PMID: 21982822 , Related PDB ids: 3AT8, 3AT9, 3ATA, 3ATB, 3ATD, 3ATE, 3ATF
Inanobe A, Nakagawa A, Kurachi Y
Interactions of cations with the cytoplasmic pores of inward rectifier K(+) channels in the closed state.
J Biol Chem. 2011 Dec 2;286(48):41801-11. Epub 2011 Oct 9.
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 Mg(2+) 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 Mg(2+) when it has a low probability of being open. The selective blocking of chemical modification of the side chain of pore-facing residues by Mg(2+) indicates that the mode of binding of Mg(2+) 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.