Engineered Membranes and Transporters for Useful Devices

Cuppoletti, John; Malinowska, Danuta H.

doi:10.5772/22965

Cited by 1 publication

(4 citation statements)

References 19 publications

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“…The anticipated potassium ion conductances from the experiments of Cuppoletti et al − (obtained by scaling the measured proton conductance downward by a factor of 30) are 4.4 pS at 300 K and 8.8 pS at 360 K. As mentioned above, these K + conductance estimates are smaller than the K + data presented in refs and (roughly 24.5 pS at 300 K), and this is likely due to the different membrane phospholipids and solvent mixtures employed in the present study. The experiments in ref were performed with a 1 M concentration of KCl, and we estimate the maximum conductance at saturation to be 6.6 pS (see ref , p 367).…”

Section: Resultscontrasting

confidence: 48%

“…The present modeling study was motivated by the recent measurements of proton conduction through the gramicidin channel at temperatures approaching the boiling point of water − and other studies of the temperature-dependent transport of K + , and H + . In this initial study, we chose to model K + transport due to the severe difficulty in accurately representing the chemical aspects of proton migration.…”

Section: Discussionmentioning

confidence: 99%

“…The channel was embedded in 20 POPE lipid molecules that provide a single surrounding shell of bilayer molecules. The membrane/channel complex was then solvated with 698 TIP3P waters, 139 glycerols, and 4 KCl pairs with the VMD code, resulting in an ion concentration of roughly 0.3 M. The added glycerol is equivalent to a 50 wt % mixture in order to mimic the conditions in the experiments of Cuppoletti et al − Some simulations were also performed for a pure water bath using the same simulation protocol. The system was modeled with hexagonal periodic boundary conditions using the CHARMM27 force field, including the CHARMM27 lipid parameters (CMAP corrections were not applied).…”

Section: Methodsmentioning

confidence: 99%

“…Gramicidin selectively transports monovalent cations, with a conduction sequence H + > NH 4 + > Cs + > K + > Na + > Li + . Recent experiments have indicated that the gramicidin channel can maintain its conductance properties at elevated temperatures near the boiling point of water. − Cuppoletti et al measured a proton conductance of 133 pS (in 1 M HCl) for the gramicidin channel in a 3:1 POPS:POPE bilayer at 298 K with a surrounding solution of 50 wt % glycerol; the conductance at 368 K was measured to be roughly twice the value at 298 K (unpublished results). These results may potentially have fuel cell implications, with the environmentally friendly gramicidin replacing Nafion as the membrane material.…”

Section: Introductionmentioning

confidence: 99%

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Temperature Dependence of Gramicidin Channel Transport and Structure

Song

Beck

2013

J. Phys. Chem. C

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The gramicidin dipeptide is a small, cation-selective ion channel. Recent experiments have indicated that gramicidin can conduct ions at elevated temperatures. Since gramicidin is an efficient proton conductor, it is possible that this channel may have applications in fuel cell technology. In this study, we examine the temperature dependence of gramicidin A channel transport and structure with molecular dynamics simulations. In particular, the potentials of mean force (PMFs) for potassium ion motion through the channel are computed at five temperatures in the range 300−360 K. The channel displays a decrease in the free energy barrier height as the temperature increases. In addition, the enthalpic and entropic components of the free energy are computed, indicating a substantial enthalpy−entropy compensation and a positive entropy change when the ion enters the channel. The positive entropy change results from a reduction in fluctuations of ion interaction energies in the pore relative to those in the bulk solvent. The overall dimeric channel structure is maintained at 360 K for time scales up to 100 ns. In addition, higher temperatures affect the distributions of hydrogen bonds at the dimer interface, conformations of the N-terminal domain that may block the pore, channel bending angles, and distances between dimers. These findings may be related to the gating of the channel, although no complete dimer dissociation events were observed in the simulations.

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