Binding Modes of Noncompetitive GABA-Channel Blockers Revisited Using Engineered Affinity-Labeling Reactions Combined with New Docking Studies

Abstract

The binding modes of noncompetitive GABA(A)-channel blockers were re-examined taking into account the recent description of the 3D structure of prokaryotic pentameric ligand-gated ion channels, which provided access to new mammalian or insect GABA receptor models, emphasizing their transmembrane portion. Two putative binding modes were deciphered for this class of compounds, including the insecticide fipronil, located nearby either the intra- or the extracellular part of the membrane, respectively. These results are in full agreement with previously described affinity-labeling reactions performed with GABA(A) noncompetitive blockers (Perret et al. J. Biol. Chem.1999, 274, 25350-25354).

Effects of the insecticide fipronil on reproductive endocrinology in the fathead minnow

“…With a wide range of applications, including agricultural, urban, and veterinary uses, FIP has been detected in agricultural and urban runoff waters at concentrations as high as 1 ug/L to 10 ug/L, although low nanogram‐per‐liter concentrations are more common. Fipronil interferes with normal GABA receptor–gated chloride channels by acting as a noncompetitive blocker , leading to increased neuronal stimulation, hyperactivity, and eventually death in target insects . Fipronil has a higher binding affinity for insect than mammalian GABA receptors , suggesting a level of safety for vertebrates.…”

GABAA Receptor Subunit Composition Drives Its Sensitivity to the Insecticide Fipronil

“…We generated homology models of α6β3 and α6β3γ2S GABA A R to predict how FPN binds to their receptor site ( Figure 7 ). The docking was guided by the prior knowledge that FPN is an open channel blocker and has two putative binding sites in the ion channel, lined by the M2 transmembrane segments ( Perret et al, 1999 ; Charon et al, 2011 ). Indeed, our docking finds two binding modes, located nearby Val257 and Ser272 ( Figures 7C,D ).…”

“…The ligands and proteins were prepared with prepare_ligand4.py and prepare_receptor4.py scripts, respectively. The docking was restricted using a docking box of 15 A side, in the upper and lower binding sites identified previously ( Charon et al, 2011 ). Figures were prepared with PyMOL ( Schrödinger and DeLano, 2020 ).…”

“…Few studies have explored the mode of action of FPN on mammalian GABA A R. It has been shown that the GABA A R subunit composition is a key feature to explain the affinity and binding of FPN to its mammalian target ( Ratra and Casida, 2001 ; Charon et al, 2011 ). The β3 subunit is proposed to contain the FPN biding site ( Ratra et al, 2001 ).…”

From Toxins Targeting Ligand Gated Ion Channels to Therapeutic Molecules

“…Picrotoxin is a non-competitive antagonists isolated from Menispermaceae. Binding modes for picrotoxin have been proposed in the ion channel [ 69 , 70 , 71 ].…”