Characterization of mosquito CYP6P7 and CYP6AA3: differences in substrate preference and kinetic properties.

Cytochrome P450 monooxygenases are involved in insecticide resistance in insects. We previously observed an increase in CYP6P7 and CYP6AA3 mRNA expression in Anopheles minimus mosquitoes during the selection for deltamethrin resistance in the laboratory. CYP6AA3 has been shown to metabolize deltamethrin, while no information is known for CYP6P7. In this study, CYP6P7 was heterologously expressed in the Spodoptera frugiperda (Sf9) insect cells via baculovirus-mediated expression system. The expressed CYP6P7 protein was used for exploitation of its enzymatic activity against insecticides after reconstitution with the An. minimus NADPH-cytochrome P450 reductase enzyme in vitro. The ability of CYP6P7 to metabolize pyrethroids and insecticides in the organophosphate and carbamate groups was compared with CYP6AA3. The results revealed that both CYP6P7 and CYP6AA3 proteins could metabolize permethrin, cypermethrin, and deltamethrin pyrethroid insecticides, but showed the absence of activity against bioallethrin (pyrethroid), chlorpyrifos (organophosphate), and propoxur (carbamate). CYP6P7 had limited capacity in metabolizing λ-cyhalothrin (pyrethroid), while CYP6AA3 displayed activity toward λ-cyhalothrin. Kinetic properties suggested that CYP6AA3 had higher efficiency in metabolizing type I than type II pyrethroids, while catalytic efficiency of CYP6P7 toward both types was not significantly different. Their kinetic parameters in insecticide metabolism and preliminary inhibition studies by test compounds in the flavonoid, furanocoumarin, and methylenedioxyphenyl groups elucidated that CYP6P7 had different enzyme properties compared with CYP6AA3. © 2011 Wiley Periodicals, Inc.

Characterization of Anopheles minimus CYP6AA3 expressed in a recombinant baculovirus system.

Metabolism by cytochrome P450 monooxygenases is a major mechanism implicated in resistance of insects to insecticides, including pyrethroids. We previously isolated the cytochrome P450 CYP6AA3 from deltamethrin-selected resistant strain of Anopheles minimus mosquito, a major malaria vector in Thailand. In the present study, we further investigated the role of CYP6AA3 enzyme in deltamethrin metabolism in vitro. The CYP6AA3 was expressed in Spodoptera frugiperda (Sf9) insect cells via baculovirus-mediated expression system. The enzymatic activity of CYP6AA3 in deltamethrin metabolism was characterized after being reconstituted with An. minimus NADPH-cytochrome P450 reductase and a NADPH-regenerating system. The contribution of CYP6AA3 responsible for deltamethrin metabolism was determined by measurement of deltamethrin disappearance following the incubation period and deltamethrin-derived compounds were detected using combined gas chromatography mass spectrometry analysis. 3-Phenoxybenzaldehyde was a major product of CYP6AA3-mediated deltamethrin metabolism. Deltamethrin degradation and formation of metabolites were NADPH-dependent and inhibited by piperonyl butoxide. Deltamethrin was catalyzed by CYP6AA3 with an apparent K(m) of 80.0 +/- 2.0 and V(max) of 60.2 +/- 3.6 pmol/min/pmol P450. Furthermore, deltamethrin cytotoxicity assays by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and trypan blue dye exclusion were examined in Sf9 insect cells, with and without expression of CYP6AA3. Results revealed that CYP6AA3 could play a role in detoxifying deltamethrin in the cells. Thus, the results of this study support the role of CYP6AA3 in deltamethrin metabolism.

Functional expression of mosquito NADPH-cytochrome P450 reductase in Escherichia coli.

A complete NADPH-cytochrome P450 reductase (CPR) cDNA was isolated from Anopheles minimus Theobald mosquitoes by using reverse transcription-polymerase chain reaction-based methods. The complete cDNA contains 2,040 bp encoding the protein of 679 amino acids, with a calculated molecular mass of 77.3 kDa The deduced amino acid sequence had a typical feature of CPR by possessing conserved domains involved in binding of flavin mononucleotide, flavin adenine dinucleotide, and NADPH cofactors. The complete CPR cDNA was expressed as 6x His-tagged fusion protein in both membrane and cytosolic fractions in Escherichia coli, both fractions contained NADPH-cytochrome c reducing activity. The membrane-bound form containing N-terminal membrane anchor was subjected to purification, and K, values were determined for NADPH and cytochrome c. The purified CPR enzyme was functionally active, as demonstrated by its ability to support CYP6AA3-mediated metabolism in the reconstituted reaction in vitro. Initial test suggested that CYP6AA3 could play a role in deltamethrin metabolism.

Cytochrome P450 genes: molecular cloning and overexpression in a pyrethroid-resistant strain of Anopheles minimus mosquito.

We previously determined that physiological resistance in a laboratory-selected pyrethroid-resistant Anopheles minimus species A Theobald mosquito is associated with increased detoxification via a P450-mediated mechanism. A CYP6 gene, CYP6AA3, was subsequently cloned and found overexpressed in 2 resistant mosquito generations (F13 and F19). We report herein the cloning of CYP6P7 and CYP6P8 genes with full coding sequences from the same An. minimus mosquito colony strain. CYP6P7 and CYP6P8 encode proteins, each with 509 amino acids. CYP6P7 had the closest (81%) amino acid identity with Anopheles gambiae CYP6P2. CYP6P8 genes had 79% identity with An. gambiae CYP6P1. Using semiquantitative reverse transcription-polymerase chain reaction analysis, the mRNA expression level of CYP6P7 presented approximately 2- and 4-fold increases in F19 and F25 deltamethrin-resistant populations, respectively, compared with the parent susceptible strain. CYP6P8 mRNA expression levels were not significantly different between the 3 filial generations. The overexpression of CYP6AA3 mRNA was greater than that of CYP6P7 in F19 and F25 resistant populations. The relative increase of both CYP6AA3 and CYP6P7 mRNA was correlated with increased resistance to deltamethrin in An. minimus.

Geographical distribution of Anopheles minimus species A and C in western Thailand.

Elucidating vector distribution based on an accurate species identification is important to understanding the nature of the species complex in order to achieve vector control. Morphologically, An. minimus s.l. is difficult to distinguish from both its species complex and its closely related species. A polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique and a single multiplex-allele specific PCR developed for species identification were applied in this study in comparison with morphological identification. Both methods were used, combining with geographical information systems to determine the distribution of An. minimus species A and C. The investigation on the breeding habitats was performed in the malarious area of western Thailand. Anopheles larvae were collected from 36 bodies of water among five districts (Sangkhaburi, Thong Pha Phum, Si Sawat, Muang, and Sai Yok) of Kanchanaburi Province, Thailand. In this study, An. minimus A larvae were present in all study districts but the association differed when focusing on study sites within each district. Although there were many reports of An. minimus A in Ban Phu Rat and Ban Phu Toei villages in Sai Yok District, we did not find the breeding sites of species A in those two areas. An. minimus A and C were found in Ban Phu Ong Ka village in Sai Yok District. The breeding habitats of An. minimus C were present covering 30-40 km of distance in northern part of Sai Yok and this species was also found in the central and southern parts of Si Sawat District.

Cloning of cytochrome P450, CYP6P5, and CYP6AA2 from Anopheles minimus resistant to deltamethrin.

Two new genes in the cytochrome P450 (CYP6) family 6 with complete coding sequences were cloned and sequenced from deltamethrin-resistant Anopheles minimus, a major malaria vector in Thailand. CYP6P5 encodes a protein of 508 amino acids, while CYP6AA2 contains 505 residues. Each encoded protein contains a hydrophobic N-terminal region and a highly conserved heme-binding region typical of P450s. Alignments of deduced amino acid sequences with other insect P450 genes indicate a high degree of identity to insect CYP6 genes. Comparative mRNA expression studies using semi-quantitative RT-PCR analysis indicated that the relative amount of CYP6AA2 transcript was greater in the deltamethrin-resistant An. minimus compared to the susceptible strain. The expression of CYP6AA2 in deltamethrin-resistant mosquitoes is associated with development of deltamethrin resistance in An. minimus mosquito. The CYP6P5 transcript is equally expressed in both resistant and susceptible mosquitoes.