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Interaction of α‐conotoxin ImII and its analogs with nicotinic receptors and acetylcholine‐binding proteins: additional binding sites on Torpedo receptor
Author(s) -
Kasheverov Igor E.,
Zhmak Maxim N.,
Fish Alexander,
Rucktooa Prakash,
Khruschov Alexey Yu.,
Osipov Alexey V.,
Ziganshin Rustam H.,
D’hoedt Dieter,
Bertrand Daniel,
Sixma Titia K.,
Smit August B.,
Tsetlin Victor I.
Publication year - 2009
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.2009.06359.x
Subject(s) - acetylcholine receptor , torpedo , nicotinic agonist , conotoxin , chemistry , nicotinic antagonist , receptor , binding site , nicotinic acetylcholine receptor , stereochemistry , biochemistry , biophysics , biology , venom
α‐Conotoxins interact with nicotinic acetylcholine receptors (nAChRs) and acetylcholine‐binding proteins (AChBPs) at the sites for agonists/competitive antagonists. α‐Conotoxins blocking muscle‐type or α7 nAChRs compete with α‐bungarotoxin. However, α‐conotoxin ImII, a close homolog of the α7 nAChR‐targeting α‐conotoxin ImI, blocked α7 and muscle nAChRs without displacing α‐bungarotoxin (Ellison et al. 2003, 2004), suggesting binding at a different site. We synthesized α‐conotoxin ImII, its ribbon isomer (ImII iso ), ‘mutant’ ImII(W10Y) and found similar potencies in blocking human α7 and muscle nAChRs in Xenopus oocytes. Both isomers displaced [ 125 I]‐α‐bungarotoxin from human α7 nAChRs in the cell line GH 4 C 1 (IC 50 17 and 23 μM, respectively) and from Lymnaea stagnalis and Aplysia californica AChBPs (IC 50 2.0–9.0 μM). According to SPR measurements, both isomers bound to immobilized AChBPs and competed with AChBP for immobilized α‐bungarotoxin ( K d and IC 50 2.5–8.2 μM). On Torpedo nAChR, α‐conotoxin [ 125 I]‐ImII(W10Y) revealed specific binding ( K d 1.5–6.1 μM) and could be displaced by α‐conotoxin ImII, ImII iso and ImII(W10Y) with IC 50 2.7, 2.2 and 3.1 μM, respectively. As α‐cobratoxin and α‐conotoxin ImI displaced [ 125 I]‐ImII(W10Y) only at higher concentrations (IC 50 ≥ 90 μM), our results indicate that α‐conotoxin ImII and its congeners have an additional binding site on Torpedo nAChR distinct from the site for agonists/competitive antagonists.