NADH-cytochrome b5 reductase from the insect Ceratitis capitata. Enzyme properties and membrane binding capacity

Identification and expression analysis of NADH-cytochrome b₅ reductase gene in the cotton bollworm, Helicoverpa armigera

NADH-cytochrome b(5) reductase (CBR) is one of the most important components of cytochrome P450s, which play an essential role in the detoxification of xenobiotics as well as insecticide resistance in insect pest. In the present study, two novel full-length cDNAs of CBR of the cotton bollworm, Helicoverpa armigera (Hübner) were amplified by means of reverse transcription-polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE) techniques. The sequencing results showed that the transcripts were 1809bp and 1518bp for HaCBR1 and HaCBR2, respectively, including 969bp and 939bp of complete open reading frame (ORF), which encoded 322 and 312 amino acids respectively. The putative structure and function of HaCBR1 and HaCBR2 were preliminarily analyzed by SMART program. HaCBR1 and HaCBR2 (GenBank accession numbers: HQ638220 and HQ190046HQ638220HQ190046) showed high identities with CBRs of other species. The expression of HaCBR1 and HaCBR2 mRNA was detected by real-time quantitative polymerase chain reaction (RT-qPCR) in most developmental stages of H. armigera with the exception of eggs, as well as in tissues such as cuticle, fatbody and midgut. The expression level of the two genes was significantly induced by phenobarbital (PB). These results would contribute to the understanding of CBR function in H. armigera and provide information for further study on the interactions of different components of cytochrome P450 enzyme systems.

Cytochrome P450 monooxygenases and insecticide resistance in insects

Cytochrome P450 monooxygenases are involved in many cases of resistance of insects to insecticides. Resistance has long been associated with an increase in monooxygenase activities and with an increase in cytochrome P450 content. However, this increase does not always account for all of the resistance. In Drosophila melanogaster, we have shown that the overproduction of cytochrome P450 can be lost by the fly without a corresponding complete loss of resistance. These results prompted the sequencing of a cytochrome P450 candidate for resistance in resistant and susceptible flies. Several mutations leading to amino-acid substitutions have been detected in the P450 gene CYP6A2 of a resistant strain. The location of these mutations in a model of the 3D structure of the CYP6A2 protein suggested that some of them may be important for enzyme activity of this molecule. This has been verified by heterologous expression of wild-type and mutated cDNA in Escherichia coli. When other resistance mechanisms are considered, relatively few genetic mutations are involved in insecticide resistance, and this has led to an optimistic view of the management of resistance. Our observations compel us to survey in more detail the genetic diversity of cytochrome P450 genes and alleles involved in resistance.