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First published on March 16, 2007; DOI: 10.1124/mol.106.030528

0026-895X/07/7106-1646-1656$20.00
Mol Pharmacol 71:1646-1656, 2007

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Subunit-Stoichiometric Evidence for Kir6.2 Channel Gating, ATP Binding, and Binding-Gating CouplingFormula

Runping Wang, Xiaoli Zhang, Ningren Cui, Jianping Wu, Hailan Piao, Xueren Wang, Junda Su, and Chun Jiang

Department of Biology, Georgia State University, Atlanta, Georgia

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 Popen, with no effect on maximum ATP inhibition. Prevention of ATP binding lowered the ATP sensitivity and maximum inhibition without affecting basal Popen. 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.

Received September 5, 2006; accepted March 16, 2007

Address correspondence to: Dr. Chun Jiang, Department of Biology, Georgia State University, 24 Peachtree Center Avenue, Atlanta, GA 30302-4010. E-mail: cjiang{at}gsu.edu




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