TY - JOUR T1 - Agonist-Induced Conformational Changes in the Extracellular Domain of α7 Nicotinic Acetylcholine Receptors JF - Molecular Pharmacology JO - Mol Pharmacol SP - 650 LP - 658 DO - 10.1124/mol.64.3.650 VL - 64 IS - 3 AU - Lisa K. Lyford AU - Adrian D. Sproul AU - Donnie Eddins AU - James T. McLaughlin AU - Robert L. Rosenberg Y1 - 2003/09/01 UR - http://molpharm.aspetjournals.org/content/64/3/650.abstract N2 - The molecular mechanisms that couple agonist binding to the gating of Cys-loop ionotropic receptors are not well understood. The crystal structure of the acetylcholine (ACh) binding protein has provided insights into the structure of the extracellular domain of nicotinic receptors and a framework for testing mechanisms of activation. Key ligand binding residues are located at the C-terminal end of the β9 strand. At the N-terminal end of this strand (loop 9) is a conserved glutamate [E172 in chick α7 nicotinic acetylcholine receptors (nAChRs)] that is important for modulating activation. We hypothesize that agonist binding induces the movement of loop 9. To test this, we used the substituted-cysteine accessibility method to examine agonist-dependent changes in the modification of cysteines introduced in loop 9 of L247T α7 nAChRs. In the absence of agonist, ACh-evoked responses of E172C/L247T α7 nAChRs were inhibited by 2-trimethylammonioethylmethane thiosulfonate (MTSET). Agonist coapplication with MTSET reduced the extent and rate of modification. The dose-dependence of ACh activation was nearly identical with that of ACh-dependent protection from modification. ACh increased the inhibition by methanethiosulfonate reagents of N170C and did not change inhibition of G171C receptors. The antagonist dihydro-β-erythroidine did not mimic the effects of ACh. Combined with a structural model, the data suggest that receptor activation includes subunit rotation and/or intrasubunit conformational changes that move N170 to a more accessible position and E172 to a more protected position away from the vestibule. Thus, loop 9, located near the junction between the extracellular and transmembrane domains, participates in conformational changes triggered by ligand binding. ER -