Probing the Transport of Ionic Liquids in Aqueous Solution through Nanopores
ABSTRACT The temperature-dependent transport of the ionic liquid 1-butyl-3-methyl-imidazolium chloride (BMIM-Cl) in aqueous solution is studied theoretically and experimentally. Using molecular dynamics simulations and ion-conductance measurements, the transport is examined in bulk as well as through a biological nanopore, that is, OmpF and its mutant D113A. This investigation is motivated by the observation that aqueous solutions of BMIM-Cl drastically reduce the translocation speed of DNA or antibiotics through nanopores in electrophysiological measurements. This makes BMIM-Cl an interesting alternative salt to improve the time resolution. In line with previous investigations of simple salts, the size of the ions and their orientation adds another important degree of freedom to the ion transport, thereby slowing the transport through nanopores. An excellent agreement between theory and conductance measurements is obtained for wild type OmpF and a reasonable agreement for the mutant. Moreover, all-atom simulations allow an atomistic analysis revealing molecular details of the rate-limiting ion interactions with the channel.
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ABSTRACT: The TOM protein complex facilitates the transfer of nearly all mitochondrial preproteins across outer mitochondrial membranes. Here we characterized the effect of temperature on facilitated translocation of a mitochondrial presequence peptide pF1 beta. Ion current fluctuations analysis through single TOM channels revealed thermodynamic and kinetic parameters of substrate binding and allowed determining the energy profile of peptide translocation. The activation energy for the on-rate and off-rate of the presequence peptide into the TOM complex was symmetric with respect to the electric field and estimated to be about 15 and 22 kT per peptide. These values are above that expected for free diffusion of ions in water (6 kT) and reflect the stronger interaction in the channel. Both values are in the range for typical enzyme kinetics and suggest one process without involving large conformational changes within the channel protein.Journal of Physical Chemistry Letters 12/2012; 4(1):78-82. DOI:10.1021/jz301790h · 6.69 Impact Factor
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ABSTRACT: Single channel electrophysiological studies have been carried out to elucidate the underlying interactions during the translocation of polypeptides through protein channels. For this we used OmpF from the outer cell membrane of E. coli and arginine-based peptides of different charges, lengths and covalently linked polyethylene glycol as a model system. In order to reveal the fast kinetics of peptide binding, we performed a temperature scan. Together with the voltage-dependent single-channel conductance, we quantify peptide binding and translocation.Biophysics of Structure and Mechanism 12/2012; 42(5). DOI:10.1007/s00249-012-0885-6 · 2.47 Impact Factor
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ABSTRACT: The outer membrane porin OprP of Pseudomonas aeruginosa forms a highly specific phosphate selective channel. This channel is responsible for the high-affinity uptake of phosphate ions into the periplasmic space of the bacteria. A detailed investigation of the structure-function relationship of OprP is inevitable to decipher the anion and phosphate selectivity of this porin in particular and to broaden the present understanding of the ion selectivity of different channels. To this end we investigated the role of the central arginine of OprP, R133, in terms of its effects in selectivity and ion transport properties of the pore. Electrophysiological bilayer measurements and free-energy molecular dynamics simulations were carried out to probe the transport of different ions through various R133 mutants. For these mutants the change in phosphate binding specificity, ion conduction and anion selectivity was determined and compared to previous molecular dynamic calculations and electrophysiological measurements with wild-type OprP. Molecular analysis revealed a rather particular role of arginine 133 and its charge, while at the same time this residue together with the network of other residues, namely D94 and Y114, has the ability to dehydrate the permeating ion. These very specific features govern the ion selectivity of OprP.Biochemistry 07/2013; 52(33). DOI:10.1021/bi400522b · 3.19 Impact Factor