Specific loops D, E and F of nicotinic acetylcholine receptor β1 subunit may confer imidacloprid selectivity between Myzus persicae and its predatory enemy Pardosa pseudoannulata

One nicotinic acetylcholine receptor non-alpha subunit was cloned from the pond wolf spider, Pardosa pseudoannulata, an important predatory enemy of some insect pests with agricultural importance, such as the green peach aphid Myzus persicae. The subunit shows high amino acid identities to insect beta 1 subunits (74-78%), and was denoted as Pp beta 1. Although high identities are found between Pp beta 1 and insect beta 1 subunits, amino acid differences are found within loops D, E and F, important segments contributing to ligand binding. The effects of amino acid differences within these loops were evaluated by introducing loops of insect or spider beta 1 subunits into rat beta 2 subunit and co-expressing with insect alpha subunit. The corresponding regions of rat beta 2 chimera beta 2(Mp beta 1) (beta 2 with loops D, E and IF from M. persicae beta 1 subunit Mp beta 1) were replaced by loops D, E and F of Pp beta 1 singly or together to construct different chimeras. When these chimeras were co-expressed with insect Nl alpha 1, it was found that the replacement of loops D, E and IF of beta 2(Mp beta 1) by that of Pp beta 1 resulted in a right-ward shift of the imidacloprid dose-response curves, reflecting increases in EC50, compared to Nl alpha 1/beta 2(Mp beta 1). By contrast, the influences on ACh potency were minimal. The further study showed that R81Q, N137G and F190W differences, within loops D, E and F respectively, contributed mainly to these sensitivity changes. This study contributes to our understanding of the molecular mechanism underlying selectivity of neonicotinoids against insects over spiders. (C) 2009 Elsevier Ltd. All rights reserved.