Referenced in: none

Automatically associated channels: Kv10.1

Title: Agonist-induced conformational changes in the extracellular domain of alpha 7 nicotinic acetylcholine receptors.

Authors: Lisa K Lyford, Adrian D Sproul, Donnie Eddins, James T McLaughlin, Robert L Rosenberg

Journal, date & volume: Mol. Pharmacol., 2003 Sep , 64, 650-8

PubMed link: http://www.ncbi.nlm.nih.gov/pubmed/12920201

Abstract
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 beta9 strand. At the N-terminal end of this strand (loop 9) is a conserved glutamate [E172 in chick alpha7 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 alpha7 nAChRs. In the absence of agonist, ACh-evoked responses of E172C/L247T alpha7 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-beta-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.