Referenced in: none

Automatically associated channels: Kv4.1 , Slo1

Title: Atypical alpha-conotoxin LtIA from Conus litteratus targets a novel microsite of the alpha3beta2 nicotinic receptor.

Authors: Sulan Luo, Kalyana Bharati Akondi, Dongting Zhangsun, Yong Wu, Xiaopeng Zhu, Yuanyan Hu, Sean Christensen, Cheryl Dowell, Norelle L Daly, David J Craik, Ching-I Anderson Wang, Richard J Lewis, Paul F Alewood, J Michael McIntosh

Journal, date & volume: J. Biol. Chem., 2010 Apr 16 , 285, 12355-66

PubMed link: http://www.ncbi.nlm.nih.gov/pubmed/20145249

Abstract
Different nicotinic acetylcholine receptor (nAChR) subtypes are implicated in learning, pain sensation, and disease states, including Parkinson disease and nicotine addiction. alpha-Conotoxins are among the most selective nAChR ligands. Mechanistic insights into the structure, function, and receptor interaction of alpha-conotoxins may serve as a platform for development of new therapies. Previously characterized alpha-conotoxins have a highly conserved Ser-Xaa-Pro motif that is crucial for potent nAChR interaction. This study characterized the novel alpha-conotoxin LtIA, which lacks this highly conserved motif but potently blocked alpha3beta2 nAChRs with a 9.8 nm IC(50) value. The off-rate of LtIA was rapid relative to Ser-Xaa-Pro-containing alpha-conotoxin MII. Nevertheless, pre-block of alpha3beta2 nAChRs with LtIA prevented the slowly reversible block associated with MII, suggesting overlap in their binding sites. nAChR beta subunit ligand-binding interface mutations were used to examine the >1000-fold selectivity difference of LtIA for alpha3beta2 versus alpha3beta4 nAChRs. Unlike MII, LtIA had a >900-fold increased IC(50) value on alpha3beta2(F119Q) versus wild type nAChRs, whereas T59K and V111I beta2 mutants had little effect. Molecular docking simulations suggested that LtIA had a surprisingly shallow binding site on the alpha3beta2 nAChR that includes beta2 Lys-79. The K79A mutant disrupted LtIA binding but was without effect on an LtIA analog where the Ser-Xaa-Pro motif is present, consistent with distinct binding modes.