Interactions of Cations with the Cytoplasmic Pores of Inward Rectifier K+ Channels in the Closed State

Ion channels gate at membrane-embedded domains by changing their conformation along the ion conduction pathway. Inward rectifier K+ (Kir) channels possess a unique extramembrane cytoplasmic domain that extends this pathway. However, the relevance and contribution of this domain to ion permeation rem...

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Bibliographic Details
Published in:The Journal of biological chemistry 2011-12, Vol.286 (48), p.41801-41811
Main Authors: Inanobe, Atsushi, Nakagawa, Atsushi, Kurachi, Yoshihisa
Format: Article
Language:English
Subjects:
Allosteric Regulation
Animals
Cations, Divalent - chemistry
Cations, Divalent - metabolism
Crystallography, X-Ray
Electrophysiology
Electrostatic Interaction
G Protein-Coupled Inwardly-Rectifying Potassium Channels - chemistry
G Protein-Coupled Inwardly-Rectifying Potassium Channels - genetics
G Protein-Coupled Inwardly-Rectifying Potassium Channels - metabolism
HEK293 Cells
Humans
Inward Rectification
Ion Channels
Magnesium - chemistry
Magnesium - metabolism
Membrane Biology
Mice
Potassium Channels
Protein Structure, Tertiary
X-ray Crystallography
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Summary:Ion channels gate at membrane-embedded domains by changing their conformation along the ion conduction pathway. Inward rectifier K+ (Kir) channels possess a unique extramembrane cytoplasmic domain that extends this pathway. However, the relevance and contribution of this domain to ion permeation remain unclear. By qualitative x-ray crystallographic analysis, we found that the pore in the cytoplasmic domain of Kir3.2 binds cations in a valency-dependent manner and does not allow the displacement of Mg2+ by monovalent cations or spermine. Electrophysiological analyses revealed that the cytoplasmic pore of Kir3.2 selectively binds positively charged molecules and has a higher affinity for Mg2+ when it has a low probability of being open. The selective blocking of chemical modification of the side chain of pore-facing residues by Mg2+ indicates that the mode of binding of Mg2+ is likely to be similar to that observed in the crystal structure. These results indicate that the Kir3.2 crystal structure has a closed conformation with a negative electrostatic field potential at the cytoplasmic pore, the potential of which may be controlled by conformational changes in the cytoplasmic domain to regulate ion diffusion along the pore.
ISSN:0021-9258
1083-351X
DOI:10.1074/jbc.M111.278531