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Nestorovich EM, Bezrukov SM. Beta-Barrel Channel Response to High Electric Fields: Functional Gating or Reversible Denaturation? Int J Mol Sci 2023; 24:16655. [PMID: 38068977 PMCID: PMC10706840 DOI: 10.3390/ijms242316655] [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: 09/30/2023] [Revised: 11/16/2023] [Accepted: 11/21/2023] [Indexed: 12/18/2023] Open
Abstract
Ion channels exhibit gating behavior, fluctuating between open and closed states, with the transmembrane voltage serving as one of the essential regulators of this process. Voltage gating is a fundamental functional aspect underlying the regulation of ion-selective, mostly α-helical, channels primarily found in excitable cell membranes. In contrast, there exists another group of larger, and less selective, β-barrel channels of a different origin, which are not directly associated with cell excitability. Remarkably, these channels can also undergo closing, or "gating", induced by sufficiently strong electric fields. Once the field is removed, the channels reopen, preserving a memory of the gating process. In this study, we explored the hypothesis that the voltage-induced closure of the β-barrel channels can be seen as a form of reversible protein denaturation by the high electric fields applied in model membranes experiments-typically exceeding twenty million volts per meter-rather than a manifestation of functional gating. Here, we focused on the bacterial outer membrane channel OmpF reconstituted into planar lipid bilayers and analyzed various characteristics of the closing-opening process that support this idea. Specifically, we considered the nearly symmetric response to voltages of both polarities, the presence of multiple closed states, the stabilization of the open conformation in channel clusters, the long-term gating memory, and the Hofmeister effects in closing kinetics. Furthermore, we contemplate the evolutionary aspect of the phenomenon, proposing that the field-induced denaturation of membrane proteins might have served as a starting point for their development into amazing molecular machines such as voltage-gated channels of nerve and muscle cells.
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Affiliation(s)
- Ekaterina M. Nestorovich
- Department of Biology, The Catholic University of America, Washington, DC 20064, USA
- Section on Molecular Transport, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA;
| | - Sergey M. Bezrukov
- Section on Molecular Transport, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA;
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2
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Fedorenko OA, Kaufman IK, Gibby WAT, Barabash ML, Luchinsky DG, Roberts SK, McClintock PVE. Ionic Coulomb blockade and the determinants of selectivity in the NaChBac bacterial sodium channel. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2020; 1862:183301. [PMID: 32360369 DOI: 10.1016/j.bbamem.2020.183301] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/03/2019] [Revised: 01/30/2020] [Accepted: 03/29/2020] [Indexed: 10/24/2022]
Abstract
Mutation-induced transformations of conductivity and selectivity in NaChBac bacterial channels are studied experimentally and interpreted within the framework of ionic Coulomb blockade (ICB), while also taking account of resonant quantised dehydration (QD) and site protonation. Site-directed mutagenesis and whole-cell patch-clamp experiments are used to investigate how the fixed charge Qf at the selectivity filter (SF) affects both valence selectivity and same-charge selectivity. The new ICB/QD model predicts that increasing ∣Qf∣ should lead to a shift in selectivity sequences toward larger ion sizes, in agreement with the present experiments and with earlier work. Comparison of the model with experimental data leads to the introduction of an effective charge Qf∗ at the SF, which was found to differ between Aspartate and Glutamate charged rings, and also to depend on position within the SF. It is suggested that protonation of the residues within the restricted space of the SF is important in significantly reducing the effective charge of the EEEE ring. Values of Qf∗ derived from experiments on divalent blockade agree well with expectations based on the ICB/QD model and have led to the first demonstration of ICB oscillations in Ca2+ conduction as a function of the fixed charge. Preliminary studies of the dependence of Ca2+ conduction on pH are qualitatively consistent with the predictions of the model.
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Affiliation(s)
- O A Fedorenko
- Division of Biomedical and Life Sciences, Lancaster University, Lancaster LA1 4YQ, UK; School of Life Sciences, University of Nottingham, Nottingham NG7 2UH, UK.
| | - I Kh Kaufman
- Department of Physics, Lancaster University, Lancaster LA1 4YB, UK
| | - W A T Gibby
- Department of Physics, Lancaster University, Lancaster LA1 4YB, UK.
| | - M L Barabash
- Department of Physics, Lancaster University, Lancaster LA1 4YB, UK.
| | - D G Luchinsky
- Department of Physics, Lancaster University, Lancaster LA1 4YB, UK; SGT, Inc., Greenbelt, MD 20770, USA.
| | - S K Roberts
- Division of Biomedical and Life Sciences, Lancaster University, Lancaster LA1 4YQ, UK.
| | - P V E McClintock
- Department of Physics, Lancaster University, Lancaster LA1 4YB, UK.
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3
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Aguilella-Arzo M, Aguilella VM. Access resistance in protein nanopores. A structure-based computational approach. Bioelectrochemistry 2020; 131:107371. [DOI: 10.1016/j.bioelechem.2019.107371] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2019] [Revised: 08/27/2019] [Accepted: 09/01/2019] [Indexed: 01/25/2023]
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4
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Porins and small-molecule translocation across the outer membrane of Gram-negative bacteria. Nat Rev Microbiol 2019; 18:164-176. [DOI: 10.1038/s41579-019-0294-2] [Citation(s) in RCA: 135] [Impact Index Per Article: 27.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/16/2019] [Indexed: 02/07/2023]
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5
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Solov'eva T, Likhatskaya G, Khomenko V, Guzev K, Kim N, Bystritskaya E, Novikova O, Stenkova A, Rakin A, Isaeva M. The impact of length variations in the L2 loop on the structure and thermal stability of non-specific porins: The case of OmpCs from the Yersinia pseudotuberculosis complex. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1860:515-525. [PMID: 29038023 DOI: 10.1016/j.bbamem.2017.10.014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2017] [Revised: 09/25/2017] [Accepted: 10/11/2017] [Indexed: 10/18/2022]
Abstract
Porins are integral proteins of the outer membranes of gram-negative bacteria. In membranes, they exist as homotrimers and the L2 loops contribute to their stability. Comparison of OmpC porins of the Yersinia pseudotuberculosis complex with other enterobacterial porins demonstrated L2 loop length diversity, which is caused by varying numbers of dipeptide/tripeptide repeats. The OmpC porins are highly homologous to each other, and they can be subdivided into five isoforms based on their L2 loop structure. Optical spectroscopy and SDS-PAGE experiments revealed that particularities of the L2 loops affected the structure and thermal stability of the porins. Thermal denaturation studies showed that porins with shorter loops, compared to porins with longer loops, had more stable tertiary and less stable secondary and quaternary structures. According to our comparative modeling results, the L2 loops differ in their structure by adopting different spatial positions and forming different polar bonds with a neighbor monomer. The replacement of asparagine with arginine at the C-terminus of the L2 loop shifts the loop upwards and causes the loss of contacts with the arginine clusters within the pores. The increase in the length of these loops ensures that they shift down toward the pore and restore their contacts with arginines on the channel wall, as is the case in classical nonspecific porins. Despite the fact that the surface charge density varies considerably among the OmpC porins, the L2 loops form a typical negatively charged region in the center of the trimer.
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Affiliation(s)
- T Solov'eva
- G.B. Elyakov Pacific Institute of Bioorganic Chemistry FEB RAS, 690022 Prospect 100-let Vladivostoku 159, Vladivostok, Russia
| | - G Likhatskaya
- G.B. Elyakov Pacific Institute of Bioorganic Chemistry FEB RAS, 690022 Prospect 100-let Vladivostoku 159, Vladivostok, Russia
| | - V Khomenko
- G.B. Elyakov Pacific Institute of Bioorganic Chemistry FEB RAS, 690022 Prospect 100-let Vladivostoku 159, Vladivostok, Russia
| | - K Guzev
- G.B. Elyakov Pacific Institute of Bioorganic Chemistry FEB RAS, 690022 Prospect 100-let Vladivostoku 159, Vladivostok, Russia
| | - N Kim
- G.B. Elyakov Pacific Institute of Bioorganic Chemistry FEB RAS, 690022 Prospect 100-let Vladivostoku 159, Vladivostok, Russia
| | - E Bystritskaya
- G.B. Elyakov Pacific Institute of Bioorganic Chemistry FEB RAS, 690022 Prospect 100-let Vladivostoku 159, Vladivostok, Russia
| | - O Novikova
- G.B. Elyakov Pacific Institute of Bioorganic Chemistry FEB RAS, 690022 Prospect 100-let Vladivostoku 159, Vladivostok, Russia
| | - A Stenkova
- G.B. Elyakov Pacific Institute of Bioorganic Chemistry FEB RAS, 690022 Prospect 100-let Vladivostoku 159, Vladivostok, Russia
| | - A Rakin
- Institute for Bacterial Infections and Zoonoses, Federal Research Institute for Animal Health, Naumburger Str. 96 a, 07743 Jena, Germany
| | - M Isaeva
- G.B. Elyakov Pacific Institute of Bioorganic Chemistry FEB RAS, 690022 Prospect 100-let Vladivostoku 159, Vladivostok, Russia.
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6
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Abstract
One of the main fundamental mechanisms of antibiotic resistance in Gram-negative bacteria comprises an effective change in the membrane permeability to antibiotics. The Gram-negative bacterial complex cell envelope comprises an outer membrane that delimits the periplasm from the exterior environment. The outer membrane contains numerous protein channels, termed as porins or nanopores, which are mainly involved in the influx of hydrophilic compounds, including antibiotics. Bacterial adaptation to reduce influx through these outer membrane proteins (Omps) is one of the crucial mechanisms behind antibiotic resistance. Thus to interpret the molecular basis of the outer membrane permeability is the current challenge. This review attempts to develop a state of knowledge pertinent to Omps and their effective role in antibiotic influx. Further, it aims to study the bacterial response to antibiotic membrane permeability and hopefully provoke a discussion toward understanding and further exploration of prospects to improve our knowledge on physicochemical parameters that direct the translocation of antibiotics through the bacterial membrane protein channels.
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Affiliation(s)
- Ishan Ghai
- School of Engineering and Life Sciences, Jacobs University, Bremen
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7
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Scorciapino MA, Acosta-Gutierrez S, Benkerrou D, D'Agostino T, Malloci G, Samanta S, Bodrenko I, Ceccarelli M. Rationalizing the permeation of polar antibiotics into Gram-negative bacteria. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:113001. [PMID: 28155846 DOI: 10.1088/1361-648x/aa543b] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The increasing level of antibiotic resistance in Gram-negative bacteria, together with the lack of new potential drug scaffolds in the pipeline, make the problem of infectious diseases a global challenge for modern medicine. The main reason that Gram-negative bacteria are particularly challenging is the presence of an outer cell-protecting membrane, which is not present in Gram-positive species. Such an asymmetric bilayer is a highly effective barrier for polar molecules. Several protein systems are expressed in the outer membrane to control the internal concentration of both nutrients and noxious species, in particular: (i) water-filled channels that modulate the permeation of polar molecules and ions according to concentration gradients, and (ii) efflux pumps to actively expel toxic compounds. Thus, besides expressing specific enzymes for drugs degradation, Gram-negative bacteria can also resist by modulating the influx and efflux of antibiotics, keeping the internal concentration low. However, there are no direct and robust experimental methods capable of measuring the permeability of small molecules, thus severely limiting our knowledge of the molecular mechanisms that ultimately control the permeation of antibiotics through the outer membrane. This is the innovation gap to be filled for Gram-negative bacteria. This review is focused on the permeation of small molecules through porins, considered the main path for the entry of polar antibiotics into Gram-negative bacteria. A fundamental understanding of how these proteins are able to filter small molecules is a prerequisite to design/optimize antibacterials with improved permeation. The level of sophistication of modern molecular modeling algorithms and the advances in new computer hardware has made the simulation of such complex processes possible at the molecular level. In this work we aim to share our experience and perspectives in the context of a multidisciplinary extended collaboration within the IMI-Translocation consortium. The synergistic combination of structural data, in vitro assays and computer simulations has proven to give new insights towards the identification and description of physico-chemical properties modulating permeation. Once similar general rules are identified, we believe that the use of virtual screening techniques will be very helpful in searching for new molecular scaffolds with enhanced permeation, and that molecular modeling will be of fundamental assistance to the optimization stage.
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Affiliation(s)
- Mariano Andrea Scorciapino
- Department of Biomedical Sciences, Biochemistry Unit, University of Cagliari, Cittadella Universitaria di Monserrato, S.P. 8 km 0.700-09042 Monserrato (CA), Italy
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8
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Acosta Gutiérrez S, Bodrenko I, Scorciapino MA, Ceccarelli M. Macroscopic electric field inside water-filled biological nanopores. Phys Chem Chem Phys 2017; 18:8855-64. [PMID: 26931352 DOI: 10.1039/c5cp07902k] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Multi-drug resistance bacteria are a challenging problem of contemporary medicine. This is particularly critical for Gram-negative bacteria, where antibiotics are hindered by the outer membrane to reach internal targets. Here more polar antibiotics make use of nanometric water-filled channels to permeate inside. We present in this work a computational all-atom approach, using water as a probe, for the calculation of the macroscopic electric field inside water-filled channels. The method allows one to compare not only different systems but also the same system under different conditions, such as pH and ion concentration. This provides a detailed picture of electrostatics in biological nanopores shedding more light on how the charged residues of proteins determine the electric field inside, and also how medium can tune it. These details are central to unveil the filtering mechanism behind the permeation of small polar molecules through nanometric water-filled channels.
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Affiliation(s)
- Silvia Acosta Gutiérrez
- Department of Physics, University of Cagliari, Cittadella universitaria di Monserrato, S.P.8 - km 0.700, 09042 Monserrato (CA), Italy.
| | - Igor Bodrenko
- Department of Physics, University of Cagliari, Cittadella universitaria di Monserrato, S.P.8 - km 0.700, 09042 Monserrato (CA), Italy.
| | - Mariano Andrea Scorciapino
- Department of Biomedical Sciences, Biochemistry Unit, University of Cagliari, Cittadella universitaria di Monserrato, S.P.8 - km 0.700, 09042 Monserrato (CA), Italy
| | - Matteo Ceccarelli
- Department of Physics, University of Cagliari, Cittadella universitaria di Monserrato, S.P.8 - km 0.700, 09042 Monserrato (CA), Italy.
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9
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Phan K, Ferenci T. The fitness costs and trade-off shapes associated with the exclusion of nine antibiotics by OmpF porin channels. ISME JOURNAL 2017; 11:1472-1482. [PMID: 28072422 DOI: 10.1038/ismej.2016.202] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2016] [Revised: 11/20/2016] [Accepted: 12/01/2016] [Indexed: 02/01/2023]
Abstract
The trade-off relationship between antibiotic exclusion and nutrient access across the Gram-negative outer membrane is determined by structural constraints in porin channels. The precise nutritional cost of exclusion is unknown for different antibiotics, as are the shapes of the nutrition-susceptibility trade-off. Using a library of 10 engineered isogenic Escherichia coli strains with structural modifications of OmpF porin expressed at a constant level, susceptibilities were measured for nine antibiotics and the nutritional fitness costs estimated by competitions in chemostats. Different antibiotics exhibited a remarkably varied range of geometries in the nutrition-susceptibility trade-off, including convex, concave and sigmoidal trade-off shapes. The trade-off patterns predict the possibility of adaptations in contributing to antibiotic resistance; exclusion of amoxicillin or trimethoprim in ompF mutants can occur with little loss of fitness whereas kanamycin and streptomycin exclusion has a high cost. Some individual OmpF changes even allow positive correlations (trade-ups), resulting in increased fitness and decreased susceptibility specifically to cephalexin or ciprofloxacin. The surprising plasticity of the nutrition-exclusion relationship means that there are no generalisable rules that apply to decreasing susceptibility for all antibiotics. The protein changes are exquisitely specific in determining nutritional fitness and adaptive outcomes in a structural constraint trade-off.
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Affiliation(s)
- Katherine Phan
- School of Life and Environmental Sciences, University of Sydney, Sydney, New South Wales, Australia
| | - Thomas Ferenci
- School of Life and Environmental Sciences, University of Sydney, Sydney, New South Wales, Australia
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10
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Why do the outer membrane proteins OmpF from E. coli and OprP from P. aeruginosa prefer trimers? Simulation studies. J Mol Graph Model 2016; 65:1-7. [DOI: 10.1016/j.jmgm.2016.02.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2015] [Revised: 12/18/2015] [Accepted: 02/06/2016] [Indexed: 01/27/2023]
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11
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Alcaraz A, Queralt-Martín M. On the different sources of cooperativity in pH titrating sites of a membrane protein channel. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2016; 39:29. [PMID: 26987733 PMCID: PMC7087919 DOI: 10.1140/epje/i2016-16029-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/02/2015] [Accepted: 01/06/2016] [Indexed: 06/05/2023]
Abstract
Cooperative interactions play a central role in the regulation of protein functions. Here we show that in multi-site systems like ion channels the application of the Hill formalism could require a combination of different experiments, even involving site-directed mutagenesis, to identify the different sources of cooperativity and to discriminate between genuine and apparent cooperativity. We discuss the implications for the channel function in the bacterial porins PorA (N. meningitidis) and OmpF (E. coli) and the viroporin SARS-CoV E.
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Affiliation(s)
- Antonio Alcaraz
- Department of Physics, Laboratory of Molecular Biophysics, Universitat Jaume I, 12080, Castellón, Spain.
| | - María Queralt-Martín
- Department of Physics, Laboratory of Molecular Biophysics, Universitat Jaume I, 12080, Castellón, Spain
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12
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Queralt-Martín M, Peiró-González C, Aguilella-Arzo M, Alcaraz A. Effects of extreme pH on ionic transport through protein nanopores: the role of ion diffusion and charge exclusion. Phys Chem Chem Phys 2016; 18:21668-75. [DOI: 10.1039/c6cp04180a] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
We combine electrophysiological experiments with the structure-based Poisson–Nernst–Planck 3D calculations to investigate the transport properties of the bacterial porin OmpF under large pH gradients and particularly low salt concentrations.
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Affiliation(s)
| | | | | | - Antonio Alcaraz
- Laboratory of Molecular Biophysics
- Department of Physics
- 12071 Castellón
- Spain
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13
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García-Giménez E, Alcaraz A, Aguilella-Arzo M, Aguilella VM. Selectivity of Protein Ion Channels and the Role of Buried Charges. Analytical Solutions, Numerical Calculations, and MD Simulations. J Phys Chem B 2015; 119:8475-9. [PMID: 26091047 DOI: 10.1021/acs.jpcb.5b03547] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The preference of large protein ion channels for cations or anions is mainly determined by the electrostatic interactions of mobile ions with charged residues of the protein. Here we discuss the widely spread paradigm that the charges determining the channel selectivity are only those that can be considered solvent-accessible because of their location near the permeation pathways of ions and water molecules. Theoretical predictions for the electric potential and average ion densities inside the pore are presented using several approaches of increasing resolution: from analytical and numerical solutions of electrostatic equations in a model channel up to all-atom molecular dynamics simulations and continuum electrostatic calculations performed in a particular biological channel, the bacterial porin OmpF. The results highlight the role of protein dieletric properties and the importance of the initial choice of the residue ionization states in the understanding of the molecular basis of large channel selectivity irrespective of the level of resolution of the computational approach used.
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Affiliation(s)
- Elena García-Giménez
- Department of Physics. Laboratory of Molecular Biophysics, Universitat Jaume I, 12080 Castellón, Spain
| | - Antonio Alcaraz
- Department of Physics. Laboratory of Molecular Biophysics, Universitat Jaume I, 12080 Castellón, Spain
| | - Marcel Aguilella-Arzo
- Department of Physics. Laboratory of Molecular Biophysics, Universitat Jaume I, 12080 Castellón, Spain
| | - Vicente M Aguilella
- Department of Physics. Laboratory of Molecular Biophysics, Universitat Jaume I, 12080 Castellón, Spain
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14
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Kumar A, Rai LC. Proteomic and biochemical basis for enhanced growth yield of Enterobacter sp. LCR1 on insoluble phosphate medium. Microbiol Res 2015; 170:195-204. [DOI: 10.1016/j.micres.2014.06.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2013] [Revised: 06/24/2014] [Accepted: 06/30/2014] [Indexed: 10/25/2022]
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15
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Alcaraz A, Queralt-Martín M, Verdiá-Báguena C, Aguilella VM, Mafé S. Entropy-enthalpy compensation at the single protein level: pH sensing in the bacterial channel OmpF. NANOSCALE 2014; 6:15210-15215. [PMID: 25375963 DOI: 10.1039/c4nr03811h] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The pH sensing mechanism of the OmpF channel operates via ligand modification: increasing acidity induces the replacement of cations with protons in critical binding sites decreasing the channel conductance. Aside from the change in enthalpy associated with the binding, there is also a change in the microscopic arrangements of ligands, receptors and the surrounding solvent. We show that the pH-modulation of the single channel conduction involves small free energy changes because large enthalpic and entropic contributions change in opposite ways, demonstrating an approximate enthalpy-entropy compensation for different salts and concentrations.
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Affiliation(s)
- Antonio Alcaraz
- Department of Physics, Laboratory of Molecular Biophysics, University Jaume I, E-12080 Castellón, Spain.
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16
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Dhakshnamoorthy B, Ziervogel BK, Blachowicz L, Roux B. A structural study of ion permeation in OmpF porin from anomalous X-ray diffraction and molecular dynamics simulations. J Am Chem Soc 2014; 135:16561-8. [PMID: 24106986 DOI: 10.1021/ja407783a] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
OmpF, a multiionic porin from Escherichia coli, is a useful protypical model system for addressing general questions about electrostatic interactions in the confinement of an aqueous molecular pore. Here, favorable anion locations in the OmpF pore were mapped by anomalous X-ray scattering of Br(–) ions from four different crystal structures and compared with Mg(2+) sites and Rb(+) sites from a previous anomalous diffraction study to provide a complete picture of cation and anion transfer paths along the OmpF channel. By comparing structures with various crystallization conditions, we find that anions bind in discrete clusters along the entire length of the OmpF pore, whereas cations find conserved binding sites with the extracellular, surface-exposed loops. Results from molecular dynamics simulations are consistent with the experimental data and help highlight the critical residues that preferentially contact either cations or anions during permeation. Analysis of these results provides new insights into the molecular mechanisms that determine ion selectivity in OmpF porin.
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Affiliation(s)
- Balasundaresan Dhakshnamoorthy
- Department of Biochemistry and Molecular Biology, Gordon Center for Integrative Science, University of Chicago Chicago, IL 60637, USA
| | - Brigitte K Ziervogel
- Department of Biochemistry and Molecular Biology, Gordon Center for Integrative Science, University of Chicago Chicago, IL 60637, USA
| | - Lydia Blachowicz
- Department of Biochemistry and Molecular Biology, Gordon Center for Integrative Science, University of Chicago Chicago, IL 60637, USA
| | - Benoît Roux
- Department of Biochemistry and Molecular Biology, Gordon Center for Integrative Science, University of Chicago Chicago, IL 60637, USA
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17
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Queralt-Martín M, Verdiá-Báguena C, Aguilella VM, Alcaraz A. Electrostatic interactions drive the nonsteric directional block of OmpF channel by La3+. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2013; 29:15320-15327. [PMID: 24256306 DOI: 10.1021/la402700m] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Ion channels regulate the transport of molecules and the electric signal transduction in living cells by means of complex and even highly sophisticated mechanisms. We focus here on the crucial role that polyvalent ions, well-known modulators of many biological nanosystems, play in ion channel function. In particular, we show that trace amounts of lanthanum are able to block the bacterial porin OmpF, a large biological pore of Escherichia coli wide enough to exchange antibiotics and other larger molecules. The underlying mechanism has a strong directional character: it is sensitive to the sign of the applied voltage and to the side of the blocker addition. We explore these channel features by combining planar lipid bilayer electrophysiology at the single channel level, site-directed mutagenesis, and inductively coupled plasma mass spectrometry (ICP-MS). In contrast to other well-described channel blockers, which seem to occlude the narrower part of the pore, we envisage a nonsteric mechanism based on electrostatic interactions.
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Affiliation(s)
- María Queralt-Martín
- Laboratory of Molecular Biophysics, Department of Physics, Universitat Jaume I , 12071 Castellón, Spain
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18
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Maffeo C, Bhattacharya S, Yoo J, Wells D, Aksimentiev A. Modeling and simulation of ion channels. Chem Rev 2012; 112:6250-84. [PMID: 23035940 PMCID: PMC3633640 DOI: 10.1021/cr3002609] [Citation(s) in RCA: 148] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- Christopher Maffeo
- Department of Physics, University of Illinois, 1110 W. Green St., Urbana, IL
| | - Swati Bhattacharya
- Department of Physics, University of Illinois, 1110 W. Green St., Urbana, IL
| | - Jejoong Yoo
- Department of Physics, University of Illinois, 1110 W. Green St., Urbana, IL
| | - David Wells
- Department of Physics, University of Illinois, 1110 W. Green St., Urbana, IL
| | - Aleksei Aksimentiev
- Department of Physics, University of Illinois, 1110 W. Green St., Urbana, IL
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19
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Alcaraz A, Queralt-Martín M, García-Giménez E, Aguilella VM. Increased salt concentration promotes competitive block of OmpF channel by protons. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1818:2777-82. [DOI: 10.1016/j.bbamem.2012.07.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/03/2012] [Revised: 07/02/2012] [Accepted: 07/03/2012] [Indexed: 10/28/2022]
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Divalent Metal Ion Transport across Large Biological Ion Channels and Their Effect on Conductance and Selectivity. Biochem Res Int 2012; 2012:245786. [PMID: 23008773 PMCID: PMC3449104 DOI: 10.1155/2012/245786] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2012] [Revised: 07/27/2012] [Accepted: 07/30/2012] [Indexed: 11/17/2022] Open
Abstract
Electrophysiological characterization of large protein channels, usually displaying multi-ionic transport and weak ion selectivity, is commonly performed at physiological conditions (moderate gradients of KCl solutions at decimolar concentrations buffered at neutral pH). We extend here the characterization of the OmpF porin, a wide channel of the outer membrane of E. coli, by studying the effect of salts of divalent cations on the transport properties of the channel. The regulation of divalent cations concentration is essential in cell metabolism and understanding their effects is of key importance, not only in the channels specifically designed to control their passage but also in other multiionic channels. In particular, in porin channels like OmpF, divalent cations modulate the efficiency of molecules having antimicrobial activity. Taking advantage of the fact that the OmpF channel atomic structure has been resolved both in water and in MgCl2 aqueous solutions, we analyze the single channel conductance and the channel selectivity inversion aiming to separate the role of the electrolyte itself, and the counterion accumulation induced by the protein channel charges and other factors (binding, steric effects, etc.) that being of minor importance in salts of monovalent cations become crucial in the case of divalent cations.
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21
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Balasubramaniam D, Arockiasamy A, Kumar PD, Sharma A, Krishnaswamy S. Asymmetric pore occupancy in crystal structure of OmpF porin from Salmonella typhi. J Struct Biol 2012; 178:233-44. [PMID: 22525817 DOI: 10.1016/j.jsb.2012.04.005] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2011] [Revised: 04/03/2012] [Accepted: 04/07/2012] [Indexed: 11/25/2022]
Abstract
OmpF is a major general diffusion porin of Salmonella typhi, a Gram-negative bacterium, which is an obligatory human pathogen causing typhoid. The structure of S. typhi Ty21a OmpF (PDB Id: 3NSG) determined at 2.8 Å resolution by X-ray crystallography shows a 16-stranded β-barrel with three β-barrel monomers associated to form a trimer. The packing observed in S. typhi Ty21a rfOmpF crystals has not been observed earlier in other porin structures. The variations seen in the loop regions provide a starting point for using the S. typhi OmpF for structure-based multi-valent vaccine design. Along one side of the S. typhi Ty21a OmpF pore there exists a staircase arrangement of basic residues (20R, 60R, 62K, 65R, 77R, 130R and 16K), which also contribute, to the electrostatic potential in the pore. This structure suggests the presence of asymmetric electrostatics in the porin oligomer. Moreover, antibiotic translocation, permeability and reduced uptake in the case of mutants can be understood based on the structure paving the way for designing new antibiotics.
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Affiliation(s)
- D Balasubramaniam
- Department of Genetic Engineering, School of Biotechnology, Madurai Kamaraj University, Madurai 625 021, India
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22
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Queralt-Martín M, García-Giménez E, Mafé S, Alcaraz A. Divalent cations reduce the pH sensitivity of OmpF channel inducing the pKashift of key acidic residues. Phys Chem Chem Phys 2011; 13:563-9. [DOI: 10.1039/c0cp01325k] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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23
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Aguilella VM, Queralt-Martín M, Aguilella-Arzo M, Alcaraz A. Insights on the permeability of wide protein channels: measurement and interpretation of ion selectivity. Integr Biol (Camb) 2010; 3:159-72. [PMID: 21132209 DOI: 10.1039/c0ib00048e] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Ion channels are hollow proteins that have evolved to exhibit discrimination between charged solutes. This property, known as ion selectivity is critical for several biological functions. By using the bacterial porin OmpF as a model system of wide protein channels, we demonstrate that significant insights can be gained when selectivity measurements are combined with electrodiffusion continuum models and simulations based on the atomic structure. A correct interpretation of the mechanisms ruling the many sources of channel discrimination is a first, indispensable step for the understanding of the controlled movement of ions into or out of cells characteristic of many physiological processes. We conclude that the scattered information gathered from several independent approaches should be appropriately merged to provide a unified and coherent picture of the channel selectivity.
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Affiliation(s)
- Vicente M Aguilella
- Dept. Physics, Lab. Molecular Biophysics, Universitat Jaume I, 12080 Castellón, Spain.
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García-Giménez E, López ML, Aguilella VM, Alcaraz A. Linearity, saturation and blocking in a large multiionic channel: divalent cation modulation of the OmpF porin conductance. Biochem Biophys Res Commun 2010; 404:330-4. [PMID: 21134352 DOI: 10.1016/j.bbrc.2010.11.118] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2010] [Accepted: 11/27/2010] [Indexed: 11/16/2022]
Abstract
Measurement of unitary conductance is a fundamental step in the characterization of a protein ion channel permeabilizing a membrane. We study here the effect of salts of divalent cations on the OmpF channel conductance with a particular emphasis in dissecting the role of the electrolyte itself, the role of the counterion accumulation induced by the protein channel charges and other effects not found in salts of monovalent cations. We show that current saturation and blocking are not exclusive properties of narrow (single-file) ion channels but may be observed in large, multiionic channels like bacterial porins. Single-channel conductance measurements performed over a wide range of salt concentrations (up to 3 M) combined with continuum electrodiffusion calculations demonstrate that current saturation cannot be simply ascribed to ion interaction with protein channel residues.
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Affiliation(s)
- Elena García-Giménez
- Laboratory of Molecular Biophysics, Department of Physics, Universitat Jaume I, Av. Sos Baynat s/n, 12080 Castellón, Spain
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López ML, García-Giménez E, Aguilella VM, Alcaraz A. Critical assessment of OmpF channel selectivity: merging information from different experimental protocols. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2010; 22:454106. [PMID: 21339594 DOI: 10.1088/0953-8984/22/45/454106] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The ion selectivity of a channel can be quantified in several ways by using different experimental protocols. A wide, mesoscopic channel, the OmpF porin of the outer membrane of E. coli, serves as a case study for comparing and analysing several measures of the channel cation-anion permeability in chlorides of alkali metals (LiCl, NaCl, KCl, CsCl). We show how different insights can be gained and integrated to rationalize the global image of channel selectivity. To this end, reversal potential, channel conductance and bi-ionic potential (two different salts with a common anion on each side of the channel but with the same concentration) experiments are discussed in light of an electrodiffusion model based on the Poisson-Nernst-Planck formalism. Measurements and calculations based on the atomic crystal structure of the channel show that each protocol displays a particular balance between the different sources of selectivity.
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Affiliation(s)
- M L López
- Department of Physics, Laboratory of Molecular Biophysics, Universitat Jaume I, Avenida Sos Baynat s/n, 12080 Castellón, Spain
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26
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Faraudo J, Calero C, Aguilella-Arzo M. Ionic partition and transport in multi-ionic channels: a molecular dynamics simulation study of the OmpF bacterial porin. Biophys J 2010; 99:2107-15. [PMID: 20923644 PMCID: PMC3042589 DOI: 10.1016/j.bpj.2010.07.058] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2010] [Revised: 07/29/2010] [Accepted: 07/30/2010] [Indexed: 11/15/2022] Open
Abstract
We performed all-atom molecular dynamics simulations studying the partition of ions and the ionic current through the bacterial porin OmpF and two selected mutants. The study is motivated by new, interesting experimental findings concerning their selectivity and conductance behavior at neutral pH. The mutations considered here are designed to study the effect of removal of negative charges present in the constriction zone of the wild-type OmpF channel (which contains, on one side, a cluster with three positive residues, and on the other side, two negatively charged residues). Our results show that these mutations induce an exclusion of cations from the constriction zone of the channel, substantially reducing the flow of cations. In fact, the partition of ions inside the mutant channels is strongly inhomogeneous, with regions containing an excess of cations and regions containing an excess of anions. Interestingly, the overall number of cations inside the channel is larger than the number of anions, this excess being different for each protein channel. We found that the differences in ionic charge inside these channels are justified by the differences in electric charge between the wild-type OmpF and the mutants, following an electroneutral balance.
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Affiliation(s)
- Jordi Faraudo
- Institut de Ciència de Materials de Barcelona, Campus de la Universitat Autònoma de Barcelona, Bellaterra, Spain
| | - Carles Calero
- Institut de Ciència de Materials de Barcelona, Campus de la Universitat Autònoma de Barcelona, Bellaterra, Spain
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The ionization state of D37 in E. coli porin OmpF and the nature of conductance fluctuations in D37 mutants. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2010; 39:1563-71. [DOI: 10.1007/s00249-010-0613-z] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/18/2010] [Revised: 05/10/2010] [Accepted: 05/12/2010] [Indexed: 10/19/2022]
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Diffusion, exclusion, and specific binding in a large channel: a study of OmpF selectivity inversion. Biophys J 2010; 96:56-66. [PMID: 19134471 DOI: 10.1016/j.bpj.2008.09.024] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2008] [Accepted: 09/26/2008] [Indexed: 11/20/2022] Open
Abstract
We find that moderate cationic selectivity of the general bacterial porin OmpF in sodium and potassium chloride solutions is inversed to anionic selectivity in concentrated solutions of barium, calcium, nickel, and magnesium chlorides. To understand the origin of this phenomenon, we consider several factors, which include the binding of divalent cations, electrostatic and steric exclusion of differently charged and differently sized ions, size-dependent hydrodynamic hindrance, electrokinetic effects, and significant "anionic" diffusion potential for bulk solutions of chlorides of divalent cations. Though all these factors contribute to the measured selectivity of this large channel, the observed selectivity inversion is mostly due to the following two. First, binding divalent cations compensates, or even slightly overcompensates, for the negative charge of the OmpF protein, which is known to be the main cause of cationic selectivity in sodium and potassium chloride solutions. Second, the higher anionic (versus cationic) transport rate expected for bulk solutions of chloride salts of divalent cations is the leading cause of the measured anionic selectivity of the channel. Interestingly, at high concentrations the binding of cations does not show any pronounced specificity within the divalent series because the reversal potentials measured in the series correlate well with the corresponding bulk diffusion potentials. Thus our study shows that, in contrast to the highly selective channels of neurophysiology that employ mostly the exclusion mechanism, quite different factors account for the selectivity of large channels. The elucidation of these factors is essential for understanding large channel selectivity and its regulation in vivo.
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García-Giménez E, Alcaraz A, Aguilella VM. Overcharging below the nanoscale: multivalent cations reverse the ion selectivity of a biological channel. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2010; 81:021912. [PMID: 20365600 DOI: 10.1103/physreve.81.021912] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2009] [Revised: 12/14/2009] [Indexed: 05/29/2023]
Abstract
We report charge inversion within a nanoscopic biological protein ion channel in salts of multivalent ions. The presence of positive divalent and trivalent counterions reverses the cationic selectivity of the OmpF channel, a general diffusion porin located in the outer membrane of E. coli. We discuss the conditions under which charge inversion can be inferred from the change in sign of the measured quantity, the channel zero current potential. By comparing experimental results in protein channels whose charge has been modified after site-directed mutagenesis, the predictions of current theories of charge inversion are critically examined. It is emphasized that charge inversion does not necessarily increase with the bare surface charge density of the interface and that even this concept of surface charge density may become meaningless in some biological ion channels. Thus, any theory based on electrostatic correlations or chemical binding should explicitly take into account the particular structure of the charged interface.
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Affiliation(s)
- Elena García-Giménez
- Department of Physics, Laboratory of Molecular Biophysics, University Jaume I, Avenida Sos Baynat, s/n 12080 Castellón, Spain
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Pezeshki S, Chimerel C, Bessonov AN, Winterhalter M, Kleinekathöfer U. Understanding ion conductance on a molecular level: an all-atom modeling of the bacterial porin OmpF. Biophys J 2009; 97:1898-906. [PMID: 19804720 PMCID: PMC2756365 DOI: 10.1016/j.bpj.2009.07.018] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2008] [Revised: 07/08/2009] [Accepted: 07/14/2009] [Indexed: 10/20/2022] Open
Abstract
All-atom molecular dynamics simulations of the ion current through OmpF, the major porin in the outer membrane of Escherichia coli, were performed. Starting from the crystal structure, the all-atom modeling allows us to calculate a parameter-free ion conductance in semiquantitative agreement with experiment. Discrepancies between modeling and experiment occur, e.g., at salt concentrations above 1 M KCl or at high temperatures. At lower salt concentrations, the ions have separate pathways along the channel surface. The constriction zone in the channel contains, on one side, a series of positively charges (R42, R82, R132), and on the opposite side, two negatively charged residues (D113, E117). Mutations generated in the constriction zone by removing cationic residues enhance the otherwise small cation selectivity, whereas removing the anionic residues reverses the selectivity. Reduction of the negatively charged residues decreases the conductance by half, whereas cationic residues enhance the conductance. Experiments on mutants confirm the results of the molecular-level simulations.
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31
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López ML, Aguilella-Arzo M, Aguilella VM, Alcaraz A. Ion Selectivity of a Biological Channel at High Concentration Ratio: Insights on Small Ion Diffusion and Binding. J Phys Chem B 2009; 113:8745-51. [DOI: 10.1021/jp902267g] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- M. Lidón López
- Department of Physics, Laboratory of Molecular Biophysics, University Jaume I, Av. Sos Baynat, s/n, 12080 Castellón, Spain
| | - Marcel Aguilella-Arzo
- Department of Physics, Laboratory of Molecular Biophysics, University Jaume I, Av. Sos Baynat, s/n, 12080 Castellón, Spain
| | - Vicente M. Aguilella
- Department of Physics, Laboratory of Molecular Biophysics, University Jaume I, Av. Sos Baynat, s/n, 12080 Castellón, Spain
| | - Antonio Alcaraz
- Department of Physics, Laboratory of Molecular Biophysics, University Jaume I, Av. Sos Baynat, s/n, 12080 Castellón, Spain
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Aguilella-Arzo M, Andrio A, Aguilella VM, Alcaraz A. Dielectric saturation of water in a membrane protein channel. Phys Chem Chem Phys 2009; 11:358-65. [DOI: 10.1039/b812775a] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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33
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Abstract
We studied the current rectification properties and selectivity of class 1 porin (PorA) from Neisseria meningitidis (strain H44/76 Delta 3 Delta 4) reconstituted in planar lipid membranes varying salt concentrations and pH. PorA channel shows voltage gating with a characteristic time remarkably longer than other porins. Its current-voltage asymmetry, evaluated as the current rectification ratio, changes nonmonotonically with salt concentration. Interestingly, it reaches its maximum value at physiological concentration. Porin selectivity, quantified by reversal potential measurements, is also significantly asymmetric. Depending on the direction of the salt gradient, the channel becomes more or less selective (10:1 vs. 5:1 Na(+)/Cl(-)). Besides, the reversal potential measurements suggest that porin inserts directionally following the concentration gradient. Measurements over a wide range of pH show that although PorA is strongly cation selective at pH >6, its selectivity gradually changes to anionic in an acidic medium (pH < 4). We show that a continuum electrodiffusion model quantitatively accounts for conductance and reversal potential measurements at positive and negative applied voltages.
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Miedema H, Vrouenraets M, Wierenga J, Meijberg W, Robillard G, Eisenberg B. A biological porin engineered into a molecular, nanofluidic diode. NANO LETTERS 2007; 7:2886-91. [PMID: 17691852 DOI: 10.1021/nl0716808] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
We changed the nonrectifying biological porin OmpF into a nanofluidic diode. To that end, we engineered a pore that possesses two spatially separated selectivity filters of opposite charge where either cations or anions accumulate. The observed current inhibition under applied reverse bias voltage reflects, we believe, the creation of a zone depleted of charge carriers, in a sense very similar to what happens at the np junction of a semiconductor device.
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Affiliation(s)
- Henk Miedema
- Department of Molecular Biophysics and Physiology, Rush University Medical Center, 1750 West Harrison Street, Suite 1291, Chicago, Illinois 60612, USA.
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