Channel-facilitated molecular transport across membranes: attraction, repulsion, and asymmetry

Transport of molecules across membrane channels is investigated theoretically using exactly solvable discrete stochastic site-binding models. It is shown that the interaction potential between molecules and the channel has a strong effect on translocation dynamics. The presence of attractive binding sites in the pore accelerates the particle current for small concentrations outside the membrane, while for large concentrations, surprisingly, repulsive binding sites yield the most optimal transport. In addition, the asymmetry of the interaction potential also strongly influences the channel transport. The mechanism underlying these phenomena is discussed using the details of particle dynamics at the binding sites.