title: Rectified Proton Grotthuss Conduction Across a Long Water-Wire in the Test Nanotube of the Polytheonamide B Channel.
abstract: A hydrogen-bonded water-chain in a nanotube is highly proton conductive, and examining the proton flux under electric fields is crucial to understanding the one-dimensional Grotthuss conduction. Here, we exploited a nanotube-forming natural product, the peptide polytheonamide B (pTB), to examine proton conduction mechanisms at a single-molecule level. The pTB nanotube has a length of ∼40 Å that spans the membrane and a uniform inner diameter of 4 Å that holds a single-file water-chain. Single-channel proton currents were measured using planar lipid bilayers in various proton concentrations and membrane potentials (±400 mV). We found, surprisingly, that the current-voltage curves were asymmetric with symmetric proton concentrations in both solutions across the membrane (rectification). The proton flux from the C-terminal to the N-terminal end was 1.6 times higher than that from the opposite. At lower proton concentrations, the degree of rectification was attenuated, but with the addition of a pH-buffer (dichloroacetate) that supplies protons near the entrance, the rectification emerged. These results indicate that the permeation processes inside the pore generate the rectification, which is masked at low concentrations by the diffusion-limited access of protons to the pore entrance. The permeation processes were characterized by a discrete-state Markov model, in which hops of a proton followed by water-chain turnovers were implemented. The optimized model revealed that the water-chain turnover exhibited unusual voltage dependence, and the distinct voltage-dependencies of the forward and backward transition rates yielded the rectification. The pTB nanotube serves as a rectified proton conductor, and the design principles can be exploited for proton-conducting materials.
authors.affiliation: Department of Molecular Physiology and Biophysics, Faculty of Medical Sciences, University of Fukui , Fukui 910-1193, Japan.|Department of Anesthesiology and Reanimatology, Faculty of Medical Sciences, University of Fukui , Fukui 910-1193, Japan.
authors.forename: Yuka
authors.initials: Y
authors.lastname: Matsuki
authors.affiliation: Department of Molecular Physiology and Biophysics, Faculty of Medical Sciences, University of Fukui , Fukui 910-1193, Japan.
authors.forename: Masayuki
authors.initials: M
authors.lastname: Iwamoto
authors.affiliation: Department of Molecular Physiology and Biophysics, Faculty of Medical Sciences, University of Fukui , Fukui 910-1193, Japan.|Department of Anesthesiology and Reanimatology, Faculty of Medical Sciences, University of Fukui , Fukui 910-1193, Japan.
authors.forename: Kenichiro
authors.initials: K
authors.lastname: Mita
authors.affiliation: Department of Anesthesiology and Reanimatology, Faculty of Medical Sciences, University of Fukui , Fukui 910-1193, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Shigemi
authors.affiliation: Laboratory of Aquatic Natural Products Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo , Bunkyo-ku, Tokyo 113-8657, Japan.
authors.forename: Shigeki
authors.initials: S
authors.lastname: Matsunaga
authors.affiliation: Department of Molecular Physiology and Biophysics, Faculty of Medical Sciences, University of Fukui , Fukui 910-1193, Japan.
authors.forename: Shigetoshi
authors.initials: S
authors.lastname: Oiki
mesh_terms: D006863:Hydrogen-Ion Concentration; D047908:Intracellular Signaling Peptides and Proteins; D008051:Lipid Bilayers / Q000737:chemistry; D008958:Models, Molecular; D043942:Nanotubes; D011506:Proteins / Q000737:chemistry*; D011522:Protons; D014867:Water / Q000737:chemistry*
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D008051:Lipid Bilayers; D011506:Proteins; D011522:Protons; C111717:polytheonamide B; D014867:Water