The Molecular Basis of K+ Exclusion by the Escherichia coli Ammonium Channel AmtB

Members of the Amt family of channels mediate the transport of ammonium. The form of ammonium, NH3 or NH4+, carried by these proteins remains controversial, and the mechanism by which they select against K+ ions is unclear. We describe here a set of Escherichia coli AmtB proteins carrying mutations...

Full description

Saved in:
Bibliographic Details
Published in:The Journal of biological chemistry 2013-05, Vol.288 (20), p.14080-14086
Main Authors: Hall, Jason A., Yan, Dalai
Format: Article
Language:English
Subjects:
Ammonium Transport
Amt Proteins
Biological Transport
Cation Transport Proteins - metabolism
Cytoplasm - metabolism
Dose-Response Relationship, Drug
Escherichia coli
Escherichia coli - metabolism
Escherichia coli Proteins - metabolism
Hydrogen-Ion Concentration
Ion Channels
Ions
Membrane Biology
Membrane Potentials
Membrane Transport
Microbiology
Mutation
Potassium - metabolism
Potassium Transport
Protein Conformation
Quaternary Ammonium Compounds - metabolism
Substrate Specificity
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:Members of the Amt family of channels mediate the transport of ammonium. The form of ammonium, NH3 or NH4+, carried by these proteins remains controversial, and the mechanism by which they select against K+ ions is unclear. We describe here a set of Escherichia coli AmtB proteins carrying mutations at the conserved twin-histidine site within the conduction pore that have altered substrate specificity and now transport K+. Subsequent work established that AmtB-mediated K+ uptake occurred against a concentration gradient and was membrane potential-dependent. These findings indicate that the twin-histidine element serves as a filter to prevent K+ conduction and strongly support the notion that Amt proteins transport cations (NH4+ or, in mutant proteins, K+) rather than NH3 gas molecules through their conduction pores. Background: The Amt family of ammonium channels does not conduct K+. Results:E. coli AmtB variants carrying certain mutations in the conserved twin-histidine element transport K+ against a concentration gradient. Conclusion: The twin-histidine element functions as a filter that prevents K+ conduction. Significance: These findings provide insight into the transport mechanism of Amt channels and the ammonium species (NH3 or NH4+) that serves as their substrate.
ISSN:0021-9258
1083-351X
DOI:10.1074/jbc.M113.457952