Selectivity of lynx proteins on insect nicotinic acetylcholine receptors in the brown planthopper, Nilaparvata lugens

Neuronal nicotinic acetylcholine receptors (nAChRs) are major excitatory neurotransmitter receptors in both vertebrates and invertebrates. Two lynx proteins (Nl-lynx1 and Nl-lynx2) have been identified in the brown planthopper, Nilaparvata lugens, which act as modulators on insect nAChRs. In the present study, two lynx proteins were found to act on the triplet receptor Nl alpha 1/Nl alpha 2/beta 2 expressed in Xenopus oocytes, increasing agonist-evoked macroscopic currents, but not changing agonist sensitivity and desensitization properties. Nl-lynx1 and Nl-lynx2 increased I-max (maximum responses) of acetylcholine to 4.85-fold and 2.40-fold of that of Nl alpha 1/Nl alpha 2/beta 2 alone, and they also increased I-max of imidacloprid to 2.57-fold and 1.25-fold. Although, on another triplet nAChRs Nl alpha 3/Nl alpha 8/beta 2, Nl-lynx2 increased I-max of acetylcholine and imidacloprid to 3.63-fold and 2.16-fold, Nl-lynx1 had no effects on I-max of either acetylcholine or imidacloprid. The results demonstrate the selectivity of lynx proteins for different insect nAChR subtypes. This selectivity was also identified in native N. Lugens. Co-immunoprecipitation was found between Nl alpha 1/Nl alpha 2-containing receptors and both Nl-lynx1 and Nl-lynx2, but was only found between Nl alpha 3/Nl alpha 8-containing receptors and Nl-lynx2. When the previously identified Nl alpha 1Y151S and Nl alpha 3Y151S mutations were included (Nl alpha 1Y151S/Nl alpha 2/beta 2 and Nl alpha 3Y151S/Nl alpha 8/beta 2), the increase in I-max of imidacloprid, but not acetylcholine, caused by co-expression of Nl-lynx1 and Nl-lynx2 was more noticeable than that of their wildtype counterparts. Taken together, these data suggest that two modulators, Nl-lynx1 and Nl-lynx2, might serve as an influencing factor in target site insensitivity in N. lugens, such as Y151S mutation.