Insecticidal 3-benzamido-N-phenylbenzamides specifically bind with high affinity to a novel allosteric site in housefly GABA receptors

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• 作者：Yoshihisa Ozoe ; Tomo Kita ; Fumiyo Ozoe ; Toshifumi Nakao ; Kazuyuki Sato ; Kangetsu Hirase
• 关键词：BPB ; 3-benzamido-N-phenylbenzamide ; EBOB ; 4&prime ; -ethynyl-4-n-propylbicycloorthobenzoate ; GABA ; 纬-aminobutyric acid ; GABAR ; GABA receptor ; IGluR ; inhibitory l-glutamate receptor ; SOS ; standard oocyte solution ; TEVC ; two-electrode voltage clamp
• 刊名：Pesticide Biochemistry and Physiology
• 出版年：November, 2013
• 年：2013
• 卷：107
• 期：3
• 页码：285-292
• 全文大小：1430 K

文摘

纬-Aminobutyric acid (GABA) receptors (GABARs) are an important target for existing insecticides such as fiproles. These insecticides act as noncompetitive antagonists (channel blockers) for insect GABARs by binding to a site within the intrinsic channel of the GABAR. Recently, a novel class of insecticides, 3-benzamido-N-phenylbenzamides (BPBs), was shown to inhibit GABARs by binding to a site distinct from the site for fiproles. We examined the binding site of BPBs in the adult housefly by means of radioligand-binding and electrophysiological experiments. 3-Benzamido-N-(2,6-dimethyl-4-perfluoroisopropylphenyl)-2-fluorobenzamide (BPB 1) (the N-demethyl BPB) was a partial, but potent, inhibitor of [³H]4鈥?ethynyl-4-n-propylbicycloorthobenzoate (GABA channel blocker) binding to housefly head membranes, whereas the 3-(N-methyl)benzamido congener (the N-methyl BPB) had low or little activity. A total of 15 BPB analogs were tested for their abilities to inhibit [³H]BPB 1 binding to the head membranes. The N-demethyl analogs, known to be highly effective insecticides, potently inhibited the [³H]BPB 1 binding, but the N-methyl analogs did not even though they, too, are considered highly effective. [³H]BPB 1 equally bound to the head membranes from wild-type and dieldrin-resistant (rdl mutant) houseflies. GABA allosterically inhibited [³H]BPB 1 binding. By contrast, channel blocker-type antagonists enhanced [³H]BPB 1 binding to housefly head membranes by increasing the affinity of BPB 1. Antiparasitic macrolides, such as ivermectin B_1a, were potent inhibitors of [³H]BPB 1 binding. BPB 1 inhibited GABA-induced currents in housefly GABARs expressed in Xenopus oocytes, whereas it failed to inhibit l-glutamate-induced currents in inhibitory l-glutamate receptors. Overall, these findings indicate that BPBs act at a novel allosteric site that is different from the site for channel blocker-type antagonists and that is probably overlapped with the site for macrolides in insect GABARs.