1
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Ramanthrikkovil Variyam A, Stolov M, Feng J, Amdursky N. Solid-State Molecular Protonics Devices of Solid-Supported Biological Membranes Reveal the Mechanism of Long-Range Lateral Proton Transport. ACS NANO 2024; 18:5101-5112. [PMID: 38314693 PMCID: PMC10867892 DOI: 10.1021/acsnano.3c11990] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2023] [Revised: 01/27/2024] [Accepted: 01/30/2024] [Indexed: 02/07/2024]
Abstract
Lateral proton transport (PT) on the surface of biological membranes is a fundamental biochemical process in the bioenergetics of living cells, but a lack of available experimental techniques has resulted in a limited understanding of its mechanism. Here, we present a molecular protonics experimental approach to investigate lateral PT across membranes by measuring long-range (70 μm) lateral proton conduction via a few layers of lipid bilayers in a solid-state-like environment, i.e., without having bulk water surrounding the membrane. This configuration enables us to focus on lateral proton conduction across the surface of the membrane while decoupling it from bulk water. Hence, by controlling the relative humidity of the environment, we can directly explore the role of water in the lateral PT process. We show that proton conduction is dependent on the number of water molecules and their structure and on membrane composition, where we explore the role of the headgroup, the tail saturation, the membrane phase, and membrane fluidity. The measured PT as a function of temperature shows an inverse temperature dependency, which we explain by the desorption and adsorption of water molecules into the solid membrane platform. We explain our findings by discussing the role of percolating hydrogen bonding within the membrane structure in a Grotthuss-like mechanism.
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Affiliation(s)
| | - Mikhail Stolov
- Wolfson
Department of Chemical Engineering, Technion
− Israel Institute of Technology, Haifa 3200003, Israel
| | - Jiajun Feng
- Schulich
Faculty of Chemistry, Technion −
Israel Institute of Technology, Haifa 3200003, Israel
| | - Nadav Amdursky
- Schulich
Faculty of Chemistry, Technion −
Israel Institute of Technology, Haifa 3200003, Israel
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2
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Knyazev DG, Silverstein TP, Brescia S, Maznichenko A, Pohl P. A New Theory about Interfacial Proton Diffusion Revisited: The Commonly Accepted Laws of Electrostatics and Diffusion Prevail. Biomolecules 2023; 13:1641. [PMID: 38002323 PMCID: PMC10669390 DOI: 10.3390/biom13111641] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2023] [Revised: 11/02/2023] [Accepted: 11/07/2023] [Indexed: 11/26/2023] Open
Abstract
The high propensity of protons to stay at interfaces has attracted much attention over the decades. It enables long-range interfacial proton diffusion without relying on titratable residues or electrostatic attraction. As a result, various phenomena manifest themselves, ranging from spillover in material sciences to local proton circuits between proton pumps and ATP synthases in bioenergetics. In an attempt to replace all existing theoretical and experimental insight into the origin of protons' preference for interfaces, TELP, the "Transmembrane Electrostatically-Localized Protons" hypothesis, has been proposed. The TELP hypothesis envisions static H+ and OH- layers on opposite sides of interfaces that are up to 75 µm thick. Yet, the separation at which the electrostatic interaction between two elementary charges is comparable in magnitude to the thermal energy is more than two orders of magnitude smaller and, as a result, the H+ and OH- layers cannot mutually stabilize each other, rendering proton accumulation at the interface energetically unfavorable. We show that (i) the law of electroneutrality, (ii) Fick's law of diffusion, and (iii) Coulomb's law prevail. Using them does not hinder but helps to interpret previously published experimental results, and also helps us understand the high entropy release barrier enabling long-range proton diffusion along the membrane surface.
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Affiliation(s)
- Denis G. Knyazev
- Institute of Biophysics, Johannes Kepler University, 4020 Linz, Austria; (D.G.K.); (S.B.); (A.M.)
| | | | - Stefania Brescia
- Institute of Biophysics, Johannes Kepler University, 4020 Linz, Austria; (D.G.K.); (S.B.); (A.M.)
| | - Anna Maznichenko
- Institute of Biophysics, Johannes Kepler University, 4020 Linz, Austria; (D.G.K.); (S.B.); (A.M.)
| | - Peter Pohl
- Institute of Biophysics, Johannes Kepler University, 4020 Linz, Austria; (D.G.K.); (S.B.); (A.M.)
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3
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Weichselbaum E, Galimzyanov T, Batishchev OV, Akimov SA, Pohl P. Proton Migration on Top of Charged Membranes. Biomolecules 2023; 13:biom13020352. [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] [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
- Correspondence:
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4
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Nesterov SV, Yaguzhinsky LS, Vasilov RG, Kadantsev VN, Goltsov AN. Contribution of the Collective Excitations to the Coupled Proton and Energy Transport along Mitochondrial Cristae Membrane in Oxidative Phosphorylation System. ENTROPY (BASEL, SWITZERLAND) 2022; 24:1813. [PMID: 36554218 PMCID: PMC9778164 DOI: 10.3390/e24121813] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/16/2022] [Revised: 12/06/2022] [Accepted: 12/09/2022] [Indexed: 06/17/2023]
Abstract
The results of many experimental and theoretical works indicate that after transport of protons across the mitochondrial inner membrane (MIM) in the oxidative phosphorylation (OXPHOS) system, they are retained on the membrane-water interface in nonequilibrium state with free energy excess due to low proton surface-to-bulk release. This well-established phenomenon suggests that proton trapping on the membrane interface ensures vectorial lateral transport of protons from proton pumps to ATP synthases (proton acceptors). Despite the key role of the proton transport in bioenergetics, the molecular mechanism of proton transfer in the OXPHOS system is not yet completely established. Here, we developed a dynamics model of long-range transport of energized protons along the MIM accompanied by collective excitation of localized waves propagating on the membrane surface. Our model is based on the new data on the macromolecular organization of the OXPHOS system showing the well-ordered structure of respirasomes and ATP synthases on the cristae membrane folds. We developed a two-component dynamics model of the proton transport considering two coupled subsystems: the ordered hydrogen bond (HB) chain of water molecules and lipid headgroups of MIM. We analytically obtained a two-component soliton solution in this model, which describes the motion of the proton kink, corresponding to successive proton hops in the HB chain, and coherent motion of a compression soliton in the chain of lipid headgroups. The local deformation in a soliton range facilitates proton jumps due to water molecules approaching each other in the HB chain. We suggested that the proton-conducting structures formed along the cristae membrane surface promote direct lateral proton transfer in the OXPHOS system. Collective excitations at the water-membrane interface in a form of two-component soliton ensure the coupled non-dissipative transport of charge carriers and elastic energy of MIM deformation to ATP synthases that may be utilized in ATP synthesis providing maximal efficiency in mitochondrial bioenergetics.
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Affiliation(s)
- Semen V. Nesterov
- Kurchatov Complex of NBICS-Technologies, National Research Center Kurchatov Institute, 123182 Moscow, Russia
- Research Center for Molecular Mechanisms of Aging and Age-Related Diseases, Moscow Institute of Physics and Technology, 141701 Dolgoprudny, Russia
| | - Lev S. Yaguzhinsky
- Research Center for Molecular Mechanisms of Aging and Age-Related Diseases, Moscow Institute of Physics and Technology, 141701 Dolgoprudny, Russia
- Department of Bioenergetics, Institute of Cytochemistry and Molecular Pharmacology, 115404 Moscow, Russia
- Belozersky Research Institute for Physico-Chemical Biology, Lomonosov Moscow State University, 119992 Moscow, Russia
| | - Raif G. Vasilov
- Kurchatov Complex of NBICS-Technologies, National Research Center Kurchatov Institute, 123182 Moscow, Russia
| | - Vasiliy N. Kadantsev
- Institute for Artificial Intelligence, Russian Technological University (MIREA), 119454 Moscow, Russia
| | - Alexey N. Goltsov
- Institute for Artificial Intelligence, Russian Technological University (MIREA), 119454 Moscow, Russia
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5
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Stuchebrukhov AA, Variyam AR, Amdursky N. Using Proton Geminate Recombination as a Probe of Proton Migration on Biological Membranes. J Phys Chem B 2022; 126:6026-6038. [PMID: 35921517 DOI: 10.1021/acs.jpcb.2c00953] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Proton migration on biological membranes plays a major role in cellular respiration and photosynthesis, but it is not yet fully understood. Here we show that proton dissociation kinetics and related geminate recombination can be used as a probe of such proton migration mechanisms. We develop a simple model for the process and apply it to analyze the results obtained using a photo-induced proton release probe (chemically modified photoacid) tethered to phosphatidylcholine membranes. In our theoretical model, we apply approximate treatment for the diffusional cloud of the geminate proton around the dissociated photoacid and consider arbitrary dimension of the system, 1 < d < 3. We observe that in d > 2, there is a kinetic phase transition between an exponential and a power-law kinetic phases. The existence of an exponential decay phase at the beginning of the proton dissociation is a signature of d > 2 systems. In most other cases, the exponential decay phase is not present, and the kinetics follows a diffusional power-law P(t) ∼ t-d/2 that develops after a short initiation time. Specifically, in a 1D case, which corresponds to the desorption of a proton from the surface, the dissociation occurs by the slow power-law ∼1/t and explains the abnormally slow desorption rate reported recently in experiments.
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Affiliation(s)
- Alexei A Stuchebrukhov
- Department of Chemistry, University of California at Davis, One Shields Avenue, Davis, California 95616, United States
| | | | - Nadav Amdursky
- Schulich Faculty of Chemistry, Technion-Israel Institute of Technology, Haifa 3200003, Israel
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6
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Nesterov SV, Smirnova EG, Yaguzhinsky LS. Mechanism of Energy Storage and Transformation in the Mitochondria at the Water-Membrane Interface. BIOCHEMISTRY. BIOKHIMIIA 2022; 87:179-190. [PMID: 35508909 DOI: 10.1134/s0006297922020092] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/01/2021] [Revised: 01/11/2022] [Accepted: 01/13/2022] [Indexed: 06/14/2023]
Abstract
In this review, we discuss the mechanisms of generation of membrane-bound protons using different energy sources in model and natural systems. Analysis of these mechanisms revealed that all three types of reactions include the same principal stage, which is dissociation of electrically neutral Brønsted acids at the interface during transition from the hydrophobic phase to water with a low dielectric constant. Special attention is paid to the fact that in one of the analyzed model systems, membrane-bound protons provide energy for the reaction of ATP synthesis. Similar mechanism for the generation of membrane-bound protons has been found in natural membranes involved in oxidative phosphorylation, in particular, on the membranes of mitoplasts and mitochondria. The energy of oxidative reactions required for ATP synthesis, is stored at the intermediate stage not only in the form of transmembrane electrochemical potential of protons, but also and perhaps mostly, as protons attached to the inner mitochondrial membrane. The process of energy storage in mitochondria is linked to the transfer of protons that simultaneously perform two functions. Protons on the membrane surface carry free energy and, at the same time, act as substrates facilitating the movement of F1F0-ATP-synthase biological machine.
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Affiliation(s)
- Semen V Nesterov
- National Research Center "Kurchatov Institute", Moscow, 123182, Russia
- Moscow Institute of Physics and Technology, Dolgoprudny, Moscow Region, 141701, Russia
| | - Elena G Smirnova
- Belozersky Research Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119992, Russia
| | - Lev S Yaguzhinsky
- Moscow Institute of Physics and Technology, Dolgoprudny, Moscow Region, 141701, Russia.
- Belozersky Research Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119992, Russia
- Institute of Cytochemistry and Molecular Pharmacology, Moscow, 115404, Russia
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7
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Yang J, Lu Y, Jin L, Zhao C, Chen Y, Xu Y, Chen F, Feng J. Dynamic Optical Visualization of Proton Transport Pathways at Water–Solid Interfaces. Angew Chem Int Ed Engl 2022. [DOI: 10.1002/ange.202112150] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Jinmei Yang
- Laboratory of Experimental Physical Biology Department of Chemistry Zhejiang University Hangzhou 310027 China
| | - Yuxian Lu
- Laboratory of Experimental Physical Biology Department of Chemistry Zhejiang University Hangzhou 310027 China
| | - Lei Jin
- College of Pharmaceutical Sciences Zhejiang University Hangzhou 310058 China
| | - Chunxiao Zhao
- Laboratory of Experimental Physical Biology Department of Chemistry Zhejiang University Hangzhou 310027 China
| | - Yuang Chen
- Laboratory of Experimental Physical Biology Department of Chemistry Zhejiang University Hangzhou 310027 China
| | - Yang Xu
- Laboratory of Experimental Physical Biology Department of Chemistry Zhejiang University Hangzhou 310027 China
| | - Fanfan Chen
- Laboratory of Experimental Physical Biology Department of Chemistry Zhejiang University Hangzhou 310027 China
| | - Jiandong Feng
- Laboratory of Experimental Physical Biology Department of Chemistry Zhejiang University Hangzhou 310027 China
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8
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Yang J, Lu Y, Jin L, Zhao C, Chen Y, Xu Y, Chen F, Feng J. Dynamic Optical Visualization of Proton Transport Pathways at Water-Solid Interfaces. Angew Chem Int Ed Engl 2021; 61:e202112150. [PMID: 34751999 DOI: 10.1002/anie.202112150] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2021] [Indexed: 11/07/2022]
Abstract
Probing proton transport is of vital importance for understanding cellular transport, surface catalysis and fuel cells. Conventional proton transport measurements rely on the use of electrochemical conductivity and do not allow for the direct visualization of proton transport pathways. The development of novel experimental techniques to spatiotemporally resolve proton transport is in high demand. Here, building upon the general conversion of aqueous proton flux into spatially resolved fluorescence signals, we optically visualize proton transport through nanopores and along hydrophilic interfaces. We observed that the fluorescence intensity increased at negative voltage due to lateral transport. Thanks to the temporal resolution of optical imaging, our technique further empowers the analysis of proton transport dynamics.
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Affiliation(s)
- Jinmei Yang
- Laboratory of Experimental Physical Biology, Department of Chemistry, Zhejiang University, Hangzhou, 310027, China
| | - Yuxian Lu
- Laboratory of Experimental Physical Biology, Department of Chemistry, Zhejiang University, Hangzhou, 310027, China
| | - Lei Jin
- College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, 310058, China
| | - Chunxiao Zhao
- Laboratory of Experimental Physical Biology, Department of Chemistry, Zhejiang University, Hangzhou, 310027, China
| | - Yuang Chen
- Laboratory of Experimental Physical Biology, Department of Chemistry, Zhejiang University, Hangzhou, 310027, China
| | - Yang Xu
- Laboratory of Experimental Physical Biology, Department of Chemistry, Zhejiang University, Hangzhou, 310027, China
| | - Fanfan Chen
- Laboratory of Experimental Physical Biology, Department of Chemistry, Zhejiang University, Hangzhou, 310027, China
| | - Jiandong Feng
- Laboratory of Experimental Physical Biology, Department of Chemistry, Zhejiang University, Hangzhou, 310027, China
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9
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Kell DB. A protet-based, protonic charge transfer model of energy coupling in oxidative and photosynthetic phosphorylation. Adv Microb Physiol 2021; 78:1-177. [PMID: 34147184 DOI: 10.1016/bs.ampbs.2021.01.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Textbooks of biochemistry will explain that the otherwise endergonic reactions of ATP synthesis can be driven by the exergonic reactions of respiratory electron transport, and that these two half-reactions are catalyzed by protein complexes embedded in the same, closed membrane. These views are correct. The textbooks also state that, according to the chemiosmotic coupling hypothesis, a (or the) kinetically and thermodynamically competent intermediate linking the two half-reactions is the electrochemical difference of protons that is in equilibrium with that between the two bulk phases that the coupling membrane serves to separate. This gradient consists of a membrane potential term Δψ and a pH gradient term ΔpH, and is known colloquially as the protonmotive force or pmf. Artificial imposition of a pmf can drive phosphorylation, but only if the pmf exceeds some 150-170mV; to achieve in vivo rates the imposed pmf must reach 200mV. The key question then is 'does the pmf generated by electron transport exceed 200mV, or even 170mV?' The possibly surprising answer, from a great many kinds of experiment and sources of evidence, including direct measurements with microelectrodes, indicates it that it does not. Observable pH changes driven by electron transport are real, and they control various processes; however, compensating ion movements restrict the Δψ component to low values. A protet-based model, that I outline here, can account for all the necessary observations, including all of those inconsistent with chemiosmotic coupling, and provides for a variety of testable hypotheses by which it might be refined.
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Affiliation(s)
- Douglas B Kell
- Department of Biochemistry and Systems Biology, Institute of Systems, Molecular and Integrative, Biology, University of Liverpool, Liverpool, United Kingdom; The Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, Lyngby, Denmark.
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10
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Ordered Clusters of the Complete Oxidative Phosphorylation System in Cardiac Mitochondria. Int J Mol Sci 2021; 22:ijms22031462. [PMID: 33540542 PMCID: PMC7867189 DOI: 10.3390/ijms22031462] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2020] [Revised: 01/26/2021] [Accepted: 01/30/2021] [Indexed: 01/10/2023] Open
Abstract
The existence of a complete oxidative phosphorylation system (OXPHOS) supercomplex including both electron transport system and ATP synthases has long been assumed based on functional evidence. However, no structural confirmation of the docking between ATP synthase and proton pumps has been obtained. In this study, cryo-electron tomography was used to reveal the supramolecular architecture of the rat heart mitochondria cristae during ATP synthesis. Respirasome and ATP synthase structure in situ were determined using subtomogram averaging. The obtained reconstructions of the inner mitochondrial membrane demonstrated that rows of respiratory chain supercomplexes can dock with rows of ATP synthases forming oligomeric ordered clusters. These ordered clusters indicate a new type of OXPHOS structural organization. It should ensure the quickness, efficiency, and damage resistance of OXPHOS, providing a direct proton transfer from pumps to ATP synthase along the lateral pH gradient without energy dissipation.
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11
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Affiliation(s)
- Nadav Amdursky
- Schulich Faculty of ChemistryTechnion – Israel Institute of Technology Haifa 3200003 Israel
| | - Yiyang Lin
- State Key Laboratory of Organic-Inorganic Composites Beijing Laboratory of Biomedical MaterialsBeijing University of Chemical Technology Beijing 100029 China
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12
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Exploring fast proton transfer events associated with lateral proton diffusion on the surface of membranes. Proc Natl Acad Sci U S A 2019; 116:2443-2451. [PMID: 30679274 DOI: 10.1073/pnas.1812351116] [Citation(s) in RCA: 39] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Proton diffusion (PD) across biological membranes is a fundamental process in many biological systems, and much experimental and theoretical effort has been employed for deciphering it. Here, we report on a spectroscopic probe, which can be tightly tethered to the membrane, for following fast (nanosecond) proton transfer events on the surface of membranes. Our probe is composed of a photoacid that serves as our light-induced proton source for the initiation of the PD process. We use our probe to follow PD, and its pH dependence, on the surface of lipid vesicles composed of a zwitterionic headgroup, a negative headgroup, a headgroup that is composed only from the negative phosphate group, or a positive headgroup without the phosphate group. We reveal that the PD kinetic parameters are highly sensitive to the nature of the lipid headgroup, ranging from a fast lateral diffusion at some membranes to the escape of protons from surface to bulk (and vice versa) at others. By referring to existing theoretical models for membrane PD, we found that while some of our results confirm the quasi-equilibrium model, other results are in line with the nonequilibrium model.
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13
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Gennis RB. Proton Dynamics at the Membrane Surface. Biophys J 2017; 110:1909-11. [PMID: 27166799 DOI: 10.1016/j.bpj.2016.04.001] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2016] [Accepted: 04/01/2016] [Indexed: 11/16/2022] Open
Affiliation(s)
- Robert B Gennis
- Department of Biochemistry, University of Illinois, Urbana, Illinois.
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14
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Weichselbaum E, Österbauer M, Knyazev DG, Batishchev OV, Akimov SA, Hai Nguyen T, Zhang C, Knör G, Agmon N, Carloni P, Pohl P. Origin of proton affinity to membrane/water interfaces. Sci Rep 2017; 7:4553. [PMID: 28674402 PMCID: PMC5495794 DOI: 10.1038/s41598-017-04675-9] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2016] [Accepted: 05/18/2017] [Indexed: 11/21/2022] Open
Abstract
Proton diffusion along biological membranes is vitally important for cellular energetics. Here we extended previous time-resolved fluorescence measurements to study the time and temperature dependence of surface proton transport. We determined the Gibbs activation energy barrier ΔG ‡r that opposes proton surface-to-bulk release from Arrhenius plots of (i) protons' surface diffusion constant and (ii) the rate coefficient for proton surface-to-bulk release. The large size of ΔG ‡r disproves that quasi-equilibrium exists in our experiments between protons in the near-membrane layers and in the aqueous bulk. Instead, non-equilibrium kinetics describes the proton travel between the site of its photo-release and its arrival at a distant membrane patch at different temperatures. ΔG ‡r contains only a minor enthalpic contribution that roughly corresponds to the breakage of a single hydrogen bond. Thus, our experiments reveal an entropic trap that ensures channeling of highly mobile protons along the membrane interface in the absence of potent acceptors.
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Affiliation(s)
- Ewald Weichselbaum
- 0000 0001 1941 5140grid.9970.7Institute of Biophysics, Johannes Kepler University Linz, 4040 Linz, Austria
| | - Maria Österbauer
- 0000 0001 1941 5140grid.9970.7Institute of Inorganic Chemistry, Johannes Kepler University Linz, 4040 Linz, Austria
| | - Denis G. Knyazev
- 0000 0001 1941 5140grid.9970.7Institute of Biophysics, Johannes Kepler University Linz, 4040 Linz, Austria
| | - Oleg V. Batishchev
- 0000 0001 2192 9124grid.4886.2A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninskiy pr. 31/4, Moscow, 119071 Russian Federation ,0000000092721542grid.18763.3bMoscow Institute of Physics and Technology, Institutsky lane, 9, 141700 Dolgoprudniy, Russian Federation
| | - Sergey A. Akimov
- 0000 0001 2192 9124grid.4886.2A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninskiy pr. 31/4, Moscow, 119071 Russian Federation ,0000 0001 0010 3972grid.35043.31National University of Science and Technology “MISiS”, Leninskiy pr. 4, Moscow, 119991 Russian Federation
| | - Trung Hai Nguyen
- 0000 0001 0728 696Xgrid.1957.aComputational Biomedicine (IAS-5 / INM-9) Forschungszentrum Jülich, 52425 Jülich, Germany, RWTH Aachen University, 52056 Aachen, Germany
| | - Chao Zhang
- 0000 0001 0728 696Xgrid.1957.aComputational Biomedicine (IAS-5 / INM-9) Forschungszentrum Jülich, 52425 Jülich, Germany, RWTH Aachen University, 52056 Aachen, Germany ,0000000121885934grid.5335.0Department of Chemistry, University of Cambridge, Lensfield Rd, Cambridge, CB2 1EW United Kingdom
| | - Günther Knör
- 0000 0001 1941 5140grid.9970.7Institute of Inorganic Chemistry, Johannes Kepler University Linz, 4040 Linz, Austria
| | - Noam Agmon
- 0000 0004 1937 0538grid.9619.7Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem, 9190401 Israel
| | - Paolo Carloni
- 0000 0001 0728 696Xgrid.1957.aComputational Biomedicine (IAS-5 / INM-9) Forschungszentrum Jülich, 52425 Jülich, Germany, RWTH Aachen University, 52056 Aachen, Germany
| | - Peter Pohl
- Institute of Biophysics, Johannes Kepler University Linz, 4040, Linz, Austria.
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15
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Xu L, Öjemyr LN, Bergstrand J, Brzezinski P, Widengren J. Protonation Dynamics on Lipid Nanodiscs: Influence of the Membrane Surface Area and External Buffers. Biophys J 2017; 110:1993-2003. [PMID: 27166807 PMCID: PMC4939474 DOI: 10.1016/j.bpj.2016.03.035] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2015] [Revised: 02/11/2016] [Accepted: 03/07/2016] [Indexed: 11/29/2022] Open
Abstract
Lipid membrane surfaces can act as proton-collecting antennae, accelerating proton uptake by membrane-bound proton transporters. We investigated this phenomenon in lipid nanodiscs (NDs) at equilibrium on a local scale, analyzing fluorescence fluctuations of individual pH-sensitive fluorophores at the membrane surface by fluorescence correlation spectroscopy (FCS). The protonation rate of the fluorophores was ∼100-fold higher when located at 9- and 12-nm diameter NDs, compared to when in solution, indicating that the proton-collecting antenna effect is maximal already for a membrane area of ∼60 nm2. Fluorophore-labeled cytochrome c oxidase displayed a similar increase when reconstituted in 12 nm NDs, but not in 9 nm NDs, i.e., an acceleration of the protonation rate at the surface of cytochrome c oxidase is found when the lipid area surrounding the protein is larger than 80 nm2, but not when below 30 nm2. We also investigated the effect of external buffers on the fluorophore proton exchange rates at the ND membrane-water interfaces. With increasing buffer concentrations, the proton exchange rates were found to first decrease and then, at millimolar buffer concentrations, to increase. Monte Carlo simulations, based on a simple kinetic model of the proton exchange at the membrane-water interface, and using rate parameter values determined in our FCS experiments, could reconstruct both the observed membrane-size and the external buffer dependence. The FCS data in combination with the simulations indicate that the local proton diffusion coefficient along a membrane is ∼100 times slower than that observed over submillimeter distances by proton-pulse experiments (Ds ∼ 10−5cm2/s), and support recent theoretical studies showing that proton diffusion along membrane surfaces is time- and length-scale dependent.
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Affiliation(s)
- Lei Xu
- Experimental Biomolecular Physics, Department of Applied Physics, KTH-Royal Institute of Technology, AlbaNova University Center, Stockholm, Sweden
| | - Linda Näsvik Öjemyr
- Department of Biochemistry and Biophysics, Arrhenius Laboratories for Natural Sciences, Stockholm University, Stockholm, Sweden
| | - Jan Bergstrand
- Experimental Biomolecular Physics, Department of Applied Physics, KTH-Royal Institute of Technology, AlbaNova University Center, Stockholm, Sweden
| | - Peter Brzezinski
- Department of Biochemistry and Biophysics, Arrhenius Laboratories for Natural Sciences, Stockholm University, Stockholm, Sweden
| | - Jerker Widengren
- Experimental Biomolecular Physics, Department of Applied Physics, KTH-Royal Institute of Technology, AlbaNova University Center, Stockholm, Sweden.
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16
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Sjöholm J, Bergstrand J, Nilsson T, Šachl R, Ballmoos CV, Widengren J, Brzezinski P. The lateral distance between a proton pump and ATP synthase determines the ATP-synthesis rate. Sci Rep 2017; 7:2926. [PMID: 28592883 PMCID: PMC5462737 DOI: 10.1038/s41598-017-02836-4] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2017] [Accepted: 04/19/2017] [Indexed: 11/09/2022] Open
Abstract
We have investigated the effect of lipid composition on interactions between cytochrome bo 3 and ATP-synthase, and the ATP-synthesis activity driven by proton pumping. The two proteins were labeled by fluorescent probes and co-reconstituted in large (d ≅ 100 nm) or giant (d ≅ 10 µm) unilamellar lipid vesicles. Interactions were investigated using fluorescence correlation/cross-correlation spectroscopy and the activity was determined by measuring ATP production, driven by electron-proton transfer, as a function of time. We found that conditions that promoted direct interactions between the two proteins in the membrane (higher fraction DOPC lipids or labeling by hydrophobic molecules) correlated with an increased activity. These data indicate that the ATP-synthesis rate increases with decreasing distance between cytochrome bo 3 and the ATP-synthase, and involves proton transfer along the membrane surface. The maximum distance for lateral proton transfer along the surface was found to be ~80 nm.
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Affiliation(s)
- Johannes Sjöholm
- Department of Biochemistry and Biophysics, The Arrhenius Laboratories for Natural Sciences, Stockholm University, SE-106 91, Stockholm, Sweden
| | - Jan Bergstrand
- Experimental Biomolecular Physics, Department of Applied Physics, Royal Institute of Technology (KTH), SE-106 91, Stockholm, Sweden
| | - Tobias Nilsson
- Department of Biochemistry and Biophysics, The Arrhenius Laboratories for Natural Sciences, Stockholm University, SE-106 91, Stockholm, Sweden
| | - Radek Šachl
- Department of Biophysical Chemistry, J. Heyrovský Institute of Physical Chemistry of the A.S.C.R. v.v.i., Prague, Czech Republic
| | | | - Jerker Widengren
- Experimental Biomolecular Physics, Department of Applied Physics, Royal Institute of Technology (KTH), SE-106 91, Stockholm, Sweden
| | - Peter Brzezinski
- Department of Biochemistry and Biophysics, The Arrhenius Laboratories for Natural Sciences, Stockholm University, SE-106 91, Stockholm, Sweden.
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17
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Jeong BS, Dyer RB. Proton Transport Mechanism of M2 Proton Channel Studied by Laser-Induced pH Jump. J Am Chem Soc 2017; 139:6621-6628. [PMID: 28467842 DOI: 10.1021/jacs.7b00617] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The M2 proton transport channel of the influenza virus A is an important model system because it conducts protons with high selectivity and unidirectionally when activated at low pH, despite the relative simplicity of its structure. Although it has been studied extensively, the molecular details of the pH-dependent gating and proton conductance mechanisms are incompletely understood. We report direct observation of the M2 proton channel activation process using a laser-induced pH jump coupled with tryptophan fluorescence as a probe. Biphasic kinetics is observed, with the fast phase corresponding to the His37 protonation, and the slow phase associated with the subsequent conformation change. Unusually fast His37 protonation was observed (2.0 × 1010 M-1 s-1), implying the existence of proton collecting antennae for expedited proton transport. The conformation change (4 × 103 s-1) was about 2 orders of magnitude slower than protonation at endosomal pH, suggesting that a transporter model is likely not feasible.
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Affiliation(s)
- Ban-Seok Jeong
- Department of Chemistry, Emory University , Atlanta, Georgia 30322, United States
| | - R Brian Dyer
- Department of Chemistry, Emory University , Atlanta, Georgia 30322, United States
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18
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Yoshinaga MY, Kellermann MY, Valentine DL, Valentine RC. Phospholipids and glycolipids mediate proton containment and circulation along the surface of energy-transducing membranes. Prog Lipid Res 2016; 64:1-15. [PMID: 27448687 DOI: 10.1016/j.plipres.2016.07.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2015] [Revised: 05/29/2016] [Accepted: 07/13/2016] [Indexed: 01/06/2023]
Abstract
Proton bioenergetics provides the energy for growth and survival of most organisms in the biosphere ranging from unicellular marine phytoplankton to humans. Chloroplasts harvest light and generate a proton electrochemical gradient (proton motive force) that drives the production of ATP needed for carbon dioxide fixation and plant growth. Mitochondria, bacteria and archaea generate proton motive force to energize growth and other physiologies. Energy transducing membranes are at the heart of proton bioenergetics and are responsible for catalyzing the conversion of energy held in high-energy electrons→electron transport chain→proton motive force→ATP. Whereas the electron transport chain is understood in great detail there are major gaps in understanding mechanisms of proton transfer or circulation during proton bioenergetics. This paper is built on the proposition that phospho- and glyco-glycerolipids form proton transport circuitry at the membrane's surface. By this proposition, an emergent membrane property, termed the hyducton, confines active/unbound protons or hydronium ions to a region of low volume close to the membrane surface. In turn, a von Grotthuß mechanism rapidly moves proton substrate in accordance with nano-electrochemical poles on the membrane surface created by powerful proton pumps such as ATP synthase.
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Affiliation(s)
- Marcos Y Yoshinaga
- University of Bremen, MARUM - Center for Marine and Environmental Sciences, Germany.
| | - Matthias Y Kellermann
- University of California Santa Barbara - Department of Earth Science and Marine Science Institute, USA
| | - David L Valentine
- University of California Santa Barbara - Department of Earth Science and Marine Science Institute, USA
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19
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Agmon N, Bakker HJ, Campen RK, Henchman RH, Pohl P, Roke S, Thämer M, Hassanali A. Protons and Hydroxide Ions in Aqueous Systems. Chem Rev 2016; 116:7642-72. [PMID: 27314430 DOI: 10.1021/acs.chemrev.5b00736] [Citation(s) in RCA: 287] [Impact Index Per Article: 35.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Understanding the structure and dynamics of water's constituent ions, proton and hydroxide, has been a subject of numerous experimental and theoretical studies over the last century. Besides their obvious importance in acid-base chemistry, these ions play an important role in numerous applications ranging from enzyme catalysis to environmental chemistry. Despite a long history of research, many fundamental issues regarding their properties continue to be an active area of research. Here, we provide a review of the experimental and theoretical advances made in the last several decades in understanding the structure, dynamics, and transport of the proton and hydroxide ions in different aqueous environments, ranging from water clusters to the bulk liquid and its interfaces with hydrophobic surfaces. The propensity of these ions to accumulate at hydrophobic surfaces has been a subject of intense debate, and we highlight the open issues and challenges in this area. Biological applications reviewed include proton transport along the hydration layer of various membranes and through channel proteins, problems that are at the core of cellular bioenergetics.
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Affiliation(s)
- Noam Agmon
- The Fritz Haber Research Center, Institute of Chemistry, The Hebrew University of Jerusalem , Jerusalem 91904, Israel
| | - Huib J Bakker
- FOM Institute AMOLF , Science Park 104, 1098 XG Amsterdam, The Netherlands
| | - R Kramer Campen
- Fritz Haber Institute of the Max Planck Society , Faradayweg 4-6, 14195 Berlin, Germany
| | - Richard H Henchman
- Manchester Institute of Biotechnology, School of Chemistry, The University of Manchester , Oxford Road, Manchester M13 9PL, United Kingdom
| | - Peter Pohl
- Johannes Kepler University Linz , Institute of Biophysics, Gruberstrasse 40, 4020 Linz, Austria
| | - Sylvie Roke
- Laboratory for Fundamental BioPhotonics (LBP), Institute of Bioengineering (IBI), and Institute of Material Science (IMX), School of Engineering (STI), and Lausanne Centre for Ultrafast Science (LACUS), École Polytechnique Fédérale de Lausanne (EPFL) , CH-1015, Lausanne, Switzerland
| | - Martin Thämer
- Fritz Haber Institute of the Max Planck Society , Faradayweg 4-6, 14195 Berlin, Germany.,Department of Chemistry, Institute for Biophysical Dynamics, and James Franck Institute, The University of Chicago , Chicago, Illinois 60637, United States
| | - Ali Hassanali
- CMSP Section, The Abdus Salaam International Center for Theoretical Physics , I-34151 Trieste, Italy
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20
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Fichtl B, Shrivastava S, Schneider MF. Protons at the speed of sound: Predicting specific biological signaling from physics. Sci Rep 2016; 6:22874. [PMID: 27216038 PMCID: PMC4877590 DOI: 10.1038/srep22874] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2015] [Accepted: 02/22/2016] [Indexed: 01/23/2023] Open
Abstract
Local changes in pH are known to significantly alter the state and activity of proteins and enzymes. pH variations induced by pulses propagating along soft interfaces (e.g. membranes) would therefore constitute an important pillar towards a physical mechanism of biological signaling. Here we investigate the pH-induced physical perturbation of a lipid interface and the physicochemical nature of the subsequent acoustic propagation. Pulses are stimulated by local acidification and propagate - in analogy to sound - at velocities controlled by the interface's compressibility. With transient local pH changes of 0.6 directly observed at the interface and velocities up to 1.4 m/s this represents hitherto the fastest protonic communication observed. Furthermore simultaneously propagating mechanical and electrical changes in the lipid interface are detected, exposing the thermodynamic nature of these pulses. Finally, these pulses are excitable only beyond a threshold for protonation, determined by the pKa of the lipid head groups. This protonation-transition plus the existence of an enzymatic pH-optimum offer a physical basis for intra- and intercellular signaling via sound waves at interfaces, where not molecular structure and mechano-enyzmatic couplings, but interface thermodynamics and thermodynamic transitions are the origin of the observations.
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Affiliation(s)
- Bernhard Fichtl
- University of Augsburg, Experimental Physics I, Augsburg, 86159, Germany.,Nanosystems Initiative Munich NIM, Schellingstr. 4, 80799 München, Germany
| | - Shamit Shrivastava
- Medizinische und Biologische Physik, Technische Universität Dortmund, Otto-Hahn Str. 4, 44227 Dortmund, Germany.,University of Oxford, IBME Old Road Campus Research Building Oxford, OX3 7DQ, UK
| | - Matthias F Schneider
- Medizinische und Biologische Physik, Technische Universität Dortmund, Otto-Hahn Str. 4, 44227 Dortmund, Germany
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21
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Lipid-mediated Protein-protein Interactions Modulate Respiration-driven ATP Synthesis. Sci Rep 2016; 6:24113. [PMID: 27063297 PMCID: PMC4827085 DOI: 10.1038/srep24113] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2015] [Accepted: 03/21/2016] [Indexed: 11/16/2022] Open
Abstract
Energy conversion in biological systems is underpinned by membrane-bound proton
transporters that generate and maintain a proton electrochemical gradient across the
membrane which used, e.g. for generation of ATP by the ATP synthase. Here, we have
co-reconstituted the proton pump cytochrome bo3 (ubiquinol
oxidase) together with ATP synthase in liposomes and studied the effect of changing
the lipid composition on the ATP synthesis activity driven by proton pumping. We
found that for 100 nm liposomes, containing 5 of each proteins, the ATP synthesis
rates decreased significantly with increasing fractions of DOPA, DOPE, DOPG or
cardiolipin added to liposomes made of DOPC; with e.g. 5% DOPG, we observed an
almost 50% decrease in the ATP synthesis rate. However, upon increasing the average
distance between the proton pumps and ATP synthases, the ATP synthesis rate dropped
and the lipid dependence of this activity vanished. The data indicate that protons
are transferred along the membrane, between cytochrome bo3 and the
ATP synthase, but only at sufficiently high protein densities. We also argue that
the local protein density may be modulated by lipid-dependent changes in
interactions between the two proteins complexes, which points to a mechanism by
which the cell may regulate the overall activity of the respiratory chain.
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22
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Simkovitch R, Huppert D. Photoprotolytic Processes of Umbelliferone and Proposed Function in Resistance to Fungal Infection. J Phys Chem B 2015; 119:14683-96. [PMID: 26488429 DOI: 10.1021/acs.jpcb.5b08439] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The photoprotolytic processes of 7-hydroxy-coumarin (Umb) were investigated by steady-state and time-resolved-fluorescence techniques. We found that the Umb compound is a photoacid with pK(a)* ≈ 0.4 and a rate constant of the excited-state proton transfer (ESPT) to water of 2 × 10(10) s(-1). Umb is also a photobase and accepts an excess proton in solution and also directly from weak acids like acetic acid. When Umb is adsorbed on cellulose it also functions as a photoacid and a photobase. Hydroxycoumarins are known to accumulate next to fungal-, bacterial-, and viral-infected regions in the leaves and stems of plants in general and also in trees. We propose that these compounds when irradiated by sunlight UV, combat the fungi or bacteria by excited-state proton-transfer reactions. These photoprotolytic reactions provide a universal resistance mechanism to infections in plants.
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Affiliation(s)
- Ron Simkovitch
- Raymond and Beverly Sackler Faculty of Exact Sciences, School of Chemistry, Tel Aviv University , Tel Aviv 69978, Israel
| | - Dan Huppert
- Raymond and Beverly Sackler Faculty of Exact Sciences, School of Chemistry, Tel Aviv University , Tel Aviv 69978, Israel
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23
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Wolf MG, Grubmüller H, Groenhof G. Anomalous surface diffusion of protons on lipid membranes. Biophys J 2015; 107:76-87. [PMID: 24988343 DOI: 10.1016/j.bpj.2014.04.062] [Citation(s) in RCA: 48] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2013] [Revised: 01/06/2014] [Accepted: 04/07/2014] [Indexed: 11/30/2022] Open
Abstract
The cellular energy machinery depends on the presence and properties of protons at or in the vicinity of lipid membranes. To asses the energetics and mobility of a proton near a membrane, we simulated an excess proton near a solvated DMPC bilayer at 323 K, using a recently developed method to include the Grotthuss proton shuttling mechanism in classical molecular dynamics simulations. We obtained a proton surface affinity of -13.0 ± 0.5 kJ mol(-1). The proton interacted strongly with both lipid headgroup and linker carbonyl oxygens. Furthermore, the surface diffusion of the proton was anomalous, with a subdiffusive regime over the first few nanoseconds, followed by a superdiffusive regime. The time- and distance dependence of the proton surface diffusion coefficient within these regimes may also resolve discrepancies between previously reported diffusion coefficients. Our simulations show that the proton anomalous surface diffusion originates from restricted diffusion in two different surface-bound states, interrupted by the occasional bulk-mediated long-range surface diffusion. Although only a DMPC membrane was considered in this work, we speculate that the restrictive character of the on-surface diffusion is highly sensitive to the specific membrane conditions, which can alter the relative contributions of the surface and bulk pathways to the overall diffusion process. Finally, we discuss the implications of our findings for the energy machinery.
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Affiliation(s)
- Maarten G Wolf
- Computational Biomolecular Chemistry Group, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany; Department of Theoretical and Computational Biophysics, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Helmut Grubmüller
- Department of Theoretical and Computational Biophysics, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Gerrit Groenhof
- Computational Biomolecular Chemistry Group, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany.
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24
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Madzvamuse A, Chung AHW, Venkataraman C. Stability analysis and simulations of coupled bulk-surface reaction-diffusion systems. Proc Math Phys Eng Sci 2015; 471:20140546. [PMID: 25792948 PMCID: PMC4353053 DOI: 10.1098/rspa.2014.0546] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2014] [Accepted: 01/12/2015] [Indexed: 11/12/2022] Open
Abstract
In this article, we formulate new models for coupled systems of bulk-surface reaction-diffusion equations on stationary volumes. The bulk reaction-diffusion equations are coupled to the surface reaction-diffusion equations through linear Robin-type boundary conditions. We then state and prove the necessary conditions for diffusion-driven instability for the coupled system. Owing to the nature of the coupling between bulk and surface dynamics, we are able to decouple the stability analysis of the bulk and surface dynamics. Under a suitable choice of model parameter values, the bulk reaction-diffusion system can induce patterning on the surface independent of whether the surface reaction-diffusion system produces or not, patterning. On the other hand, the surface reaction-diffusion system cannot generate patterns everywhere in the bulk in the absence of patterning from the bulk reaction-diffusion system. For this case, patterns can be induced only in regions close to the surface membrane. Various numerical experiments are presented to support our theoretical findings. Our most revealing numerical result is that, Robin-type boundary conditions seem to introduce a boundary layer coupling the bulk and surface dynamics.
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Affiliation(s)
- Anotida Madzvamuse
- School of Mathematical and Physical Sciences, Department of Mathematics, University of Sussex, Brighton BN19QH, UK
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25
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Medvedev ES, Stuchebrukhov AA. Mechanisms of generation of local ΔpH in mitochondria and bacteria. BIOCHEMISTRY (MOSCOW) 2015; 79:425-34. [PMID: 24954593 DOI: 10.1134/s000629791405006x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The concepts of global and local coupling between proton generators, the enzymes of the respiratory chain, and the consumer, the ATP synthase, coexist in the theory of oxidative phosphorylation. Global coupling is trivial proton transport via the aqueous medium, whereas local coupling implies that the protons pumped are consumed before they escape to the bulk phase. In this work, the conditions for the occurrence of local coupling are explored. It is supposed that the membrane retains protons near its surface and that the proton current generated by the proton pumps rapidly decreases with increasing proton motive force (pmf). It is shown that the competition between the processes of proton translocation across the membrane and their dissipation from the surface to the bulk can result in transient generation of a local ΔpH in reply to a sharp change in pmf; the appearance of local ΔpH, in turn, leads to rapid recovery of the pmf, and hence, it provides for stabilization of the potential at the membrane. Two mechanisms of such kind are discussed: 1) pH changes in the surface area due to proton pumping develop faster than those due to proton escape to the bulk; 2) the former does not take place, but the protons leaving the surface do not equilibrate with the bulk immediately; rather, they give rise to a non-equilibrium concentration near the surface and, as a result, to a back proton flow to the surface. The first mechanism is more efficient, but it does not occur in mitochondria and neutrophilic bacteria, whereas the second can produce ΔpH on the order of unity. In the absence of proton retardation at the surface, local ΔpH does not arise, whereas the formation of global ΔpH is possible only at buffer concentration of less than 10 mM. The role of the mechanisms proposed in transitions between States 3 and 4 of the respiratory chain is discussed. The main conclusion is that surface protons, under conditions where they play a role, support stabilization of the membrane pmf and rapid communication between proton generators and consumers, while their contribution to the energetics is not significant.
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Affiliation(s)
- E S Medvedev
- Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, Moscow Region, 142432, Russia.
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