Ionic Coulomb blockade and anomalous mole fraction effect in NaChBac bacterial ion channels

• Main Authors: Kaufman, I. Kh, Fedorenko, O. A, Luchinsky, D. G, Gibby, W. A. T, McClintock, S. K. Roberts. P. V. E, Eisenberg, R. S
• Format: Journal Article
• Language: English
• Published: 08-12-2016
• Subjects: Physics - Biological Physics; Quantitative Biology - Cell Behavior; Quantitative Biology - Subcellular Processes
• DOI: 10.48550/arxiv.1612.02744

We report an experimental study of the influences of the fixed charge and
bulk ionic concentrations on the conduction of biological ion channels, and we
consider the results within the framework of the ionic Coulomb blockade model
of permeation and selectivity. Voltage clamp recordings were used to
investigate the Na$^+$/Ca$^{2+}$ anomalous mole fraction effect (AMFE)
exhibited by the bacterial sodium channel NaChBac and its mutants.
Site-directed mutagenesis was used to study the effect of either increasing or
decreasing the fixed charge in their selectivity filters for comparison with
the predictions of the Coulomb blockade model. The model was found to describe
well some aspects of the experimental (divalent blockade and AMFE) and
simulated (discrete multi-ion conduction and occupancy band) phenomena,
including a concentration-dependent shift of the Coulomb staircase. These
results substantially extend the understanding of ion channel selectivity and
may also be applicable to biomimetic nanopores with charged walls.