Mechanisms Of Selective Transport Through Nano-channels: Theory Vs. Experiment

Abstract

Functioning of living cells requires selective molecular transport, which is provided by transport channels that are able to selectively transport certain molecular species while filtering others, even similar ones. Such channels can selectively transport their specific molecules in the presence of vast amounts of non-specific competition. In many biological channels, efficient and selective transport occurs without direct input of metabolic energy and without transitions from an ‘open’ to a ‘closed’ state during the transport event. Examples include selective permeability of porins and transport through the nuclear pore complex. Mechanisms of selectivity of such channels have inspired design of artificial selective nano-channels, which mimic the selective biological channels and are built upon the same principles(e.g [3]). Precise mechanisms of selective transport through such nano-channels are still unknown. I present a theoretical model to explain the of selectivity of transport through nano-channels, which contains only two essential ingredients: i) transient trapping of the cargoes inside the channel (e.g. due to binding inside the channel) ii) competition between the transported molecules for the limited space inside the channel [1,2]. The theory provides a mechanism for selectivity based on the differences in the kinetics of transport through the channel between different molecules. The theory explains how the specific molecules are able to filter out the non-specific competitors - and proposes a mechanism for sharp molecular discrimination. The theoretical predictions [1,2] account for previous experimental results [3] and have been verified in ongoing experiments. [1] A. Zilman et al. Efficiency, Selectivity and Robustness of Nucleo-cytoplasmic transport, PLoS Comp. Biol. (2007), e125. [2] A. Zilman, Effects of inter-particle interactions on selective transport in narrow channels, Biophys J (2008), to appear. [3] P. Kohli et al. (2004) Functionalized Nanotube Membranes with Single-Base Mismatch Selectivity, Science, 305, 984.