pH regulates cation selectivity of poly-(R)-3-hydroxybutyrate/polyphosphate channels from E. coli in planar lipid bilayers

Biochemistry
S Das, Rosetta N Reusch

Abstract

Poly-(R)-3-hydroxybutyrate/polyphosphate (PHB/polyP) complexes, whether isolated from the plasma membranes of bacteria or prepared from the synthetic polymers, form ion channels in planar lipid bilayers that are highly selective for Ca(2+) over Na(+) at physiological pH. This preference for divalent over monovalent cations is attributed to a high density of negative charge along the polyP backbone and the higher binding energies of divalent cations. Here we modify the charge density of polyP by varying the pH, and observe the effect on cation selectivity. PHB/polyP complexes, isolated from E. coli, were incorporated into planar lipid bilayers, and unitary current-voltage relations were determined as a function of pH. When Ca(2+) was the sole permeant cation, conductance diminished steadily from 97 +/- 6 pS at pH 7.4 to 47 +/- 3 pS at pH 5.5. However, in asymmetric solutions of Ca(2+) and Na(+), there was a moderate increase in conductance from 98 +/- 4 at pH 7.4 to 129 +/- 4 pS at pH 6.5, and a substantially larger increase to 178 +/- 6 pS at pH 5.6, signifying an increase in Na(+) permeability or disorganization of channel structure. Reversal potentials point to a sharp decrease in preference for Ca(2+) over Na(+) over a relat...Continue Reading

Citations

Mar 17, 2004·Biochemical and Biophysical Research Communications·E Zakharian, R N Reusch
Mar 16, 2007·Proceedings of the National Academy of Sciences of the United States of America·Alexander NegodaRosetta N Reusch
Apr 7, 2015·Mikrobiologiia·I V Shemarova, V P Nesterov
Oct 8, 2004·Molecular Microbiology·Delfina C Dominguez
Nov 20, 2012·Chemistry & Biodiversity·Rosetta N Reusch
Sep 1, 2004·Biochemical and Biophysical Research Communications·E Zakharian, R N Reusch
Feb 13, 2009·Biochimica Et Biophysica Acta·Alexander NegodaRosetta N Reusch
Mar 18, 2008·Biochimica Et Biophysica Acta·Riffat NaseemAnthony K Campbell
Apr 7, 2005·Zhurnal evoliutsionnoĭ biokhimii i fiziologii·I V Shemarova, V P Nesterov

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