Molecular characterization of genes encoding trypsin-like enzymes from Aedes aegypti larvae and identification of digestive enzymes

Genome resequencing and genome-wide polymorphisms in mosquito vectors Aedes aegypti and Aedes albopictus from south India

Aedes aegypti and Aedes albopictus mosquitoes spread major vector-borne viral diseases in tropical and sub-tropical regions of the globe. In this study, we sequenced the genome of Indian Ae. aegypti and Ae. albopictus and mapped to their reference genomes. Comparative genomics were performed between our strain and the reference strains. A total of 14,416,484 single nucleotide polymorphisms (SNPs) and 156,487 insertions and deletions (InDels) were found in Ae. aegypti, and 28,940,433 SNPs and 188,987 InDels in Ae. albopictus. Particular emphasis was given to gene families involved in mosquito digestion, development, and innate immunity, which could be putative candidates for vector control. Serine protease cascades and their inhibitors called serpins, play a central role in these processes. We extracted high-impact variants in genes associated with serine proteases and serpins. This study reports for the first time a high coverage genome sequence data of an Indian Ae. albopictus mosquito. The results from this study will provide insights into Indian Aedes specific polymorphisms and the evolution of immune related genes in mosquitoes, which can serve as a resource for future comparative genomics and those pursuing the development of targeted biopesticides for effective mosquito control strategies.

The Set of Serine Peptidases of the Tenebrio molitor Beetle: Transcriptomic Analysis on Different Developmental Stages

Serine peptidases (SPs) of the chymotrypsin S1A subfamily are an extensive group of enzymes found in all animal organisms, including insects. Here, we provide analysis of SPs in the yellow mealworm Tenebrio molitor transcriptomes and genomes datasets and profile their expression patterns at various stages of ontogeny. A total of 269 SPs were identified, including 137 with conserved catalytic triad residues, while 125 others lacking conservation were proposed as non-active serine peptidase homologs (SPHs). Seven deduced sequences exhibit a complex domain organization with two or three peptidase units (domains), predicted both as active or non-active. The largest group of 84 SPs and 102 SPHs had no regulatory domains in the propeptide, and the majority of them were expressed only in the feeding life stages, larvae and adults, presumably playing an important role in digestion. The remaining 53 SPs and 23 SPHs had different regulatory domains, showed constitutive or upregulated expression at eggs or/and pupae stages, participating in regulation of various physiological processes. The majority of polypeptidases were mainly expressed at the pupal and adult stages. The data obtained expand our knowledge on SPs/SPHs and provide the basis for further studies of the functions of proteins from the S1A subfamily in T. molitor.

Clogmia albipunctata (Williston, 1893) midgut physiology: pH control and functional relationship with Lower Diptera (nematoceran) especially with hematophagous species

Clogmia albipunctata (Williston, 1893) is a non-hematophagous insect belonging to the order Diptera, suborder Nematocera (Lower Diptera) and family Psychodidae. In the present work, we investigated how C. albipunctata control their midgut pH under different physiological conditions, comparing their midgut physiology with some nematoceran hematophagous species. The C. albipunctata midgut pH was measured after ingestion of sugar, protein and under the effect of the alkalinizing hormone released in the hemolymph of the hematophagous sand fly Lutzomyia longipalpis obtained just after a blood meal. The midgut pH of unfed or sugar-fed C. albipunctata is 5.5-6, and its midgut underwent alkalinization after protein ingestion or under treatment with hemolymph collected from blood fed L. longipalpis. These results suggested that in nematocerans, mechanisms for pH control seem shared between hematophagous and non-hematophagous species. This kind of pH control is convenient for successful blood digestion. The independent evolution of many hematophagous groups from the Lower Diptera suggests that characteristics involved in midgut pH control were already present in non-hematophagous species and represent a readiness for adaptation to this feeding mode.

Insights into the differences related to the resistance mechanisms to the highly toxic fruit Hippomane mancinella (Malpighiales: Euphorbiaceae) between the larvae of the sister species Anastrepha acris and Anastrepha ludens (Diptera: Tephritidae) through comparative transcriptomics

The Manchineel, Hippomane mancinella ("Death Apple Tree") is one of the most toxic fruits worldwide and nevertheless is the host plant of the monophagous fruit fly species Anastrepha acris (Diptera: Tephritidae). Here we aimed at elucidating the detoxification mechanisms in larvae of A. acris reared on a diet enriched with the toxic fruit (6% lyophilizate) through comparative transcriptomics. We compared the performance of A. acris larvae with that of the sister species A. ludens, a highly polyphagous pest species that is unable to infest H. mancinella in nature. The transcriptional alterations in A. ludens were significantly greater than in A. acris. We mainly found two resistance mechanisms in both species: structural, activating cuticle protein biosynthesis (chitin-binding proteins likely reducing permeability to toxic compounds in the intestine), and metabolic, triggering biosynthesis of serine proteases and xenobiotic metabolism activation by glutathione-S-transferases and cytochrome P450 oxidoreductase. Some cuticle proteins and serine proteases were not orthologous between both species, suggesting that in A. acris, a structural resistance mechanism has been selected allowing specialization to the highly toxic host plant. Our results represent a nice example of how two phylogenetically close species diverged over recent evolutionary time related to resistance mechanisms to plant secondary metabolites.

Boophilin D1, a Kunitz type protease inhibitor, as a source of inhibitors for the ZIKA virus NS2B-NS3 protease

Arboviruses are a global concern for a multitude of reasons, including their increased incidence and human mortality. Vectors associated with arboviruses include the mosquito Aedes sp., which is responsible for transmitting the Zika virus. Flaviviruses, like the Zika virus, present only one chymotrypsin-like serine protease (NS3) in their genome. Together with host enzymes, the NS2B co-factor NS3 protease complex are essential for the viral replication cycle by virus polyprotein processing. To search for Zika virus NS2B-NS3 protease (ZIKVPro) inhibitors, a phage display library was constructed using the Boophilin domain 1 (BoophD1), a thrombin inhibitor from the Kunitz family. A BoophilinD1 library mutated at positions P1-P4' was constructed, presenting a titer of 2.9x106 (cfu), and screened utilizing purified ZIKVPro. The results demonstrated at the P1-P4' positions the occurrence of 47% RALHA sequence (mut 12) and 11.8% RASWA sequence (mut14), SMRPT, or KALIP (wt) sequence. BoophD1-wt and mutants 12 and 14 were expressed and purified. The purified BoophD1 wt, mut 12 and 14, presented Ki values for ZIKVPro of 0.103, 0.116, and 0.101 μM, respectively. The BoophD1 mutant inhibitors inhibit the Dengue virus 2 protease (DENV2) with Ki values of 0.298, 0.271, and 0.379 μM, respectively. In conclusion, BoophD1 mut 12 and 14 selected for ZIKVPro demonstrated inhibitory activity like BoophD1-wt, suggesting that these are the strongest Zika inhibitors present in the BoophD1 mutated phage display library. Furthermore, BoophD1 mutants selected for ZIKVPro inhibit both Zika and Dengue 2 proteases making them potential pan-flavivirus inhibitors.

Identification and expression profiling of serine protease-related genes in Tenebrio molitor

In insects, serine proteases and serine protease homologs (SPs/SPHs) are involved in a variety of physiological processes including digestion, development, and immunity. Here, we identified 112 SP and 88 SPH genes in the genome of the yellow mealworm, Tenebrio molitor. Based on the features of domain structure, they were divided into "S" group containing single Tryp-SPc or Tryp-SPHc domain, "C" group containing 1-4 CLIP domain (CLIPA-D) and "M" group containing the CBD, CUB, EGF, Fz, Gd, LDLa, PAN, SEA, SR, Sushi, and TSP domains, and have 115, 48, and 37 gene members, respectively. According to the active sites in the catalytic triad, the putative trypsin, chymotrypsin, or elastase-like enzyme specificity of the identified SPs/SPHs were predicted. Phylogenetic and genomic location analyses revealed that gene duplication exists in the large amount of SPs/SPHs. Gene expression profiling using RNA-seq data along with real time reverse transcription-polymerase chain reaction analysis showed that most SP/SPH genes display life stage specific expression patterns, indicating their important roles in development. Many SP/SPH genes are specifically or highly expressed in the gut, salivary gland, fat body, hemocyte, ovary, and testis, suggesting that they participate in digestion, immunity, and reproduction. The findings lay the foundation for further functional characterization of SPs/SPHs in T. molitor.

A versatile inhibitor of digestive enzymes in Aedes aegypti larvae selected from a pacifastin (TiPI) phage display library

In Brazil, the major vector of arboviruses is Aedes aegypti, which can transmit several alpha and flaviviruses. In this work, a pacifastin protease inhibitor library was constructed and used to select mutants for Ae. aegypti larvae digestive enzymes. The library contained a total of 3.25 × 10⁵ cfu with random mutations in the reactive site (P2-P2'). The most successfully selected mutant, TiPI6, a versatile inhibitor, was able to inhibit all three Ae. aegypti larvae proteolytic activities, trypsin-like, chymotrypsin-like and elastase-like activities, with IC₅₀ values of 0.212 nM, 0.107 nM and 0.109 nM, respectively. In conclusion, the TiPI mutated phage display library was shown to be a useful tool for the selection of an inhibitor of proteolytic activities combined in a mix. TiPI6 is capable of controlling all three digestive enzyme activities present in the larval midgut extract. To our knowledge, this is the first time that one inhibitor containing a Gln at the P1 position showed inhibitory activity against trypsin, chymotrypsin, and elastase-like activities. TiPI6 can be a candidate for further larvicidal studies.

First insights into insecticidal activity against Aedes aegypti and partial biochemical characterization of a novel low molecular mass chymotrypsin-trypsin inhibitor purified from Lonchocarpus sericeus seeds

BACKGROUND

Arboviroses such as dengue, Zika and chikungunya represent a serious public health issue as a consequence of the absence of approved vaccines or specific antiviral drugs against the arboviruses that cause them. One way to prevent these diseases is by combating the vector mosquito, Aedes aegypti (Diptera), which has serine proteases in the midgut. Protease inhibitors are molecules that can block enzyme activity, impairing digestion and nutrition, which can lead to death. Thus, we purified and characterized a novel chymotrypsin-trypsin inhibitor (LsCTI) from Lonchocarpus sericeus seeds and investigated its effect upon Ae. aegypti egg hatching, larval development and digestive proteases.

RESULTS

LsCTI showed a single protein band in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and the molecular mass determined by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was 8870.45 Da. Kinetics analyses revealed a noncompetitive type of inhibition and low inhibition constant (K_i ) for chymotrypsin (8.24 x 10^-8 m). The thermal resistance was remarkable, even at 100 °C for 180 min. The inhibitor concentration required for 50-percent enzyme inhibition (IC₅₀ ) of LsCTI was 4.7 x 10^-7 m for Ae. aegypti midgut larval enzymes. LsCTI did not affect egg hatchability at 0.3 mg mL^-1 , but caused a high larval mortality rate (77%) and delayed development (37%).

CONCLUSIONS

LsCTI is a novel protease inhibitor with remarkable biochemical characteristics and is a potential tool to control Ae. aegypti development. © 2017 Society of Chemical Industry.

The genomic and transcriptomic analyses of serine proteases and their homologs in an endoparasitoid, Pteromalus puparum

In insects, serine proteases (SPs) and serine protease homologs (SPHs) constitute a large family of proteins involved in multiple physiological processes such as digestion, development, and immunity. Here we identified 145 SPs and 38 SPHs in the genome of an endoparasitoid, Pteromalus puparum. Gene duplication and tandem repeats were observed in this large SPs/SPHs family. We then analyzed the expression profiles of SP/SPH genes in response to different microbial infections (Gram-positive bacterium Micrococcus luteus, Gram-negative bacterium Escherichia coli, and entomopathogenic fungus Beauveria bassiana), as well as in different developmental stages and tissues. Some SPs/SPHs also displayed distinct expression patterns in venom gland, suggesting their specific physiological functions as venom proteins. Our finding lays groundwork for further research of SPs and SPHs expressed in the venom glands.

A midgut-specific serine protease, BmSP36, is involved in dietary protein digestion in the silkworm, Bombyx mori

Serine proteases play important roles in digestion and immune responses during insect development. In the present study, the serine protease gene BmSP36, which encodes a 292-residue protein, was cloned from the midgut cells of Bombyx mori. BmSP36 contains an intact catalytic triad (H57, D102 and S195) and a conserved substrate-binding site (G189, H216 and G226), suggesting that it is a serine protease with chymotrypsin-like specificity. The temporal and spatial expression patterns of BmSP36 indicated that its messenger RNA and protein expression mainly occurred in the midgut at the feeding stages. Western blotting, immunofluorescence and liquid chromatography-tandem mass spectrometry analyses revealed secretion of BmSP36 protein from epithelial cells into the midgut lumen. The transcriptional and translational expression of BmSP36 was down-regulated after starvation but up-regulated after refeeding. Moreover, expression of the BmSP36 gene could be up-regulated by a juvenile hormone analogue. These results enable us to better define the potential role of BmSP36 in dietary protein digestion at the feeding stages during larval development.

Molecular studies with Aedes (Stegomyia) aegypti (Linnaeus, 1762), mosquito transmitting the dengue virus

Dengue is an infectious viral disease, which can present a wide clinical picture, ranging from oligo or asymptomatic forms, to bleeding and shock, and can progress to death. The disease problem has increased in recent years, especially in urban and suburban areas of tropical and subtropical regions. There are five dengue viruses, called serotypes (DEN-1, DEN-2, DEN-3, DEN-4, and DEN-5), which belong to the Flaviviridae family and are transmitted to humans through infected mosquito bites, with the main vector the Aedes aegypti mosquito (Linnaeus, 1762). Studies performed with Ae. aegypti, aimed at their identification and analysis of their population structure, are fundamental to improve understanding of the epidemiology of dengue, as well for the definition of strategic actions that reduce the transmission of this disease. Therefore, considering the importance of such research to the development of programs to combat dengue, the present review considers the techniques used for the molecular identification, and evaluation of the genetic variability of Ae. aegypti.

Transcriptome Sequencing Reveals Large-Scale Changes in Axenic Aedes aegypti Larvae

Mosquitoes host communities of microbes in their digestive tract that consist primarily of bacteria. We previously reported that Aedes aegypti larvae colonized by a native community of bacteria and gnotobiotic larvae colonized by only Escherichia coli develop very similarly into adults, whereas axenic larvae never molt and die as first instars. In this study, we extended these findings by first comparing the growth and abundance of bacteria in conventional, gnotobiotic, and axenic larvae during the first instar. Results showed that conventional and gnotobiotic larvae exhibited no differences in growth, timing of molting, or number of bacteria in their digestive tract. Axenic larvae in contrast grew minimally and never achieved the critical size associated with molting by conventional and gnotobiotic larvae. In the second part of the study we compared patterns of gene expression in conventional, gnotobiotic and axenic larvae by conducting an RNAseq analysis of gut and nongut tissues (carcass) at 22 h post-hatching. Approximately 12% of Ae. aegypti transcripts were differentially expressed in axenic versus conventional or gnotobiotic larvae. However, this profile consisted primarily of transcripts in seven categories that included the down-regulation of select peptidases in the gut and up-regulation of several genes in the gut and carcass with roles in amino acid transport, hormonal signaling, and metabolism. Overall, our results indicate that axenic larvae exhibit alterations in gene expression consistent with defects in acquisition and assimilation of nutrients required for growth.

Digestion of Yeasts and Beta-1,3-Glucanases in Mosquito Larvae: Physiological and Biochemical Considerations

Aedes aegypti larvae ingest several kinds of microorganisms. In spite of studies regarding mosquito digestion, little is known about the nutritional utilization of ingested cells by larvae. We investigated the effects of using yeasts as the sole nutrient source for A. aegypti larvae. We also assessed the role of beta-1,3-glucanases in digestion of live yeast cells. Beta-1,3-glucanases are enzymes which hydrolyze the cell wall beta-1,3-glucan polyssacharide. Larvae were fed with cat food (controls), live or autoclaved Saccharomyces cerevisiae cells and larval weight, time for pupation and adult emergence, larval and pupal mortality were measured. The presence of S. cerevisiae cells inside the larval gut was demonstrated by light microscopy. Beta-1,3-glucanase was measured in dissected larval samples. Viability assays were performed with live yeast cells and larval gut homogenates, with or without addition of competing beta-1,3-glucan. A. aegypti larvae fed with yeast cells were heavier at the 4^th instar and showed complete development with normal mortality rates. Yeast cells were efficiently ingested by larvae and quickly killed (10% death in 2h, 100% in 48h). Larvae showed beta-1,3-glucanase in head, gut and rest of body. Gut beta-1,3-glucanase was not derived from ingested yeast cells. Gut and rest of body activity was not affected by the yeast diet, but head homogenates showed a lower activity in animals fed with autoclaved S. cerevisiae cells. The enzymatic lysis of live S. cerevisiae cells was demonstrated using gut homogenates, and this activity was abolished when excess beta-1,3-glucan was added to assays. These results show that live yeast cells are efficiently ingested and hydrolyzed by A. aegypti larvae, which are able to fully-develop on a diet based exclusively on these organisms. Beta-1,3-glucanase seems to be essential for yeast lytic activity of A. aegypti larvae, which possess significant amounts of these enzyme in all parts investigated.

Production of serine protease inhibitors by mutagenesis and their effects on the mortality of Aedes aegypti L. larvae

Background

Dengue, transmitted primarily by the bites of infected Aedes aegypti L., is transmitted to millions of individuals each year in tropical and subtropical areas. Dengue control strategies are primarily based on controlling the vector, using insecticides, but the appearance of resistance poses new challenges. Recently, highly selective protease inhibitors by phage display were obtained for digestive enzymes of the 4th instar larvae (L4) midgut. These mutants were not confirmed as a larvicide due to the low yield of the expression of these inhibitors. In the present study, chimera molecules were constructed based on the mutations at positions P1-P4’ selected previously. The T6, T23 and T149 mutants were mixed with another Kunitz inhibitor, domain 1 of the inhibitor boophilin (D1).

Methods

The chimeras T6/D1, T149/D1 and T23/D1 were expressed at high levels in P. pastoris yeast, purified by ionic exchange chromatography and their homogeneity was analyzed by SDS-PAGE. The chimera inhibitors were assayed against larval trypsin, chymotrypsin and elastase using specific chromogenic substrates. The inhibitors were assayed for their larvicide potential against L4.

Results

The chimeras exhibited strong inhibitory activities against the larval digestive enzymes in a dose-dependent manner. T6/D1, T149/D1 and T23/D1 exhibited strong larvicidal activity against L4 of Ae. aegypti with inhibitor concentrations in the μM range. A synergistic increase in mortality was observed when a mixture of the three chimeric inhibitors was tested.

Conclusions

The strategy for constructing the chimeric inhibitors was successful. The chimeras showed strong larvicidal activity against Ae. aegypti. In the future, our findings can be used to design synthetic inhibitors for larvae digestive enzymes as an alternative method to control the dengue vector.

In-depth characterization of trypsin-like serine peptidases in the midgut of the sugar fed Culex quinquefasciatus

BACKGROUND

Culex quinquefasciatus is a hematophagous insect from the Culicidae family that feeds on the blood of humans, dogs, birds and livestock. This species transmits a wide variety of pathogens between humans and animals. The midgut environment is the first location of pathogen-vector interactions for blood-feeding mosquitoes and the expression of specific peptidases in the early stages of feeding could influence the outcome of the infection. Trypsin-like serine peptidases belong to a multi-gene family that can be expressed in different isoforms under distinct physiological conditions. However, the confident assignment of the trypsin genes that are expressed under each condition is still a challenge due to the large number of trypsin-coding genes in the Culicidae family and most likely because they are low abundance proteins.

METHODS

We used zymography for the biochemical characterization of the peptidase profile of the midgut from C. quinquefasciatus females fed on sugar. Protein samples were also submitted to SDS-PAGE followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis for peptidase identification. The peptidases sequences were analyzed with bioinformatics tools to assess their distinct features.

RESULTS

Zymography revealed that trypsin-like serine peptidases were responsible for the proteolytic activity in the midgut of females fed on sugar diet. After denaturation in SDS-PAGE, eight trypsin-like serine peptidases were identified by LC-MS/MS. These peptidases have structural features typical of invertebrate digestive trypsin peptidases but exhibited singularities at the protein sequence level such as: the presence of different amino acids at the autocatalytic motif and substrate binding regions as well as different number of disulfide bounds. Data mining revealed a group of trypsin-like serine peptidases that are specific to C. quinquefasciatus when compared to the culicids genomes sequenced so far.

CONCLUSION

We demonstrated that proteomics approaches combined with bioinformatics tools and zymographic analysis can lead to the functional annotation of trypsin-like serine peptidases coding genes and aid in the understanding of the complexity of peptidase expression in mosquitoes.

Trypsin isozymes in the lobster Panulirus argus (Latreille, 1804): from molecules to physiology

Trypsin enzymes have been studied in a wide variety of animal taxa due to their central role in protein digestion as well as in other important physiological and biotechnological processes. Crustacean trypsins exhibit a high number of isoforms. However, while differences in properties of isoenzymes are known to play important roles in regulating different physiological processes, there is little information on this aspect for decapod trypsins. The aim of this review is to integrate recent findings at the molecular level on trypsin enzymes of the spiny lobster Panulirus argus, into higher levels of organization (biochemical, organism) and to interpret those findings in relation to the feeding ecology of these crustaceans. Trypsin in lobster is a polymorphic enzyme, showing isoforms that differ in their biochemical features and catalytic efficiencies. Molecular studies suggest that polymorphism in lobster trypsins may be non-neutral. Trypsin isoenzymes are differentially regulated by dietary proteins, and it seems that some isoenzymes have undergone adaptive evolution coupled with a divergence in expression rate to increase fitness. This review highlights important but poorly studied issues in crustaceans in general, such as the relation among trypsin polymorphism, phenotypic (digestive) flexibility, digestion efficiency, and feeding ecology.

Defense response in non-genomic model species: methyl jasmonate exposure reveals the passion fruit leaves' ability to assemble a cocktail of functionally diversified Kunitz-type trypsin inhibitors and recruit two of them against papain

Multiplicity of protease inhibitors induced by predators may increase the understanding of a plant's intelligent behavior toward environmental challenges. Information about defense mechanisms of non-genomic model plant passion fruit (Passiflora edulis Sims) in response to predator attack is still limited. Here, via biochemical approaches, we showed its flexibility to build-up a broad repertoire of potent Kunitz-type trypsin inhibitors (KTIs) in response to methyl jasmonate. Seven inhibitors (20-25 kDa) were purified from exposed leaves by chromatographic techniques. Interestingly, the KTIs possessed truncated Kunitz motif in their N-terminus and some of them also presented non-consensus residues. Gelatin-Native-PAGE established multiple isoforms for each inhibitor. Significant differences regarding inhibitors' activity toward trypsin and chymotrypsin were observed, indicating functional polymorphism. Despite its rarity, two of them also inhibited papain, and such bifunctionality suggests a recruiting process onto another mechanistic class of target protease (cysteine-type). All inhibitors acted strongly on midgut proteases from sugarcane borer, Diatraea saccharalis (a lepidopteran insect) while in vivo assays supported their insecticide properties. Moreover, the bifunctional inhibitors displayed activity toward midgut proteases from cowpea weevil, Callosobruchus maculatus (a coleopteran insect). Unexpectedly, all inhibitors were highly effective against midgut proteases from Aedes aegypti a dipteran insect (vector of neglected tropical diseases) opening new avenues for plant-derived PIs for vector control-oriented research. Our results reflect the KTIs' complexities in passion fruit which could be wisely exploited by influencing plant defense conditions. Therefore, the potential of passion fruit as source of bioactive compounds with diversified biotechnological application was strengthened.

Trypsin-like serine peptidase profiles in the egg, larval, and pupal stages of Aedes albopictus

BACKGROUND

Aedes albopictus, a ubiquitous mosquito, is one of the main vectors of dengue and yellow fever, representing an important threat to public health worldwide. Peptidases play key roles in processes such as digestion, oogenesis, and metamorphosis of insects. However, most of the information on the proteolytic enzymes of mosquitoes is derived from insects in the adult stages and is often directed towards the understanding of blood digestion. The aim of this study was to investigate the expression of active peptidases from the preimaginal stages of Ae. albopictus.

METHODS

Ae. albopictus eggs, larvae, and pupae were analyzed using zymography with susbtrate-SDS-PAGE. The pH, temperature and peptidase inhibitor sensitivity was evaluated. In addition, the proteolytic activities of larval instars were assayed using the fluorogenic substrate Z-Phe-Arg-AMC.

RESULTS

The proteolytic profile of the larval stage was composed of 8 bands ranging from 17 to 130 kDa. These enzymes displayed activity in a broad range of pH values, from 5.5 to 10.0. The enzymatic profile of the eggs was similar to that of the larvae, although the proteolytic bands of the eggs showed lower intensities. The pupal stage showed a complex proteolytic pattern, with at least 6 bands with apparent molecular masses ranging from 30 to 150 kDa and optimal activity at pH 7.5. Peptidases from larval instars were active from 10°C to 60°C, with optimal activity at temperatures between 37°C and 50°C. The proteolytic profile of both the larval and pupal stages was inhibited by phenyl-methyl sulfonyl-fluoride (PMSF) and Nα-Tosyl L-lysine chloromethyl ketone hydrochloride (TLCK), indicating that the main peptidases expressed during these developmental stages are trypsin-like serine peptidases.

CONCLUSION

The preimaginal stages of Ae. albopictus exhibited a complex profile of trypsin-like serine peptidase activities. A comparative analysis of the active peptidase profiles revealed differential expression of trypsin-like isoforms among the preimaginal stages, suggesting that some of these enzymes are stage specific. Additionally, a comparison of the peptidase expression between larvae from eggs collected in the natural environment and larvae obtained from the eggs of female mosquitoes maintained in colonies for a long period of time demonstrated that the proteolytic profile is invariable under such conditions.

Selective inhibitors of digestive enzymes from Aedes aegypti larvae identified by phage display

Dengue is a serious disease transmitted by the mosquito Aedes aegypti during blood meal feeding. It is estimated that the dengue virus is transmitted to millions of individuals each year in tropical and subtropical areas. Dengue control strategies have been based on controlling the vector, Ae. aegypti, using insecticide, but the emergence of resistance poses new challenges. The aim of this study was the identification of specific protease inhibitors of the digestive enzymes from Ae. aegypti larvae, which may serve as a prospective alternative biocontrol method. High affinity protein inhibitors were selected by all of the digestive serine proteases of the 4th instar larval midgut, and the specificity of these inhibitors was characterized. These inhibitors were obtained from a phage library displaying variants of HiTI, a trypsin inhibitor from Haematobia irritans, that are mutated in the reactive loop (P1-P4'). Based on the selected amino acid sequence pattern, seven HiTI inhibitor variants were cloned, expressed and purified. The results indicate that the HiTI variants named T6 (RGGAV) and T128 (WNEGL) were selected by larval trypsin-like (IC(50) of 1.1 nM) and chymotrypsin-like enzymes (IC(50) of 11.6 nM), respectively. The variants T23 (LLGGL) and T149 (GGVWR) inhibited both larval chymotrypsin-like (IC(50) of 4.2 nM and 29.0 nM, respectively) and elastase-like enzymes (IC(50) of 1.2 nM for both). Specific inhibitors were successfully obtained for the digestive enzymes of Ae. aegypti larvae by phage display. Our data also strongly suggest the presence of elastase-like enzymes in Ae. aegypti larvae. The HiTI variants T6 and T23 are good candidates for the development as a larvicide to control the vector.