title: The molecular basis of K+ exclusion by the Escherichia coli ammonium channel AmtB.
abstract: 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.
authors.affiliation: Division of Biological Sciences, University of California San Diego, La Jolla, California 92093-0374. Electronic address: jahall@ucsd.edu.
authors.forename: Jason A
authors.initials: JA
authors.lastname: Hall
authors.affiliation: Department of Microbiology and Immunology, Indiana University School of Medicine, Indianapolis, Indiana 46202-5120.
authors.forename: Dalai
authors.initials: D
authors.lastname: Yan
mesh_terms: D001692:Biological Transport; D027682:Cation Transport Proteins / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007477:Ions; D008564:Membrane Potentials; D009154:Mutation; D011188:Potassium / Q000378:metabolism*; D011487:Protein Conformation; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: C111096:AmtB protein, E coli; D027682:Cation Transport Proteins; D029968:Escherichia coli Proteins; D007477:Ions; D000644:Quaternary Ammonium Compounds; D011188:Potassium
keywords: Ammonium Transport; Amt Proteins; Escherichia coli; Ion Channels; Membrane Transport; Microbiology; Potassium Transport
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