Condensed Matter Physics, 2016, vol. 19, No. 1, 13802
DOI:10.5488/CMP.19.13802           arXiv:1603.02440

Title: Simulation study of a rectifying bipolar ion channel: Detailed model versus reduced model
Author(s):
  Z. Ható ( Department of Physical Chemistry, University of Pannonia, P. O. Box 158, Veszprem, H-8201, Hungary ) ,
  D. Boda ( Department of Physical Chemistry, University of Pannonia, P. O. Box 158, Veszprem, H-8201, Hungary ) ,
  D. Gillespie ( Department Molecular Biophysics and Physiology, Rush University Medical Center, Chicago, IL 60612, USA ) ,
  J. Vrabec ( University of Paderborn, Laboratory of Thermodynamics and Energy Technology, 100 Warburger St., 33098 Paderborn, Germany ) ,
  G. Rutkai ( University of Paderborn, Laboratory of Thermodynamics and Energy Technology, 100 Warburger St., 33098 Paderborn, Germany ) ,
  T. Kristóf ( Department of Physical Chemistry, University of Pannonia, P. O. Box 158, Veszprem, H-8201, Hungary )

We study a rectifying mutant of the OmpF porin ion channel using both all-atom and reduced models. The mutant was created by Miedema et al. [Nano Lett., 2007, 7, 2886] on the basis of the NP semiconductor diode, in which an NP junction is formed. The mutant contains a pore region with positive amino acids on the left-hand side and negative amino acids on the right-hand side. Experiments show that this mutant rectifies. Although we do not know the structure of this mutant, we can build an all-atom model for it on the basis of the structure of the wild type channel. Interestingly, molecular dynamics simulations for this all-atom model do not produce rectification. A reduced model that contains only the important degrees of freedom (the positive and negative amino acids and free ions in an implicit solvent), on the other hand, exhibits rectification. Our calculations for the reduced model (using the Nernst-Planck equation coupled to Local Equilibrium Monte Carlo simulations) reveal a rectification mechanism that is different from that seen for semiconductor diodes. The basic reason is that the ions are different in nature from electrons and holes (they do not recombine). We provide explanations for the failure of the all-atom model including the effect of all the other atoms in the system as a noise that inhibits the response of ions (that would be necessary for rectification) to the polarizing external field.

Key words: Monte Carlo, primitive model electrolytes, ion channel, selectivity
PACS: 87.16.Vy, 87.10.Tf, 05.10.Ln, 82.45.Gj, 61.20.Ja


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