A unique primary structure of RDL (resistant to dieldrin) confers resistance to GABA‐gated chloride channel blockers in the two‐spotted spider mite Tetranychus urticae Koch

Abstract

The primary structure of the second transmembrane (M2) segment of resistant to dieldrin (RDL), an ionotropic γ-aminobutyric acid receptor (GABAR) subunit, and the structure-function relationships in RDL are well conserved among insect species. An amino acid substitution at the 2′ position in the M2 segment (Ala to Ser or Gly) confers resistance to non-competitive antagonists (NCAs) of GABARs. Here, a cDNA encoding RDL was cloned from the two-spotted spider mite Tetranychus urticae Koch. Unlike insect homologs, native TuRDL has His at the 2′ position (H305) and Ile at 6′ (I309) in the M2 segment and is insensitive to NCAs. Single and multiple mutations were introduced in the M2 segment of TuRDL, and the mutant proteins were expressed in Xenopus oocytes and examined for the restoration of sensitivity to NCAs. The sensitivity of a double mutant (H305A and I309T in the M2 segment) was greatly increased but was still considerably lower than that of insect RDLs. We therefore | 509 KOBAYASHI et Al.

Activity, selection response and molecular mode of action of the isoxazoline afoxolaner in Tetranychus urticae

“…By contrast, TuRdl1 sensitivity to fipronil and endosulfan was partially restored when double-and triple-reversed mutations were introduced without any additional effect of the third mutation. Similar findings recently were reported by Kobayashi 69 where single and multiple mutations (A301S/H and I305A) were introduced in TM2 of TuRdl to examine their sensitivities to picrotoxinin and fipronil and the cyclodiene dieldrin. The double (H301A and I305T) mutation significantly increased the channel's sensitivity to all three compounds, but the introduction of single mutations had no effect.…”

Molecular Targets of Neurotoxic Insecticides in Apis mellifera

“…[99] Although substitution at T6' has never been described in NCA field-isolated resistant species, T6' mutation in Drosophila melanogaster RDL suppresses picrotoxin antagonism, [100] suggesting that this threonine plays a critical role in the formation of NCA binding site in RDL. [101] In molecular modelling of RDL subunits from different species (including Apis mellifera) fipronil is erected in the channel pore surrounded by the five M2 segments, the trifluoromethyl group being oriented toward the intracellular compartment. [75,102,103] The binding site of fipronil is located between L9' (which defines the narrowest point of the pore) and P-2', with A2' and T6' critically involved in direct interaction with phenylpyrazole.…”

“…A2’ and T6’ were often replaced by other amino acids in certain RDL subunits from Varroa destructor , [82] Bombyx mori [98] or Plutella xylostella [99] . Although substitution at T6’ has never been described in NCA field‐isolated resistant species, T6’ mutation in Drosophila melanogaster RDL suppresses picrotoxin antagonism, [100] suggesting that this threonine plays a critical role in the formation of NCA binding site in RDL [101] . In molecular modelling of RDL subunits from different species (including Apis mellifera ) fipronil is erected in the channel pore surrounded by the five M2 segments, the trifluoromethyl group being oriented toward the intracellular compartment [75,102,103] .…”