Structural characterization of an aldo-keto reductase (AKR2E5) from the silkworm Bombyx mori

Phylogenetic and transcriptomic study of aldo-keto reductases in Haemonchus contortus and their inducibility by flubendazole

Aldo-keto reductases (AKRs), a superfamily of NADP(H)-dependent oxidoreductases, catalyze the oxidoreduction of a wide variety of eobiotic and xenobiotic aldehydes and ketones. In mammals, AKRs play essential roles in hormone and xenobiotic metabolism, oxidative stress, and drug resistance, but little is known about these enzymes in the parasitic nematode Haemonchus contortus. In the present study, 22 AKR genes existing in the H. contortus genome were investigated and a phylogenetic analysis with comparison to AKRs in Caenorhabditis elegans, sheep and humans was conducted. The constitutive transcription levels of all AKRs were measured in eggs, larvae, and adults of H. contortus, and their expression was compared in a drug-sensitive strain (ISE) and a benzimidazole-resistant strain (IRE) previously derived from the sensitive strain by imposing benzimidazole selection pressure. In addition, the inducibility of AKRs by exposure of H. contortus adults to benzimidazole anthelmintic flubendazole in vitro was tested. Phylogenetic analysis demonstrated that the majority of AKR genes in H. contortus lack orthologues in the sheep genome, which is a favorable finding for considering AKRs as potential drug targets. Large differences in the expression levels of individual AKRs were observed, with AKR1, AKR3, AKR8, and AKR10 being the most highly expressed at most developmental stages. Significant changes in the expression of AKRs during the life cycle and pronounced sex differences were found. Comparing the IRE and ISE strains, three AKRs were upregulated, and seven AKRs were downregulated in adults. In addition, the expression of three AKRs was induced by flubendazole exposure in adults of the ISE strain. Based on these results, AKR1, AKR2, AKR3, AKR5, AKR10 and AKR19 in particular merit further investigation and functional characterization with respect to their potential involvement in drug biotransformation and anthelmintic resistance in H. contortus.

Novel aldo-keto reductase AKR2E9 regulates aldehyde content in the midgut and antennae of the silkworm (Bombyx mori)

We studied the effects of green leaf volatiles (including reactive aldehydes) emitted by plants on insects that feed on these plants. The silkworm (Bombyx mori) is a model lepidopteran that eats mulberry leaves. Defense-related enzymes in silkworms can be targeted for developing new pest control methods. The aldo-keto reductase (AKR) superfamily catalyzes aldehyde reduction by converting a carbonyl group into an alcohol group. Here, we characterized a novel silkworm AKR, designated as AKR2E9. Recombinant AKR2E9 was overexpressed in Escherichia coli. The recombinant protein was used, along with nicotinamide adenine dinucleotide phosphate as a coenzyme, to reduce aldehydes present in mulberry (Morus alba) leaves. The catalytic efficiency of AKR2E9 toward various aldehyde substrates and its inhibitor sensitivity was lower than those of AKR2E8. High expression levels of akr2e9 messenger RNA (mRNA) were detected in the midgut and antennae of silkworms. In the antennae of adult silkworms, akr2e9 mRNA was more abundant than akr2e8 mRNA. The catalytic efficiency of AKR2E9 was low because of steric hindrance, due to which its active site is blocked. High expression levels of AKR2E9 in the midgut and antennae suggest that it may regulate the detoxification of toxic aldehydes in silkworms.

Novel silkworm (Bombyx mori) sulfotransferase swSULT ST3 is involved in metabolism of polyphenols from mulberry leaves

Polyphenols in plants are important for defense responses against microorganisms, insect herbivory, and control of feeding. Owing to their antioxidant, anti-cancer, and anti-inflammatory activities, their importance in human nutrition has been acknowledged. However, metabolism of polyphenols derived from mulberry leaves in silkworms (Bombyx mori) remains unclear. Sulfotransferases (SULT) are involved in the metabolism of xenobiotics and endogenous compounds. The purpose of this study is to investigate the metabolic mechanism of polyphenols mediated by B. mori SULT. Here, we identified a novel SULT in silkworms (herein, swSULT ST3). Recombinant swSULT ST3 overexpressed in Escherichia coli effectively sulfated polyphenols present in mulberry leaves. swSULT ST3 showed high specific activity toward genistein among the polyphenols. Genistein-7-sulfate was produced by the activity of swSULT ST3. Higher expression of swSULT ST3 mRNA was observed in the midgut and fat body than in the hemocytes, testis, ovary, and silk gland. Polyphenols inhibited the aldo-keto reductase detoxification of reactive aldehydes from mulberry leaves, and the most noticeable inhibition was observed with genistein. Our results suggest that swSULT ST3 plays a role in the detoxification of polyphenols, including genistein, and contributes to the effects of aldo-keto reductase in the midgut of silkworms. This study provides new insight into the functions of SULTs and the molecular mechanism responsible for host plant selection in lepidopteran insects.

Mosaic Evolution of Molecular Pathways for Sex Pheromone Communication in a Butterfly

Unraveling the origin of molecular pathways underlying the evolution of adaptive traits is essential for understanding how new lineages emerge, including the relative contribution of conserved ancestral traits and newly evolved derived traits. Here, we investigated the evolutionary divergence of sex pheromone communication from moths (mostly nocturnal) to butterflies (mostly diurnal) that occurred ~119 million years ago. In moths, it is the females that typically emit pheromones to attract male mates, but in butterflies males emit pheromones that are used by females for mate choice. The molecular bases of sex pheromone communication are well understood in moths, but they have remained relatively unexplored in butterflies. We used a combination of transcriptomics, real time qPCR, and phylogenetics to identify genes involved in the different steps (i.e., production, regulation, and reception) of sex pheromone communication of the butterfly Bicyclus anynana. Our results show that the biosynthesis and reception of sex pheromones relies both on moth-specific gene families (reductases) and on more ancestral insect gene families (desaturases, olfactory receptors, odorant binding proteins). Interestingly, B. anynana appears to use what was believed to be the moth-specific neuropeptide Pheromone Biosynthesis Activating Neuropeptide (PBAN) for regulating sex pheromone production. Altogether, our results suggest that a mosaic pattern best explains how sex pheromone communication evolved in butterflies, with some molecular components derived from moths, and others conserved from more ancient insect ancestors. This is the first large-scale investigation of the genetic pathways underlying sex pheromone communication in a butterfly.

Bombyx mori-derived aldo-keto reductase AKR2E8 detoxifies aldehydes present in mulberry leaves

Lepidopterans are agricultural pests. Since the silkworm is a model for lepidopterans, analysis of the enzymes produced by silkworms is of great interest for developing methods of pest control. The aldo-keto reductase (AKR) superfamily catalyzes the reduction of aldehydes by converting a carbonyl group to an alcohol group. Here, we characterized a new AKR present in the silkworm Bombyx mori, which has been designated as AKR2E8. Amino acid sequence and phylogenetic analyses showed that AKR2E8 is similar to human AKR1B1 and AKR1B10. Three amino acid residues in the active site were identical among AKR2E8, AKR1B1, and AKR1B10. Recombinant AKR2E8 overexpressed in Escherichia coli used nicotinamide adenine dinucleotide phosphate as a coenzyme to reduce the aldehydes present in mulberry (Morus alba) leaves. AKR2E8 was found to reduce benzaldehyde, hexanal, heptanal, nonanal, trans-2-nonenal, and citral. No nicotinamide adenine dinucleotide-dependent activity was detected. Akr2e8 mRNA was detected in the testes, ovaries, and fat body; the highest expression was found in the midgut. The substrate specificity and highest observed expression of AKR2E8 in the midgut suggests that AKR2E8 may play a major role in aldehyde detoxification in silkworms. The findings of this study may assist in the development of pest control methods for controlling the population of lepidopterans, such as silkworms, that damage crops.

Exploring the Terminal Pathway of Sex Pheromone Biosynthesis and Metabolism in the Silkworm

Simple Summary

Insect sex pheromone biosynthesis has received widespread attention, while the terminal pathway related to aldehyde synthesis and metabolism is still poorly understood at a molecular level. Previous studies found that the silkworm, Bombyx mori (Lepidoptera, Bombycidae), has two pheromone compounds, bombykol and bombykal, with a ratio of 11:1, while its closest wild relative, B. mandarina, only uses bombykol as a pheromone. In this study, sex pheromone gland transcriptomes were compared between the domestic and wild silkworms. All the candidate gene families were identified. Then we used the differentially expressed information, tissue and developmental expression profiles, and phylogenetic analysis to identify the putative causal genes involved in the terminal pathway. Our findings provide insights into the aldehyde synthesis and metabolism pathways and evolutionary conservation in moths.

Abstract

Sex pheromones are vital to sexual communication and reproduction in insects. Although some key enzymes in pheromone production have been well studied, information on genes involved in the terminal pathway is limited. The domestic silkworm employs a pheromone blend containing (E,Z)-10,12-hexadecadienol (bombykol) and analogous (E,Z)-10,12-hexadecadienal (bombykal); whereas, its wild ancestor B. mandarina uses only bombykol. The two closely related moths might be a good model for exploring the genes involved in aldehyde pheromone synthesis and metabolism. By deep sequencing and analyzing the sex pheromone gland (PG) transcriptomes; we identified 116 candidate genes that may be related to pheromone biosynthesis, metabolism, and chemoreception. Spatiotemporal expression profiles and differentially expressed analysis revealed that four alcohol oxidases (BmorAO1; 2; 3; and 4); one aldehyde reductase (BmorAR1); and one aldehyde oxidase (BmorAOX5) might be involved in the terminal pathway. Phylogenetic analysis showed that, except for BmorAO3 and MsexAO3, AOs did not show a conversed orthologous relationship among moths; whereas, ARs and AOXs were phylogenetically conserved. This study provides crucial candidates for further functional elucidation, and which may be utilized as potential targets to disrupt sexual communication in other moth pests.

Identification of genes involved in sex pheromone biosynthesis and metabolic pathway in the Chinese oak silkworm, Antheraea pernyi

The Chinese oak silkworm, Antheraea pernyi, has not only been semi-domesticated as an important economical insect but also used for genetic research. The female moths of A. pernyi employ a pheromone blend containing (E,Z)-6,11-hexadecadienal (E6,Z11-16:Ald), (E,Z)-6,11-hexadecadienyl acetate (E6,Z11-16:OAc), and (E,Z)-4,9-tetradecadienyl acetate (E4,Z9-14:OAc). While its biosynthesis pathway is largely unknown. By deep sequencing and de novo assembly of sex pheromone gland (PG) transcriptome, we identified 141 candidate genes that are putatively related to pheromone biosynthesis, degradation, and chemoreception in A. pernyi. Gene expression patterns and phylogenetic analysis revealed that two desaturases (AperDES1 and 2), two fatty acid reductase (AperFAR1 and 2), and three acetyltransferase genes (AperACT1, 2 and 3) showed PG-biased or specific expression and were phylogenetically related to genes known to be involved in pheromone synthesis in other species. Furthermore, two carboxylesterases (AperCOE6 and 11) and two chemosensory protein (AperCSP1 and 6) were also expressed specifically or predominantly in the PGs, which might be related to sex pheromone degradation and transportation, respectively. Based on these results, the sex pheromone biosynthesis and metabolic pathway was proposed in A. pernyi. This study provides some crucial candidates for further functional elucidation, and may be used for interfering sexual communication in other Saturniidae pests.

Functional characterization of an aldose reductase (bmALD1) obtained from the silkworm Bombyx mori

We describe a new member of the aldo-keto reductase (AKR) superfamily in the silkworm Bombyx mori. On the basis of its amino acid sequence and phylogenetic tree, this AKR belongs to the AKR1B family and has been designated as bmALD1. In the current study, recombinant bmALD1 was overexpressed, purified to homogeneity and kinetically characterized. We discovered that bmALD1 uses NADPH as a coenzyme to reduce carbonyl compounds such as DL-glyceraldehyde, glucose and 2-nonenal. No NADH-dependent activity was detected. To the best of our knowledge, bmALD1 is only the third AKR characterized in silkworm which, given its substrate specificity, could play a major role in glucose metabolism and antioxidant reactions. Our data provide an increased understanding of insect AKR function.

iTRAQ-Based Quantitative Proteomic Analysis of Digestive Juice across the First 48 Hours of the Fifth Instar in Silkworm Larvae

The silkworm is an oligophagous insect for which mulberry leaves are the sole diet. The nutrients needed for vital activities of the egg, pupal, and adult stages, and the proteins formed in the cocoon, are all derived from the larval stages. The silkworm feeds and grows quickly during the larval stages. In particular, the amount of leaf ingested and digested quickly increases from the ecdysis to the gluttonous stage in the fifth instar period. In this study, we used the iTRAQ proteomic technique to identify and analyze silkworm larval digestive juice proteins during this period. A total of 227 proteins were successfully identified. These were primarily serine protease activity, esterase activity, binding, and serine protease inhibitors, which were mainly involved in the digestion and overcoming the detrimental effects of mulberry leaves. Moreover, 30 genes of the identified proteins were expressed specifically in the midgut. Temporal proteomic analysis of digestive juice revealed developmental dynamic features related to molecular mechanisms of the principal functions of digesting, resisting pathogens, and overruling the inhibitory effects of mulberry leaves protease inhibitors (PIs) with a dynamic strategy, although overruling the inhibitory effects has not yet been confirmed by previous study. These findings will help address the potential functions of digestive juice in silkworm larvae.

A unique xylose reductase from Thermomyces lanuginosus: Effect of lignocellulosic substrates and inhibitors and applicability in lignocellulosic bioconversion

In this study, the xylose reductase gene (XRTL) from Thermomyces lanuginosus SSBP was expressed in Pichia pastoris GS115 and Saccharomyces cerevisiae Y294. The purified 39.2 kDa monomeric enzyme was optimally active at pH 6.5 and 50 °C and showed activity over a wide range of temperatures (30-70 °C) and pH (4.0-9.0), with a half-life of 1386 min at 50 °C. The enzyme preferred NADPH as cofactor and showed broad substrate specificity. The enzyme was inhibited by Cu²⁺, Fe²⁺ and Zn²⁺, while ferulic acid was found to be the most potent lignocellulosic inhibitor. Recombinant S. cerevisiae with the XRTL gene showed 34% higher xylitol production than the control strain. XRTL can therefore be used in a cell-free xylitol production process or as part of a pathway for utilization of xylose from lignocellulosic waste.

Recombinant expression and molecular insights into the catalytic mechanism of an NADPH-dependent conjugated polyketone reductase for the asymmetric synthesis of (R)-pantolactone

(R)-pantolactone is a key chiral intermediate for synthesizing calcium (R)-pantothenate. The commercial synthesis of (R)-pantolactone is performed through the resolution of racemic pantolactone using lactonase-catalyzed enantioselective hydrolysis. The process needs highly toxic hydrogen cyanide and a tedious dynamic kinetic resolution. In this study, we investigated an alternative method to prepare (R)-pantolactone through asymmetric reduction of ketopantolactone (KPL). An NADPH-dependent conjugated polyketone reductase gene from Candida dubliniensis CD36 (CduCPR) was functionally overexpressed in Escherichia coli BL21 (DE3). Recombinant CduCPR belonged to the aldo-keto reductase superfamily, and showed high catalytic activity and stereoselectivity using KPL as the substrate. In a continuous feeding reaction, 200 mM ketopantolactone was reduced to (R)-pantolactone with 98% conversion and 99% enantiomeric excess (e.e.) within 2.0 h. The catalytic mechanism was further investigated. Tyr66 functions as a proton donor following hydrogen transfer from NADPH. Thr30 and His128 are critical residues to bind and orient KPL. Therefore, the recombinant CduCPR from C. dubliniensis exhibited potential application in the asymmetric synthesis of (R)-pantolactone.

A reference gene set for sex pheromone biosynthesis and degradation genes from the diamondback moth, Plutella xylostella, based on genome and transcriptome digital gene expression analyses

Background

Female moths synthesize species-specific sex pheromone components and release them to attract male moths, which depend on precise sex pheromone chemosensory system to locate females. Two types of genes involved in the sex pheromone biosynthesis and degradation pathways play essential roles in this important moth behavior. To understand the function of genes in the sex pheromone pathway, this study investigated the genome-wide and digital gene expression of sex pheromone biosynthesis and degradation genes in various adult tissues in the diamondback moth (DBM), Plutella xylostella, which is a notorious vegetable pest worldwide.

Results

A massive transcriptome data (at least 39.04 Gb) was generated by sequencing 6 adult tissues including male antennae, female antennae, heads, legs, abdomen and female pheromone glands from DBM by using Illumina 4000 next-generation sequencing and mapping to a published DBM genome. Bioinformatics analysis yielded a total of 89,332 unigenes among which 87 transcripts were putatively related to seven gene families in the sex pheromone biosynthesis pathway. Among these, seven [two desaturases (DES), three fatty acyl-CoA reductases (FAR) one acetyltransferase (ACT) and one alcohol dehydrogenase (AD)] were mainly expressed in the pheromone glands with likely function in the three essential sex pheromone biosynthesis steps: desaturation, reduction, and esterification. We also identified 210 odorant-degradation related genes (including sex pheromone-degradation related genes) from seven major enzyme groups. Among these genes, 100 genes are new identified and two aldehyde oxidases (AOXs), one aldehyde dehydrogenase (ALDH), five carboxyl/cholinesterases (CCEs), five UDP-glycosyltransferases (UGTs), eight cytochrome P450 (CYP) and three glutathione S-transferases (GSTs) displayed more robust expression in the antennae, and thus are proposed to participate in the degradation of sex pheromone components and plant volatiles.

Conclusions

To date, this is the most comprehensive gene data set of sex pheromone biosynthesis and degradation enzyme related genes in DBM created by genome- and transcriptome-wide identification, characterization and expression profiling. Our findings provide a basis to better understand the function of genes with tissue enriched expression. The results also provide information on the genes involved in sex pheromone biosynthesis and degradation, and may be useful to identify potential gene targets for pest control strategies by disrupting the insect-insect communication using pheromone-based behavioral antagonists.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3592-y) contains supplementary material, which is available to authorized users.