Soluble and membrane-bound Drosophila melanogaster CYP6G1 expressed in Escherichia coli: purification, activity, and binding properties toward multiple pesticides

Trial and error: New insights into recombinant expression of membrane-bound insect cytochromes P450 in Escherichia coli systems

Insect cytochromes P450 (CYP450s) are key enzymes responsible for a wide array of oxidative transformations of both endogenous and exogenous substrates. However, there is currently no a universal guideline established for heterologous expression of membrane-bound CYP450s, which hampers their downstream biochemical and structural studies. In this study, we conducted large-scale screening of protein overexpression in Escherichia coli using 71 insect CYP450 sequences and optimized the expression of a difficult-to-express CYP450 (CYP6HX3) using eight different optimizations, including selection of host strains and expression vectors, alternative of leader signal peptides, and N-terminal modifications. We confirmed that 1) Only insect CYP450s belonging to the CYP347 family could be expressed with N-terminal fusion of ompA2+ signal peptide in E. coli expression system. 2) E. coli Lemo 21 (DE3) effectively improved the expression of CYP6HX3 in the plasma membrane. 3) A brick-red appearance occurred frequently in the expressed thallus or membrane proteins, but this phenomenon could not necessarily indicate successful overexpression of target CYP450s. These findings provide new insights into the recombinant expression of insect CYP450s in E. coli systems and will facilitate the theoretical approaches for functional expression and production of eukaryotic CYP450s.

Computational redesign of taxane-10β-hydroxylase for de novo biosynthesis of a key paclitaxel intermediate

Paclitaxel (Taxol®) is the most popular anticancer diterpenoid predominantly present in Taxus. The core skeleton of paclitaxel is highly modified, but researches on the cytochrome P450s involved in post-modification process remain exceedingly limited. Herein, the taxane-10β-hydroxylase (T10βH) from Taxus cuspidata, which is the third post-modification enzyme that catalyzes the conversion of taxadiene-5α-yl-acetate (T5OAc) to taxadiene-5α-yl-acetoxy-10β-ol (T10OH), was investigated in Escherichia coli by combining computation-assisted protein engineering and metabolic engineering. The variant of T10βH, M3 (I75F/L226K/S345V), exhibited a remarkable 9.5-fold increase in protein expression, accompanied by respective 1.3-fold and 2.1-fold improvements in turnover frequency (TOF) and total turnover number (TTN). Upon integration into the engineered strain, the variant M3 resulted in a substantial enhancement in T10OH production from 0.97 to 2.23 mg/L. Ultimately, the titer of T10OH reached 3.89 mg/L by fed-batch culture in a 5-L bioreactor, representing the highest level reported so far for the microbial de novo synthesis of this key paclitaxel intermediate. This study can serve as a valuable reference for further investigation of other P450s associated with the artificial biosynthesis of paclitaxel and other terpenoids. KEY POINTS: • The T10βH from T. cuspidata was expressed and engineered in E. coli unprecedentedly. • The expression and activity of T10βH were improved through protein engineering. • De novo biosynthesis of T10OH was achieved in E. coli with a titer of 3.89 mg/L.

Systematic engineering pinpoints a versatile strategy for the expression of functional cytochrome P450 enzymes in Escherichia coli cell factories

Production of plant secondary metabolites in engineered microorganisms provides a scalable and sustainable alternative to their sourcing from nature or through chemical synthesis. However, the biosynthesis of many valuable plant-derived products relies on cytochromes P450 - enzymes notoriously difficult to express in microbes. To improve their expression in Escherichia coli, an arsenal of engineering strategies was developed, often paired with an extensive screening of enzyme variants. Here, attempting to identify a broadly applicable strategy, we systematically evaluated six common cytochrome P450 N-terminal modifications and their effect on in vivo activity of enzymes from the CYP79 and CYP83 families. We found that transmembrane domain truncation was the only modification with a significantly positive effect for all seven tested enzymes, increasing their product titres by 2- to 170-fold. Furthermore, when comparing the changes in the protein titre and product generation, we show that higher protein expression does not directly translate to higher in vivo activity, thus making the protein titre an unreliable screening target in the context of cell factories. We propose the transmembrane domain truncation as a first-line approach that enables the expression of wide range of highly active P450 enzymes in E. coli and circumvents the time-consuming screening process. Our results challenge the notion that the engineering strategy must be tailored for each individual cytochrome P450 enzyme and have the potential to simplify and accelerate the future design of E. coli cell factories.

Enthralling genetic regulatory mechanisms meddling insecticide resistance development in insects: role of transcriptional and post-transcriptional events

Insecticide resistance in insects severely threatens both human health and agriculture, making insecticides less compelling and valuable, leading to frequent pest management failures, rising input costs, lowering crop yields, and disastrous public health. Insecticide resistance results from multiple factors, mainly indiscriminate insecticide usage and mounted selection pressure on insect populations. Insects respond to insecticide stress at the cellular level by modest yet significant genetic propagations. Transcriptional, co-transcriptional, and post-transcriptional regulatory signals of cells in organisms regulate the intricate processes in gene expressions churning the genetic information in transcriptional units into proteins and non-coding transcripts. Upregulation of detoxification enzymes, notably cytochrome P450s (CYPs), glutathione S-transferases (GSTs), esterases [carboxyl choline esterase (CCE), carboxyl esterase (CarE)] and ATP Binding Cassettes (ABC) at the transcriptional level, modification of target sites, decreased penetration, or higher excretion of insecticides are the noted insect physiological responses. The transcriptional regulatory pathways such as AhR/ARNT, Nuclear receptors, CncC/Keap1, MAPK/CREB, and GPCR/cAMP/PKA were found to regulate the detoxification genes at the transcriptional level. Post-transcriptional changes of non-coding RNAs (ncRNAs) such as microRNAs (miRNA), long non-coding RNAs (lncRNA), and epitranscriptomics, including RNA methylation, are reported in resistant insects. Additionally, genetic modifications such as mutations in the target sites and copy number variations (CNV) are also influencing insecticide resistance. Therefore, these cellular intricacies may decrease insecticide sensitivity, altering the concentrations or activities of proteins involved in insecticide interactions or detoxification. The cellular episodes at the transcriptional and post-transcriptional levels pertinent to insecticide resistance responses in insects are extensively covered in this review. An overview of molecular mechanisms underlying these biological rhythms allows for developing alternative pest control methods to focus on insect vulnerabilities, employing reverse genetics approaches like RNA interference (RNAi) technology to silence particular resistance-related genes for sustained insect management.

The variation of a cytochrome P450 gene, CYP6G4, drives the evolution of Musca domestica L. (Diptera: Muscidae) resistance to insecticides in China

Long term and excessive insecticide use has resulted in some environmental problems and especially, insecticide resistance evolution in insect pests. The variation of cytochrome P450 monooxygenases (P450s), associated with the metabolic detoxification of toxic xenobiotics, is often involved in insecticide resistance. Here, we found that the variation in a P450 gene, CYP6G4, is the most important driver of carbamates resistance in the house fly (Musca domestica). Deciphering the detailed molecular mechanisms of the insecticide resistance is critical for performing suitable insecticide resistance management strategies. Our research results revealed that the combination of amino acid mutations (110C-330E-360N/S, 110C-330E-360S) of CYP6G4 could improve the resistance to propoxur. The nucleotide variations in the promoter region of CYP6G4 significantly increased the luciferase activity by the reporter gene assays. Additionally, miR-281-1-5p was confirmed to post-transcriptionally down-regulate the expression of CYP6G4. These findings suggest that three independent mechanisms; amino acid mutations of the P450 protein, mutations in the promoter region and low expression of post-trans-regulatory factors, as the powerful strategies for the insect resistance to toxic compounds, play a crucial role in the evolutionary processes of insecticide resistance.

Biosynthesis of aliphatic plastic monomers with amino residues in Yarrowia lipolytica

Introduciton: The α,ω-diamines (NH₂-(CH₂)_n-NH₂) and ω -amino fatty acids (NH₂-(CH₂)_n-COOH) have been widely used as building blocks in polymerindustries. Medium- to long-chain (C₈ to C₁₈) fatty acid monomers with amino residues are almost exclusively produced via chemical processes that generate hazardous waste and induce severe environmental problems, such as global warming and pollution. Here, we present the construction platformstrains of Yarrowia lipolytica a cheese-ripening yeast, for direct biotransformation of hydrocarbons into medium- to long-chain α,ω-diamines and ωamino fatty acids using metabolic engineering of endogenous fatty acid ω- and β-oxidation pathways and introducing heterologous ω-transaminase in Y. lipolytica. Methods: We deleted six genes encoding the acyl-CoA oxidase (ACO1-6) and four fatty aldehyde dehydrogenase genes (FALDH1-4), which catalyze fatty acid β-oxidation and downstream oxidation of fatty aldehydes in Y. lipolytica, respectively. The ω-transaminase from Chromobacterium violaceum DSM30191 was introduced into the genome of the ΔPOX ΔFALDH strain under the control of Y. lipolytica-derived EXP1 promoters. Results and Discussion: The ΔPOX ΔFALDH strains with ω-CvTA successfully accumulated the corresponding C12 αω-diamines into a shaking culture medium with dodecane or dodecanol. In addition, these strains accumulated C₁₂ ω-amino fatty acids from dodecanoic acid. With the commercially available α,ω-diacid bioprocess, this yeast biosynthesis producing medium- and longchain α,ω-diamines and ω-amino fatty acids could complete the yeast platform technology generating all medium- and long-chain aliphatic polyamide monomers, α,ω-biofunctionalized with one or both carboxylic acid and amino residues.

Resistance to dicyclanil and imidacloprid in the sheep blowfly, Lucilia cuprina, in Australia

BACKGROUND

The sheep blowfly, Lucila cuprina, is a myiasis-causing parasite responsible for significant production losses and welfare issues for the Australian sheep industry. Control relies largely on the use of insecticides. The pyrimidine compound, dicyclanil, is the predominant control chemical, although other insecticides also are used, including imidacloprid, ivermectin, cyromazine and spinosad. We investigated in vitro resistance patterns and mechanisms in field-collected blowfly strains.

RESULTS

The Walgett 2019 strain showed significant levels of resistance to both dicyclanil and imidacloprid, with resistance factors at the IC₅₀ of 26- and 17-fold, respectively, in in vitro bioassays. Co-treatment with the cytochrome P450 inhibitor, aminobenzotriazole, resulted in significant levels of synergism for dicyclanil and imidacloprid (synergism ratios of 7.2- and 6.1-fold, respectively), implicating cytochrome P450 in resistance to both insecticides. Cyp12d1 transcription levels were increased up to 40-fold throughout the larval life stages in the resistant strain compared to a reference susceptible strain, whereas transcription levels of some other cyp genes (6g1, 4d1, 28d1) did not differ between the strains. Similar resistance levels also were observed in flies collected from the same property in two subsequent years.

CONCLUSION

This study indicates that in vitro resistance to both dicyclanil and imidacloprid in this field-collected blowfly strain is likely mediated by cytochrome P450, with Cyp12d1 implicated as the enzyme responsible; however, it remains possible that another P450 also may be involved. A common resistance mechanism for the two drugs has important implications for drug rotation strategies designed to prolong the useful life of flystrike control chemicals. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

The overexpression and variant of CYP6G4 associated with propoxur resistance in the housefly, Musca domestica L

BACKGROUND

The control of the housefly, Musca domestica, heavily relies on the application of insecticides. Propoxur, a carbamate, has been widely used for vector control. The housefly populations with high propoxur resistance display point mutations and overexpression of acetylcholinesterase. However, the roles of cytochrome P450 monoxygenases (P450s), as important detoxification enzymes, remain poorly understand in the housefly resistant to propoxur.

RESULTS

P450s were implied to contribute to propoxur resistance based on the synergism of piperonyl butoxide (PBO) and the increase of P450 enzyme activity in the near-isogenic line propoxur resistant strain (N-PRS). Five P450 genes (CYP6G4, CYP6A25, CYP304A1, CYP6D3, and CYP6A1) by RNA-sequencing comparison were significantly up-regulated in the N-PRS strain with >1035-fold resistance to propoxur. A total of 13 non-synonymous mutations of three P450 genes (CYP6G4, CYP6D3, and CYP6D8) were found in the N-PRS strain. The amino acid substitutions of CYP6D3 and CYP6D8 were probably not resistance-associated single nucleotide polymorphisms (SNPs) because they were also found in the aabys susceptible strain. However, CYP6G4 variant in the N-PRS strain was not found in the aabys strain. The conjoint analysis of mutations and a series of genetic crosses exhibited that the housefly propoxur resistance was strongly associated with the mutations of CYP6G4 gene.

CONCLUSION

Our results suggested that a combination of up-regulated transcript levels and mutations of CYP6G4 contributed to propoxur resistance in the housefly. © 2021 Society of Chemical Industry.

Transcriptional regulation of xenobiotic detoxification genes in insects - An overview

Arthropods have well adapted to the vast array of chemicals they encounter in their environment. Whether these xenobiotics are plant allelochemicals or anthropogenic insecticides one of the strategies they have developed to defend themselves is the induction of detoxification enzymes. Although upregulation of detoxification enzymes and efflux transporters in response to specific inducers has been well described, in insects, yet, little is known on the transcriptional regulation of these genes. Over the past twenty years, an increasing number of studies with insects have used advanced genetic tools such as RNAi, CRISPR/Cas9 and reporter gene assays to dissect the genomic grounds of their xenobiotic response and hence contributed substantially in improving our knowledge on the players involved. Xenobiotics are partly recognized by various "xenobiotic sensors" such as membrane-bound or nuclear receptors. This initiates a molecular reaction cascade ultimately leading to the translocation of a transcription factor to the nucleus that recognizes and binds to short sequences located upstream their target genes to activate transcription. To date, a number of signaling pathways were shown to mediate the upregulation of detoxification enzymes in arthropods and to play a role in either metabolic resistance to insecticides or host-plant adaptation. These include nuclear receptors AhR/ARNT and HR96, GPCRs, CncC and MAPK/CREB. Recent work reveals that upregulation and activation of some components of these pathways as well as polymorphism in the binding motifs of transcription factors are linked to insects' adaptive processes. The aim of this mini-review is to summarize and describe recent work that shed some light on the main regulatory routes of detoxification gene expression in insects.

Heterologous expression of insect P450 enzymes that metabolize xenobiotics

Insect cytochrome P450-monooxygenases (P450s) are an enzyme superfamily involved in the oxidative transformation of endogenous and exogenous substrates, including insecticides. They were also shown to determine insecticide selectivity in beneficial arthropods such as bee pollinators, and to detoxify plant secondary metabolites. The recent explosion in numbers of P450s due to increased invertebrate genomes sequenced, allowed researchers to study their functional relevance for xenobiotic metabolism by recombinant expression using different expression systems. Troubleshooting strategies, including different systems and protein modifications typically adapted from mammalian P450s, have been applied to improve the functional expression, with partial success. The aim of this mini review is to critically summarize different strategies recently developed and used to produce recombinant insect P450s for xenobiotic metabolism studies.

Differential metabolism of neonicotinoids by brown planthopper, Nilaparvata lugens, CYP6ER1 variants

Imidacloprid is very effective in controlling Nilaparvata lugens Stål, which severely damages rice plants. Following heavy imidacloprid use, imidacloprid-resistant N. lugens, which showed cross-resistance to other neonicotinoids, appeared. We used the baculovirus/Sf9 expression system to express CYP6ER1 variants carrying A375del + A376G (del3) mutations, either with or without T318S mutation, which confer imidacloprid resistance in N. lugens. These CYP6ER1 variants metabolized imidacloprid but did not metabolize dinotefuran. Moreover, Drosophila expressing a CYP6ER1 variant carrying T318S + del3 mutations were resistant to imidacloprid, with a resistance ratio of 288.7, whereas the resistance ratio to dinotefuran was 3.6. These findings indicate that N. lugens has a low level of resistance to dinotefuran, and the increase of resistance is slow. We also studied the metabolism of other neonicotinoids, as well as sulfoxaflor and flupyradifurone, by CYP6ER1 variants carrying del3 mutations, either with or without the T318S mutation. Sulfoxaflor, was not metabolized by either CYP6ER1-del3 or CYP6ER1-T318Sdel3 variants. However, these variants did metabolize flupyradifurone. This study sheds light on the substrate selectivity of CYP6ER1 variants.

Differential metabolism of imidacloprid and dinotefuran by Bemisia tabaci CYP6CM1 variants

Imidacloprid has been used to control one of most serious pests, Bemisia tabaci. However, B. tabaci has developed imidacloprid resistance mainly by over-expressing CYP6CM1. It was reported that imidacloprid-resistant B. tabaci showed no or low level of cross-resistance against dinotefuran. Here, we expressed CYP6CM1 variants using Sf9/baculovirus and/or Drosophila S2 cells and showed that CYP6CM1 variants metabolized imidacloprid but not dinotefuran. In addition, we demonstrated that imidacloprid and pymetrozine competed for a CYP6CM1 variant more efficiently than dinotefuran, using a luminescent substrate competition assay. These results suggest that lack of metabolic activity of CYP6CM1 variants against dinotefuran caused no or low level of cross-resistance.

Downregulation of carboxylesterase contributes to cyflumetofen resistance in Tetranychus cinnabarinus (Boisduval)

BACKGROUND

Increased expression or point mutations of carboxyl/cholinesterases (CCEs) have been involved in many cases of insecticide and acaricide resistance. However, it has been only rarely documented that downregulation of CCE genes is associated with resistance, although many insecticides and acaricides need hydrolytic activation in vivo. Previously, expression analysis of a laboratory-selected cyflumetofen-resistant strain of Tetranychus cinnabarinus indicated that resistance was associated with increased expression of a CCE gene of TcCCE04, but also the downregulation of two CCE genes, TcCCE12 and TcCCE23.

RESULTS

Synergism experiments revealed the importance of ester hydrolysis in cyflumetofen toxicity, because treatment with S,S,S-tributylphosphorotrithioate (DEF) caused strong inhibition of cyflumetofen hydrolysis, in both the susceptible and resistant strains. Moreover, silencing expression of TcCCE12 and TcCCE23 via RNAi further decreased the susceptibility of mites to cyflumetofen significantly, suggesting that downregulated CCE genes could be involved in cyflumetofen resistance. In addition, it was shown that recombinant TcCCE12 protein could hydrolyze cyflumetofen effectively.

CONCLUSION

Decreased esterase activity via downregulation of specific CCE genes most likely contributes to cyflumetofen resistance by decreased activation of cyflumetofen to its active metabolite. Mixtures of cyflumetofen and esterase-inhibition acaricides (e.g. organophosphates or carbamates) should be avoided in field applications. © 2019 Society of Chemical Industry.

Identification and biochemical characterization of carboxylesterase 001G associated with insecticide detoxification in Helicoverpa armigera

Carboxylesterases (CarEs) are a major class of detoxification enzymes involved in insecticide resistance in various insect species. In this study, a novel CarE 001G was isolated from the cotton bollworm Helicoverpa armigera, one of the most destructive agricultural insect pests. The open reading frame of 001G has 2244 nucleotides and putatively encodes 747 amino acid residues. The deduced CarE possessed the highly conserved catalytic triads(Ser-Glu-His) and pentapeptide motifs (Gly-X-Ser-X-Gly), suggesting 001G is biologically active. The truncated 001G was successfully expressed in Escherichia coli, and the recombinant proteins were purified and tested. The enzyme kinetic assay showed the purified proteins could catalyze two model substrates, α-naphthyl acetate and β-naphthyl acetate, with a kcat of 8.8 and 2.3 s^-1, a Km of 9.6 and 16.2 μM, respectively. The inhibition study with pyrethroid, organophosphate and neonicotinoid insecticides showed different inhibition profile against the purified CarE. The HPLC assay demonstrated that the purified proteins were able to metabolize β-cypermethrin, λ-cyhalothrin and fenvalerate insecticides, exhibiting respective specific activities of 1.7, 1.4 and 0.5 nM/min/mg protein. However, the purified proteins were not able to metabolize the chlorpyrifos, parathion-methyl, paraoxon-ethyl and imidacloprid. The modeling and docking analyses consistently demonstrated that the pyrethroid molecule fits snugly into the catalytic pocket of the CarE 001G. Collectively, our results suggest that 001G may play a role in pyrethroids detoxification in H. armigera.

Functional analysis of four upregulated carboxylesterase genes associated with fenpropathrin resistance in Tetranychus cinnabarinus (Boisduval)

BACKGROUND

Carboxylesterases (CarEs) are important in pesticide resistance. Four overexpressed CarE genes with inducible character were screened out in fenpropathrin-resistant Tetranychus cinnabarinus, but their functional roles remained to be further analyzed by RNAi and protein expression.

RESULTS

Feeding a single double-stranded (ds)RNA of each of four genes led to gene-specific downregulation of mRNA, decreased esterase activity and diminished resistance in T. cinnabarinus. More interestingly, feeding four dsRNAs simultaneously led to a more significant decrease in enzymatic activity and fold resistance than feeding a single dsRNA individually, suggesting that these CarE genes were involved in fenpropathrin-resistance and had cooperative roles. The gene CarE6 was regarded as the primary and representative candidate to be functionally expressed, because silencing of CarE6 led to the most significant decrease in resistance level. The activity of CarE6 protein was competitively inhibited by fenpropathrin. It could effectively decompose 41.7 ± 0.09% of fenpropathrin within 3 h, proving that CarE6 protein was capable of metabolizing fenpropathrin effectively in T. cinnabarinus.

CONCLUSION

The results confirm that four CarE genes are cooperatively involved in fenpropathrin resistance and the metabolic enzymes encoded by these overexpressed genes do indeed metabolize acaricide in resistant T. cinnabarinus in the evolution of acaricide resistance. © 2018 Society of Chemical Industry.

Characterization of Cytochrome P450 Enzymes and Their Applications in Synthetic Biology

The cytochrome P450 monooxygenase enzymes (P450s) catalyze a diverse array of chemical transformations, most originating from the insertion of an oxygen atom into a substrate that binds close to the P450 heme. The oxygen is delivered by a highly reactive heme iron-oxo species (compound I) and, according to the chemical nature of the substrate and its position in the active site, the P450 can catalyze a wide range of reactions including, e.g., hydroxylation, reduction, decarboxylation, sulfoxidation, N- and O-demethylation, epoxidation, deamination, CC bond formation and breakage, nitration, and dehalogenation. In this chapter, we describe the structural, biochemical, and catalytic properties of the P450s, along with spectroscopic and analytical methods used to characterize P450 enzymes and their redox partners. Important uses of P450 enzymes are highlighted, including how various P450s have been exploited for applications in synthetic biology.

Evidence for activation of nitenpyram by a mitochondrial cytochrome P450 in Drosophila melanogaster

BACKGROUND

Nitenpyram is a member of the economically important neonicotinoid class of insecticides. The in vivo metabolism of nitenpyram is not well characterised, but cytochrome P450 activity is the major mechanism of resistance to neonicotinoids identified in insect pests, and P450s metabolise other neonicotinoids including imidacloprid.

RESULTS

Here, we used the GAL4-UAS targeted expression system to direct RNA interference (RNAi) against the cytochrome P450 redox partners to interrupt P450 functions in specific tissues in Drosophila melanogaster. RNAi of the mitochondrial redox partner defective in the avoidance of repellents (dare) in the digestive tissues reduced nitenpyram mortality, suggesting an activation step in the metabolism of nitenpyram carried out by a mitochondrial P450. RNAi of the mitochondrial cytochrome P450 Cyp12a5, which is expressed in the digestive tissues, resulted in the same phenotype, and transgenic overexpression of Cyp12a5 increased nitenpyram sensitivity.

CONCLUSION

These results suggest that in vivo metabolism of nitenpyram by the mitochondrial P450 CYP12A5 results in the formation of a product with higher toxicity than the parent compound. © 2018 Society of Chemical Industry.

Recombinant production of eukaryotic cytochrome P450s in microbial cell factories

Cytochrome P450s (P450s) comprise one of the largest known protein families. They occur in every kingdom of life and catalyze essential reactions, such as carbon source assimilation, synthesis of hormones and secondary metabolites, or degradation of xenobiotics. Due to their outstanding ability of specifically hydroxylating complex hydrocarbons, there is a great demand to use these enzymes for biocatalysis, including applications at an industrial scale. Thus, the recombinant production of these enzymes is intensively investigated. However, especially eukaryotic P450s are difficult to produce. Challenges are faced due to complex cofactor requirements and the availability of a redox-partner (cytochrome P450 reductase, CPR) can be a key element to get active P450s. Additionally, most eukaryotic P450s are membrane bound which complicates the recombinant production. This review describes current strategies for expression of P450s in the microbial cell factories Escherichia coli, Saccharomyces cerevisiae, and Pichia pastoris.

Strategies for the construction of insect P450 fusion enzymes

Cytochrome P450 monooxygenases (P450s) are ubiquitous enzymes with a broad substrate spectrum. Insect P450s are known to catalyze reactions such as the detoxification of insecticides and the synthesis of hydrocarbons, which makes them useful for many industrial processes. Unfortunately, it is difficult to utilize P450s effectively because they must be paired with cytochrome P450 reductases (CPRs) to facilitate electron transfer from reduced nicotinamide adenine dinucleotide phosphate (NADPH). Furthermore, eukaryotic P450s and CPRs are membrane-anchored proteins, which means they are insoluble and therefore difficult to purify when expressed in their native state. Both challenges can be addressed by creating fusion proteins that combine the P450 and CPR functions while eliminating membrane anchors, allowing the production and purification of soluble multifunctional polypeptides suitable for industrial applications. Here we discuss several strategies for the construction of fusion enzymes combining insect P450 with CPRs.

Phylogenetic and functional characterization of ten P450 genes from the CYP6AE subfamily of Helicoverpa armigera involved in xenobiotic metabolism

The cotton bollworm, Helicoverpa armigera, is a generalist herbivore widely distributed over the world and is a major lepidopteran pest on cotton. Studies, especially from Asia, show that it relies on cytochrome P450 monooxygenases with broad substrate specificities to protect itself from pesticides. The number of P450s may have expanded in the processes of coping with the wide diversity of phytochemicals that the insect encounters among its numerous host plants. In order to examine the metabolic capabilities of these P450s, we focused here on all ten P450s of the Helicoverpa armigera CYP6AE subfamily, which can be easily induced by plant toxins and pyrethroids. These P450s, along with cytochrome P450 reductase, were heterologously expressed in insect cells and compared functionally. In vitro metabolism showed that all CYP6AE subfamily members can convert esfenvalerate to 4'-hydroxyesfenvalerate efficiently except CYP6AE20. In contrast, none of the recombinant CYP6AE enzymes could metabolise gossypol under our experimental conditions. Epoxidation capabilities were observed in the CYP6AE subfamily, aldrin can be converted to dieldrin at rates up to 0.45 ± 0.04 pmol/min/pmol P450. Seven P450s in this subfamily can metabolise imidacloprid, but with lower efficiency than Bemisia tabaci CYP6CM1vQ. CYP6AE20 had virtually no metabolic competence to these four compounds but could metabolise several model fluorogenic substrates. These results showed the broad substrate spectrum of H. armigera CYP6AE P450s and suggest a limited role of gossypol upon the evolution of H. armigera CYP6AE genes.

Prokaryotic functional expression and activity comparison of three CYP9A genes from the polyphagous pest Helicoverpa armigera

Cytochrome P450s (CYPs or P450s) have been long recognized as very important enzymes in the metabolism of xenobiotic and endogenous compounds, but only a few CYPs have been functionally characterized in insects. The effort in functional characterization of insect P450s is heavily hindered by technical difficulties in preparing active, individual P450 enzymes directly from the target insect. In this paper, we describe the functional expression of two additional pyrethroid resistance-associated CYP9A genes (CYP9A12 and CYP9A17) from the polyphagous pest Helicoverpa armigera in the facile Escherichia coli. The functionality of E. coli produced CYP9A12, CYP9A14, and CYP9A17 was investigated and activities of these CYP9As were compared against three probe substrates after reconstitution with NADPH-dependent cytochrome P450 reductase. The results showed that active forms of CYP9A12 and CYP9A17 were expressed in E. coli with a content of about 1.0-1.5 nmol mg-1 protein in membrane preparations. In vitro assays showed that CYP9A14 was capable of catalyzing O-dealkylation of methoxyresorufin (MROD), ethoxyresorufin (EROD), and benzyloxyresorufin (BROD), while CYP9A12 and CYP9A17 exhibited only MROD and EROD activities. Kinetic studies demonstrated that CYP9A14 had the greatest k cat/K m value for MROD, and CYP9A17 for EROD, while the lowest k cat/K m values for both MROD and EROD were observed for CYP9A12. The distinct biochemical traits suggest that the three paralogous CYP9As may play different roles in xenobiotic metabolism in this important pest.

Recombinant expression and characterization of Lucilia cuprina CYP6G3: Activity and binding properties toward multiple pesticides

The Australian sheep blowfly, Lucilia cuprina, is a primary cause of sheep flystrike and a major agricultural pest. Cytochrome P450 enzymes have been implicated in the resistance of L. cuprina to several classes of insecticides. In particular, CYP6G3 is a L. cuprina homologue of Drosophila melanogaster CYP6G1, a P450 known to confer multi-pesticide resistance. To investigate the basis of resistance, a bicistronic Escherichia coli expression system was developed to co-express active L. cuprina CYP6G3 and house fly (Musca domestica) P450 reductase. Recombinant CYP6G3 showed activity towards the high-throughput screening substrates, 7-ethoxycoumarin and p-nitroanisole, but not towards p-nitrophenol, coumarin, 7-benzyloxyresorufin, or seven different luciferin derivatives (P450-Glo™ substrates). The addition of house fly cytochrome b₅ enhanced the k_cat for p-nitroanisole dealkylation approximately two fold (17.8 ± 0.5 vs 9.6 ± 0.2 min^-1) with little effect on K_M (13 ± 1 vs 10 ± 1 μM). Inhibition studies and difference spectroscopy revealed that the organochlorine compounds, DDT and endosulfan, and the organophosphate pesticides, malathion and chlorfenvinphos, bind to the active site of CYP6G3. All four pesticides showed type I binding spectra with spectral dissociation constants in the micromolar range suggesting that they may be substrates of CYP6G3. While no significant inhibition was seen with the organophosphate, diazinon, or the neonicotinoid, imidacloprid, diazinon showed weak binding in spectral assays, with a Kd value of 23 ± 3 μM CYP6G3 metabolised diazinon to the diazoxon and hydroxydiazinon metabolites and imidacloprid to the 5-hydroxy and olefin metabolites, consistent with a proposed role of CYP6G enzymes in metabolism of phosphorothioate and neonicotinoid insecticides in other species.

Heterologous expression of Helicoverpa armigera cytochrome P450 CYP6B7 in Pichia pastoris and interactions of CYP6B7 with insecticides

BACKGROUND

Previous studies indicated that constitutive over-expression of cytochrome P450 CYP6B7 was involved in fenvalerate resistance in Helicoverpa armigera. In this study, the CYP6B7 gene from H. armigera (namely HaCYP6B7), was heterologously expressed in Pichia pastoris GS115. A vector pPICZA-HaCYP6B7 was constructed and transformed into P. pastoris GS115, the transformant of pPICZA-HaCYP6B7-GS115 was then cultured and induced by 1% (v/v) methanol and the heterologous expression of HaCYP6B7 protein in P. pastoris was confirmed by SDS-PAGE and western blot.

RESULTS

Microsomes containing the expressed HaCYP6B7 showed activities against model substrate p-nitroanisole and 7-ethoxycoumarin, with p-nitroanisole O-demethylation (PNOD) and 7-ethoxycoumarin O-deethylation (ECOD) activities of 15.66- and 4.75-fold of the control, respectively. Moreover, it showed degradation activities against the insecticides bifenthrin, fenvalerate and chlorpyrifos, with clearance activities of 6.88-, 1.49- and 2.27-fold of the control, respectively. The interactions of HaCYP6B7 with insecticides were further confirmed by molecular docking in silico with binding scores of 5.450, 5.295 and 2.197 between putative HaCYP6B7 protein and bifenthrin, fenvalerate and chlorpyrifos, respectively.

CONCLUSION

The results of present study provided more direct and important evidence on the role of HaCYP6B7 conferring pyrethroid resistance in H. armigera. © 2017 Society of Chemical Industry.

Genomic innovations, transcriptional plasticity and gene loss underlying the evolution and divergence of two highly polyphagous and invasive Helicoverpa pest species

BACKGROUND

Helicoverpa armigera and Helicoverpa zea are major caterpillar pests of Old and New World agriculture, respectively. Both, particularly H. armigera, are extremely polyphagous, and H. armigera has developed resistance to many insecticides. Here we use comparative genomics, transcriptomics and resequencing to elucidate the genetic basis for their properties as pests.

RESULTS

We find that, prior to their divergence about 1.5 Mya, the H. armigera/H. zea lineage had accumulated up to more than 100 more members of specific detoxification and digestion gene families and more than 100 extra gustatory receptor genes, compared to other lepidopterans with narrower host ranges. The two genomes remain very similar in gene content and order, but H. armigera is more polymorphic overall, and H. zea has lost several detoxification genes, as well as about 50 gustatory receptor genes. It also lacks certain genes and alleles conferring insecticide resistance found in H. armigera. Non-synonymous sites in the expanded gene families above are rapidly diverging, both between paralogues and between orthologues in the two species. Whole genome transcriptomic analyses of H. armigera larvae show widely divergent responses to different host plants, including responses among many of the duplicated detoxification and digestion genes.

CONCLUSIONS

The extreme polyphagy of the two heliothines is associated with extensive amplification and neofunctionalisation of genes involved in host finding and use, coupled with versatile transcriptional responses on different hosts. H. armigera's invasion of the Americas in recent years means that hybridisation could generate populations that are both locally adapted and insecticide resistant.

CYP6B6 is involved in esfenvalerate detoxification in the polyphagous lepidopteran pest, Helicoverpa armigera

The cotton bollworm, Helicoverpa armigera, is a polyphagous pest that has a strong capacity to evolve resistance against various classes of insecticides. Cytochrome P450 enzymes have been suspected involved in pyrethroid metabolism and resistance in this pest. However, how many and which P450s are involved in pyrethroid metabolism is largely unknown. In this study, CYP6B6 and NADPH-cytochrome P450 reductase (HaCPR) from H. armigera were successfully co-expressed in Escherichia coli. Incubation of esfenvalerate with the recombinant CYP6B6-HaCPR monooxygenase complex revealed that CYP6B6 was able to transform esfenvalerate into 4'-hydroxy fenvalerate. Kcat and Km values for the formation of 4'-hydroxyfenvalerate by the E. coli-produced CYP6B6 were determined to be 1.65±0.11min^-1 and 4.10±0.84μM respectively. Our results demonstrate that CYP6B6 has the ability to hydroxylate esfenvalerate, thus plays a role in fenvalerate detoxification.

Comparative Analysis of Recombinant Cytochrome P450 CYP9A61 from Cydia pomonella Expressed in Escherichia coli and Pichia pastoris

On the basis of prior work, cytochrome P450 CYP9A61 was found to be enriched in fat bodies and during feeding stages, and transcription was induced by λ-cyhalothrin in Cydia pomonella. In this study, recombinant CYP9A61 was expressed in Escherichia coli and Pichia pastoris, and its biochemical properties were investigated. Substrate saturation curves and biochemical properties revealed that, in the presence of glycosylation, the yeast-secreted CYP9A61 exhibited a higher affinity for the substrate p-nitroanisole and was found to be more stable at certain pHs and temperatures than bacterially produced CYP9A61. Half-inhibitory concentrations (IC₅₀) of three synthetic pyrethroids on both the bacterium- and yeast-expressed CYP9A61 suggested that recombinant CYP9A61 expressed in different hosts exhibits different inhibition properties. Taken together, our findings show that yeast-expressed CYP9A61 exhibits enzyme activity that is better than that expressed in bacteria and might be used for further metabolism assays to reveal the insecticide-detoxifying role of CYP9A61 in C. pomonella.

Resistance evolution in Drosophila: the case of CYP6G1

The massive use of DDT as an insecticide between 1940 and 1970 has resulted in the emergence of a resistant population of insects. One of the main metabolic mechanisms developed by resistant insects involves detoxification enzymes such as cytochrome P450s. These enzymes can metabolise the insecticide to render it less toxic and facilitate its elimination from the organism. The P450 Cyp6g1 was identified as the major factor responsible for DDT resistance in Drosophila melanogaster field populations. In this article, we review the data available for this gene since it was associated with resistance in 2002. The knowledge gained on Cyp6g1 allows a better understanding of the evolution of insecticide resistance mechanisms and highlights the major role of transposable elements in evolutionary processes. © 2016 Society of Chemical Industry.

Bacterial Expression and Kinetic Analysis of Carboxylesterase 001D from Helicoverpa armigera

Carboxylesterasesare an important class of detoxification enzymes involved in insecticide resistance in insects. A subgroup of Helicoverpa armigera esterases, known as Clade 001, was implicated in organophosphate and pyrethroid insecticide resistance due to their overabundance in resistant strains. In this work, a novel carboxylesterasegene 001D of H. armigera from China was cloned, which has an open reading frame of 1665 nucleotides encoding 554 amino acid residues. We used a series of fusion proteins to successfully express carboxylesterase 001D in Escherichia coli. Three different fusion proteins were generated and tested. The enzyme kinetic assay towards 1-naphthyl acetate showed all three purified fusion proteins are active with a Kcat between 0.35 and 2.29 s⁻¹, and a Km between 7.61 and 19.72 μM. The HPLC assay showed all three purified fusion proteins had low but measurable hydrolase activity towards β-cypermethrin and fenvalerate insecticides (specific activities ranging from 0.13 to 0.67 μM·min⁻¹·(μM⁻¹·protein)). The enzyme was stable up to 40 °C and at pH 6.0–11.0. The results imply that carboxylesterase 001D is involved in detoxification, and this moderate insecticide hydrolysis may suggest that overexpression of the gene to enhance insecticide sequestration is necessary to allow carboxylesterases to confer resistance to these insecticides in H. armigera.

Functional Analysis of Esterase TCE2 Gene from Tetranychus cinnabarinus (Boisduval) involved in Acaricide Resistance

The carmine spider mite, Tetranychus cinnabarinus is an important pest of crops and vegetables worldwide, and it has the ability to develop resistance against acaricides rapidly. Our previous study identified an esterase gene (designated TCE2) over-expressed in resistant mites. To investigate this gene's function in resistance, the expression levels of TCE2 in susceptible, abamectin-, fenpropathrin-, and cyflumetofen-resistant strains were knocked down (65.02%, 63.14%, 57.82%, and 63.99%, respectively) via RNA interference. The bioassay data showed that the resistant levels to three acaricides were significantly decreased after the down-regulation of TCE2, indicating a correlation between the expression of TCE2 and the acaricide-resistance in T. cinnabarinus. TCE2 gene was then re-engineered for heterologous expression in Escherichia coli. The recombinant TCE2 exhibited α-naphthyl acetate activity (483.3 ± 71.8 nmol/mg pro. min(-1)), and the activity of this enzyme could be inhibited by abamectin, fenpropathrin, and cyflumetofen, respectively. HPLC and GC results showed that 10 μg of the recombinant TCE2 could effectively decompose 21.23% fenpropathrin and 49.70% cyflumetofen within 2 hours. This is the first report of a successful heterologous expression of an esterase gene from mites. This study provides direct evidence that TCE2 is a functional gene involved in acaricide resistance in T. cinnabarinus.

Functional characterization of NADPH-cytochrome P450 reductase from Bactrocera dorsalis: Possible involvement in susceptibility to malathion

NADPH cytochrome P450 reductase (CPR) is essential for cytochrome P450 catalysis, which is important in the detoxification and activation of xenobiotics. In this study, two transcripts of Bactrocera dorsalis CPR (BdCPR) were cloned, and the deduced amino-acid sequence had an N-terminus membrane anchor for BdCPR-X1 and three conserved binding domains (FMN, FAD, and NADP), as well as an FAD binding motif and catalytic residues for both BdCPR-X1 and BdCPR-X2. BdCPR-X1 was detected to have the high expression levels in adults and in Malpighian tubules, fat bodies, and midguts of adults, but BdCPR-X2 expressed lowly in B. dorsalis. The levels of BdCPRs were similar in malathion-resistant strain compared to susceptible strain. However, injecting adults with double-stranded RNA against BdCPR significantly reduced the transcript levels of the mRNA, and knockdown of BdCPR increased adult susceptibility to malathion. Expressing complete BdCPR-X1 cDNA in Sf9 cells resulted in high activity determined by cytochrome c reduction and these cells had higher viability after exposure to malathion than control. The results suggest that BdCPR could affect the susceptibility of B. dorsalis to malathion and eukaryotic expression of BdCPR would lay a solid foundation for further investigation of P450 in B. dorsalis.

Nrf2/Maf-binding-site-containing functional Cyp6a2 allele is associated with DDT resistance in Drosophila melanogaster

BACKGROUND

Increased insecticide detoxification mediated by cytochrome P450s is a common mechanism of insecticide resistance. Although Cyp6a2 has been observed to be overexpressed in many 4,4'-dichlorodiphenyltrichloroethane (DDT)-resistant strains of Drosophila melanogaster, how Cyp6a2 is regulated and whether its overproduction confers DDT resistance remain elusive.

RESULTS

Molecular analysis identified five Cyp6a2 alleles (Cyp6a2(Canton) (-S-1) , Cyp6a2(Canton) (-S-2) , Cyp6a2(91-C) , Cyp6a2(91-R) and Cyp6a2(Wisconsin) (-) (WD) ) from four D. melanogaster strains, notably differing in the presence or absence of an intact Nrf2/Maf (a transcription factor) binding site in the 5'-promoter core region, a 'G1410' frameshift deletion mutation in the heme-binding region and a long terminal repeat (LTR) of transposable element 17.6 in the 3'-untranslated region (UTR). Linkage analysis confirmed that DDT resistance was genetically linked to a Nrf2/Maf-binding-site-containing, LTR-lacking functional allele of Cyp6a2 (Cyp6a2(91-R) ). The qRT-PCR results showed that overexpression of functional Cyp6a2 was consistently associated with DDT resistance. Luciferase reporter gene assays revealed that an intact Nrf2/Maf binding site in the 5'-promoter core region enhanced the constitutive transcription of Cyp6a2.

CONCLUSION

The results suggest that the Nrf2/Maf binding-site-containing functional Cyp6a2 allele is associated with DDT resistance in the D. melanogaster strains under study.

How many genetic options for evolving insecticide resistance in heliothine and spodopteran pests?

The widely accepted paradigm for the development of insecticide resistance in field populations of insects is of selection for one or a very few genes of major effect. Limited genetic mapping data for organophosphate and pyrethroid resistance in heliothine and spodopteran pests generally agrees with this paradigm. However, other biochemical and transcriptomic data suggest a more complex set of changes in multiple P450 and esterase gene/enzyme systems in resistant strains of these species. We discuss possible explanations for this paradox, including the likely embedding of these genes in regulatory cascades and emerging evidence for their arrangement in large clusters of closely related genes. We conclude that there could indeed be an unusually large number of genetic options for evolving resistance in these species.