Molecular characterization of two serine proteases expressed in gut tissue of the African trypanosome vector, Glossina morsitans morsitans

Key enzymes and proteins of crop insects as candidate for RNAi based gene silencing

RNA interference (RNAi) is a mechanism of homology dependent gene silencing present in plants and animals. It operates through 21-24 nucleotides small RNAs which are processed through a set of core enzymatic machinery that involves Dicer and Argonaute proteins. In recent past, the technology has been well appreciated toward the control of plant pathogens and insects through suppression of key genes/proteins of infecting organisms. The genes encoding key enzymes/proteins with the great potential for developing an effective insect control by RNAi approach are actylcholinesterase, cytochrome P450 enzymes, amino peptidase N, allatostatin, allatotropin, tryptophan oxygenase, arginine kinase, vacuolar ATPase, chitin synthase, glutathione-S-transferase, catalase, trehalose phosphate synthase, vitellogenin, hydroxy-3-methylglutaryl coenzyme A reductase, and hormone receptor genes. Through various studies, it is demonstrated that RNAi is a reliable molecular tool which offers great promises in meeting the challenges imposed by crop insects with careful selection of key enzymes/proteins. Utilization of RNAi tool to target some of these key proteins of crop insects through various approaches is described here. The major challenges of RNAi based insect control such as identifying potential targets, delivery methods of silencing trigger, off target effects, and complexity of insect biology are very well illustrated. Further, required efforts to address these challenges are also discussed.

Independent pathways can transduce the life-cycle differentiation signal in Trypanosoma brucei

African trypanosomes cause disease in humans and livestock, generating significant health and welfare problems throughout sub-Saharan Africa. When ingested in a tsetse fly bloodmeal, trypanosomes must detect their new environment and initiate the developmental responses that ensure transmission. The best-established environmental signal is citrate/cis aconitate (CCA), this being transmitted through a protein phosphorylation cascade involving two phosphatases: one that inhibits differentiation (TbPTP1) and one that activates differentiation (TbPIP39). Other cues have been also proposed (mild acid, trypsin exposure, glucose depletion) but their physiological relevance and relationship to TbPTP1/TbPIP39 signalling is unknown. Here we demonstrate that mild acid and CCA operate through TbPIP39 phosphorylation, whereas trypsin attack of the parasite surface uses an alternative pathway that is dispensable in tsetse flies. Surprisingly, glucose depletion is not an important signal. Mechanistic analysis through biophysical methods suggests that citrate promotes differentiation by causing TbPTP1 and TbPIP39 to interact.

African trypanosomes are important pathogens transmitted by tsetse flies in sub-Saharan Africa. Upon transmission, trypanosomes detect citrate and cis-aconitate in the bloodmeal, this inactivating a negative regulator of differentiation, the tyrosine phosphatase TbPTP1. One TbPTP1 substrate is another phosphatase, TbPIP39, which is more active when phosphorylated (after TbPTP1 inhibition) and promotes differentiation. These differentiation regulators have provided tools to monitor whether one or more environmental signals are used to initiate trypanosome development and their relevance in vivo. This is important because different studies over the last 30 years have disputed the physiological importance of different signals. Here we have, firstly, compared the efficacy of the different reported differentiation signals, establishing their relative importance. We then monitored TbPIP39 phosphorylation to show that two signalling pathways operate: one signalled by citrate or mild acid, the other stimulated by external protease activity. Thereafter, we showed that, of these different signals, protease activity is dispensable for differentiation in tsetse flies. Finally, we used biophysical methods to investigate how citrate causes TbPIP39 and TbPTP1 to interact, enabling their regulatory cross-talk. These studies have established the importance of different developmental signals in trypanosomes, providing molecular insight into how the development signal is transduced within the pathogen.

Host generated siRNAs attenuate expression of serine protease gene in Myzus persicae

Background

Sap sucking hemipteran aphids damage diverse crop species. Although delivery of ds-RNA or siRNA through microinjection/feeding has been demonstrated, the efficacy of host-mediated delivery of aphid-specific dsRNA in developing aphid resistance has been far from being elucidated.

Methodology/Principal Findings

Transgenic Arabidopsis expressing ds-RNA of Myzus persicae serine protease (MySP) was developed that triggered the generation of corresponding siRNAs amenable for delivery to the feeding aphids. M. persicae when fed on the transgenic plants for different time intervals under controlled growth conditions resulted in a significant attenuation of the expression of MySP and a commensurate decline in gut protease activity. Although the survivability of these aphids was not affected, there was a noticeable decline in their fecundity resulting in a significant reduction in parthenogenetic population.

Conclusions/Significance

The study highlighted the feasibility of developing host based RNAi-mediated resistance against hemipteran pest aphids.

Properties and secretory mechanism of Musca domestica digestive chymotrypsin and its relation with Drosophila melanogaster homologs

Musca domestica larvae present two different digestive chymotryptic activities found in the posterior midgut (PMG): one major soluble activity in the lumen and another minor present in cell membrane fractions. Both soluble and membrane-bound chymotryptic activities have different half lives of thermal inactivation (46 °C) in the presence and absence of 10 mM Triton X-100, indicating that they are two different molecular species. Purified soluble chymotryptic activity has pH optimum 7.4 and a molecular mass of 28 kDa in SDS-PAGE. It does not cleave short substrates, such as Suc-F-MCA, preferring longer substrates, such as Suc-AAPF-MCA, with a primary specificity (kcat/Km) for Phe rather than Tyr and Leu residues. In-gel activity revealed a unique band against S-AAPF-MCA with the same migration as purified chymotrypsin. One chymotrypsinogen-like sequence (MdChy1) was sequenced, cloned and recombinantly expressed in Escherichia coli (DE3) Star. MdChy1 is expressed in the proximal posterior midgut (PMG1), as seen by RT-PCR. Expression analysis of other chymotrypsin genes revealed genes expressed at the anterior midgut (AMG) and PMG. Western blot of M. domestica midgut tissues using anti-MdChy1 antiserum showed a single band in samples from AMG and PMG, co-migrating with recombinant and purified enzymes. Immunogold labeling corresponding to Mdchy1 was found in small vesicles (thus indicating exocytosis) and in the lumen of AMG and PMG, corroborating the existence of two similar groups of chymotrypsins. Transcriptomes of M. domestica AMG and whole midgut prepared by pyrosequencing disclosed 41 unique sequences of chymotrypsin-like enzymes (19 probably functional), from which MdChy1 is highly expressed. Phylogenetic reconstruction of Drosophila melanogaster and M. domestica chymotrypsin-like sequences revealed that the chymotrypsin genes expanded before the evolutionary separation of Musca and Drosophila.

Chymotrypsin-like peptidases from Tribolium castaneum: a role in molting revealed by RNA interference

Chymotrypsin-like peptidases (CTLPs) of insects are primarily secreted into the gut lumen where they act as digestive enzymes. We studied the gene family encoding CTLPs in the genome of the red flour beetle, Tribolium castaneum. Using an extended search pattern, we identified 14 TcCTLP genes that encode peptidases with S1 specificity pocket residues typically found in chymotrypsin-like enzymes. We further analyzed the expression patterns of seven TcCTLP genes at various developmental stages. While some TcCTLP genes were exclusively expressed in feeding larval and adult stages (TcCTLP-5A/B, TcCTLP-6A), others were also detected in non-feeding embryonic (TcCTLP-5C, TcCTLP-6D) and pupal stages (TcCTLP-5C, TcCTLP-6C/D/E). TcCTLP genes were expressed predominantly in the midgut, where they presumably function in digestion. However, TcCTLP-6C and TcCTLP-5C also showed considerable expression in the carcass. The latter two genes might therefore encode peptidases that act as molting fluid enzymes. To test this hypothesis, we performed western blots using protein extracts from larval exuviae. The extracts reacted with antibodies to TcCTLP-5C and TcCTLP-6E suggesting that the corresponding peptidases are secreted into the molting fluid. Finally, we performed systemic RNAi experiments. While injections of five TcCTLP-dsRNAs into penultimate larvae did not affect growth or development, injection of dsRNA for TcCTLP-5C and TcCTLP-6C resulted in severe molting defects.

Cloning and expression analysis of midgut chymotrypsin-like proteinases in the tobacco hornworm

Digestion of proteins in the midgut of lepidopteran larvae relies on different trypsin and chymotrypsin isoforms. In this study we describe three chymotrypsin-like proteinases (CTLP2-4) from the larval midgut of Manduca sexta, which are closely related to CTLP1 and less closely related to another chymotrypsin (CT), two previously described proteinases present in the larval midgut of M. sexta. CTLP1-4 fit perfectly into a novel subgroup of insect CTLPs by sequence similarity and by the replacement of GP by SA in the highly conserved GDSGGP motif. When we examined CTLP expression in different tissues, most of the proteinases were predominantly expressed in the anterior and median midgut, while some were found in the Malpighian tubules. When we examined CTLP expression at different physiological states, we observed that the CTLP mRNA amounts did not differ considerably in feeding and starving larvae except for CTLP2, whose mRNA dropped significantly upon starvation. During moulting, however, the mRNA amounts of all CTLPs dropped significantly. When we immunologically examined CTLP amounts, mature proteinases were only detectable in the gut lumen of feeding and re-fed larvae, but not in that of starving or moulting larvae, suggesting that CTLP secretion is suspended during starvation or moult.

Functional characterization of HFR1, a high-mannose N-glycan-specific wheat lectin induced by Hessian fly larvae

We previously cloned and characterized a novel jacalin-like lectin gene from wheat (Triticum aestivum) plants that responds to infestation by Hessian fly (Mayetiola destructor) larvae, a major dipteran pest of this crop. The infested resistant plants accumulated higher levels of Hfr-1 (for Hessian fly-responsive gene 1) transcripts compared with uninfested or susceptible plants. Here, we characterize the soluble and active recombinant His(6)-HFR1 protein isolated from Escherichia coli. Functional characterization of the protein using hemagglutination assays revealed lectin activity. Glycan microarray-binding assays indicated strong affinity of His(6)-HFR1 to Manalpha1-6(Manalpha1-3)Man trisaccharide structures. Resistant wheat plants accumulated high levels of HFR1 at the larval feeding sites, as revealed by immunodetection, but the avirulent larvae were deterred from feeding and consumed only small amounts of the lectin. Behavioral studies revealed that avirulent Hessian fly larvae on resistant plants exhibited prolonged searching and writhing behaviors as they unsuccessfully attempted to establish feeding sites. During His(6)-HFR1 feeding bioassays, Drosophila melanogaster larvae experienced significant delays in growth and pupation, while percentage mortality increased with progressively higher concentrations of His(6)-HFR1 in the diet. Thus, HFR1 is an antinutrient to dipteran larvae and may play a significant role in deterring Hessian fly larvae from feeding on resistant wheat plants.

A chymotrypsin-like serine protease interacts with the chitin synthase from the midgut of the tobacco hornworm

The chitin portion of the peritrophic matrix in the midgut of the tobacco hornworm, Manduca sexta, is produced by chitin synthase 2 (CHS2), a transmembrane family II glycosyltransferase, located at the apical tips of brush border microvilli. To look for proteins that potentially interact with CHS2, we performed yeast two-hybrid screening, identifying a novel chymotrypsin-like protease (CTLP1) that binds to the extracellular carboxyterminal domain of CHS2. The occurrence of this interaction in vivo is supported by co-localization and co-immunoprecipitation data. Based on our findings we propose that chitin synthesis is controlled by an intestinal proteolytic signalling cascade linking chitin synthase activity to the nutritional state of the larvae.

Protein turnover and differentiation in Leishmania

Leishmania occurs in several developmental forms and thus undergoes complex cell differentiation events during its life-cycle. Those are required to allow the parasite to adapt to the different environmental conditions. The sequencing of the genome of L. major has facilitated the identification of the parasite’s vast arsenal of proteolytic enzymes, a few of which have already been carefully studied and found to be important for the development and virulence of the parasite. This review focuses on these peptidases and their role in the cellular differentiation of Leishmania through their key involvement in a variety of degradative pathways in the lysosomal and autophagy networks.

Glossina proteolytic lectin does not require a carbohydrate moiety for enzymatic or trypanosome-transforming activities

The developmental cycle of the cyclically transmitted African trypanosome involves an obligatory passage through the tsetse fly, Glossina spp. This intricate relationship requires the presence of molecules within the insect vector, including a midgut lectin, that interact with the trypanosome. Recently, a gene encoding for a proteolytic lectin, with trypanosome-transforming activity, was isolated from a midgut cDNA library of Glossina fuscipes fuscipes Austen in our laboratory. Using the same approach, we have identified a similar gene from a midgut cDNA library of Glossina austeni (Newstead). The protein encoded by this gene was expressed in bacteria and a baculovirus-based expression system. The baculovirus-expressed lectin was found in the medium of baculovirus-infected Sf-21 cell cultures, indicating that the tsetse fly-derived signal peptide was recognized and cleaved by the Sf-21 cells. The baculovirus-expressed protein also was glycosylated despite the absence of classical O-linked and N-linked sugar attachment motifs. Both the baculovirus- and bacterium-expressed lectin proteins were shown to agglutinate trypanosomes and rabbit red blood cells in vitro. This agglutination was strongly inhibited by D-glucosamine. D-Glucosamine also inhibited the action of the authentic and recombinant lectins upon the chromogenic substrate Chromozym TRY. Interestingly, both baculovirus- and bacterium-expressed lectins showed no significant differences in terms of these activities, indicating that a sugar moiety is not essential for biological activity. Our results provide an important molecular tool for further characterization of Glossina proteolytic lectin.

A serine protease gene from the firefly, Pyrocoelia rufa: gene structure, expression, and enzyme activity

The gene structure, expression and enzyme activity of a serine protease from the firefly, Pyrocoelia rufa (PrSP) were examined. The PrSP gene spans 1474 bp and consists of two introns and three exons coding for 257 amino acid residues. Southern blot analysis of genomic DNA suggested the presence of PrSP gene as a single copy. Western blot analysis and enzyme activity assay exhibited midgut-specific expression, suggesting that the midgut is the prime site where large quantities of PrSP are synthesized for degrading the absorbed protein from the diet. The cDNA encoding PrSP was expressed as a 31 kDa polypeptide in the baculovirus-infected insect Sf9 cells and the recombinant PrSP showed activity in the protease enzyme assay using gelatin as a substrate.

Serine proteinases of the human body louse (Pediculus humanus): sequence characterization and expression patterns

After the previous characterization of one trypsin gene (Try1) of the human body louse Pediculus humanus, genes encoding a second trypsin (Try2) and a chymotrypsin (Chy1) have been cloned using degenerate serine proteinase primers and 5'- and 3'-RACE, and sequenced. The deduced 259 and 267 amino acid sequences of Try2 and Chy1 show an identity of 33%-40% to trypsinogens and chymotrypsinogens of other insects. Considering previously published partial sequences, P. humanus possesses at least one Try1 gene, five variants/isoforms of Try2 and six variants/isoforms of Chy1. The genomic DNA of Try2 contains three introns and Chy1 contains five introns. Using whole mount in situ hybridization, gene expression of Try1, Try2 and Chy1 has been localized not only in the distensible anterior region of the midgut of lice but sometimes also in the area following the distensible region. The Try2 gene was always expressed at much lower levels than Try1 or Chy1. This lower expression, the constitutive expression of Try1 and Chy1 at 1, 2, 6, 12 and 24 h after feeding of adults and the regional differences have been verified in quantitative real-time PCR.

Cloning and characterization of a trypsin-encoding cDNA of the human body louse Pediculus humanus

From a cDNA library of the whole insect, a trypsin gene of Pediculus humanus has been cloned and sequenced. The 908 bp clone has an open reading frame of 759 bp, which encodes a pre-proenzyme with 253 amino acid residues. A sixteen-residue N-terminal signal peptide is followed by a twelve-residue activation peptide with putative cleavage sites at Gly16 and Tyr28. The deduced amino acid sequence has several features typical of trypsin proteases and an overall identity of 35-43% with the trypsins of several haematophagous Diptera. The 1.0 kb genomic trypsin gene contains three introns of 102, 79 and 80 nucleotides following the codons for Gly16, Gln74 and Ala155, respectively. Only a single gene seems to be present. In Northern blot analysis, unfed first instar larvae have an identical or slightly lower level of trypsin mRNA than fed adult lice, and in adults 2-24 h after the bloodmeal this gene shows a constitutive expression. After in vitro transcription and translation, the activation peptide is cleaved by chymotrypsin, a so far unreported phenomenon in trypsin activation.

Interactions between tsetse and trypanosomes with implications for the control of trypanosomiasis

Tsetse flies (Diptera: Glossinidae) are vectors of several species of pathogenic trypanosomes in tropical Africa. Human African trypanosomiasis (HAT) is a zoonosis caused by Trypanosoma brucei rhodesiense in East Africa and T. b. gambiense in West and Central Africa. About 100000 new cases are reported per year, with many more probably remaining undetected. Sixty million people living in 36 countries are at risk of infection. Recently, T. b. gambiense trypanosomiasis has emerged as a major public health problem in Central Africa, especially in the Democratic Republic of Congo, Angola and southern Sudan where civil war has hampered control efforts. African trypanosomes also cause nagana in livestock. T. vivax and T. congolense are major pathogens of cattle and other ruminants, while T. simiae causes high mortality in domestic pigs; T. brucei affects all livestock, with particularly severe effects in equines and dogs. Central to the control of these diseases is control of the tsetse vector, which should be very effective since trypanosomes rely on this single insect for transmission. However, the area infested by tsetse has increased in the past century. Recent advances in molecular technologies and their application to insects have revolutionized the field of vector biology, and there is hope that such new approaches may form the basis for future tsetse control strategies. This article reviews the known biology of trypanosome development in the fly in the context of the physiology of the digestive system and interactions of the immune defences and symbiotic flora.

Purification, identification, and biochemical characterization of a host-encoded cysteine protease that cleaves a leishmaniavirus gag-pol polyprotein

Leishmania RNA virus (LRV) is a double-stranded RNA virus that infects some strains of the protozoan parasite leishmania As with other totiviruses, LRV presumably expresses its polymerase by a ribosomal frameshift, resulting in a capsid-polymerase fusion protein. We have demonstrated previously that an LRV capsid-polymerase polyprotein is specifically cleaved by a Leishmania-encoded cysteine protease. This study reports the purification of this protease through a strategy involving anion-exchange chromatography and affinity chromatography. By using a Sepharose-immobilized lectin, concanavalin A, we isolated a fraction enriched with LRV polyprotein-specific protease activity. Analysis of the active fraction by sodium dodecyl sulfate-polyacrylamide gel electrophoreses and silver staining revealed a 50-kDa protein that, upon characterization by high-pressure liquid chromatography electrospray tandem mass spectrometry (electrospray ionization/MS/MS), was identified as a cysteine protease of trypanosomes. A partial amino acid sequence derived from the MS/MS data was compared with a protein database using BLAST software, revealing homology with several cysteine proteases of Leishmania and other trypanosomes. The protease exhibited remarkable temperature stability, while inhibitor studies characterized the protease as a trypsin-like cysteine protease-a novel finding for leishmania. To elucidate substrate preferences, a panel of deletion mutations and single-amino-acid mutations were engineered into a Gag-Pol fusion construct that was subsequently transcribed and translated in vitro and then used in cleavage assays. The data suggest that there are a number of cleavage sites located within a 153-amino-acid region spanning both the carboxy-terminal capsid region and the amino-terminal polymerase domain, with LRV capsid exhibiting the greatest susceptibility to proteolysis.

Cleavage of trypanosome surface glycoproteins by alkaline trypsin-like enzyme(s) in the midgut of Glossina morsitans

EP and GPEET procyclin, the major surface glycoproteins of procyclic forms of Trypanosoma brucei, are truncated by proteases in the midgut of the tsetse fly Glossina morsitans morsitans. We show that soluble extracts from the midguts of teneral flies contain trypsin-like enzymes that cleave the N-terminal domains from living culture-derived parasites. The same extract shows little activity against a variant surface glycoprotein on living bloodstream form T. brucei (MITat 1.2) and none against glutamic acid/alanine-rich protein, a major surface glycoprotein of Trypanosoma congolense insect forms although both these proteins contain potential trypsin cleavage sites. Gel filtration of tsetse midgut extract revealed three peaks of tryptic activity against procyclins. Trypsin alone would be sufficient to account for the cleavage of GPEET at a single arginine residue in the fly. In contrast, the processing of EP at multiple sites would require additional enzymes that might only be induced or activated during feeding or infection. Unexpectedly, the pH optima for both the procyclin cleavage reaction and digestion of the trypsin-specific synthetic substrate Chromozym-TRY were extremely alkaline (pH 10). Direct measurements were made of the pH within different compartments of the tsetse digestive tract. We conclude that the gut pH of teneral flies, from the proventriculus to the hindgut, is alkaline, in contradiction to previous measurements indicating that it was mildly acidic. When tsetse flies were analysed 48 h after their first bloodmeal, a pH gradient from the proventriculus (pH 10.6+/-0.6) to the posterior midgut (pH 7.9+/-0.4) was observed.

Cloning and characterization of trypsin- and chymotrypsin-like proteases from the midgut of the sand fly vector Phlebotomus papatasi

Trypsin and chymotrypsin serine proteases are the main digestive proteases in Diptera midguts and are also involved in many aspects of the vector-parasite relationship. In sand flies, these proteases have been shown to be a potential barrier to Leishmania growth and development within the midgut. Here we describe the sequence and partial characterization of six Phlebotomus papatasi midgut serine proteases: two chymotrypsin-like (Ppchym1 and Ppchym2) and four trypsin-like (Pptryp1-Pptryp4). All six enzymes show structural features typical to each type, including the histidine, aspartic acid, and serine (H/D/S) catalytic triad, six conserved cysteine residues, and other amino acid residues involved in substrate specificity. They also show a high degree of homology (40-60% identical residues) with their counterparts from other insect vectors, such as Anopheles gambiae and Aedes aegypti. The mRNA expression profiles of these six proteases vary considerably: two trypsin-like proteases (Pptryp1 and Pptryp2) are downregulated and one (Pptryp4) upregulated upon blood feeding. The two chymotrypsin-like enzymes display expression behavior similar to that of the early and late trypsins from Ae. aegypti.

The major protein in the midgut of teneral Glossina morsitans morsitans is a molecular chaperone from the endosymbiotic bacterium Wigglesworthia glossinidia

Molecules in the midgut of the tsetse fly (Diptera: Glossinidiae) are thought to play an important role in the life cycle of African trypanosomes by influencing their initial establishment in the midgut and subsequent differentiation events that ultimately affect parasite transmission. It is thus important to determine the molecular composition of the tsetse midgut to aid in understanding disease transmission by these medically important insect vectors. Here, we report that the most abundant protein in the midguts of teneral (unfed) Glossina morsitans morsitans is a 60 kDa molecular chaperone of bacterial origin. Two species of symbiotic bacteria reside in the tsetse midgut, Sodalis glossinidius and Wigglesworthia glossinidia. To determine the exact origin of the 60 kDa molecule, a protein microchemical approach involving two-dimensional (2-D) gel electrophoresis and mass spectrometry was used. Peptide mass maps were compared to virtual peptide maps predicted for S. glossinidius and W. glossinidia 60 kDa chaperone sequences. Four signature peptides were identified, revealing that the source of the chaperone was W. glossinidia. Comparative 2-D gel electrophoresis and immunoblotting further revealed that this protein was localized to the bacteriome and not the distal portion of the tsetse midgut. The possible function of this highly abundant endosymbiont chaperone in the tsetse midgut is discussed.

Cloning and functional expression of a fat body-specific chitinase cDNA from the tsetse fly, Glossina morsitans morsitans

A chitinase cDNA, GChit1 was isolated from Glossina morsitans morsitans and shown to be specifically expressed in fat body tissue. GChit1 is encoded by a 1.6 kb mRNA with a putative open reading frame (ORF) of 460 amino acids (predicted pI=7.5, m.w.=51kDa) that contains a signal peptide domain and two potential N-linked glycosylation sites. The ORF exhibits homology to various chitinases characterized from insects. It has the conserved catalytic site residues and the cysteine-rich 3'-end domain associated with chitin binding although the serine/threonine rich domain is apparently missing. Southern blot data indicate that GChit1 is present as a single-copy locus in the Glossina genome. Northern analysis indicates that transcripts for GChit1 can be detected only from the fat body of adult flies. Similarly, chitinase activity could be detected in fat body but not in the gut or salivary gland tissues. The full-length cDNA was expressed in vitro in Drosophila S2 cells and the molecule was produced in a soluble form. Polyclonal antibodies raised against recGChit1 could recognize a protein of about 50 kDa in adult fat body extracts. In addition to fat body, chitinase protein was detected by Western analysis from the milk gland tissue of pregnant females as well as from the intrauterine larval and pupal developmental stages. No chitinase specific mRNA transcripts could be observed, however from larvae and pupae. The intrauterine larva of tsetse may receive the protein from its mother via the milk gland route. The molecular characteristics of GChit and its product and the potential role of this chitinase in tsetse biology are discussed.

Molecular characterization of three gut genes from Glossina morsitans morsitans: cathepsin B, zinc-metalloprotease and zinc-carboxypeptidase

Insect gut enzymes are involved in digestion of dietary proteins. Additionally, these enzymes have been implicated in the process of pathogen establishment in several insects including the tsetse fly (Diptera:Glossinidae), which is the vector for African trypanosomes. Both the male and female tsetse can transmit trypanosomes and are strict blood feeders during all stages of their development. Here, we describe the molecular characterization of three gut genes: cathepsin B (GmCatB), zinc-metalloprotease (GmZmp) and zinc-carboxypeptidase (GmZcp). The cDNA for GmCatB encodes a protein for 340 amino acids with a predicted molecular mass of 38.2 kDa, while the 854 bp GmZmp cDNA encodes a protein of 254 amino acids with a molecular mass of 29 kDa. The GmZcp cDNA is 1319 bp in length and has a 354 amino acids open reading frame for coding a 40 kDa protein. All three cDNAs have signal peptide sequences associated with their N-terminal domains and structure analysis indicates that GmCatB and GmZmp are expressed as zymogens with pro-domains proteolytically removed for activity. The activation domain associated with the carboxypeptidase sequences is lacking in GmZcp. While GmCatB transcription is constitutive, teneral flies express very low levels of transcripts for GmZmp and GmZcp prior to the first bloodmeal. Transcription of all genes is induced and remains high throughout the digestion cycle within a few hours following the first bloodmeal ingestion. Both GmCatB and GmZcp are parasite responsive, with the expression of both genes being higher in trypanosome infected flies.