Interfacial effects break the canonical permeability-selectivity trade-off in biological nanopores.

Abstract

Hypothesis: Transport in membrane systems involves a classic trade-off between permeability (how many particles can pass through) and selectivity (the ability to sort specific particles) ruled by the pore size and the inner channel charges. By using interfacial effects from charges on the outer surface of the pore, it is possible to change the channel's conductive properties without altering its physical pore size. This suggests a new way to overcome the permeability-selectivity compromise in unexpected ways.

Experiments and theoretical analysis: We perform an exhaustive electrophysiological analysis of the conductive properties of two wide biological ion channels, the bacterial porin OmpF from E. coli and the mitochondrial Voltage Dependent Anion Channel (VDAC), paying attention to the role of membrane lipid charges in the interplay between permeability and selectivity. We examine this interplay using an equivalent circuit model based on the principle of ionic current independence and with numerical simulations derived from Poisson-Nernst-Planck equations based on 3D protein structures at atomic resolution.

Findings: We demonstrate that membrane and pore charges do not compensate for each other. Rather, they function as complementary interaction sites giving rise to unique transport characteristics that can enhance simultaneously both permeability and selectivity beyond the predicted upper limit. Traditionally, efforts have concentrated on functionalizing inner channel surfaces; however, our findings highlight how separately modifying outer channel surfaces can enable nanofluidic devices to overcome the permeability-selectivity trade-off.