Structure, expression and gene sequence of a juvenile hormone esterase-related protein from metamorphosing larvae of Trichoplusia ni

Molecular characterization of an ecdysteroid inducible carboxylesterase with GQSCG motif in the corn borer, Sesamia nonagrioides

We obtained a full-length cDNA encoding a carboxylesterase in Sesamia nonagrioides. The complete cDNA sequence is comprised of 1838 bp with an open reading frame encoding 576 amino acid residues with predicted molecular mass of 64.24 kDa. The deduced amino acid sequence showed high identity to JHE-Related of Trichoplusia ni (65% amino acid identity) and 49-46% amino acid identity to JHEs of other lepidopterans and contained all five functional motifs of insect JHEs. The gene has been termed as SnJHE-Related (SnJHER) to denote its similarity to other insect JHE genes and the occurrence of an unusual cysteine residue immediately adjacent to the catalytic serine, instead of the conventional alanine residue. Phylogenetic analyses localised SnJHER together with TnJHER in a branch of the lepidopteran's JHEs group, with other carboxylesterases (COEs) occuring in separated groups. The JH analog methoprene did not affect the expression of SnJHER in contrast to other insect JHEs. Additionally, ecdysteroid analogs induced SnJHER gene expression. The SnJHER mRNA levels were higher in long-day non-diapausing larvae than in short-day diapausing ones. In the fifth instar of non-diapausing and ninth instar of diapausing larvae, the SnJHER mRNAs reached higher expression levels on the days close to each larval molt. In the last (sixth) non-diapausing larval instar, SnJHER mRNA levels peaked in the intermolt period but were lower than during the fifth instar.

Juvenile hormone esterase: biochemistry and structure

Normal insect development requires a precisely timed, precipitous drop in hemolymph juvenile hormone (JH) titer. This drop occurs through a coordinated halt in JH biosynthesis and increase in JH metabolism. In many species, JH esterase (JHE) is critical for metabolism of the resonance-stabilized methyl ester of JH. JHE metabolizes JH with a high kcat/KM ratio that results primarily from an exceptionally low KM. Here we review the biochemistry and structure of authentic and recombinant JHEs from six insect orders, and present updated diagnostic criteria that help to distinguish JHEs from other carboxylesterases. The use of a JHE-encoding gene to improve the insecticidal efficacy of biopesticides is also discussed.

Molecular cloning and characterization of a juvenile hormone esterase gene from brown planthopper, Nilaparvata lugens

Juvenile hormone (JH) plays key roles in the regulation of growth, development, diapause and reproduction in insects, and juvenile hormone esterase (JHE) plays an important role in regulating JH titers. We obtained a full-length cDNA encoding JHE in Nilaparvata lugens (NlJHE), the first JHE gene cloned from the hemipteran insects. The deduced protein sequence of Nljhe contains the five conserved motifs identified in JHEs of other insect species, including a consensus GQSAG motif that is required for the enzymatic activity of JHE proteins. Nljhe showed high amino acid similarities with Athalia rosae JHE (40%) and Apis mellifera JHE (39%). Recombinant NlJHE protein expressed in the baculovirus expression system hydrolyzed [3H] JH III at high activity and yielded the specificity constants (kcat/KM=4.28x10(6) M(-1) s(-1)) close to those of the validated JHEs from other insect species, indicating that Nljhe cDNA encodes a functional JH esterase. The Nljhe transcript was expressed mainly in the fat body and the expression level reached a peak at 48 h after ecdysis of the 5th instar nymphs. In the 5th instar, macropterous insects showed significantly higher Nljhe mRNA levels and JHE activities, but much lower JH III levels, than those detected in the brachypterous insects soon after ecdysis and at 48 h after ecdysis. These data suggest that NlJHE might play important roles in regulation of JH levels and wing form differentiation.

Developmental and hormonal regulation of juvenile hormone esterase gene in Drosophila melanogaster

Quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) was used to study developmental expression and hormonal regulation of the juvenile hormone esterase gene (DmJhe) in the fruit fly, Drosophila melanogaster. The levels of DmJhe mRNA were low during the embryonic stage. A peak of Dmjhe mRNA was detected in the first, second and third instar larvae. The Dmjhe mRNA levels also increased soon after pupal ecdysis. The Dmjhe mRNA was detected in both male and female adult flies. The peaks of Dmjhe mRNA observed in the larvae coincided with the peaks of juvenile hormone (JH). In contrast, the mRNA for ecdysone-induced transcription factor, Drosophila hormone receptor 3 (DHR3) showed peaks of expression that coincided with the ecdysteroid peaks in embryo, larva and pupa. JH III induced Dmjhe mRNA but not DHR3 mRNA in explanted tissues cultured in Grace's medium. 20-hydroxyecdysone induced DHR3 mRNA and suppressed JH III induction of DmJhe mRNA. These studies show that the expression of jhe in D. melanogaster is regulated by both JH and 20E.

cDNA cloning and characterization of Bombyx mori juvenile hormone esterase: an inducible gene by the imidazole insect growth regulator KK-42

The insect growth regulator (IGR) imidazole KK-42 induces hemolymph juvenile hormone esterase activity and precocious metamorphosis in Bombyx mori. As an initial step to understand the molecular action of KK-42, we isolated a full-length of juvenile hormone esterase cDNA from B. mori (BmJHE). The deduced amino acid sequence of BmJHE showed high identity to JHEs of Heliothis virescens (54%) and Choristoneura fumiferana (52%). Recombinant BmJHE protein expressed in the baculovirus expression system hydrolyzed 3H-JH III and JH analog, HEPTAT, indicating that BmJHE cDNA encodes functional JH esterase. Northern blot analysis showed that the BmJHE transcript was present predominantly in the fat body at the beginning of the last larval instar. During this instar, BmJHE transcript increased gradually until day 7, then decreased, and increased again on day 10 in the fat body. This temporary expression pattern was similar to that of JHE enzyme activity in hemolymph. In contrast, in the 4th instar, the BmJHE transcript was present in the fat body even though hemolymph JHE activity was very low. Western blot analysis using anti-BmJHE antiserum showed BmJHE protein was present in hemolymph during the 5th instar but not during the 4th instar. These results indicate that BmJHE protein is secreted into hemolymph at the metamorphic stage. Hemolymph JHE activity was high in precociously metamorphosed 4th instar larvae (treated KK-42) but low in normal 4th and extra-molted 6th instar larvae (fed 20E). KK-42-treated larvae showed high expression level of BmJHE transcript in the fat body, suggesting that KK-42 enhances BmJHE gene expression in the fat body.

Purification of juvenile hormone esterase and molecular cloning of the cDNA from Manduca sexta

Juvenile hormone esterase (JHE) is a highly specific enzyme important for regulating the onset of metamorphosis in lepidopteran insects. After affinity chromatography of the hemolymph proteins of Manduca sexta, the pure JHE protein was digested with Lys-C and the resultant peptides were purified by microbore HPLC. Two peptides were selected for sequencing. Based upon these amino acid sequences, degenerate RT-PCR was performed in order to amplify a partial cDNA sequence from mRNA from the fat body of M. sexta. A 1512bp partial cDNA was generated and found to be highly homologous to the JHE from Heliothis virescens. 5' and 3' RACE were performed to obtain the full length cDNA sequence. The cDNA has a total length of 2220bp, with a 1749bp coding region. The deduced protein sequence contains 573 amino acids.

Distinctive structural and kinetic properties of an unusual juvenile hormone-hydrolyzing esterase

The insect juvenile hormone specific esterases (JHEs), related to acetylcholinesterases but exhibiting substrate specificity for juvenile hormone (JH), are essential enzymes for normal insect development, making them attractive targets for biorationally designed, environmentally safe pesticides. We examine here a new enzyme, JHER, related to, but yet structurally, biochemically, and kinetically distinct from, the classical JHE. Both classical JHE and baculovirus-expressed JHER hydrolyze JH show disproportionately higher catalytic rates at higher substrate concentrations (in contrast to substrate inhibition reported for acetylcholinesterase) and are similarly inhibited by an organophosphate. However, JHER, which possesses an unusual cysteine residue at +1 to the catalytic serine, is less sensitive to trifluoromethyl ketone transition state analogs designed around the structure of JH. We propose a model in which JHER is expressed just prior to metamorphosis for hydrolysis of a JH-like substrate with hydrophobic backbone, a proximal ester, and a terminal expoxide or related substitution.

Spruce budworm (Choristoneura fumiferana) juvenile hormone esterase: hormonal regulation, developmental expression and cDNA cloning

We have used the differential display of mRNAs technique to identify Choristoneura fumiferana genes that are induced by juvenile hormone I (JH I). Of the six PCR products identified, one bound to a 2.8-kb mRNA from CF-203 cells whose abundance increased when the cells were grown in the presence of JH I. The same 2.8-kb mRNA decreased to undetectable levels when the CF-203 cells were grown in the presence of 20-hydroxyecdysone (20E). The PCR fragment probe also detected a 2.8-kb mRNA in the C. fumiferana larval tissues. This 2.8-kb mRNA was present on the first day of the first, third, fourth, fifth and sixth larval and pupal stadia, but was conspicuously absent on the first day of the second larval stadium, as well as during the intermolt periods of the first to fifth instar larval stages. In the sixth instar larvae the 2.8-kb mRNA was detected in the fat body, epidermis and midgut during the intermolt period. The PCR fragment was used as a probe to screen a cDNA library. The deduced amino acid sequence of this 2.8-kb cDNA clone showed similarity with the deduced amino acid sequences of Heliothis virescens juvenile hormone esterases (HvJHE). The deduced amino acid sequence of the cDNA clone contained all five functional motifs that are present in most of esterases, proteases and lipases. The cDNA clone was expressed in the baculovirus expression system, producing a protein that showed JHE activity.

Evidence for two juvenile hormone esterase-related genes in the Colorado potato beetle

Juvenile hormone esterase (JHE) activity in the haemolymph of the Colorado potato beetle is necessary to initiate pupation in larvae as well as diapause in adults. The enzyme appears in the haemolymph as a dimer consisting of two 57 kDa subunits. The sequence of an encoding cDNA, JHE.A, is distinct from lepidopteran JHEs. In this study, RT-PCR using primers designed on the basis of the 5'- and 3'-ends of the coding region revealed the existence of a related gene, JHE.B. The presence of two JHE-related genes was also shown by PCR amplification on genomic DNA from different individual beetles followed by restriction enzyme analysis. Both forms, probably paralogues, were transcribed since they could be amplified on messenger RNA from fat bodies. The size of the PCR products generated with mRNA and genomic DNA were both 1.6 kb, suggesting the absence of introns in the genomic JHE coding sequence. The sequence of a genomic clone, which encoded JHE.B, was 77% identical and 82% similar in amino acids compared to JHE.A. No introns were found in the coding sequence of these coleopteran JHE-related genes, in contrast to lepidopteran JHE genes. Southern blot analysis of digested genomic DNA confirmed the presence of two JHE-related genes.

The mammalian carboxylesterases: from molecules to functions

Multiple carboxylesterases (EC 3.1.1.1) play an important role in the hydrolytic biotransformation of a vast number of structurally diverse drugs. These enzymes are major determinants of the pharmacokinetic behavior of most therapeutic agents containing ester or amide bonds. Carboxylesterase activity can be influenced by interactions of a variety of compounds either directly or at the level of enzyme regulation. Since a significant number of drugs are metabolized by carboxylesterase, altering the activity of this enzyme class has important clinical implications. Drug elimination decreases and the incidence of drug-drug interactions increases when two or more drugs compete for hydrolysis by the same carboxylesterase isozyme. Exposure to environmental pollutants or to lipophilic drugs can result in induction of carboxylesterase activity. Therefore, the use of drugs known to increase the microsomal expression of a particular carboxylesterase, and thus to increase associated drug hydrolysis capacity in humans, requires caution. Mammalian carboxylesterases represent a multigene family, the products of which are localized in the endoplasmic reticulum of many tissues. A comparison of the nucleotide and amino acid sequence of the mammalian carboxylesterases shows that all forms expressed in the rat can be assigned to one of three gene subfamilies with structural identities of more than 70% within each subfamily. Considerable confusion exists in the scientific community in regards to a systematic nomenclature and classification of mammalian carboxylesterase. Until recently, adequate sequence information has not been available such that valid links among the mammalian carboxylesterase gene family or evolutionary relationships could be established. However, sufficient basic data are now available to support such a novel classification system.

Cloning and sequence analysis of cDNA encoding a putative juvenile hormone esterase from the Colorado potato beetle

In the Colorado potato beetle, Leptinotarsa decemlineata, reproduction and diapause are mediated by the juvenile hormone (JH) titer in the hemolymph. This titer is controlled by JH synthesis in the corpora allata and by JH degradation. The main pathway of JH degradation is by JH esterase in the hemolymph. The native JH esterase appeared to be a dimer consisting of two 57 kDa subunits (Vermunt et al., 1997). The 57 kDa subunit of JH esterase was digested with endoproteinase Lys-C and the digestion products were separated by reversed phase HPLC. Three different peptides were collected and sequenced. The amino acid sequence of one peptide showed high similarity to fragments of other insect esterases. Based on the amino acid sequence of these peptides, degenerate primers were constructed for RT-PCR. A PCR product of 1.3 kb was obtained and sequenced. This product was used to screen a cDNA library for a complete cDNA copy and to analyze the messenger RNA from larvae and adult beetles. The size of the messenger RNA was 1.7 kb. The complete amino acid sequence of the protein was deduced from the nucleotide sequence of overlapping clones from a cDNA library and a 5'RACE product. An open reading frame (ORF) of 1545 base pairs encoded a 57 kDa protein with a predicted pI of 5.5. The ORF contained the sequence of the three peptides. It showed no significant homology to other proteins present in databases, but it did contain several functional esterase motifs.

Duplication and divergence of the genes of the alpha-esterase cluster of Drosophila melanogaster

The alpha-esterase cluster of D. melanogaster contains 11 esterase genes dispersed over 60 kb. Embedded in the cluster are two unrelated open reading frames that have sequence similarity with genes encoding ubiquitin-conjugating enzyme and tropomyosin. The esterase amino acid sequences show 37-66% identity with one another and all but one have all the motifs characteristic of functional members of the carboxyl/cholinesterase multigene family. The exception has several frameshift mutations and appears to be a pseudogene. Patterns of amino acid differences among cluster members in relation to generic models of carboxyl/cholinesterase protein structure are broadly similar to those among other carboxyl/cholinesterases sequenced to date. However the alpha-esterases differ from most other members of the family in: their lack of a signal peptide; the lack of conservation in cysteines involved in disulfide bridges; and in four indels, two of which occur in or adjacent to regions that align with proposed substrate-binding sites of other carboxyl/cholinesterases. Phylogenetic analyses clearly identify three simple gene duplication events within the cluster. The most recent event involved the pseudogene which is located in an intron of another esterase gene. However, relative rate tests suggest that the pseudogene remained functional after the duplication event and has become inactive relatively recently. The distribution of indels also suggests a deeper node in the gene phylogeny that separates six genes at the two ends of the cluster from a block of five in the middle.

Non-classical actions of cholinesterases: role in cellular differentiation, tumorigenesis and Alzheimer's disease

The cholinesterases are members of the serine hydrolase family, which utilize a serine residue at the active site. Acetylcholinesterase (AChE) is distinguished from butyrylcholinesterase (BChE) by its greater specificity for hydrolysing acetylcholine. The function of AChE at cholinergic synapses is to terminate cholinergic neurotransmission. However, AChE is expressed in tissues that are not directly innervated by cholinergic nerves. AChE and BChE are found in several types of haematopoietic cells. Transient expression of AChE in the brain during embryogenesis suggests that AChE may function in the regulation of neurite outgrowth. Overexpression of cholinesterases has also been correlated with tumorigenesis and abnormal megakaryocytopoiesis. Acetylcholine has been shown to influence cell proliferation and neurite outgrowth through nicotinic and muscarinic receptor-mediated mechanisms and thus, that the expression of AChE and BChE at non-synaptic sites may be associated with a cholinergic function. However, structural homologies between cholinesterases and adhesion proteins indicate that cholinesterases could also function as cell-cell or cell-substrate adhesion molecules. Abnormal expression of AChE and BChE has been detected around the amyloid plaques and neurofibrillary tangles in the brains of patients with Alzheimer's disease. The function of the cholinesterases in these regions of the Alzheimer brain is unknown, but this function is probably unrelated to cholinergic neurotransmission. The presence of abnormal cholinesterase expression in the Alzheimer brain has implications for the pathogenesis of Alzheimer's disease and for therapeutic strategies using cholinesterase inhibitors.

Overview of the regulation of metamorphosis-associated genes in Trichoplusia ni

A review is presented of our ongoing research program on the regulation of metamorphosis-associated proteins in Trichoplusia ni. Toward the identification of mechanisms by which juvenile hormone (JH) regulates expression of metamorphosis-associated proteins, we have identified a protein that is induced by JH (juvenile hormone esterase) and a related esterase that is not JH-inducible. We have also identified three hexamerins that are suppressible by JH, and one hexamerin that is not JH-suppressible. Expression of the hexamerins is regulated at the transcriptional, translational, and posttranslational levels in T. ni. The rate of transcription of the JH esterase gene increases at the time of the prepupal peak in JH, and exogenous application of JH can cause, within 3 h, the rate of transcription to be the markedly elevated above normal. Using in vitro functional transcription assay, cell line transfection functional assay, and preliminary DNase I hypersensitive site mapping we were able to identify the functional TATA box and transcription start sites of JH-sensitive genes. These methods were also observed to be powerful in the detection of regulatory DNA motifs involved in the modulation of transcriptional activity constitutively imparted by a core promoter. The experimental systems described here will also be effective in identifying those components through which JH regulatory effects are mediated. Should JH act on the genes in a primary manner, then the transcription factor mediating that action may be the (a) JH receptor. Should the JH action be in a secondary manner, then the transcription factor(s) whose activity at the JHE gene is regulated by JH will provide the tool to track back to the location and nature of the primary JH action.