New Views of Multi-Ion Channels

Thus, most site-directed mutagenesis data render it untenable to consider that two or more roughly equivalent high affinity sites govern selectivity in multi-ion pores. The papers by Dang and McCleskey and Kiss et al. respond to this challenge by showing that a model with a single high affinity site, flanked by two binding sites of lower affinity close to the pore entrances, can generate much of the classical multi-ion behavior. The sites need not interact, and the two flanking sites could arise from one of several mechanisms: a featureless charged vestibule, a dehydration step, or a specific weak binding site. The multi-ion pore remains a cornerstone of permeation theory, but the new theory features only a single high affinity site and no mutual repulsion. The high flux rate occurs because ions pause at the flanking sites and reequilibrate thermally, gaining enough energy to move over the next barrier