Analyzing the components of the free-energy landscape in a calcium selective ion channel by Widoms particle insertion method

D. Boda, Janhavi Giri, Douglas Henderson, Bob Eisenberg, Dirk Gillespie

Research output: Contribution to journalArticle

29 Citations (Scopus)

Abstract

The selectivity filter of the L-type calcium channel works as a Ca 2 binding site with a very large affinity for Ca2 versus Na+. Ca2 replaces half of the Na+ ions in the filter even when these ions are present in 1 M and 30 mM concentrations in the bath, respectively. The energetics of this strong selectivity is analyzed in this paper. We use Widoms particle insertion method to compute the space-dependent profiles of excess chemical potential in our grand canonical Monte Carlo simulations. These profiles define the free-energy landscape for the various ions. Following Gillespie [Biophys. J. 94, 1169 (2008)], the difference of the excess chemical potentials for the two competing ions defines the advantage that one of the ions has over the other in the competition for space in the crowded selectivity filter. These advantages depend on ionic bath concentrations: the ion that is present in the bath in larger quantity (Na +) has the number advantage which is balanced by the free-energy advantage of the other ion (Ca2). The excess chemical potentials are decomposed into hard sphere exclusion and electrostatic components. The electrostatic terms correspond to interactions with the mean electric field produced by ions and induced charges as well to ionic correlations beyond the mean field description. Dielectrics are needed to produce micromolar Ca 2 versus Na+ selectivity in the L-type channel. We study the behavior of these terms with changes in bath concentrations of ions, charges, and diameters of ions, as well as geometrical parameters such as radius of the pore and the dielectric constant of the protein. Ion selectivity in calcium binding proteins probably has a similar mechanism.

Original languageEnglish
Article number055102
JournalThe Journal of Chemical Physics
Volume134
Issue number5
DOIs
Publication statusPublished - Feb 7 2011

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Calcium Channels
Ion Channels
Free energy
calcium
insertion
free energy
Ions
Calcium
ions
selectivity
Baths
baths
Chemical potential
filters
Static Electricity
Electrostatics
electrostatics
proteins
ion charge
L-Type Calcium Channels

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry
  • Medicine(all)

Cite this

Analyzing the components of the free-energy landscape in a calcium selective ion channel by Widoms particle insertion method. / Boda, D.; Giri, Janhavi; Henderson, Douglas; Eisenberg, Bob; Gillespie, Dirk.

In: The Journal of Chemical Physics, Vol. 134, No. 5, 055102, 07.02.2011.

Research output: Contribution to journalArticle

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