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Can gramicidin ion channel affect the dipole potential of neighboring phospholipid headgroups?

Authors
  • Becucci, Lucia1
  • Guidelli, Rolando2
  • 1 Department of Chemistry "Ugo Schiff", Florence University, Via della Lastruccia 3, Sesto Fiorentino, Firenze, Italy. Electronic address: [email protected] , (Italy)
  • 2 Department of Chemistry "Ugo Schiff", Florence University, Via della Lastruccia 3, Sesto Fiorentino, Firenze, Italy. , (Italy)
Type
Published Article
Journal
Bioelectrochemistry (Amsterdam, Netherlands)
Publication Date
Dec 01, 2015
Volume
106
Issue
Pt B
Pages
343–352
Identifiers
DOI: 10.1016/j.bioelechem.2015.06.008
PMID: 26190793
Source
Medline
Keywords
License
Unknown

Abstract

The cyclic voltammetry behavior of a mercury-supported tethered bilayer lipid membrane (tBLM) incorporating gramicidin A was investigated in aqueous 0.1 M KCl at pH 6.8, 5.4 and 3. The distal leaflet of the lipid bilayer consisted of dioleoylphosphatidylcholine (DOPC), dioleoylphosphatidylserine (DOPS), dioleoylphosphatidic acid or a DOPC/cholesterol mixture. In passing from pH 6.8 to pH 3, the midpoint potential between the negative current peak, due to K(+) inflow into the spacer, and the positive current peak, due to K(+) ejection into the aqueous solution, shifts toward more positive potentials, while the separation between these two peaks decreases. This behavior is interpreted quantitatively on the basis of a model relying on tBLM structural features estimated independently in previous works. The only adjustable parameter is the rate constant for cation translocation across a potential energy barrier located in the hydrocarbon tail region. The behavior is ascribed to a dragging of the lipid headgroups adjacent to the gramicidin channel mouth toward the hydrocarbon tail region, with a resulting decrease in the negative charge of the DOPC phosphate group, or of the DOPS carboxyl group, with decreasing pH.

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