BPS2026 - Revisiting the mechanism of β-barrel channel gating: Salt-concentration effects, selectivity inversion, and an electrochemical gating hypothesis

Voltage-induced gating is a fundamental property exhibited by most β-barrel pores, by which they transition from an open state to one or several low-conducting states upon application of relatively high transmembrane potentials. Unlike flexible α-helical channels, the more rigid β-barrel structures lack a defined molecular mechanism for gating, with no single voltage sensor or large conformational change identified so far. Previous investigations tested how environmental factors such as solution pH and membrane composition modulate β-barrel channel gating. Here, we focus on the bacterial porin OmpF from E. coli as a model system for the β-barrel channel family to tackle the overlooked role of electrolyte concentration on voltage gating. We demonstrate a novel non-linear concentration dependence of OmpF gating kinetics and rationalize this behavior with a theoretical model based on Debye screening, modified to include a term accounting for non-linear high-concentration effects. Furthermore, we characterize the low-conductance states resulting from channel closure, observing that selectivity strikingly inverts from cationic to anionic. We also find that closed states exhibit wide variability in both conductance and selectivity values, indicating the existence of a multiplicity of low-conductance states rather than a single defined one. Based on this and previous data, we hypothesize that OmpF channel closure could be understood as an electrochemical gating process. An external voltage may induce subtle, collective reorganizations of residues, leading to localized surface dewetting at various points within the channel. Such critical alterations of the electrochemical gradient could interrupt the current through different pathways without requiring major structural changes or a physical narrowing. This hypothesis aligns with reported dependencies of voltage-gating on external stimuli and the lack of a defined closed-state structure, challenging conventional understanding, and providing new insights into β-barrel channel closure.