Dependence of the Channel Properties of a Colicin E1-Lipid Toroidal Pore. J Biol Chem 2006; 281:14408-16. [PMID: 16556601 DOI: 10.1074/jbc.m513634200] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Colicin E1 belongs to a group of bacteriocins whose cytotoxicity toward Escherichia coli is exerted through formation of ion channels that depolarize the cytoplasmic membrane. The lipid dependence of colicin single-channel conductance demonstrated intimate involvement of lipid in the structure of this channel. The colicin formed "small" conductance 60-picosiemens (pS) channels, with properties similar to those previously characterized, in 1,2-dieicosenoyl-sn-glycero-3-phosphocholine (C20) or thinner membranes, whereas it formed a novel "large" conductance 600-pS state in thicker 1,2-dierucoyl-sn-glycero-3-phosphocholine (C22) bilayers. Both channel states were anion-selective and voltage-gated and displayed a requirement for acidic pH. Lipids having negative spontaneous curvature inhibited the formation of both channels but increased the ratio of open 600 pS to 60 pS conductance states. Different diameters of small and large channels, 12 and 16 A, were determined from the dependence of single-channel conductance on the size of nonelectrolyte solute probes. Colicin-induced lipid "flip-flop" and the decrease in anion selectivity of the channel in the presence of negatively charged lipids implied a significant contribution of lipid to the structure of the channel, most readily described as toroidal organization of lipid and protein to form the channel pore.
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Affiliation(s)
- Alexander A Sobko
- A. N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, 119992 Moscow, Russia
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17
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Yamada M, Honma I. Biomembranes for fuel cell electrolytes employing anhydrous proton conducting uracil composites. Biosens Bioelectron 2006; 21:2064-9. [PMID: 16530401 DOI: 10.1016/j.bios.2006.01.022] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2005] [Revised: 01/12/2006] [Accepted: 01/24/2006] [Indexed: 10/24/2022]
Abstract
The controls of proton transfer through membranes involve fundamental properties of chemical energy conversion in industrial devices as well as living systems. In particular, ion-exchange membranes are generally used as superior proton conductors for polymer electrolyte fuel cells (PEFC) due to the fluidic nature of water, although the cell operation above the boiling point (>100 degrees C) has been considered to provide a higher efficiency and an easier humidity management. We show that biomembranes consisting of uracil and chitin phosphate have large anhydrous proton conductivities over a wide temperature range from room temperature to 160 degrees C with sufficient thermal stabilities. Water-free conductivities exceeding 10(-3) S cm(-1) have been obtained in the elastic polymeric material, and the fuel cell employing the biomembrane as an electrolyte exhibited a stable current generation under non-humidified H2/O2 conditions at 160 degrees C.
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Affiliation(s)
- Masanori Yamada
- Energy Technology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568, Japan
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18
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Chernyshev A, Cukierman S. Proton transfer in gramicidin water wires in phospholipid bilayers: attenuation by phosphoethanolamine. Biophys J 2006; 91:580-7. [PMID: 16617081 PMCID: PMC1483085 DOI: 10.1529/biophysj.106.083352] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The transfer of protons in water wires was studied in native gramicidin A (gA), and in the SS- and RR-diastereoisomers of dioxolane-linked gA channels (SS and RR channels). These peptides were incorporated into membranes comprised of distinct combinations of phospholipid headgroups and acyl chains. Quantitative relationships between single channel conductances to H+ (g(H)) and [H+] were determined in distinct phospholipid membranes, and are in remarkable contrast with results previously obtained in monoglyceride membranes. In particular: 1), g(H)-[H+] relationships for the various gA channels in distinct phospholipid membranes are well fitted by single adsorption isotherms. A simple kinetic model assuming mono-occupancy of channels by protons fits said relationships. This does not occur with monoglyceride membranes. 2), Under nonsaturating [H+], g(H) is approximately 1 order of magnitude larger in phospholipid than in monoglyceride membranes. 3), Differences between rates of H+ transfer in various gA channels are still present but considerably attenuated in phospholipid relative to monoglyceride membranes. 4), Charged phospholipid headgroups affect g(H) via changes in [H+] at the membrane/solution interfaces. 5), Phosphoethanolamine groups caused a marked attenuation of g(H) relative to membranes with other phospholipid headgroups. This attenuation is voltage-dependent and tends to saturate H+ currents at voltages larger than 250 mV. This effect is likely to occur by limiting the access and exit of H+ in and out of the channel due to relatively strong oriented H-bonds between waters and phosphoethanolamine groups at channel interfaces. The differential effects of phospholipids on proton transfer could be reasoned by considering solvation effects of side chain residues of gramicidin channels by double acyl chains and by the presence of polar headgroups facilitating the entrance/exit of protons through the channel mouths.
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Affiliation(s)
- Anatoly Chernyshev
- Department of Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, Ilinois 60153, USA
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