Beta-Barrel Channel Response to High Electric Fields: Functional Gating or Reversible Denaturation?

Abstract

Ion channels exhibit gating behavior, fluctuating between open and closed states, with the transmembrane voltage serving as one of the essential regulators of this process. Voltage gating is a fundamental functional aspect underlying the regulation of ion-selective, mostly α-helical, channels primarily found in excitable cell membranes. In contrast, there exists another group of larger, and less selective, β-barrel channels of a different origin, which are not directly associated with cell excitability. Remarkably, these channels can also undergo closing, or “gating”, induced by sufficiently strong electric fields. Once the field is removed, the channels reopen, preserving a memory of the gating process. In this study, we explored the hypothesis that the voltage-induced closure of the β-barrel channels can be seen as a form of reversible protein denaturation by the high electric fields applied in model membranes experiments—typically exceeding twenty million volts per meter—rather than a manifestation of functional gating. Here, we focused on the bacterial outer membrane channel OmpF reconstituted into planar lipid bilayers and analyzed various characteristics of the closing-opening process that support this idea. Specifically, we considered the nearly symmetric response to voltages of both polarities, the presence of multiple closed states, the stabilization of the open conformation in channel clusters, the long-term gating memory, and the Hofmeister effects in closing kinetics. Furthermore, we contemplate the evolutionary aspect of the phenomenon, proposing that the field-induced denaturation of membrane proteins might have served as a starting point for their development into amazing molecular machines such as voltage-gated channels of nerve and muscle cells.

The Effect of Lipopolysaccharides on the Electrostatic Properties of Gram‐Negative General Porins from Enterobacteriaceae

“…Future simulations with an external electric field might verify if the excess calcium is enough to give a change in selectivity, as shown in electrophysiology using a symmetric bilayer [29,30,61] . We know that an external electric field can induce pore gating, as observed experimentally at voltages as low as 200 mV [62] . In simulations, however, we can reach up to 1 V, resulting in few observable gating events on the microsecond timescale, particularly with mutants [63] .…”

“…[29,30,61] We know that an external electric field can induce pore gating, as observed experimentally at voltages as low as 200 mV. [62] In simulations, however, we can reach up to 1 V, resulting in few observable gating events on the microsecond timescale, particularly with mutants. [63] Ultimately, only simulations employing an external electric field combined with enhanced sampling techniques may elucidate the gating mechanism at low voltages and determine whether it is influenced by the presence of divalent cations.…”