Molecular Composition and Ligand Binding Characteristics of Native Ionotropic GABA Receptors in Rice Stem Borer, Chilo suppressalis

The ionotropic γ-aminobutyric acid receptor (iGABAR) is an important insecticidal molecular target. However, the native iGABARs composition remains unknown in insect. Here, CsRdl1, truncated transcripts of CsRdl2 and CsLcch3 were obtained in the rice stem borer (RSB), Chilo suppressalis Walker. The N-terminal-truncated CsRDL2 (∆N-CsRDL2) and N-terminal-truncated CsLCCH3 (∆N-CsLCCH3) were deduced and studied in vivo, and desmethyl-broflanilide (DMBF) binding characteristics were simulated in silico. Genome and transcriptome analyses revealed truncated transcripts of CsRdl2 and CsLcch3 encoded 48 kDa of ∆N-CsRDL2 and 37 kDa of ∆N-CsLCCH3, respectively. The CsRDL1, CsRDL2 and CsLCCH3 were detected respectively from native iGABARs at molecular weights (Mws) ≥ 440 kDa in BN-PAGE. In BN/SDS-PAGE, three CsRDL1 bands (~54, ~55 and ~70 kDa), one CsRDL2 band (~48 kDa) and one CsLCCH3 band (~37 kDa) were identified in native iGABARs at Mws ≥ 669 kDa, and corresponded to CsRDL1ad, CsRDL1bd, post-translationally modified CsRDL1, ∆N-CsRDL2 and ∆N-CsLCCH3, respectively. Immunofluorescence confirmed these three subunits distributed in the same region of adult heads. Finally, DMBF displayed higher binding affinities for heteromeric iGABARs than for homomeric CsRDL1 iGABAR in silico. These findings confirm that ∆N-CsRDL2 and ∆N-CsLCCH3 in native iGABARs might support the rational design of novel insecticides.