Role of Human GABAA Receptor β3 Subunit in Insecticide Toxicity

Ratra, Gurpreet S.; Kamita, Shizuo G.; Casida, John E.

doi:10.1006/taap.2001.9154

Cited by 110 publications

(117 citation statements)

References 34 publications

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“…Recombinant receptors help define the relationship between subunit composition and insecticide action. [3][4][5] (Table 1). The b3 homopentameric GABAR is readily expressed and functional.…”

Section: Human Gabar B3 Homopentamer Conserves the Pharmacological Prmentioning

confidence: 99%

“…The more compact NCAs require only Ala-2Ј and Thr-6Ј, whereas the potency of long or extended NCA molecules is enhanced by the Leu-9Ј In comparison, the affinity ratio for EBOB is 5.0. 3,4) side chain. Favorable GABAR-NCA interactions (hydrophobic and hydrogen bonding) are illustrated in Fig.…”

Section: Structural Model For Gabar-nca Interactions With Structurallmentioning

confidence: 99%

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Insecticide interactions with .GAMMA.-aminobutyric acid and nicotinic receptors: predictive aspects of structural models

Casida¹,

Tomizawa²

2008

J. Pestic. Sci.

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An insecticide binding site may be blocked by widely diverse chemicals, as with the g-aminobutyric acid receptor (GABAR), or accept only closely related compounds, as illustrated by the nicotinic acetylcholine (ACh) receptor (nAChR). The human GABAR b3-homopentamer resembles the insect receptor in sensitivity and specificity for noncompetitive antagonists (NCAs), prompting exhaustive site-directed mutagenesis (cysteine scanning), which pinpointed the critical active site as pore-facing residues Ala-2Ј, Thr-6Ј and Leu-9Ј and led to a binding site model which fits several classes of insecticidal NCAs. The nAChR agonist site was approached with an ACh binding protein (AChBP) by photoaffinity labeling and neonicotinoid docking. Chloropyridinyl chlorine contacts Ile-106/Met-116 and nitrogen is directed to Ile-118/Trp-147 via a solvent bridge(s). The guanidine/amidine plane undergoes p-stacking with Tyr-188, and the nitro/cyano pharmacophore interacts with Ser-189/Cys-190, thereby defining the binding pocket that models AChBP and possibly nAChR potency and selectivity.

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Section: Human Gabar B3 Homopentamer Conserves the Pharmacological Prmentioning

confidence: 99%

Section: Structural Model For Gabar-nca Interactions With Structurallmentioning

confidence: 99%

Insecticide interactions with .GAMMA.-aminobutyric acid and nicotinic receptors: predictive aspects of structural models

Casida¹,

Tomizawa²

2008

J. Pestic. Sci.

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“…All of these insecticides and the botanical picrotoxinin (PTX) have widely diverse chemical structures but appear to act at the same nerve target. It is therefore important to understand how these compounds work in mammals and insects, or how they do not work when resistant insect strains appear.The GABA-gated chloride channel is the target for the insecticides and toxicants referred to above based on radioligand binding and electrophysiology studies (3)(4)(5)(6)(7)(8)(9)(10) (Fig. 1A).…”

mentioning

confidence: 99%

mentioning

confidence: 99%

“…The GABA-gated chloride channel is the target for the insecticides and toxicants referred to above based on radioligand binding and electrophysiology studies (3)(4)(5)(6)(7)(8)(9)(10). Important radioligands in these developments are [ 3 H]dihydroPTX (4,11), [ 35 S]tbutylbicyclophosphorothionate (TBPS) (5,12), [ 3 H]1-(4-ethynylphenyl)-4-n-propyl-2,6,7-trioxabicyclo[2.2.2]octane (EBOB) (6), and [ 3 H]3,3-bis-trif luoromethyl-bicyclo[2,2,1]heptane-2,2-dicarbonitrile (BIDN) (8) (Fig.…”

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Structural model for γ-aminobutyric acid receptor noncompetitive antagonist binding: Widely diverse structures fit the same site

Chen

Durkin

Casida

2006

Proc. Natl. Acad. Sci. U.S.A.

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Several major insecticides, including ␣-endosulfan, lindane, and fipronil, and the botanical picrotoxinin are noncompetitive antagonists (NCAs) for the GABA receptor. We showed earlier that human ␤3 homopentameric GABAA receptor recognizes all of the important GABAergic insecticides and reproduces the high insecticide sensitivity and structure-activity relationships of the native insect receptor. Despite large structural diversity, the NCAs are proposed to fit a single binding site in the chloride channel lumen lined by five transmembrane 2 segments. This hypothesis is examined with the ␤3 homopentamer by mutagenesis, pore structure studies, NCA binding, and molecular modeling. The 15 amino acids in the cytoplasmic half of the pore were mutated to cysteine, serine, or other residue for 22 mutants overall. Localization of A-1 C, A2 C, T6 C, and L9 C (index numbers for the transmembrane 2 region) in the channel lumen was established by disulfide cross-linking. Binding of two NCA radioligands ␤3 homopentamer ͉ transmembrane 2 ͉ insecticide ͉ disulfide trapping ͉ receptor model P est insect control in the past 60 years was achieved, in part, by application of Ͼ3 billion (3 ϫ 10 9 ) pounds of polychlorocycloalkane insecticides, including cyclodienes (e.g., ␣-endosulfan and dieldrin), lindane and its isomers, and others, which are now highly restricted or banned except for endosulfan and some uses of lindane (1-3). One of the replacement compounds is the phenylpyrazole fipronil. All of these insecticides and the botanical picrotoxinin (PTX) have widely diverse chemical structures but appear to act at the same nerve target. It is therefore important to understand how these compounds work in mammals and insects, or how they do not work when resistant insect strains appear.The GABA-gated chloride channel is the target for the insecticides and toxicants referred to above based on radioligand binding and electrophysiology studies (3)(4)(5)(6)(7)(8)(9)(10) (Fig. 1A). All of these compounds act in mammals and insects as noncompetitive antagonists (NCAs) to block chloride flux so the target is referred to as the GABA receptor NCA-binding site. Vertebrate GABA receptors consist of ␣, ␤, ␥, , and other subunits in various combinations, for example, ␣ 1 ␤ 2 ␥ 2 as a heteropentamer and 1 as a homopentamer (13-15). The molecular localization of the NCA site defined here (Fig. 1B) was first indicated by mutagenesis studies (16) as A2Ј (17-20), T6Ј (21, 22), and L9Ј (23, 24) in the cytoplasmic half of the transmembrane 2 domain of the channel (Fig. 2). Drosophila resistant to dieldrin (RDL) have a mutation conferring GABA receptor insensitivity identified as A2ЈS (17). The NCA target of the GABA A receptor requires a ␤ subunit, and a ␤ 3 homopentamer is sufficient for binding (9,26). Importantly, the ␤ 3 subunit from human brain, when expressed in insect Sf9 cells, assembles to form a receptor sensitive to all of the important GABAergic insecticides (9) and, surprisingly, reproduces the insecticide sensitivity and structureactivit...

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