Abstract
The potassium channel from Streptomyces lividans (KcsA) is an integral membrane protein with sequence similarity to all known potassium channels, particularly in the selectivity filter region. A recently proposed model for ion channels containing either n or single-file ions in their selectivity filters [P. H. Nelson, J. Chem. Phys. 177, 11396 (2002)] is applied to published KcsA channel permeation data that exhibit a high-affinity process at low concentrations and a low-affinity process at high concentrations [M. LeMasurier et al., J. Gen. Physiol. 118, 303 (2001)]. The kinetic model is shown to provide a reasonable first-order explanation for both the high- and low-concentration permeation modes observed experimentally. The low-concentration mode has a 200-mV dissociation constant of and a conductance of 88 pS. The high-concentration mode has a 200-mV dissociation constant of and a conductance of 500 pS. Based on the permeation model, and x-ray analysis [J. H. Morais-Cabral et al., Nature (London) 414, 37 (2001)], it is suggested that the experimentally observed permeation modes correspond to an mechanism at high concentrations and an mechanism at low concentrations. The ratio of the electrical dissociation distances for the high- and low-concentration modes is 3:2, also consistent with the proposed and modes. Model predictions for channels that exhibit asymmetric current-voltage curves are presented, and further validation of the kinetic model via molecular simulation and experiment is discussed. The qualitatively distinct characteristics exhibited experimentally by and ions at concentration can also be explained using the model, but more extensive experimental tests are required for quantitative validation of the model predictions.
- Received 16 February 2003
DOI:https://doi.org/10.1103/PhysRevE.68.061908
©2003 American Physical Society