Effect of stochastic gating on channel-facilitated transport of non-interacting and strongly repelling solutes

Theoretical insights into mechanisms of channel-facilitated molecular transport in the presence of stochastic gating

Molecular motion through pores plays a crucial role in various natural and industrial processes. One of the most fascinating features of biological channel-facilitated transport is a stochastic gating process, when the channels dynamically fluctuate between several conformations during the translocation. Although this phenomenon has been intensively investigated, many properties of translocation in a dynamically changing environment remain not well understood microscopically. We developed a discrete-state stochastic framework to analyze the molecular mechanisms of transport processes with stochastic gating by explicitly calculating molecular fluxes through the pores. Two scenarios are specifically investigated: (1) symmetry preserving stochastic gating with free-energy changes and (2) stochastic gating with symmetry changes but without modifications in the overall particle-pore interactions. It is found that stochastic gating can either accelerate or slow down the molecular translocation depending on the specific parameters of the system. We argue that biological systems might optimize their performance by utilizing conformational fluctuations of channels. Our theoretical analysis clarifies physical-chemical aspects of the molecular mechanisms of transport with stochastic gating.

Effect of stochastic gating on the flux through a membrane channel: a steady-state approach

This paper deals with the effect of stochastic gating on the flux of solute molecules through a membrane channel. According to the conventional approach, this flux is given by the product of the flux through the open channel and the probability of finding the channel in the open state. Recently we derived an expression for the flux through a stochastically gated channel (Berezhkovskii and Bezrukov 2017 J. Chem. Phys. 147 084109) that showed that the conventional approach may underestimate the flux at fast gating by orders of magnitude. The present work proposes a novel approach to the problem: while our initial derivation of the expression for the flux focuses on the molecule propagator in the channel, here we treat the problem by considering the steady-state flux through an ensemble of identical stochastically gated channels. We show now that the effect of gating on the flux is independent of the gate position, i.e. whether the gate is located at the channel entrance or exit.

Stochastic Gating as a Novel Mechanism for Channel Selectivity

An ideal channel, responsible for metabolite fluxes in and out of the cells and cellular compartments, is supposed to be selective for a particular set of molecules only. However, such a channel has to be wide enough to accommodate relatively large metabolites, and, therefore, it allows passage of smaller solutes, for example, sodium, potassium, and chloride ions, thus compromising membrane's barrier function. Here we show that stochastic gating is able to provide a mechanism for the selectivity of wide channels in favor of large metabolites. Specifically, applying our recent theory of the stochastic gating effect on channel-facilitated transport, we demonstrate that under certain conditions gating hinders translocation of fast-diffusing small solutes to a significantly higher degree than that of large solutes that diffuse much slower. We hypothesize that this can be used by Nature to minimize the shunting effect of wide channels with respect to small solutes.