LAUSR

ABSTRACT Peptide and protein neurotoxins, such as &agr;‐conotoxins from Cone snails and &agr;‐neurotoxins from snake venoms, are excellent tools to identify distinct nicotinic acetylcholine receptor (nAChR) subtypes. Here we compared the rat/human species specificity of &agr;7 nAChR towards peptide and protein neurotoxins and found that &agr;‐conotoxin analogues [K11A]TxIB and [H5D]RegIIA are much more potent on the rat versus human &agr;7 receptor expressed in Xenopus oocytes. In the hope to determine the key residue responsible for the difference in &agr;‐conotoxin analogues affinities, ten single mutants of rat &agr;7 nAChR were obtained because there are 10 differences in the extracellular ligand‐binding domains of these species, and only K185R mutation decreased the affinity for &agr;‐conotoxins [K11A]TxIB and [H5D]RegIIA, down to their low affinities for human &agr;7 nAChR. On the other hand, the reverse mutation R185K in human &agr;7 nAChR resulted in the greatest increase in the affinity for both conotoxins, while a double mutation h&agr;7[S183N, R185K] made the potency of the receptor for them as high as that of rat &agr;7 nAChR. The effects of mutations at position 185 were investigated also with some other &agr;‐conotoxins and cobra venom &agr;‐cobratoxin and found to have similar but much less pronounced effects on their species specificity. Molecular modeling provided possible explanation for the high species selectivity of [K11A]TxIB and [H5D]RegIIA towards &agr;7 nAChR, opening the new way for design of their analogues with improved affinity to the human receptor. HIGHLIGHTS&agr;‐Conotoxin [K11A]TxIB and [H5D]RegIIA are more potent on rat versus human &agr;7 nAChR.Lys185 in r&agr;7 subunit mainly confers high specificity of [K11A]TxIB and [H5D]RegIIA.The residue 185 had effects on the &agr;7 species specificity towards other neurotoxins.Molecular modeling provided explanation for the high species selectivity of &agr;7 nAChR.