Functional evidence for a supramolecular structure for the Streptomyces lividans potassium channel KcsA.
Here we present functional evidence for involvement of poly-(R)-3-hydroxybutyrate (PHB) and inorganic polyphosphate (polyP) in ion conduction and selection at the intracellular side of the Streptomyces lividans potassium channel, KcsA. At < or = 25 degrees C, KcsA forms channels in planar bilayers that display signal characteristics of PHB/polyP channels at the intracellular side; i.e., a preference for divalent Mg(2+) cations at pH 7.2, and a preference for monovalent K+ cations at pH 6.8. Between 25 and 26 degrees C, KcsA undergoes a transition to a new conformation in which the channel exhibits high selectivity for K+, regardless of solution pH. This suggests that basic residues of the C-terminal polypeptides have moved closer to the polyP end unit, reducing its negative charge. The data support a supramolecular structure for KcsA in which influx of ions is prevented by the selectivity pore, whereas efflux of K+ is governed by a conductive core of PHB/polyP in partnership with the C-terminal polypeptide strands.
Zakharian
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Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI 48824, USA.
Reusch
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D001426:Bacterial Proteins / Q000187:drug effects / Q000302:isolation & purification / Q000502:physiology*; D002413:Cations, Divalent / Q000494:pharmacology; D002712:Chlorides / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D008051:Lipid Bilayers; D008274:Magnesium / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000302:isolation & purification / Q000502:physiology*; D013302:Streptomyces / Q000502:physiology*; D013816:Thermodynamics
D001426:Bacterial Proteins; D002413:Cations, Divalent; D002712:Chlorides; D008051:Lipid Bilayers; D015221:Potassium Channels; C107790:prokaryotic potassium channel; D008274:Magnesium