Effect of Interactions on Molecular Fluxes and Fluctuations in the Transport Across Membrane Channels

TL;DR

This paper presents a theoretical analysis of molecular transport through membrane channels using exactly solvable stochastic models, revealing how interactions and potential symmetry influence fluxes and fluctuations.

Contribution

It introduces a detailed stochastic model that accounts for interaction energies and potential asymmetry, providing new insights into optimizing molecular translocation.

Findings

Attractive sites maximize flux and fluctuations at low concentration gradients.

Repulsive interactions lead to higher fluxes at large concentration gradients.

Symmetry of interaction potentials affects the relationship between maximal flux and fluctuations.

Abstract

Transport of molecules across membrane channels is investigated theoretically using exactly solvable one-dimensional discrete-state stochastic models. An interaction between molecules and membrane pores is modeled via a set of binding sites with different energies. It is shown that the interaction potential strongly influences the particle currents as well as fluctuations in the number of translocated molecules. For small concentration gradients the attractive sites lead to largest currents and fluctuations, while the repulsive interactions yield the largest fluxes and dispersions for large concentration gradients. Interaction energies that lead to maximal currents and maximal fluctuations are the same only for locally symmetric potentials, while they differ for the locally asymmetric potentials. The conditions for the most optimal translocation transport with maximal current and minimal dispersion are discussed. It is argued that in this case the interaction strength is independent of local symmetry of the potential of mean forces. In addition, the effect of the global asymmetry of the interaction potential is investigated, and it is shown that it also strongly affects the particle translocation dynamics. These phenomena can be explained by analyzing the details of the particle entering and leaving the binding sites in the channel.