Control of rectification and permeation by residues in two distinct domains in an inward rectifier K+ channel.
Inwardly rectifying K+ channels conduct more inward than outward current as a result of voltage-dependent block of the channel pore by intracellular Mg2+ and polyamines. We investigated the molecular mechanism and structural determinants of inward rectification and ion permeation in a strongly rectifying channel, IRK1. Block by Mg2+ and polyamines is found not to conform to one-to-one binding, suggesting that a channel pore can accommodate more than one blocking particle. A negatively charged amino acid in the hydrophilic C-terminal domain is found to be critical for both inward rectification and ion permeation. This residue and a negatively charged residue in the putative second transmembrane segment (M2) contribute independently to high affinity binding of Mg2+ and polyamines. Mutation of this residue also induces Mg(2+)- and polyamine-independent inward rectification and dramatically alters single-channel behavior. We propose that the hydrophilic C-terminal domain comprises part of the channel pore and that involvement of both hydrophilic and hydrophobic domains in pore lining may provide a molecular basis for the multi-ion, long-pore nature of inwardly rectifying K+ channels.
Yang
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Howard Hughes Medical Institute, Department of Physiology and Biochemistry, University of California, San Francisco 94143, USA.
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D000596:Amino Acids / Q000737:chemistry; D000818:Animals; D004553:Electric Conductivity; D004563:Electrochemistry; D005260:Female; D008274:Magnesium / Q000378:metabolism / Q000494:pharmacology; D016254:Mutagenesis, Insertional; D016297:Mutagenesis, Site-Directed; D009865:Oocytes / Q000378:metabolism; D011073:Polyamines / Q000378:metabolism / Q000494:pharmacology; D016133:Polymerase Chain Reaction; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D013095:Spermidine / Q000378:metabolism / Q000494:pharmacology; D013329:Structure-Activity Relationship; D013816:Thermodynamics; D014982:Xenopus laevis
D000596:Amino Acids; D011073:Polyamines; D015221:Potassium Channels; D008274:Magnesium; D011188:Potassium; D013095:Spermidine