Identification of two Lynx proteins in Nilaparvata lugens and the modulation on insect nicotinic acetylcholine receptors

Abstract

Nicotinic acetylcholine receptors (nAChRs) mediate fast cholinergic synaptic transmission in the insect brain and are targets for neonicotinoid insecticides. Some proteins, other than nAChRs themselves, might play important roles in insect nAChRs function in vivo and in vitro, such as the chaperone, regulator and modulator. Here we report the identification of two nAChR modulators (Nl-lynx1 and Nl-lynx2) in the brown planthopper, Nilaparvata lugens. Analysis of amino acid sequences of Nl-lynx1 and Nl-lynx2 reveals that they are two members of the Ly-6/neurotoxin superfamily, with a cysteine-rich consensus signature motif. Nl-lynx1 and Nl-lynx2 only increased agonist-evoked macroscopic currents of hybrid receptors Nlalpha1/beta2 expressed in Xenopus oocytes, but not change the agonist sensitivity and desensitization properties. For example, Nl-lynx1 increased I(max) of acetylcholine and imidacloprid to 3.56-fold and 1.72-fold of that of Nlalpha1/beta2 alone, and these folds for Nl-lynx2 were 3.25 and 1.51. When the previously identified Nlalpha1(Y151S) mutation was included (Nlalpha1(Y151S)/beta2), the effects of Nl-lynx1 and Nl-lynx2 on imidacloprid responses, but not acetylcholine response, were different from that in Nlalpha1/beta2. The increased folds in imidacloprid responses by Nl-lynx1 and Nl-lynx2 were much higher in Nlalpha1(Y151S)/beta2 (3.25-fold and 2.86-fold) than in Nlalpha1/beta2 (1.72-fold and 1.51-fold), which indicated Nl-lynx1 and Nl-lynx2 might also serve as an influencing factor in target-site insensitivity in N. lugens. These findings indicate that nAChRs chaperone, regulator and modulator may be of importance in assessing the likely impact of the target-site mutations such as Y151S upon neonicotinoid insecticide resistance.