TY - JOUR T1 - Salt Bridge Switching from Arg290/Glu167 to Arg290/ATP Promotes the Closed-to-open Transition of the P2X2 Receptor JF - Molecular Pharmacology JO - Mol Pharmacol DO - 10.1124/mol.112.081489 SP - mol.112.081489 AU - Ralf Hausmann AU - Janka Gunther AU - Achim Kless AU - Daniel Kuhlmann AU - Matthias U. Kassack AU - Gregor Bahrenberg AU - Fritz Markwardt AU - Gunther Schmalzing Y1 - 2012/10/05 UR - http://molpharm.aspetjournals.org/content/early/2012/10/05/mol.112.081489.abstract N2 - P2X receptors are trimeric ATP-gated cation channels involved in fast signal transduction in many cell types. In this study, we used homology modeling of the rat P2X2 receptor with the zebrafish P2X4 X-ray template to determine that the side chains of the Glu167 and Arg290 residues are in close spatial vicinity within the ATP-binding pocket when the rat P2X2 channel is closed. Through charge reversal mutation analysis and mutant cycle analysis, we obtained evidence that Glu167 and Arg290 form an electrostatic interaction. In addition, disulfide trapping indicated the close proximity of Glu167 and Arg290 when the channel is in the closed-state, but not in the ATP-bound open-state. Consistent with a gating-induced movement that disrupts the Glu167/Arg290 salt bridge, a comparison of the closed and open rat P2X2 receptor models revealed a significant rearrangement of the protein backbone and the side chains of the Glu167 and Arg290 residues during the closed-to-open transition. The associated release of the Glu167/Arg290 salt bridge during channel opening allows a strong ionic interaction between Arg290 and a γ-phosphate oxygen of ATP. We concluded from these results that the state-dependent salt bridge switching from Arg290/Glu167 to Arg290/ATP fulfills a dual role: (i) to destabilize the closed-state of the receptor and (ii) to promote the ionic coordination of ATP in the ATP-binding pocket. ER -