2002 Fiscal Year Final Research Report Summary
Structure of ligand-binding site of mutated GABA receptors of insects with resistance for antagonists
| Project/Area Number |
13660109
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Bioproduction chemistry/Bioorganic chemistry
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| Research Institution | Shimane University |
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Principal Investigator |
OZOE Yoshihisa Shimane University, Department of Life Science and Biotechnology, Professor, 生物資源科学部, 教授 (80112118)
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| Project Period (FY) |
2001 – 2002
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| Keywords | GABA / receptor / antagonist / insecticide / resistance / insect / EBOB / neurotransmitter |
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| Research Abstract |
OCR houseflies with an A299S mutation in the binding site of noncompetitive GABA antagonists displayed 1 or 2 orders lower resistance to the insecticide fipronil and EBOB than to the insecticide dieldrin (several thousand-fold resistance). Scatchard analysis showed that OCR receptors had 4-fold lower affinity for [^3H]EBOB and 1.3-fold less binding sites than receptors of susceptible WHO files. Dieldrin was 45-fold less potent in inhibiting [^3H]EBOB binding in OCR receptors than in WHO receptors, while fipronil and EBOB were 2-and 6-fold less potent in OCR receptors than in WHO receptors, respectively. 3, 4, 5,-substituted 1-(2,6-dichioro-4-trifluoromethylphenyl)pyrazoles, fipronil analogues, exhibited different structure-activity relationships in OCR receptors from those in WHO receptors. Although most of the analogues had remarkably low affinities for OCR receptors, several analogues with an electron-withdrawing group in the 4-position of the pyrazole ring showed relatively high affinity. However, the affinities were several hundred-fold lower than the affinities for WHO receptors; IC_<50s> were in the micromolar order. An analogue with a bromine atom in the 4-position had >1600-fold lower affinity for OCR receptors than that for WHO receptors. Although the introduction of an amino group into the 5-position led to a decrease in affinity for OCR receptors in one case, three compounds with an amino group in the 5-position, compounds structurally closely related to fipronil, showed only <4-fold decrease in affinity for OCR receptors, compared to that for WHO receptors. The results indicate that only limited compounds with special structures seem to fit into the GABA antagonist-binding site of dieldrin-resistant houseflies. Factor(s) apart from decrease in affinity might be involved in the mechanism underlying the resistance of OCR files for noncompetitive GABA antagonists.
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