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Sokolov VS, Tashkin VY, Zykova DD, Kharitonova YV, Galimzyanov TR, Batishchev OV. Electrostatic Potentials Caused by the Release of Protons from Photoactivated Compound Sodium 2-Methoxy-5-nitrophenyl Sulfate at the Surface of Bilayer Lipid Membrane. MEMBRANES 2023; 13:722. [PMID: 37623783 PMCID: PMC10456422 DOI: 10.3390/membranes13080722] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2023] [Revised: 08/03/2023] [Accepted: 08/06/2023] [Indexed: 08/26/2023]
Abstract
Lateral transport and release of protons at the water-membrane interface play crucial roles in cell bioenergetics. Therefore, versatile techniques need to be developed for investigating as well as clarifying the main features of these processes at the molecular level. Here, we experimentally measured the kinetics of binding of protons released from the photoactivated compound sodium 2-methoxy-5-nitrophenyl sulfate (MNPS) at the surface of a bilayer lipid membrane (BLM). We developed a theoretical model of this process describing the damage of MNPS coupled with the release of the protons at the membrane surface, as well as the exchange of MNPS molecules and protons between the membrane and solution. We found that the total change in the boundary potential difference across the membrane, ∆ϕb, is the sum of opposing effects of adsorption of MNPS anions and release of protons at the membrane-water interface. Steady-state change in the ∆ϕb due to protons decreased with the concentration of the buffer and increased with the pH of the solution. The change in the concentration of protons evaluated from measurements of ∆ϕb was close to that in the unstirred water layer near the BLM. This result, as well as rate constants of the proton exchange between the membrane and the bulk solution, indicated that the rate-limiting step of the proton surface to bulk release is the change in the concentration of protons in the unstirred layer. This means that the protons released from MNPS remain in equilibrium between the BLM surface and an adjacent water layer.
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Affiliation(s)
- Valerij S. Sokolov
- Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky Prospekt, 31, Moscow 119071, Russia (O.V.B.)
| | - Vsevolod Yu. Tashkin
- Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky Prospekt, 31, Moscow 119071, Russia (O.V.B.)
| | - Darya D. Zykova
- Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky Prospekt, 31, Moscow 119071, Russia (O.V.B.)
- Moscow Institute of Physics and Technology, Institutski Per., 9, Moscow Region, Dolgoprudny 141701, Russia
| | - Yulia V. Kharitonova
- Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky Prospekt, 31, Moscow 119071, Russia (O.V.B.)
| | - Timur R. Galimzyanov
- Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky Prospekt, 31, Moscow 119071, Russia (O.V.B.)
| | - Oleg V. Batishchev
- Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky Prospekt, 31, Moscow 119071, Russia (O.V.B.)
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Weichselbaum E, Galimzyanov T, Batishchev OV, Akimov SA, Pohl P. Proton Migration on Top of Charged Membranes. Biomolecules 2023; 13:352. [PMID: 36830721 PMCID: PMC9953355 DOI: 10.3390/biom13020352] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2022] [Revised: 01/23/2023] [Accepted: 02/07/2023] [Indexed: 02/15/2023] Open
Abstract
Proton relay between interfacial water molecules allows rapid two-dimensional diffusion. An energy barrier, ΔGr‡, opposes proton-surface-to-bulk release. The ΔGr‡-regulating mechanism thus far has remained unknown. Here, we explored the effect interfacial charges have on ΔGr‡'s enthalpic and entropic constituents, ΔGH‡ and ΔGS‡, respectively. A light flash illuminating a micrometer-sized membrane patch of a free-standing planar lipid bilayer released protons from an adsorbed hydrophobic caged compound. A lipid-anchored pH-sensitive dye reported protons' arrival at a distant membrane patch. Introducing net-negative charges to the bilayer doubled ΔGH‡, while positive net charges decreased ΔGH‡. The accompanying variations in ΔGS‡ compensated for the ΔGH‡ modifications so that ΔGr‡ was nearly constant. The increase in the entropic component of the barrier is most likely due to the lower number and strength of hydrogen bonds known to be formed by positively charged residues as compared to negatively charged moieties. The resulting high ΔGr‡ ensured interfacial proton diffusion for all measured membranes. The observation indicates that the variation in membrane surface charge alone is a poor regulator of proton traffic along the membrane surface.
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Affiliation(s)
- Ewald Weichselbaum
- Institute of Biophysics, Johannes Kepler University Linz, 4040 Linz, Austria
| | - Timur Galimzyanov
- A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Moscow 119071, Russia
- Department of Theoretical Physics and Quantum Technologies, National University of Science and Technology “MISiS”, Moscow 119991, Russia
| | - Oleg V. Batishchev
- A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Moscow 119071, Russia
| | - Sergey A. Akimov
- A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Moscow 119071, Russia
- Department of Theoretical Physics and Quantum Technologies, National University of Science and Technology “MISiS”, Moscow 119991, Russia
| | - Peter Pohl
- Institute of Biophysics, Johannes Kepler University Linz, 4040 Linz, Austria
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Choi S, Park I, Lee SH, Yeo KI, Min G, Woo SH, Kim YS, Lee SY, Lee SW. On-Chip Single-Cell Bioelectrical Analysis for Identification of Cell Electrical Phenotyping in Response to Sequential Electric Signal Modulation. BIOSENSORS 2022; 12:1037. [PMID: 36421154 PMCID: PMC9688586 DOI: 10.3390/bios12111037] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/12/2022] [Revised: 11/12/2022] [Accepted: 11/12/2022] [Indexed: 06/16/2023]
Abstract
In recent years, an interesting biomarker called membrane breakdown voltage has been examined using artificial planar lipid bilayers. Even though they have great potential to identify cell electrical phenotyping for distinguishing similar cell lines or cells under different physiological conditions, the biomarker has not been evaluated in the context of living cell electrical phenotyping. Herein, we present a single-cell analysis platform to continuously measure the electric response in a large number of cells in parallel using electric frequency and voltage variables. Using this platform, we measured the direction of cell displacement and transparent cell image alteration as electric polarization of the cell responds to signal modulation, extracting the dielectrophoretic crossover frequency and membrane breakdown voltage for each cell, and utilizing the measurement results in the same spatiotemporal environment. We developed paired parameters using the dielectrophoretic crossover frequency and membrane breakdown voltage for each cell and evaluated the paired parameter efficiency concerning the identification of two different breast cancer cells and cell drug response. Moreover, we showed that the platform was able to identify cell electrical phenotyping, which was generated by subtle changes in cholesterol depletion-induced cell membrane integrity disruption when the paired parameter was used. Our platform introduced in this paper is extremely useful for facilitating more accurate and efficient evaluation of cell electrical phenotyping in a variety of applications, such as cell biology and drug discovery.
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Affiliation(s)
- Seungyeop Choi
- Department of Biomedical Engineering, Yonsei University, Wonju 26493, Republic of Korea
| | - Insu Park
- Holonyak Micro and Nanotechnology Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
- Department of Biomedical Engineering, Konyang University, Daejeon 35365, Republic of Korea
| | - Sang Hyun Lee
- Department of Biomedical Engineering, Yonsei University, Wonju 26493, Republic of Korea
| | - Kang In Yeo
- Department of Biomedical Engineering, Yonsei University, Wonju 26493, Republic of Korea
| | - Gyeongjun Min
- Department of Biomedical Engineering, Yonsei University, Wonju 26493, Republic of Korea
| | - Sung-Hun Woo
- Department of Biomedical Laboratory Science, Yonsei University, Wonju 26493, Republic of Korea
| | - Yoon Suk Kim
- Department of Biomedical Laboratory Science, Yonsei University, Wonju 26493, Republic of Korea
| | - Sei Young Lee
- Department of Biomedical Engineering, Yonsei University, Wonju 26493, Republic of Korea
| | - Sang Woo Lee
- Department of Biomedical Engineering, Yonsei University, Wonju 26493, Republic of Korea
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Hybrid bilayer membranes as platforms for biomimicry and catalysis. Nat Rev Chem 2022; 6:862-880. [PMID: 37117701 DOI: 10.1038/s41570-022-00433-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/20/2022] [Indexed: 11/08/2022]
Abstract
Hybrid bilayer membrane (HBM) platforms represent an emerging nanoscale bio-inspired interface that has broad implications in energy catalysis and smart molecular devices. An HBM contains multiple modular components that include an underlying inorganic surface with a biological layer appended on top. The inorganic interface serves as a support with robust mechanical properties that can also be decorated with functional moieties, sensing units and catalytic active sites. The biological layer contains lipids and membrane-bound entities that facilitate or alter the activity and selectivity of the embedded functional motifs. With their structural complexity and functional flexibility, HBMs have been demonstrated to enhance catalytic turnover frequency and regulate product selectivity of the O2 and CO2 reduction reactions, which have applications in fuel cells and electrolysers. HBMs can also steer the mechanistic pathways of proton-coupled electron transfer (PCET) reactions of quinones and metal complexes by tuning electron and proton delivery rates. Beyond energy catalysis, HBMs have been equipped with enzyme mimics and membrane-bound redox agents to recapitulate natural energy transport chains. With channels and carriers incorporated, HBM sensors can quantify transmembrane events. This Review serves to summarize the major accomplishments achieved using HBMs in the past decade.
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El-Beyrouthy J, Makhoul-Mansour MM, Freeman EC. Studying the Mechanics of Membrane Permeabilization through Mechanoelectricity. ACS APPLIED MATERIALS & INTERFACES 2022; 14:6120-6130. [PMID: 35073482 DOI: 10.1021/acsami.1c19880] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
In this research, real-time monitoring of lipid membrane disruption is made possible by exploiting the dynamic properties of model lipid bilayers formed at oil-water interfaces. This involves tracking an electrical signal generated through rhythmic membrane perturbation translated into the adsorption and penetration of charged species within the membrane. Importantly, this allows for the detection of membrane surface interactions that occur prior to pore formation that may be otherwise undetected. The requisite dynamic membranes for this approach are made possible through the droplet interface bilayer (DIB) technique. Membranes are formed at the interface of lipid monolayer-coated aqueous droplets submerged in oil. We present how cyclically alternating the membrane area leads to the generation of mechanoelectric current. This current is negligible without a transmembrane voltage until a composition mismatch between the membrane monolayers is produced, such as a one-sided accumulation of disruptive agents. The generated mechanoelectric current is then eliminated when an applied electric field compensates for this asymmetry, enabling measurement of the transmembrane potential offset. Tracking the compensating voltage with respect to time then reveals the gradual accumulation of disruptive agents prior to membrane permeabilization. The innovation of this work is emphasized in its ability to continuously track membrane surface activity, highlighting the initial interaction steps of membrane disruption. In this paper, we begin by validating our proposed approach against measurements taken for fixed composition membranes using standard electrophysiological techniques. Next, we investigate surfactant adsorption, including hexadecyltrimethylammonium bromide (CTAB, cationic) and sodium decyl sulfate (SDS, anionic), demonstrating the ability to track adsorption prior to disruption. Finally, we investigate the penetration of lipid membranes by melittin, confirming that the peptide insertion and disruption mechanics are, in part, modulated by membrane composition.
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Affiliation(s)
- Joyce El-Beyrouthy
- Biomembranes Engineering Laboratory, School of Environment, Civil, Agriculture and Mechanical Engineering, The University of Georgia, Athens, Georgia 30602, United States
| | - Michelle M Makhoul-Mansour
- Biomembranes Engineering Laboratory, School of Environment, Civil, Agriculture and Mechanical Engineering, The University of Georgia, Athens, Georgia 30602, United States
| | - Eric C Freeman
- Biomembranes Engineering Laboratory, School of Environment, Civil, Agriculture and Mechanical Engineering, The University of Georgia, Athens, Georgia 30602, United States
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Pohl P. Biophysical Reviews' "Meet the Councilor Series"-a profile of Peter Pohl. Biophys Rev 2021; 13:839-844. [PMID: 35035592 PMCID: PMC8724173 DOI: 10.1007/s12551-021-00897-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2021] [Accepted: 11/01/2021] [Indexed: 10/30/2022] Open
Abstract
It is my pleasure to write a few words to introduce myself to the readers of Biophysical Reviews as part of the "Meet the Councilor Series." Currently, I am serving the second period as IUPAB councilor after having been elected first in 2017. Initially, I studied Biophysics in Moscow (Russia) and later Medicine in Halle (Germany). My scientific carrier took me from the Medical School of the Martin Luther University of Halle-Wittenberg, via the Leibniz Institute for Molecular Pharmacology (Berlin) and the Institute for Biology at the Humboldt University (Berlin) to the Physics Department of the Johannes Kepler University in Linz (Austria). My key research interests lie in the molecular mechanisms of transport phenomena occurring at the lipid membrane, including (i) spontaneous and facilitated transport of water and other small molecules across membranes in reconstituted systems, (ii) proton migration along the membrane surface, (iii) protein translocation, and (iv) bilayer mechanics. Training of undergraduate, graduate, and postdoctoral researchers from diverse academic disciplines has been-and shall remain-a consistent part of my work.
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Affiliation(s)
- Peter Pohl
- Institute of Biophysics, Johannes Kepler University, Linz, Austria
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El-Beyrouthy J, Freeman E. Characterizing the Structure and Interactions of Model Lipid Membranes Using Electrophysiology. MEMBRANES 2021; 11:319. [PMID: 33925756 PMCID: PMC8145864 DOI: 10.3390/membranes11050319] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/02/2021] [Revised: 04/22/2021] [Accepted: 04/25/2021] [Indexed: 11/16/2022]
Abstract
The cell membrane is a protective barrier whose configuration determines the exchange both between intracellular and extracellular regions and within the cell itself. Consequently, characterizing membrane properties and interactions is essential for advancements in topics such as limiting nanoparticle cytotoxicity. Characterization is often accomplished by recreating model membranes that approximate the structure of cellular membranes in a controlled environment, formed using self-assembly principles. The selected method for membrane creation influences the properties of the membrane assembly, including their response to electric fields used for characterizing transmembrane exchanges. When these self-assembled model membranes are combined with electrophysiology, it is possible to exploit their non-physiological mechanics to enable additional measurements of membrane interactions and phenomena. This review describes several common model membranes including liposomes, pore-spanning membranes, solid supported membranes, and emulsion-based membranes, emphasizing their varying structure due to the selected mode of production. Next, electrophysiology techniques that exploit these structures are discussed, including conductance measurements, electrowetting and electrocompression analysis, and electroimpedance spectroscopy. The focus of this review is linking each membrane assembly technique to the properties of the resulting membrane, discussing how these properties enable alternative electrophysiological approaches to measuring membrane characteristics and interactions.
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Affiliation(s)
| | - Eric Freeman
- School of Environmental, Civil, Agricultural and Mechanical Engineering, College of Engineering, University of Georgia, Athens, GA 30602, USA;
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Kreiter J, Rupprecht A, Škulj S, Brkljača Z, Žuna K, Knyazev DG, Bardakji S, Vazdar M, Pohl EE. ANT1 Activation and Inhibition Patterns Support the Fatty Acid Cycling Mechanism for Proton Transport. Int J Mol Sci 2021; 22:ijms22052490. [PMID: 33801254 PMCID: PMC7958136 DOI: 10.3390/ijms22052490] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2021] [Revised: 02/22/2021] [Accepted: 02/24/2021] [Indexed: 01/26/2023] Open
Abstract
Adenine nucleotide translocase (ANT) is a well-known mitochondrial exchanger of ATP against ADP. In contrast, few studies have shown that ANT also mediates proton transport across the inner mitochondrial membrane. The results of these studies are controversial and lead to different hypotheses about molecular transport mechanisms. We hypothesized that the H+-transport mediated by ANT and uncoupling proteins (UCP) has a similar regulation pattern and can be explained by the fatty acid cycling concept. The reconstitution of purified recombinant ANT1 in the planar lipid bilayers allowed us to measure the membrane current after the direct application of transmembrane potential ΔΨ, which would correspond to the mitochondrial states III and IV. Experimental results reveal that ANT1 does not contribute to a basal proton leak. Instead, it mediates H+ transport only in the presence of long-chain fatty acids (FA), as already known for UCPs. It depends on FA chain length and saturation, implying that FA’s transport is confined to the lipid-protein interface. Purine nucleotides with the preference for ATP and ADP inhibited H+ transport. Specific inhibitors of ATP/ADP transport, carboxyatractyloside or bongkrekic acid, also decreased proton transport. The H+ turnover number was calculated based on ANT1 concentration determined by fluorescence correlation spectroscopy and is equal to 14.6 ± 2.5 s−1. Molecular dynamic simulations revealed a large positively charged area at the protein/lipid interface that might facilitate FA anion’s transport across the membrane. ANT’s dual function—ADP/ATP and H+ transport in the presence of FA—may be important for the regulation of mitochondrial membrane potential and thus for potential-dependent processes in mitochondria. Moreover, the expansion of proton-transport modulating drug targets to ANT1 may improve the therapy of obesity, cancer, steatosis, cardiovascular and neurodegenerative diseases.
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Affiliation(s)
- Jürgen Kreiter
- Institute of Physiology, Pathophysiology and Biophysics, Department of Biomedical Sciences, University of Veterinary Medicine, 1210 Vienna, Austria; (J.K.); (A.R.); (K.Ž.); (S.B.)
| | - Anne Rupprecht
- Institute of Physiology, Pathophysiology and Biophysics, Department of Biomedical Sciences, University of Veterinary Medicine, 1210 Vienna, Austria; (J.K.); (A.R.); (K.Ž.); (S.B.)
- Institute of Pharmacology and Toxicology, Rostock University Medical Center, 18057 Rostock, Germany
| | - Sanja Škulj
- Division of Organic Chemistry and Biochemistry, Rudjer Bošković Institute,10000 Zagreb, Croatia; (S.Š.); (Z.B.); (M.V.)
| | - Zlatko Brkljača
- Division of Organic Chemistry and Biochemistry, Rudjer Bošković Institute,10000 Zagreb, Croatia; (S.Š.); (Z.B.); (M.V.)
| | - Kristina Žuna
- Institute of Physiology, Pathophysiology and Biophysics, Department of Biomedical Sciences, University of Veterinary Medicine, 1210 Vienna, Austria; (J.K.); (A.R.); (K.Ž.); (S.B.)
| | - Denis G. Knyazev
- Institute of Biophysics, Johannes Kepler University, 4020 Linz, Austria;
| | - Sarah Bardakji
- Institute of Physiology, Pathophysiology and Biophysics, Department of Biomedical Sciences, University of Veterinary Medicine, 1210 Vienna, Austria; (J.K.); (A.R.); (K.Ž.); (S.B.)
| | - Mario Vazdar
- Division of Organic Chemistry and Biochemistry, Rudjer Bošković Institute,10000 Zagreb, Croatia; (S.Š.); (Z.B.); (M.V.)
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, 16610 Prague 6, Czech Republic
| | - Elena E. Pohl
- Institute of Physiology, Pathophysiology and Biophysics, Department of Biomedical Sciences, University of Veterinary Medicine, 1210 Vienna, Austria; (J.K.); (A.R.); (K.Ž.); (S.B.)
- Correspondence:
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Mechanism of Long-Chain Free Fatty Acid Protonation at the Membrane-Water Interface. Biophys J 2019; 114:2142-2151. [PMID: 29742407 DOI: 10.1016/j.bpj.2018.04.011] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2017] [Revised: 03/19/2018] [Accepted: 04/02/2018] [Indexed: 01/06/2023] Open
Abstract
Long-chain free fatty acids (FFAs) play an important role in several physiological and pathological processes such as lipid fusion, adjustments of membrane permeability and fluidity, and the regulation of enzyme and protein activities. FFA-facilitated membrane proton transport (flip-flop) and FFA-dependent proton transport by membrane proteins (e.g., mitochondrial uncoupling proteins) are governed by the difference between FFA's intrinsic pKa value and the pH in the immediate membrane vicinity. Thus far, a quantitative understanding of the process has been hampered, because the pKa value shifts upon moving the FFA from the aqueous solution into the membrane. For the same FFA, pKa values between 5 and 10.5 were reported. Here, we systematically evaluated the dependence of pKa values on chain length and number of double bonds by measuring the ζ-potential of liposomes reconstituted with FFA at different pH values. The experimentally obtained intrinsic pKa values (6.25, 6.93, and 7.28 for DOPC membranes) increased with FFA chain length (C16, C18, and C20), indicating that the hydrophobic energy of transfer into the bilayer is an important pKa determinant. The observed pKa decrease in DOPC with increasing number of FFA double bonds (7.28, 6.49, 6.16, and 6.13 for C20:0, C20:1, C20:2, and C20:4, respectively) is in line with a decrease in transfer energy. Molecular dynamic simulations revealed that the ionized carboxylic group of the FFAs occupied a fixed position in the bilayer independent of chain length, underlining the importance of Born energy. We conclude that pKa is determined by the interplay between the energetic costs for 1) burying the charged moiety into the lipid bilayer and 2) transferring the hydrophobic protonated FFA into the bilayer.
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Škulj S, Vazdar M. Calculation of apparent pK a values of saturated fatty acids with different lengths in DOPC phospholipid bilayers. Phys Chem Chem Phys 2019; 21:10052-10060. [PMID: 31046041 DOI: 10.1039/c9cp01204d] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
We performed all-atom molecular dynamics simulations and calculated free energy profiles and apparent pKa values for neutral and anionic forms of single myristic (C14:0), palmitic (C16:0) and stearic (C18:0) fatty acid embedded in a DOPC bilayer and explicit water solvent. We showed that the neutral forms of the fatty acids are stabilized inside the bilayer by hydrogen bonding of a fatty acid carboxylic group with DOPC phosphate and carbonyl groups. In contrast to the neutral form, the anionic forms of the fatty acids are shifted towards the water-membrane interface and are instead stabilized by hydrogen bonding to interfacial water. By using umbrella sampling simulations, we calculated free energies of stabilization and revealed that the free energy of stabilization inside the bilayer increases with the chain length for both the neutral and deprotonated forms. On the other hand, the free energies of flip-flop of both the neutral and anionic forms are constant upon the prolongation of the fatty acid. Based on the free energy curves, we also calculated apparent fatty acid pKa,app values in the bilayer, which are 7.0, 7.2 and 6.3 for myristic, palmitic and stearic acid and are increased by several pKa units compared to the corresponding pKa values in water. By further analysis of the calculated curves we found that spontaneous protonation of fatty acid anions takes place in the bilayer interior at ca. 1.4 nm from the bilayer center for all studied fatty acids.
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Affiliation(s)
- Sanja Škulj
- Division of Organic Chemistry and Biochemistry, Ruđer Bošković Institute, Bijenička 54, HR-10000 Zagreb, Croatia.
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11
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Verma S, Utreja P. Vesicular nanocarrier based treatment of skin fungal infections: Potential and emerging trends in nanoscale pharmacotherapy. Asian J Pharm Sci 2018; 14:117-129. [PMID: 32104444 PMCID: PMC7042486 DOI: 10.1016/j.ajps.2018.05.007] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2018] [Revised: 03/22/2018] [Accepted: 05/21/2018] [Indexed: 11/18/2022] Open
Abstract
Occurrence of skin fungal infections is increasing nowadays and their presence is more prominent in patients suffering from immunocompromised diseases like AIDS. Skin fungal infections are a major cause of visits by patients to dermatology clinics. Although, a large number of antifungal agents are available for treatment of skin fungal infections, but, their toxic profile and physicochemical characteristics reduce therapeutic outcome. When these antifungal agents are delivered topically using conventional formulations like creams and gels, they may cause various side effects like redness, burning, and swelling at the site of application. Therefore, various vesicular formulations (phospholipid based or non phospholipid based) have been explored by pharmaceutical scientists to treat skin fungal infections topically. Vesicular formulation explored for the purpose are liposomes, ethosomes, transfersomes, transethosomes, niosomes, spanlastics, oleic acid vesicles, and nanoparticles. These formulations show various advantages like bioavailability enhancement of bioactives, high skin permeation power, no side effects at application site, dosing frequency reduction, and sustained drug release. Therefore, in the present article, we have discussed about the utility of various vesicular nanocarrier systems to treat skin fungal infections.
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Affiliation(s)
- Shivani Verma
- Department of Pharmaceutics, Rayat-Bahra College of Pharmacy, Hoshiarpur, Punjab 146001, India.,I. K. Gujral Punjab Technical University, Jalandhar, Punjab 144601, India
| | - Puneet Utreja
- I. K. Gujral Punjab Technical University, Jalandhar, Punjab 144601, India.,Faculty of Pharmaceutical Sciences, Department of Pharmaceutics, PCTE Group of Institutes, Ludhiana, Punjab 142021, India
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The Flip-Flop Diffusion Mechanism across Lipids in a Hybrid Bilayer Membrane. Biophys J 2017; 110:2451-2462. [PMID: 27276263 DOI: 10.1016/j.bpj.2016.04.041] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2015] [Revised: 04/03/2016] [Accepted: 04/25/2016] [Indexed: 12/31/2022] Open
Abstract
In this study, we examine the mechanism of flip-flop diffusion of proton carriers across the lipid layer of a hybrid bilayer membrane (HBM). The HBM consists of a lipid monolayer appended on top of a self-assembled monolayer containing a Cu-based O2 reduction catalyst on a Au electrode. The flip-flop diffusion rates of the proton carriers dictate the kinetics of O2 reduction by the electrocatalyst. By varying both the tail lengths of the proton carriers and the lipids, we find the combinations of lengths that maximize the flip-flop diffusion rate. These experimental results combined with biophysical modeling studies allow us to propose a detailed mechanism for transmembrane flip-flop diffusion in HBM systems, which involves the bending of the alkyl tail of the proton carrier as the rate-determining step. Additional studies with an unbendable proton carrier further validate these mechanistic findings.
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Strbak O, Kanuchova Z, Krafcik A. Proton Gradients as a Key Physical Factor in the Evolution of the Forced Transport Mechanism Across the Lipid Membrane. ORIGINS LIFE EVOL B 2016; 46:523-531. [PMID: 27038470 DOI: 10.1007/s11084-016-9496-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2015] [Accepted: 12/15/2015] [Indexed: 12/29/2022]
Abstract
A critical phase in the transition from prebiotic chemistry to biological evolution was apparently an asymmetric ion flow across the lipid membrane. Due to imbalance in the ion flow, the early lipid vesicles could selectively take the necessary molecules from the environment, and release the side-products from the vesicle. Natural proton gradients played a definitively crucial role in this process, since they remain the basis of energy transfer in the present-day cells. On the basis of this supposition, and the premise of the early vesicle membrane's impermeability to protons, we have shown that the emergence of the proton gradient in the lipid vesicle could be a key physical factor in the evolution of the forced transport mechanism (pore formation and active transport) across the lipid bilayer. This driven flow of protons across the membrane is the result of the electrochemical proton gradient and osmotic pressures on the integrity of the lipid vesicle. At a critical number of new lipid molecules incorporated into the vesicle, the energies associated with the creation of the proton gradient exceed the bending stiffness of the lipid membrane, and overlap the free energy of the lipid bilayer pore formation.
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Affiliation(s)
- Oliver Strbak
- Department of Imaging Methods, Institute of Measurement Science, Slovak Academy of Sciences, Dubravska cesta 9, 841 04, Bratislava, Slovakia.
| | - Zuzana Kanuchova
- Astronomical Institute, Slovak Academy of Sciences, 059 60, Tatranska Lomnica, Slovakia
| | - Andrej Krafcik
- Department of Imaging Methods, Institute of Measurement Science, Slovak Academy of Sciences, Dubravska cesta 9, 841 04, Bratislava, Slovakia
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Kumar L, Verma S, Kumar S, Prasad DN, Jain AK. Fatty acid vesicles acting as expanding horizon for transdermal delivery. ARTIFICIAL CELLS NANOMEDICINE AND BIOTECHNOLOGY 2016; 45:251-260. [PMID: 26890090 DOI: 10.3109/21691401.2016.1146729] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
The body is protected against the external environment by the skin due to its physical barrier nature. Stratum corneum composed of corneocytes surrounded by lipid region performs a major barrier function as it lies in the uppermost area of skin. Alteration in barrier function, increase in permeability, and disorganization of stratum corneum represent diseased skin. Drugs applied to the diseased skin should induce a local effect at the site of application or area close to it along with cutaneous absorption rather than percutaneous absorption. Conventional formulations like ointments, gels, and creams suffer from the drawback of limited local activity. For the enhancement of drug penetration and localization of the drug at the site of action approaches explored are liposomes, niosomes, ethosomes microparticles, and solid lipid nanoparticles. Vesicles composed of fatty acids like oleic acid and linoleic acid represent the new approach used for transdermal penetration and localization. In this review article, our major aim was to explore the applications of fatty acid vesicles for transdermal delivery of various bioactives.
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Affiliation(s)
- Lalit Kumar
- a Department of Pharmaceutics , Shivalik College of Pharmacy , Nangal , Punjab , India.,b I. K. Gujral Punjab Technical University , Jallandhar , Punjab , India
| | - Shivani Verma
- b I. K. Gujral Punjab Technical University , Jallandhar , Punjab , India.,c Department of Pharmaceutics , Rayat Bahra College of Pharmacy , Hoshiarpur , Punjab , India
| | - Sanjeev Kumar
- a Department of Pharmaceutics , Shivalik College of Pharmacy , Nangal , Punjab , India
| | - Deo Nandan Prasad
- d Department of Pharmaceutical Chemistry , Shivalik College of Pharmacy , Nangal , Punjab , India
| | - Amit Kumar Jain
- b I. K. Gujral Punjab Technical University , Jallandhar , Punjab , India.,e Department of Pharmaceutics , Guru Nanak Institute of Pharmacy , Hoshiarpur , Punjab , India
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15
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Wei C, Pohorille A. Flip-flop of oleic acid in a phospholipid membrane: rate and mechanism. J Phys Chem B 2014; 118:12919-26. [PMID: 25319959 DOI: 10.1021/jp508163e] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Flip-flop of protonated oleic acid molecules dissolved at two different concentrations in membranes made of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine is studied with the aid of molecular dynamics simulations at a time scale of several microseconds. Direct, single-molecule flip-flop events are observed at this time scale, and the flip-flop rate is estimated at 0.2-0.3 μs(-1). As oleic acid molecules move toward the center of the bilayer during flip-flop, they undergo gradual, correlated translational, and rotational motion. Rare, double-flipping events of two hydrogen-bonded oleic acid molecules are also observed. A two-dimensional free energy surface is obtained for the translational and rotational degree of freedom of the oleic acid molecule, and the minimum energy path on this surface is determined. A barrier to flip-flop of ~4.2 kcal/mol is found at the center of the bilayer. A two-dimensional diffusion model is found to provide a good description of the flip-flop process. The fast flip-flop rate lends support to the proposal that fatty acids permeate membranes without assistance of transport proteins. It also suggests that desorption rather than flip-flop is the rate-limiting step in fatty acid transport through membranes. The relation of flip-flop rates to the evolution of ancestral cellular systems is discussed.
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Affiliation(s)
- Chenyu Wei
- NASA Ames Research Center , Mail Stop 229-1, Moffett Field, California 94035, United States
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16
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Horner A, Goetz F, Tampé R, Klussmann E, Pohl P. Mechanism for targeting the A-kinase anchoring protein AKAP18δ to the membrane. J Biol Chem 2012; 287:42495-501. [PMID: 23095754 DOI: 10.1074/jbc.m112.414946] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A-kinase anchoring proteins (AKAPs) are a family of scaffolding proteins that target PKA and other signaling molecules to cellular compartments and thereby spatiotemporally define cellular signaling events. The AKAP18 family comprises AKAP18α, AKAP18β, AKAP18γ, and AKAP18δ. The δ isoform targets PKA and phosphodiesterase PDE4D to AQP2 (aquaporin-2)-bearing vesicles to orchestrate the acute regulation of body water balance. Therefore, AKAP18δ must adopt a membrane localization that seems at odds with (i) its lack of palmitoylation or myristoylation sites that tailor its isoforms AKAP18α and AKAP18β to membrane compartments and (ii) the high sequence identity to the preferentially cytoplasmic AKAP18γ. Here, we show that the electrostatic attraction of the positively charged amino acids of AKAP18δ to negatively charged lipids explains its membrane targeting. As revealed by fluorescence correlation spectroscopy, the binding constant of purified AKAP18δ fragments to large unilamellar vesicles correlates (i) with the fraction of net negatively charged lipids in the bilayer and (ii) with the total amount of basic residues in the protein. Although distantly located on the sequence, these positively charged residues concentrate in the tertiary structure and form a clear binding surface. Thus, specific recruitment of the AKAP18δ-based signaling module to membranes such as those of AQP2-bearing vesicles must be achieved by additional mechanisms, most likely compartment-specific protein-protein interactions.
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Affiliation(s)
- Andreas Horner
- Institut für Biophysik, Johannes Kepler Universität Linz, 4040 Linz, Austria
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17
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Rupprecht A, Sokolenko EA, Beck V, Ninnemann O, Jaburek M, Trimbuch T, Klishin SS, Jezek P, Skulachev VP, Pohl EE. Role of the transmembrane potential in the membrane proton leak. Biophys J 2010; 98:1503-11. [PMID: 20409469 DOI: 10.1016/j.bpj.2009.12.4301] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2009] [Revised: 11/08/2009] [Accepted: 12/08/2009] [Indexed: 11/25/2022] Open
Abstract
The molecular mechanism responsible for the regulation of the mitochondrial membrane proton conductance (G) is not clearly understood. This study investigates the role of the transmembrane potential (DeltaPsim) using planar membranes, reconstituted with purified uncoupling proteins (UCP1 and UCP2) and/or unsaturated FA. We show that high DeltaPsim (similar to DeltaPsim in mitochondrial State IV) significantly activates the protonophoric function of UCPs in the presence of FA. The proton conductance increases nonlinearly with DeltaPsim. The application of DeltaPsim up to 220 mV leads to the overriding of the protein inhibition at a constant ATP concentration. Both, the exposure of FA-containing bilayers to high DeltaPsim and the increase of FA membrane concentration bring about the significant exponential Gm increase, implying the contribution of FA in proton leak. Quantitative analysis of the energy barrier for the transport of FA anions in the presence and absence of protein suggests that FA- remain exposed to membrane lipids while crossing the UCP-containing membrane. We believe this study shows that UCPs and FA decrease DeltaPsim more effectively if it is sufficiently high. Thus, the tight regulation of proton conductance and/or FA concentration by DeltaPsim may be key in mitochondrial respiration and metabolism.
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Affiliation(s)
- Anne Rupprecht
- Department of Biomedical Sciences, University of Veterinary Medicine, Vienna, Austria
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18
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Missner A, Pohl P. 110 years of the Meyer-Overton rule: predicting membrane permeability of gases and other small compounds. Chemphyschem 2009; 10:1405-14. [PMID: 19514034 PMCID: PMC3045804 DOI: 10.1002/cphc.200900270] [Citation(s) in RCA: 162] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2009] [Indexed: 01/04/2023]
Abstract
The transport of gaseous compounds across biological membranes is essential in all forms of life. Although it was generally accepted that gases freely penetrate the lipid matrix of biological membranes, a number of studies challenged this doctrine as they found biological membranes to have extremely low gas-permeability values. These observations led to the identification of several membrane-embedded "gas" channels, which facilitate the transport of biological active gases, such as carbon dioxide, nitric oxide, and ammonia. However, some of these findings are in contrast to the well-established solubility-diffusion model (also known as the Meyer-Overton rule), which predicts membrane permeabilities from the molecule's oil-water partition coefficient. Herein, we discuss recently reported violations of the Meyer-Overton rule for small molecules, including carboxylic acids and gases, and show that Meyer and Overton continue to rule.
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Affiliation(s)
- Andreas Missner
- Institut für Biophysik, Johannes Kepler Universität, Altenberger Str. 69, 4040 Linz (Austria), Fax: (+43) 732-2468-9270
| | - Peter Pohl
- Institut für Biophysik, Johannes Kepler Universität, Altenberger Str. 69, 4040 Linz (Austria), Fax: (+43) 732-2468-9270
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19
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Raja M, Vales E. Changing Val-76 towards Kir channels drastically influences the folding and gating properties of the bacterial potassium channel KcsA. Biophys Chem 2009; 144:95-100. [PMID: 19665280 DOI: 10.1016/j.bpc.2009.06.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2009] [Revised: 06/12/2009] [Accepted: 06/21/2009] [Indexed: 11/17/2022]
Abstract
All K(+)-channels are stabilized by K(+)-ions in the selectivity filter. However, they differ from each other with regard to their selectivity filter. In this study, we changed specific residue Val-76 in the selectivity filter of KcsA to its counterpart Ile in inwardly rectifying K(+)-channels (Kir). The tetramer was exclusively converted into monomers as determined by conventional gel electrophoresis. However, by perfluoro-octanoic acid (PFO) gel electrophoresis mutant channel was mostly detected as tetramer. Tryptophan fluorescence and acrylamide quenching experiments demonstrated significant alteration in channel folding properties via increase in hydrophilicity of local environment. Furthermore, in planar lipid bilayer experiments V76I exhibited drastically lower conductance and decreased channel open time as compared to the unmodified KcsA. These studies suggest that V76I might contribute to determine the stabilizing, folding and channel gating properties in a selective K(+)-channel.
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Affiliation(s)
- Mobeen Raja
- Institute for Biophysics, Johannes Kepler University Linz, 4040 Linz, Austria.
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20
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Arcisio-Miranda M, Abdulkader F, Brunaldi K, Curi R, Procopio J. Proton flux induced by free fatty acids across phospholipid bilayers: New evidences based on short-circuit measurements in planar lipid membranes. Arch Biochem Biophys 2009; 484:63-9. [DOI: 10.1016/j.abb.2009.01.019] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2008] [Revised: 12/29/2008] [Accepted: 01/20/2009] [Indexed: 01/27/2023]
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21
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Vermathen M, Vermathen P, Simonis U, Bigler P. Time-dependent interactions of the two porphyrinic compounds chlorin e6 and mono-L-aspartyl-chlorin e6 with phospholipid vesicles probed by NMR spectroscopy. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2008; 24:12521-12533. [PMID: 18823137 DOI: 10.1021/la802040v] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
The distribution processes of chlorin e6 (CE) and monoaspartyl-chlorin e6 (MACE) between the outer and inner phospholipid monolayers of 1,2-dioleoyl-phosphatidylcholine (DOPC) vesicles were monitored by 1H NMR spectroscopy through analysis of chemical shifts and line widths of the DOPC vesicle resonances. Chlorin adsorption to the outer vesicle monolayer induced changes in the DOPC 1H NMR spectrum. Most pronounced was a split of the N-methyl choline resonance, allowing for separate analysis of inner and outer vesicle layers. Transbilayer distribution of the chlorin compounds was indicated by time-dependent characteristic spectral changes of the DOPC resonances. Kinetic parameters for the flip-flop processes, that is, half-lives and rate constants, were obtained from the experimental data points. In comparison to CE, MACE transbilayer movement was significantly reduced, with MACE remaining more or less attached to the outer membrane layer. The distribution coefficients for CE and MACE between the vesicular and aqueous phase were determined. Both CE and MACE exhibited a high affinity for the vesicular phase. For CE, a positive correlation was found between transfer rate and increasing molar ratio CE/DOPC. Enhanced membrane rigidity induced by increasing amounts of cholesterol into the model membrane was accompanied by a decrease of CE flip-flop rates across the membrane. The present study shows that the movement of porphyrins across membranes can efficiently be investigated by 1H NMR spectroscopy and that small changes in porphyrin structure can have large effects on membrane kinetics.
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Affiliation(s)
- Martina Vermathen
- Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, CH-3012 Bern, Switzerland.
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22
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Sommer K, Kaiser S, Krylova OO, Kressler J, Pohl P, Busse K. Influence of amphiphilic block copolymer induced changes in membrane ion conductance on the reversal of multidrug resistance. J Med Chem 2008; 51:4253-9. [PMID: 18588278 DOI: 10.1021/jm800177c] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Block copolymers are able to reverse multidrug resistance (MDR) of tumor cells by a yet unknown mechanism. The drug efflux system's direct and indirect inhibition mediated by polymer P-glycoprotein (Pgp) interactions or adenosine triphosphate (ATP) depletion, respectively, may be involved in MDR reversal as well as damage to the membrane barrier caused by polymer insertion into the membrane. To test the latter hypothesis, cellular drug accumulation was monitored in the presence of both overexpressed fluorescently labeled Pgp and different block copolymers. Therefore, a new triblock copolymer (poly(ethylene oxide)- block-poly(hexafluoropropylene oxide)- block-poly(ethylene oxide)) was designed and synthesized by combined polymerization and polymer analogous reaction. Its administration induced drug uptake, whereas control cells with high Pgp expression levels showed no drug accumulation. Drug uptake was even more pronounced in the presence of another triblock copolymer: (poly(perfluorohexylethyl methacrylate)- block-poly(ethylene oxide)- block-poly(perfluorohexylethyl methacrylate). The latter polymer's lack of ionophoric activity suggests that ion transport facilitation by polymers is not a determinative factor for MDR reversal.
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Affiliation(s)
- Klaus Sommer
- Johannes Kepler Universitat, Fachbereich Physik, Institut fur Biophysik, Altenbergerstrasse 69, 4040 Linz, Austria
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23
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Missner A, Horner A, Pohl P. Cholesterol's decoupling effect on membrane partitioning and permeability revisited: is there anything beyond Fick's law of diffusion? BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2008; 1778:2154-6. [PMID: 18510944 DOI: 10.1016/j.bbamem.2008.05.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2008] [Revised: 04/10/2008] [Accepted: 05/02/2008] [Indexed: 01/04/2023]
Abstract
In general, Fick's law of diffusion describes membrane permeation of hydrophobic or amphiphilic molecules. In contrast to this, Thomae et al. recently identified the volume ratio between barrier and aqueous compartments as important additional determinants of membrane permeability (Pm) [A.V. Thomae, T. Koch, C. Panse, H. Wunderli-Allenspach, and S.D. Kramer, Comparing the lipid membrane affinity and permeation of drug-like acids: the intriguing effects of cholesterol and charged lipids, Pharm. Res. 24 (2007) 1457-1472.]. This new theory was supported by the striking observation that low concentrations of cholesterol increased Pm of salicylic acid. As Fick's law is of fundamental importance to all membrane transport processes, we reinvestigated this phenomenon. We measured the electrophoretic mobility of vesicles and used electrochemical scanning microscopy to study the adsorption of the SA anion to lipid vesicular bilayers and SA transport through planar lipid bilayers, respectively. As predicted by Fick's law, Pm of SA decreased continuously with increasing cholesterol content. Thomae et al. made the contrasting artifactual observation because their kinetic approach lacked the required time resolution and led to an underestimation of Pm by five orders of magnitude. We conclude that there is nothing beyond Fick's law of diffusion. It is still valid.
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Affiliation(s)
- Andreas Missner
- Institut für Biophysik, Johannes Kepler Universität, Linz, Austria
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24
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Pohl EE, Voltchenko AM, Rupprecht A. Flip-flop of hydroxy fatty acids across the membrane as monitored by proton-sensitive microelectrodes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2008; 1778:1292-7. [PMID: 18313391 DOI: 10.1016/j.bbamem.2008.01.025] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/12/2007] [Revised: 01/06/2008] [Accepted: 01/31/2008] [Indexed: 10/22/2022]
Abstract
Hydroxyl group-containing fatty acids play an important role in anti-inflammatory action, neuroprotection, bactericide and anti-cancer defense. However, the mechanism of long-chain hydroxy fatty acids (HFA) transport across plasma membranes is still disputed. Two main hypotheses have been suggested: firstly, that protonated HFAs traverse across the membranes spontaneously and, secondly, that the transport is facilitated by proteinaceous carriers. Here, we demonstrate that the protonated HFA are able to move across planar lipid bilayers without protein assistance. This transport step is accompanied by the acidification of the buffer in receiving compartment and the pH augmentation in the donating compartment. The latter contained liposomes doped with HFA. As revealed by scanning pH-sensitive microelectrodes, the pH shift occurred only in the immediate vicinity of the membrane, while bulk pH remained unchanged. In concurrence with the theoretical model of weak acid transport, the pH value at maximum proton flux was almost equal to the pK of the studied HFA. Intrinsic pKi values were calculated from the electrophoretic mobilities of HFA-containing liposomes and were 5.4, 6.5, 6.9 and 6.3 for 2-hydroxyhexadecanoic, 16-hydroxyhexadecanoic, 12-hydroxydodecanoic and 9,10,16-trihydroxyhexadecanoic acids, respectively.
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Affiliation(s)
- Elena E Pohl
- Institute of Cell Biology and Neurobiology, Charité-Universitätsmedizin, Charitéplatz 1, 10117 Berlin, Germany.
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25
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Membrane Transporters & Exchangers. Biophys J 2008. [DOI: 10.1016/s0006-3495(08)79013-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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26
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Li H, Black PN, Chokshi A, Sandoval-Alvarez A, Vatsyayan R, Sealls W, DiRusso CC. High-throughput screening for fatty acid uptake inhibitors in humanized yeast identifies atypical antipsychotic drugs that cause dyslipidemias. J Lipid Res 2007; 49:230-44. [PMID: 17928635 DOI: 10.1194/jlr.d700015-jlr200] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Fatty acids are implicated in the development of dyslipidemias, leading to type 2 diabetes and cardiovascular disease. We used a standardized small compound library to screen humanized yeast to identify compounds that inhibit fatty acid transport protein (FATP)-mediated fatty acid uptake into cells. This screening procedure used live yeast cells expressing human FATP2 to identify small compounds that reduced the import of a fluorescent fatty acid analog, 4,4-difluoro-5-methyl-4-bora-3a,4a-diaza-s-indacene-3-dodecanoic acid (C(1)-BODIPY-C(12)). The library used consisted of 2,080 compounds with known biological activities. Of these, approximately 1.8% reduced cell-associated C(1)-BODIPY-C(12) fluorescence and were selected as potential inhibitors of human FATP2-mediated fatty acid uptake. Based on secondary screens, 28 compounds were selected as potential fatty acid uptake inhibitors. Some compounds fell into four groups with similar structural features. The largest group was structurally related to a family of tricyclic, phenothiazine-derived drugs used to treat schizophrenia and related psychiatric disorders, which are also known to cause metabolic side effects, including hypertriglyceridemia. Potential hit compounds were studied for specificity of interaction with human FATP and efficacy in human Caco-2 cells. This study validates this screening system as useful to assess the impact of drugs in preclinical screening for fatty acid uptake.
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Affiliation(s)
- Hong Li
- Center for Metabolic Disease, Ordway Research Institute, Inc., Albany Medical College, Albany, NY 12208, USA
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27
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Thomas JA, Rana FR. The influence of environmental conditions, lipid composition, and phase behavior on the origin of cell membranes. ORIGINS LIFE EVOL B 2007; 37:267-85. [PMID: 17361322 DOI: 10.1007/s11084-007-9065-6] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2006] [Accepted: 01/13/2007] [Indexed: 10/23/2022]
Abstract
At some point in life's development, membranes formed, providing barriers between the environment and the interior of the 'cell.' This paper evaluates the research to date on the prebiotic origin of cell membranes and highlights possible areas of continuing study. A careful review of the literature uncovered unexpected factors that influence membrane evolution. The major stages in primitive membrane formation and the transition to contemporary cell membranes appear to require an exacting relationship between environmental conditions and amphiphile composition and phase behavior. Also, environmental and compositional requirements for individual stages are in some instances incompatible with one another, potentially stultifying the pathway to contemporary membranes. Previous studies in membrane evolution have noted the effects composition and environment have on membrane formation but the crucial dependence and interdependence on these two factors has not been emphasized. This review makes clear the need to focus future investigations away from proof-of-principle studies towards developing a better understanding of the roles that environmental factors and lipid composition and polymorphic phase behavior played in the origin and evolution of cell membranes.
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Affiliation(s)
- Jacquelyn A Thomas
- Department of Chemistry, Southwestern College, 900 Otay Lakes Road, Chula Vista, CA, 91910, USA.
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28
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Beck V, Jabůrek M, Demina T, Rupprecht A, Porter RK, Jezek P, Pohl EE. Polyunsaturated fatty acids activate human uncoupling proteins 1 and 2 in planar lipid bilayers. FASEB J 2007; 21:1137-44. [PMID: 17242157 DOI: 10.1096/fj.06-7489com] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Uncoupling proteins 1 (UCP1) and 2 (UCP2) belong to the family of mitochondrial anion transporters and share 59% sequence identity with each other. Whereas UCP1 was shown to be responsible for the rapid production of heat in brown adipose tissue, the primary function and transport properties of ubiquitously expressed UCP2 are controversially discussed. Here, for the first time, the activation pattern of the recombinant human UCP2 in comparison to the recombinant human UCP1 are studied using a well-defined system of planar lipid bilayers. It is shown that despite apparently different physiological functions, hUCP2 exhibited its protonophoric function similar to hUCP1--exclusively in the presence of long-chain fatty acids (FA). The calculated hUCP2 transport rate of 4.5 s(-1) is the same order of magnitude, as shown previously for UCP1. It leads to the conclusion that the differences in the activity of both proteins in living mitochondria are based exclusively on their different expression level. Both proteins are activated much more effectively by polyunsaturated than by saturated FA. The proton and total membrane conductances increased in the range palmitic < oleic < eicosatrienoic < linoleic < retinoic < arachidonic acids. The higher uncoupling protein (UCP)-dependent conductance in the presence of polyunsaturated FA is explained on the basis of the FA cycling hypothesis.
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Affiliation(s)
- Valeri Beck
- Institute of Cell Biology and Neurobiology, Charité Universitätsmedizin, Charitéplatz 1, 10117 Berlin, Germany
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29
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Abdulkader F, Arcisio-Miranda M, Curi R, Procopio J. Surface potential determination in planar lipid bilayers: a simplification of the conductance-ratio method. ACTA ACUST UNITED AC 2007; 70:515-8. [PMID: 17303247 DOI: 10.1016/j.jbbm.2007.01.003] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2006] [Revised: 12/28/2006] [Accepted: 01/10/2007] [Indexed: 10/23/2022]
Abstract
One of the methods available for the measurement of surface potentials of planar lipid bilayers uses the conductance ratio between a charged and a neutral bilayer doped with ionophores to calculate the surface potential of the charged bilayer. We have devised a simplification of that method which does not require the use of an electrically neutral bilayer as control. The conductance of the charged bilayer is measured before and after the addition of divalent cations (Ba(2+)) to the bathing solution. Ba(2+) ions screen fixed surface charges, decreasing the surface potential. If the membrane is negatively charged the screening has the effect of decreasing the membrane conductance to cations. The resulting conductance ratio is used to calculate the surface potential change, which is fed into an iterative computer program. The program generates pairs of surface potential values and calculates the surface charge density for the two conditions. Since the surface charge density remains constant during this procedure, there is only one pair of surface potentials that satisfies the condition of constant charge density. Applying this method to experimental data from McLaughlin et al. [McLaughlin, S.G.A., Szabo, G. and Eisenman, G., Divalent ions and the surface potential of charged phospholipid membranes, J. Gen. Physiol., 58 (1971) 667-687.] we have found very similar results. We have also successfully used this method to determine the effect of palmitic acid on the surface potential of asolectin membranes.
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Affiliation(s)
- Fernando Abdulkader
- Departmento de Fisiologia e Biofísica, Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, Brazil
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30
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Vitha MF, Clarke RJ. Comparison of excitation and emission ratiometric fluorescence methods for quantifying the membrane dipole potential. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2007; 1768:107-14. [PMID: 16904627 DOI: 10.1016/j.bbamem.2006.06.022] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2006] [Revised: 06/28/2006] [Accepted: 06/29/2006] [Indexed: 10/24/2022]
Abstract
We are interested in developing fluorescence methods for quantifying lateral variations in the dipole potential across cell surfaces. Previous work in this laboratory showed that the ratio of fluorescence intensities of the voltage-sensitive dye di-8-ANEPPS using excitation wavelengths at 420 and 520 nm correlates well with measurements of the dipole potential. In the present work we evaluate the use of di-8-ANEPPS and an emission ratiometric method for measuring dipole potentials, as Bullen and Saggau (Biophys. J. 65 (1999) 2272-2287) have done to follow changes in the membrane potential in the presence of an externally applied field. Emission ratiometric methods have distinct advantages over excitation methods when applied to fluorescence microscopy because only a single wavelength is needed for excitation. We found that unlike the excitation ratio, the emission ratio does not correlate with the dipole potential of vesicles made from different lipids. A difference in the behaviour of the emission ratio in saturated compared to unsaturated lipid vesicles was noted. Furthermore, the emission ratio did not respond in the same way as the excitation ratio when cholesterol, 6-ketocholestanol, 7-ketocholesterol, and phloretin were added to dimyristoylphosphatidylcholine (DMPC) vesicles. We attribute the lack of correlation between the emission ratio and the dipole potential to simultaneous changes in membrane fluidity caused by changes in membrane composition, which do not occur when the electric field is externally applied as in the work of Bullen and Saggau. Di-8-ANEPPS can, thus, only be used via an excitation ratiometric method to quantify the dipole potential.
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Affiliation(s)
- Mark F Vitha
- Department of Chemistry, Drake University, Des Moines, Iowa 50311, USA
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Fahr A, van Hoogevest P, Kuntsche J, Leigh MLS. Lipophilic drug transfer between liposomal and biological membranes: what does it mean for parenteral and oral drug delivery? J Liposome Res 2006; 16:281-301. [PMID: 16952882 DOI: 10.1080/08982100600848702] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
This review presents the current knowledge on the interaction of lipophilic, poorly water soluble drugs with liposomal and biological membranes. The center of attention will be on drugs having the potential to dissolve in a lipid membrane without perturbing them too much. The degree of interaction is described as solubility of a drug in phospholipid membranes and the kinetics of transfer of a lipophilic drug between membranes. Finally, the consequences of these two factors on the design of lipid-based carriers for oral, as well as parenteral use, for lipophilic drugs and lead selection of oral lipophilic drugs is described. Since liposomes serve as model-membranes for natural membranes, the assessment of lipid solubility and transfer kinetics of lipophilic drug using liposome formulations may additionally have predictive value for bioavailability and biodistribution and the pharmacokinetics of lipophilic drugs after parenteral as well as oral administration.
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Affiliation(s)
- Alfred Fahr
- Department of Pharmaceutical Technology, Friedrich-Schiller-Universität Jena, Jena, Germany.
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Kampf JP, Cupp D, Kleinfeld AM. Different Mechanisms of Free Fatty Acid Flip-Flop and Dissociation Revealed by Temperature and Molecular Species Dependence of Transport across Lipid Vesicles. J Biol Chem 2006; 281:21566-21574. [PMID: 16737957 DOI: 10.1074/jbc.m602067200] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The mechanism of free fatty acid (FFA) transport across membranes is a subject of intense investigation. We have demonstrated recently that flip-flop is the rate-limiting step for transport of oleic acid across phospholipid vesicles (Cupp, D., Kampf, J. P., and Kleinfeld, A. M. (2004) Biochemistry 43, 4473-4481). To better understand the nature of the flip-flop barrier, we measured the temperature dependence of a series of saturated and monounsaturated FFA. We determined the rate constants for flip-flop and dissociation for small (SUV), large (LUV), and giant (GUV) unilamellar vesicles composed of egg phosphatidylcholine. For all FFA and vesicle types, dissociation was faster than flip-flop, and for all FFA, flip-flop and dissociation were faster in SUV than in LUV or GUV. Rate constants for both flip-flop and dissociation decreased exponentially with increasing FFA size. However, only the flip-flop rate constants increased significantly with temperature; the barrier to flip-flop was virtually entirely due to an enthalpic activation free energy. The barrier to dissociation was primarily entropic. Analysis in terms of a simple free volume (V(f)) model revealed V(f) values for flip-flop that ranged between approximately 12 and 15 Angstroms(3), with larger values for SUV than for LUV or GUV. V(f) values increased with temperature, and this temperature dependence generated the enthalpic barrier to flip-flop. The barrier for dissociation and its size dependence primarily reflect the aqueous solubility of FFA. These are the first results to distinguish the energetics of flipflop and dissociation. This should lead to a better understanding of the mechanisms governing FFA transport across biological membranes.
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Affiliation(s)
- J Patrick Kampf
- Torrey Pines Institute for Molecular Studies, San Diego, California 92121
| | - David Cupp
- Torrey Pines Institute for Molecular Studies, San Diego, California 92121
| | - Alan M Kleinfeld
- Torrey Pines Institute for Molecular Studies, San Diego, California 92121.
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Saparov SM, Antonenko YN, Pohl P. A new model of weak acid permeation through membranes revisited: does Overton still rule? Biophys J 2006; 90:L86-8. [PMID: 16603491 PMCID: PMC1459524 DOI: 10.1529/biophysj.106.084343] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
According to a recent publication by Thomae, A. V., H. Wunderli-Allenspach, and S. D. Krämer (2005. Biophys. J. 89:1802-1811), membrane bilayers are well-permeable to the charged species of aromatic carboxylic acids. At physiological pH, the anions were claimed to be the major diffusing species. In contrast, calculation of the Born energy barrier predicts a 10(5)-fold higher permeability for the uncharged (protonated) form. To test the new model, we now have measured both the current carried by the salicylate anion through solvent-free planar membranes and the amount of protons transported by the neutral species. The corresponding membrane permeabilities of the charged and protonated forms were 4 x 10(-7) cm/s and 1.2 cm/s. These data are in perfect agreement with literature data gathered in the last three decades (compare, e.g., Gutknecht, J., and D. C. Tosteson. 1973. Science. 182:1258-1261). They indicate that the report by Thomae at al. represents an experimental artifact. The well-documented role of neutral species in the permeation process of weak acids and bases across artificial and natural membranes is not in question. Overton still rules.
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Affiliation(s)
- Sapar M Saparov
- Institut für Biophysik, Johannes Kepler Universität-Linz, Linz, Austria
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Beck V, Jabůrek M, Breen EP, Porter RK, Jezek P, Pohl EE. A new automated technique for the reconstitution of hydrophobic proteins into planar bilayer membranes. Studies of human recombinant uncoupling protein 1. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2006; 1757:474-9. [PMID: 16626624 DOI: 10.1016/j.bbabio.2006.03.006] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/2005] [Revised: 03/07/2006] [Accepted: 03/07/2006] [Indexed: 01/21/2023]
Abstract
Electrophysiological characterisation of the vast number of annotated channel and transport proteins in the postgenomic era would be greatly facilitated by the introduction of rapid and robust methods for the functional incorporation of membrane proteins into defined lipid bilayers. Here, we describe an automated technique for reconstitution of membrane proteins into lipid bilayer membranes, which substantially reduces both the reconstitution time and the amount of protein required for the membrane formation. The method allows the investigation of single protein channels as well as insertion of multiple copies (approximately 10(7)) into a single bilayer. Despite a comparatively large membrane area (up to 300 microm diameter), the high stability of the membrane permits the application of transmembrane voltages up to 300 mV. This feature is especially important for studies of inner membrane mitochondrial proteins, since they act at potentials up to approximately 200 mV under physiological conditions. It is a combination of these advantages that enables the detailed investigation of the minuscule single protein conductances typical for proton transporters. We have applied the new technique for the reconstitution and electrophysiological characterisation of human recombinant uncoupling protein 1, hUCP1, that has been overexpressed in E. coli and purified from inclusion bodies. We demonstrate that hUCP1 activity in the presence of fatty acids is comparable to the activity of UCP1 isolated from brown adipose tissue.
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Affiliation(s)
- Valeri Beck
- Institute of Cell Biology and Neurobiology, Charité Universitätsmedizin, Schumannstr. 20/21, 10098 Berlin, Germany
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35
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van Meer G, Halter D, Sprong H, Somerharju P, Egmond MR. ABC lipid transporters: extruders, flippases, or flopless activators? FEBS Lett 2005; 580:1171-7. [PMID: 16376334 DOI: 10.1016/j.febslet.2005.12.019] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2005] [Revised: 12/06/2005] [Accepted: 12/06/2005] [Indexed: 01/02/2023]
Abstract
Many mammalian ABC transporters move membrane lipids to acceptor lipid assemblies in the extracellular aqueous milieu. Because the desorption from the membrane costs more energy than provided by two ATPs, the transporter probably only translocates the lipid to a partially hydrophilic site on its extracellular face. From this high-energy site, the lipid may efficiently move to the acceptor, which ideally is bound to the transporter, or, in the absence of an acceptor, fall back into the membrane. If the lipid originated from the cytosolic membrane surface, this represents lipid flop and is probably a side activity of the transporters.
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Affiliation(s)
- Gerrit van Meer
- Membrane Enzymology, Bijvoet Center and Institute of Biomembranes, Utrecht University, Padualaan 8, 3584 CH, Utrecht, The Netherlands.
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36
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Fahr A, van Hoogevest P, May S, Bergstrand N, S Leigh ML. Transfer of lipophilic drugs between liposomal membranes and biological interfaces: Consequences for drug delivery. Eur J Pharm Sci 2005; 26:251-65. [PMID: 16112849 DOI: 10.1016/j.ejps.2005.05.012] [Citation(s) in RCA: 128] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2004] [Revised: 03/30/2005] [Accepted: 05/23/2005] [Indexed: 10/25/2022]
Abstract
This review paper describes the present knowledge on the interaction of lipophilic, poorly water soluble, drugs with liposomal membranes and the reversibility of this interaction. This interaction is discussed in the context of equilibrium and spontaneous transfer kinetics of the drug, when the liposomes are brought in co-dispersion with other artificial or natural phospholipid membranes in an aqueous medium. The focus is on drugs, which have the potential to partition (dissolve) in a lipid membrane but do not perturb membranes. The degree of interaction is described as solubility of a drug in phospholipid membranes and the kinetics of transfer of a lipophilic drug between membranes. Finally, the consequences of these two factors on the design of lipid based carriers for oral, as well as parenteral use, for lipophilic drugs and lead selection of oral lipophilic drugs is described. Since liposomes serve as model-membranes for natural membranes, the assessment of lipid solubility and transfer kinetics of lipophilic drug using liposome formulations may additionally have predictive value for bioavailability and biodistribution and the pharmacokinetics of lipophilic drugs after parenteral as well as oral administration.
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Affiliation(s)
- Alfred Fahr
- Department of Pharmaceutical Technology, Friedrich-Schiller-Universität Jena, Lessingstrasse 8, D-07743 Jena, Germany.
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37
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Geißler D, Antonenko YN, Schmidt R, Keller S, Krylova OO, Wiesner B, Bendig J, Pohl P, Hagen V. (Cumarin-4-yl)methylester als hocheffiziente und ultraschnelle Phototrigger für Protonen und ihre Anwendung zur Oberflächenansäuerung von Membranen. Angew Chem Int Ed Engl 2005. [DOI: 10.1002/ange.200461567] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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38
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Geissler D, Antonenko YN, Schmidt R, Keller S, Krylova OO, Wiesner B, Bendig J, Pohl P, Hagen V. (Coumarin-4-yl)methyl Esters as Highly Efficient, Ultrafast Phototriggers for Protons and Their Application to Acidifying Membrane Surfaces. Angew Chem Int Ed Engl 2005; 44:1195-8. [PMID: 15696594 DOI: 10.1002/anie.200461567] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Daniel Geissler
- Forschungsinstitut für Molekulare Pharmakologie, Robert-Rössle-Strasse 10, 13125 Berlin, Germany
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39
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Starke-Peterkovic T, Turner N, Else PL, Clarke RJ. Electric field strength of membrane lipids from vertebrate species: membrane lipid composition and Na+-K+-ATPase molecular activity. Am J Physiol Regul Integr Comp Physiol 2004; 288:R663-70. [PMID: 15539609 DOI: 10.1152/ajpregu.00434.2004] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Intramembrane electric field strength is a very likely determinant of the activity of ion-transporting membrane proteins in living cells. In the absence of any transmembrane electrical potential or surface potential, its magnitude is determined by the dipole potential of the membrane's lipid components and their associated water of hydration. Here we have used a fluorometric method to quantify the dipole potential of vesicles formed from lipids extracted from kidney and brain of 11 different animal species from four different vertebrate classes. The dipole potential was compared with the fatty acid composition and with the Na(+)-K(+)-ATPase molecular activity of each preparation. The magnitude of the dipole potential was found to be relatively constant across all animal species, i.e., 236-334 mV for vesicles prepared from the total membrane lipids and 223-256 mV for phospholipids alone. The significantly lower value for phospholipids alone is potentially related to the removal of cholesterol and/or other common soluble lipid molecules from the membrane. Surprisingly, no significant dependence of the dipole potential on fatty acid composition was found. This may, however, be due to concomitant compensatory variations in lipid head group composition. The molecular activity of the Na(+)-K(+)-ATPase was found to increase with increasing dipole potential. The fact that the dipole potential is maintained at a relatively constant value over a wide range of animal species suggests that it may play a fundamental role in ensuring correct ion pump conformation and function within the membrane.
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40
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Hagge SO, Wiese A, Seydel U, Gutsmann T. Inner field compensation as a tool for the characterization of asymmetric membranes and Peptide-membrane interactions. Biophys J 2004; 86:913-22. [PMID: 14747327 PMCID: PMC1303939 DOI: 10.1016/s0006-3495(04)74167-3] [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: 11/26/2022] Open
Abstract
Symmetric and asymmetric planar lipid bilayers prepared according to the Montal-Mueller method are a powerful tool to characterize peptide-membrane interactions. Several electrical properties of lipid bilayers such as membrane current, membrane capacitance, and the inner membrane potential differences and their changes can be deduced. The time-resolved determination of peptide-induced changes in membrane capacitance and inner membrane potential difference are of high importance for the characterization of peptide-membrane interactions. Intercalation and accumulation of peptides lead to changes in membrane capacitance, and membrane interaction of charged peptides induces changes in the charge distribution within the membrane and with that to changes in the membrane potential profile. In this study, we establish time-resolved measurements of the capacitance minimization potential DeltaPsi on various asymmetric planar lipid bilayers using the inner field compensation method. The results are compared to the respective ones of inner membrane potential differences DeltaPhi determined from ion carrier transport measurements. Finally, the time courses of membrane capacitances and of DeltaPsi have been used to characterize the interaction of cathelicidins with reconstituted lipid matrices of various Gram-negative bacteria.
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Affiliation(s)
- Sven O Hagge
- Research Center Borstel, Leibniz Center for Medicine and Biosciences, Department of Immunochemistry and Biochemical Microbiology, Division of Biophysics, D-23845 Borstel, Germany
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41
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Chen IA, Szostak JW. Membrane growth can generate a transmembrane pH gradient in fatty acid vesicles. Proc Natl Acad Sci U S A 2004; 101:7965-70. [PMID: 15148394 PMCID: PMC419540 DOI: 10.1073/pnas.0308045101] [Citation(s) in RCA: 131] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Electrochemical proton gradients are the basis of energy transduction in modern cells, and may have played important roles in even the earliest cell-like structures. We have investigated the conditions under which pH gradients are maintained across the membranes of fatty acid vesicles, a model of early cell membranes. We show that pH gradients across such membranes decay rapidly in the presence of alkali-metal cations, but can be maintained in the absence of permeable cations. Under such conditions, when fatty acid vesicles grow through the incorporation of additional fatty acid, a transmembrane pH gradient is spontaneously generated. The formation of this pH gradient captures some of the energy released during membrane growth, but also opposes and limits further membrane area increase. The coupling of membrane growth to energy storage could have provided a growth advantage to early cells, once the membrane composition had evolved to allow the maintenance of stable pH gradients.
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Affiliation(s)
- Irene A Chen
- Howard Hughes Medical Institute and Department of Molecular Biology, Massachusetts General Hospital, Boston, MA 02114, USA
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42
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Urbánková E, Voltchenko A, Pohl P, Jezek P, Pohl EE. Transport kinetics of uncoupling proteins. Analysis of UCP1 reconstituted in planar lipid bilayers. J Biol Chem 2003; 278:32497-500. [PMID: 12826670 DOI: 10.1074/jbc.m303721200] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
According to alternative hypotheses, mitochondrial uncoupling protein 1 (UCP1) is either a proton channel ("buffering model") or a fatty acid anion carrier ("fatty acid cycling"). Transport across the proton channel along a chain of hydrogen bonds (Grotthus mechanism) may include fatty acid carboxyl groups or occur in the absence of fatty acids. In this work, we demonstrate that planar bilayers reconstituted with UCP1 exhibit an increase in membrane conductivity exclusively in the presence of fatty acids. Hence, we can exclude the hypothesis considering a preexisting H+ channel in UCP1, which does not require fatty acid for function. The augmented conductivity is nearly completely blocked by ATP. Direct application of transmembrane voltage and precise current measurements allowed determination of ATP-sensitive conductances at 0 and 150 mV as 11.5 and 54.3 pS, respectively, by reconstituting nearly 3 x 10(5) copies of UCP1. The proton conductivity measurements carried out in presence of a pH gradient (0.4 units) allowed estimation of proton turnover numbers per UCP1 molecule. The observed transport rate of 14 s-1 is compatible both with carrier and channel nature of UCP1.
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Affiliation(s)
- Eva Urbánková
- Department of Membrane Transport Biophysics, Institute of Physiology, Academy of Sciences of the Czech Republic, Prague, Czech Republic
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43
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Pownall HJ, Hamilton JA. Energy translocation across cell membranes and membrane models. ACTA PHYSIOLOGICA SCANDINAVICA 2003; 178:357-65. [PMID: 12864740 DOI: 10.1046/j.1365-201x.2003.01154.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Fatty acid transport is an important process in cellular energy distribution and storage in both normal and pathological states, especially obesity-linked type 2 diabetes mellitus. Fatty acid transport has been studied by the complementary approaches of cell biology and biophysics. According to the latter approach, specific proteins that enhance the uptake and storage of fatty acids are posited as fatty acid translocases, which facilitate fatty acid movement from the outer to inner leaflets of the plasma membrane. According to biophysical studies conducted in vitro, fatty acid translocation occurs by a rapid diffusive process that does not require a protein. Herein, we critically review these two mechanisms and their importance in the regulation of fatty acid uptake in vivo.
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Affiliation(s)
- H J Pownall
- Department of Medicine, Baylor College of Medicine, Houston, TX 77030, USA
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Abstract
PURPOSE OF REVIEW The rates by which unesterified fatty acids and cholesterol move through and desorb from membranes have been difficult to measure, in part because of the simple structures of these lipids but also because methods have generally not clearly distinguished the two steps of membrane transport. Lack of definitive knowledge has given rise to speculation about the mechanism(s) of membrane 'transport' proteins for fatty acids and cholesterol. RECENT FINDINGS New biophysical and biochemical approaches have provided evidence that fatty acids and cholesterol exhibit rapid diffusion (flip-flop), as fast as milliseconds, across both protein-free phospholipid bilayers and cell membranes. In contrast, desorption of the cholesterol molecule from a membrane surface (hours) is much slower than that of common dietary fatty acids (milliseconds to seconds). SUMMARY Knowledge of these properties provides a framework for understanding transport and metabolism of cholesterol and fatty acids and how their putative membrane and intracellular transporters might function.
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Affiliation(s)
- James A Hamilton
- Department of Biophysics, Boston University School of Medicine, Boston, MA 02118, USA.
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45
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Kamp F, Guo W, Souto R, Pilch PF, Corkey BE, Hamilton JA. Rapid flip-flop of oleic acid across the plasma membrane of adipocytes. J Biol Chem 2003; 278:7988-95. [PMID: 12499383 DOI: 10.1074/jbc.m206648200] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Nonesterified long-chain fatty acids may enter cells by free diffusion or by membrane protein transporters. A requirement for proteins to transport fatty acids across the plasma membrane would imply low partitioning of fatty acids into the membrane lipids, and/or a slower rate of diffusion (flip-flop) through the lipid domains compared to the rates of intracellular metabolism of fatty acids. We used both vesicles of the plasma membrane of adipocytes and intact adipocytes to study transmembrane fluxes of externally added oleic acid at concentrations below its solubility limit at pH 7.4. Binding of oleic acid to the plasma membrane was determined by measuring the fluorescent fatty acid-binding protein ADIFAB added to the external medium. Changes in internal pH caused by flip-flop and metabolism were measured by trapping a fluorescent pH indicator in the cells. The metabolic end products of oleic acid were evaluated over the time interval required for the return of intracellular pH to its initial value. The primary findings were that (i) oleic acid rapidly binds with high avidity in the lipid domains of the plasma membrane with an apparent partition coefficient similar to that of protein-free phospholipid bilayers; (ii) oleic acid rapidly crosses the plasma membrane by the flip-flop mechanism (both events occur within 5 s); and (iii) the kinetics of esterification of oleic acid closely follow the time dependence of the recovery of intracellular pH. Any postulated transport mechanism for facilitating translocation of fatty acid across the plasma membrane of adipocytes, including a protein transporter, would have to compete with the highly effective flip-flop mechanism.
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Affiliation(s)
- Frits Kamp
- Obesity Research Center, Boston Medical Center, Massachusetts 02118, USA
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46
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Pownall HJ, Hamilton JA. Physical aspects of fatty acid transport between and through biological membranes. ACTA ACUST UNITED AC 2003. [DOI: 10.1016/s1569-2558(03)33009-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/12/2023]
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47
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Peterson U, Mannock DA, Lewis RNAH, Pohl P, McElhaney RN, Pohl EE. Origin of membrane dipole potential: contribution of the phospholipid fatty acid chains. Chem Phys Lipids 2002; 117:19-27. [PMID: 12191841 DOI: 10.1016/s0009-3084(02)00013-0] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The large intrinsic membrane dipole potential, phi(d), is important for protein insertion and functioning as well as for ion transport across natural and model membranes. However, the origin of phi(d) is controversial. From experiments carried out with lipid monolayers, a significant dependence on the fatty acid chain length is suggested, whereas in experiments with lipid bilayers, the contribution of additional -CH(2)-groups seems negligibly small compared with that of the phospholipid carbonyl groups and lipid-bound water molecules. To compare the impact of the -CH(2)-groups of dipalmitoylphosphatidylcholine (DPPC) near and far from the glycerol backbone, we have varied the structure of DPPC by incorporation of sulfur atoms in place of methylene groups in different positions of the fatty acid chain. The phi(d) of symmetric lipid bilayers containing one heteroatom was obtained from the charge relaxation of oppositely charged hydrophobic ions. We have found that the substitution for a S-atom of a -CH(2)-group decreases phi(d). The effect (deltaphi(d) = -22.6 mV) is most pronounced for S-atoms near the lipid head group while a S-atom substitution in the C(13)- or C(14)-position of the hydrocarbon chain does not effect the bilayer dipole potential. Most probably deltaphi(d) does not originate from an altered dipole potential of the acyl chain containing an heteroatom but is mediated by the disruption of chain packing, leading to a decreased density of lipid dipoles in the membrane.
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Affiliation(s)
- Uwe Peterson
- Institut für Medizinische Physik und Biophysik, Martin-Luther-Universität, 06097 Halle, Germany
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48
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