title: Subunit-stoichiometric evidence for kir6.2 channel gating, ATP binding, and binding-gating coupling.
abstract: ATP-sensitive K(+) channels are gated by intracellular ATP, allowing them to couple intermediary metabolism to cellular excitability, whereas the gating mechanism remains unclear. To understand subunit stoichiometry for the ATP-dependent channel gating, we constructed tandem-multimeric Kir6.2 channels by selective disruption of the binding or gating mechanism in certain subunits. Stepwise disruptions of channel gating caused graded losses in ATP sensitivity and increases in basal P(open), with no effect on maximum ATP inhibition. Prevention of ATP binding lowered the ATP sensitivity and maximum inhibition without affecting basal P(open). The ATP-dependent gating required a minimum of two functional subunits. Two adjacent subunits are more favorable for ATP binding than two diagonal ones. Subunits showed negative cooperativity in ATP binding and positive cooperativity in channel gating. Joint disruptions of the binding and gating mechanisms in the same or alternate subunits of a concatemer revealed that both intra- and intersubunit couplings contributed to channel gating, although the binding-gating coupling preferred the intrasubunit to intersubunit configuration within the C terminus. No such preference was found between the C and N termini. These phenomena are well-described with the operational model used widely for ligand-receptor interactions.
authors: Department of Biology, Georgia State University, Atlanta, GA 30302-4010, USA.
authors: Runping
authors: R
authors: Wang
authors: Xiaoli
authors: X
authors: Zhang
authors: Ningren
authors: N
authors: Cui
authors: Jianping
authors: J
authors: Wu
authors: Hailan
authors: H
authors: Piao
authors: Xueren
authors: X
authors: Wang
authors: Junda
authors: J
authors: Su
authors: Chun
authors: C
authors: Jiang
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D019281:Dimerization; D006801:Humans; D051379:Mice; D015221:Potassium Channels / Q000378:metabolism; D024661:Potassium Channels, Inwardly Rectifying / Q000378:metabolism*; D021122:Protein Subunits / Q000378:metabolism*; D014982:Xenopus laevis; D000099161:Kcnj11 Channel
chemical_list: D000255:Adenosine Triphosphate; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D021122:Protein Subunits; D000099161:Kcnj11 Channel; C117780:mitochondrial K(ATP) channel