PMID:21911483
| Citation |
Piasta, KN, Theobald, DL and Miller, C (2011) Potassium-selective block of barium permeation through single KcsA channels. J. Gen. Physiol. 138:421-36 |
|---|---|
| Abstract |
Ba(2+), a doubly charged analogue of K(+), specifically blocks K(+) channels by virtue of electrostatic stabilization in the permeation pathway. Ba(2+) block is used here as a tool to determine the equilibrium binding affinity for various monovalent cations at specific sites in the selectivity filter of a noninactivating mutant of KcsA. At high concentrations of external K(+), the block-time distribution is double exponential, marking at least two Ba(2+) sites in the selectivity filter, in accord with a Ba(2+)-containing crystal structure of KcsA. By analyzing block as a function of extracellular K(+), we determined the equilibrium dissociation constant of K(+) and of other monovalent cations at an extracellular site, presumably S1, to arrive at a selectivity sequence for binding at this site: Rb(+) (3 µM) > Cs(+) (23 µM) > K(+) (29 µM) > NH(4)(+) (440 µM) > Na(+) and Li(+) (>1 M). This represents an unusually high selectivity for K(+) over Na(+), with |ΔΔG(0)| of at least 7 kcal mol(-1). These results fit well with other kinetic measurements of selectivity as well as with the many crystal structures of KcsA in various ionic conditions. |
| Links |
PubMed PMC3182450 Online version:10.1085/jgp.201110684 |
| Keywords |
Bacterial Proteins/genetics; Bacterial Proteins/metabolism; Barium/metabolism; Binding Sites; Cell Membrane/physiology; Cesium; Dose-Response Relationship, Drug; Escherichia coli/genetics; Escherichia coli/metabolism; Gene Expression Regulation, Bacterial; Mutagenesis, Site-Directed; Mutation; Permeability; Potassium/metabolism; Potassium Channels, Voltage-Gated/genetics; Potassium Channels, Voltage-Gated/metabolism; Quaternary Ammonium Compounds; Rubidium |
| edit table |
Significance
You can help EcoliWiki by summarizing why this paper is useful
Useful Materials and Methods
You can help Ecoliwiki by describing the useful materials (strains, plasmids, antibodies, etc) described in this paper.
Annotations
<annotationlinks/>
EcoliWiki Links
Add links to pages that link here (e.g. gene, product, method pages)
See also
References
See Help:References for how to manage references in EcoliWiki.