Parasite prolyl oligopeptidases and the challenge of designing chemotherapeuticals for Chagas disease, leishmaniasis and African trypanosomiasis

Recent advances in genome editing of bloodstream forms of Trypanosoma congolense using CRISPR-Cas9 ribonucleoproteins: Proof of concept

African Animal Trypanosomosis (AAT or Nagana) is a vector-borne disease caused by Trypanosomatidae, genus Trypanosoma. The disease is transmitted by the bite of infected hematophagous insects, mainly tsetse flies but also other blood-sucking insects including stomoxes and tabanids. Although many trypanosome species infect animals, the main agents responsible for this disease with a strong socio-economic and veterinary health impact are Trypanosoma congolense (T. congolense or Tc), Trypanosoma vivax (T.vivax), and to a lesser extent, Trypanosoma brucei brucei (T.brucei brucei or Tbb). These parasites mainly infect livestock, including cattle, in sub-Saharan Africa, with major repercussions in terms of animal productivity and poverty for populations which are often already very poor. As there is currently no vaccine, the fight against the disease is primarily based on diagnosis, treatment and vector control. To develop new tools (particularly therapeutic tools) to fight against the disease, we need to know both the biology and the genes involved in the pathogenicity and virulence of the parasites. To date, unlike for Trypanosoma brucei (T.brucei) or Trypanosoma cruzi (T.cruzi), genome editing tools has been relatively little used to study T. congolense. We present an efficient, reproducible and stable CRISPR-Cas9 genome editing system for use in Tc bloodstream forms (Tc-BSF). This plasmid-free system is based on transient expression of Cas9 protein and the use of a ribonucleoprotein formed by the Cas9 and sgRNA complex. This is the first proof of concept of genome editing using CRISPR-Cas9 ribonucleoproteins on Tc-BSF. This adapted protocol enriches the "toolbox" for the functional study of genes of interest in blood forms of the Trypanosoma congolense. This proof of concept is an important step for the scientific community working on the study of trypanosomes and opens up new perspectives for the control of and fight against animal trypanosomosis.

Anti-Trypanosoma cruzi Properties of Sesquiterpene Lactones Isolated from Stevia spp.: In Vitro and In Silico Studies

Stevia species (Asteraceae) have been a rich source of terpenoid compounds, mainly sesquiterpene lactones, several of which show antiprotozoal activity. In the search for new trypanocidal compounds, S. satureiifolia var. satureiifolia and S. alpina were studied. Two sesquiterpene lactones, santhemoidin C and 2-oxo-8-deoxyligustrin, respectively, were isolated. These compounds were assessed in vitro against Trypanosoma cruzi stages, showing IC₅₀ values of 11.80 and 4.98 on epimastigotes, 56.08 and 26.19 on trypomastigotes and 4.88 and 20.20 µM on amastigotes, respectively. Cytotoxicity was evaluated on Vero cells by the MTT assay. The effect of the compounds on trypanothyone reductase (TcTR), Trans-sialidase (TcTS) and the prolyl oligopeptidase of 80 kDa (Tc80) as potential molecular targets of T. cruzi was investigated. Santhemoidin C inhibited oligopeptidase activity when tested against recombinant Tc80 using a fluorometric assay, reaching an IC₅₀ of 34.9 µM. Molecular docking was performed to study the interaction between santhemoidin C and the Tc80 protein, reaching high docking energy levels. Plasma membrane shedding and cytoplasmic vacuoles, resembling autophagosomes, were detected by transmission microscopy in parasites treated with santhemoidin C. Based on these results, santhemoidin C represents a promising candidate for further studies in the search for new molecules for the development of trypanocidal drugs.

Post-Proline Cleaving Enzymes (PPCEs): Classification, Structure, Molecular Properties, and Applications

Proteases or peptidases are hydrolases that catalyze the breakdown of polypeptide chains into smaller peptide subunits. Proteases exist in all life forms, including archaea, bacteria, protozoa, insects, animals, and plants due to their vital functions in cellular processing and regulation. There are several classes of proteases in the MEROPS database based on their catalytic mechanisms. This review focuses on post-proline cleaving enzymes (PPCEs) from different peptidase families, as well as prolyl endoprotease/oligopeptidase (PEP/POP) from the serine peptidase family. To date, most PPCEs studied are of microbial and animal origins. Recently, there have been reports of plant PPCEs. The most common PEP/POP are members of the S9 family that comprise two conserved domains. The substrate-limiting β-propeller domain prevents unwanted digestion, while the α/β hydrolase catalyzes the reaction at the carboxyl-terminal of proline residues. PPCEs display preferences towards the Pro-X bonds for hydrolysis. This level of selectivity is substantial and has benefited the brewing industry, therapeutics for celiac disease by targeting proline-rich substrates, drug targets for human diseases, and proteomics analysis. Protein engineering via mutagenesis has been performed to improve heat resistance, pepsin-resistant capability, specificity, and protein turnover of PPCEs for pharmacological applications. This review aims to synthesize recent structure-function studies of PPCEs from different families of peptidases to provide insights into the molecular mechanism of prolyl cleaving activity. Despite the non-exhaustive list of PPCEs, this is the first comprehensive review to cover the biochemical properties, biological functions, and biotechnological applications of PPCEs from the diverse taxa.

NMR structure and dynamics of Q4DY78, a conserved kinetoplasid-specific protein from Trypanosoma cruzi

The 106-residue protein Q4DY78 (UniProt accession number) from Trypanosoma cruzi is highly conserved in the related kinetoplastid pathogens Trypanosoma brucei and Leishmania major. Given the essentiality of its orthologue in T. brucei, the high sequence conservation with other trypanosomatid proteins, and the low sequence similarity with mammalian proteins, Q4DY78 is an attractive protein for structural characterization. Here, we solved the structure of Q4DY78 by solution NMR and evaluated its backbone dynamics. Q4DY78 is composed of five α -helices and a small, two-stranded antiparallel β-sheet. The backbone RMSD is 0.22 ± 0.05 Å for the representative ensemble of the 20 lowest-energy structures. Q4DY78 is overall rigid, except for N-terminal residues (V⁸ to I¹⁰), residues at loop 4 (K⁵⁷ to G⁶⁵) and residues at the C-terminus (F⁸⁹ to F¹¹²). Q4DY78 has a short motif FPCAP that could potentially mediate interactions with the host cytoskeleton via interaction with EVH1 (Drosophila Enabled (Ena)/Vasodilator-stimulated phosphoprotein (VASP) homology 1) domains. Albeit Q4DY78 lacks calcium-binding motifs, its fold resembles that of eukaryotic calcium-binding proteins such as calcitracin, calmodulin, and polcacin Bet V4. We characterized this novel protein with a calcium binding fold without the capacity to bind calcium.

Update on relevant trypanosome peptidases: Validated targets and future challenges

Trypanosoma cruzi, the agent of the American Trypanosomiasis, Chagas disease, and Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense, the agents of Sleeping sickness (Human African Trypanosomiasis, HAT), as well as Trypanosoma brucei brucei, the agent of the cattle disease nagana, contain cysteine, serine, threonine, aspartyl and metallo peptidases. The most abundant among these enzymes are the cysteine proteases from the Clan CA, the Cathepsin L-like cruzipain and rhodesain, and the Cathepsin B-like enzymes, which have essential roles in the parasites and thus are potential targets for chemotherapy. In addition, several other proteases, present in one or both parasites, have been characterized, and some of them are also promising candidates for the developing of new drugs. Recently, new inhibitors, with good selectivity for the parasite proteasomes, have been described and are very promising as lead compounds for the development of new therapies for these neglected diseases. This article is part of a Special Issue entitled: "Play and interplay of proteases in health and disease".

Prolyl Oligopeptidase From Leishmania infantum: Biochemical Characterization and Involvement in Macrophage Infection

Leishmania infantum is a flagellated protozoan and one of the main causative agents of visceral leishmaniasis. This disease usually affects the human reticuloendothelial system, can cause death and available therapies may lead to serious side effects. Since it is a neglected tropical disease, the incentives for the development of new drugs are insufficient. It is important to know Leishmania virulence factors that contribute most to the disease in order to develop drugs. In the present work, we have produced L. infantum prolyl oligopeptidase (rPOPLi) in Escherichia coli, and investigated its biochemical properties as well as the effect of POP inhibitors on its enzymatic activity and on the inhibition of the macrophage infection by L. infantum. The optimal activity occurred at pH 7.5 and 37°C in the presence of DTT, the latter increased rPOPLi catalytic efficiency 5-fold on the substrate N-Suc-Gly-Pro-Leu-Gly-Pro-AMC. The enzyme was inhibited by TPCK, TLCK and by two POP specific inhibitors, Z-Pro-prolinal (ZPP, IC₅₀ 4.2 nM) and S17092 (IC₅₀ 3.5 nM). Besides being a cytoplasmic enzyme, POPLi is also found in punctuate structures within the parasite cytoplasm or associated with the parasite plasma membrane in amastigotes and promastigotes, respectively. Interestingly, S17092 and ZPP prevented parasite invasion in murine macrophages, supporting the involvement of POPLi in the invasive process of L. infantum. These data suggest POPLi as a virulence factor that offers potential as a target for designing new antileishmanial drugs.

Prolyl endopeptidase gene disruption attenuates high fat diet-induced nonalcoholic fatty liver disease in mice by improving hepatic steatosis and inflammation

Background

Prolyl endopeptidase (PREP) is a serine endopeptidase that regulates inflammatory responses. PREP inhibitors can reduce hepatocyte lipid accumulation and may participate in the progression of nonalcoholic fatty liver disease (NAFLD). We investigated whether disruption of PREP regulates hepatic steatosis and inflammation in mice with NAFLD.

Methods

Wild-type and PREP gene disrupted mice were randomly divided into low-fat diet wild-type (LFD-WT), high-fat diet wild-type (HFD-WT), low-fat diet PREP disruption (LFD-PREP^gt), and high-fat diet PREP disruption (HFD-PREP^gt) groups. Animals were euthanized at the endpoint of 32 weeks. The NAFLD activity score and number of inflammatory cells were determined by hematoxylin-eosin staining and immunohistochemical staining of liver tissue. The expression levels of inflammation- and lipid metabolism-associated genes in the liver and serum were detected by quantitative reverse transcription PCR, mass spectrometry, or enzyme-linked immunosorbent assay.

Results

The body weight and epididymal fat tissue index of the HFD-PREP^gt mice were significantly decreased compared with that of the HFD-WT mice. Moreover, the NAFLD activity score and liver function were attenuated in the HFD-PREP^gt mice. Fat accumulation and the level of expression of mRNAs associated with lipid metabolism and proinflammatory responses were improved in the HFD-PREP^gt mice. The number of CD68-positive cells in liver tissue and the serum levels of inflammation-associated factors were significantly decreased in the HFD-PREP^gt mice compared with those in the HFD-WT mice. Further mechanistic investigations indicated that the protective effect of PREP disruption on liver inflammation was associated with the suppressed production of matrix metalloproteinases (MMPs) and proline-glycine-proline (PGP) and the inhibition of neutrophil infiltration.

Conclusions

Loss of PREP lowers the severity of hepatic steatosis and inflammatory responses in a high-fat diet-induced nonalcoholic steatohepatitis model. PREP inhibition may protect against NAFLD.

Exoproteome profiling of Trypanosoma cruzi during amastigogenesis early stages

Chagas disease is caused by the protozoan Trypanosoma cruzi, affecting around 8 million people worldwide. After host cell invasion, the infective trypomastigote form remains 2–4 hours inside acidic phagolysosomes to differentiate into replicative amastigote form. In vitro acidic-pH-induced axenic amastigogenesis was used here to study this step of the parasite life cycle. After three hours of trypomastigote incubation in amastigogenesis promoting acidic medium (pH 5.0) or control physiological pH (7.4) medium samples were subjected to three rounds of centrifugation followed by ultrafiltration of the supernatants. The resulting exoproteome samples were trypsin digested and analysed by nano flow liquid chromatography coupled to tandem mass spectrometry. Computational protein identification searches yielded 271 and 483 protein groups in the exoproteome at pH 7.4 and pH 5.0, respectively, with 180 common proteins between both conditions. The total amount and diversity of proteins released by parasites almost doubled upon acidic incubation compared to control. Overall, 76.5% of proteins were predicted to be secreted by classical or non-classical pathways and 35.1% of these proteins have predicted transmembrane domains. Classical secretory pathway analysis showed an increased number of mucins and mucin-associated surface proteins after acidic incubation. However, the number of released trans-sialidases and surface GP63 peptidases was higher at pH 7.4. Trans-sialidases and mucins are anchored to the membrane and exhibit an enzyme-substrate relationship. In general, mucins are glycoproteins with immunomodulatory functions in Chagas disease, present mainly in the epimastigote and trypomastigote surfaces and could be enzymatically cleaved and released in the phagolysosome during amastigogenesis. Moreover, evidence for flagella discard during amastigogenesis are addressed. This study provides the first comparative analysis of the exoproteome during amastigogenesis, and the presented data evidence the dynamism of its profile in response to acidic pH-induced differentiation.

Tinkering with targeting nucleotide signaling for control of intracellular Leishmania parasites

Nucleotides are one of the most primitive extracellular signalling molecules across all phyla and regulate a multitude of responses. The biological effects of extracellular nucleotides/sides are mediated via the specific purinergic receptors present on the cell surface. In mammalian system, adenine nucleotides are the predominant nucleotides found in the extracellular milieu and mediate a constellation of physiological functions. In the context of host-pathogen interaction, extracellular ATP is recognized as a danger signal and potentiates the release of pro-inflammatory mediators from activated immune cells, on the other hand, its breakdown product adenosine exerts potential anti-inflammatory and immunosuppressive actions. Therefore, it is increasingly apparent that the interplay between extracellular ATP/adenosine ratios has a significant role in coordinating the regulation of the immune system in health and diseases. Several pathogens express ectonucleotidases on their surface and exploit the purinergic signalling as one of the mechanisms to modulate the host immune response. Leishmania pathogens are one of the most successful intracellular pathogens which survive within host macrophages and manipulate protective Th1 response into disease promoting Th2 response. In this review, we discuss the regulation of extracellular ATP and adenosine levels, the role of ATP/adenosine counter signalling in regulating the inflammation and immune responses during infection and how Leishmania parasites exploit the purinergic signalling to manipulate host response. We also discuss the challenges and opportunities in targeting purinergic signalling and the future prospects.

Isoquinoline Alkaloids from Berberis vulgaris as Potential Lead Compounds for the Treatment of Alzheimer's Disease

Three new alkaloids, bersavine (3), muraricine (4), and berbostrejdine (8), together with seven known isoquinoline alkaloids (1-2, 5-7, 9, and 10) were isolated from an alkaloidal extract of the root bark of Berberis vulgaris. The structures of the isolated compounds were determined by spectroscopic methods, including 1D and 2D NMR techniques, HRMS, and optical rotation, and by comparison of the obtained data with those in the literature. The NMR data of berbamine (5), aromoline (6), and obamegine (7) were completely assigned employing 2D NMR experiments. Alkaloids isolated in sufficient amounts were evaluated for their in vitro acetylcholinesterase, butyrylcholinesterase (BuChE), prolyl oligopeptidase, and glycogen synthase kinase-3β inhibitory activities. Selected compounds were studied for their ability to permeate through the blood-brain barrier. Significant human BuChE ( hBuChE) inhibitory activity was demonstrated by 6 (IC₅₀ = 0.82 ± 0.10 μM). The in vitro data were further supported by computational analysis that showed the accommodation of 6 in the active site of hBuChE.

Leishmanicidal therapy targeted to parasite proteases

Leishmaniasis is considered a serious public health problem and the current available therapy has several disadvantages, which makes the search for new therapeutic targets and alternative treatments extremely necessary. In this context, this review focuses on the importance of parasite proteases as target drugs against Leishmania parasites, as a chemotherapy approach. Initially, we discuss about the current scenario for the treatment of leishmaniasis, highlighting the main drugs used and the problems related to their use. Subsequently, we describe the inhibitors of major proteases of Leishmania already discovered, such as Compound s9 (aziridine-2,3-dicarboxylate), Compound 1c (benzophenone derivative), Au2Phen (gold complex), AubipyC (gold complex), MDL 28170 (dipeptidyl aldehyde), K11777, Hirudin, diazo-acetyl norleucine methyl ester, Nelfinavir, Saquinavir, Nelfinavir, Saquinavir, Indinavir, Saquinavir, GNF5343 (azabenzoxazole), GNF6702 (azabenzoxazole), Benzamidine and TPCK. Next, we discuss the importance of the protease gene to parasite survival and the aspects of the validation of proteases as target drugs, with emphasis on gene disruption. Then, we describe novel important strategies that can be used to support the research of new antiparasitic drugs, such as molecular modeling and nanotechnology, whose main targets are parasitic proteases. And finally, we discuss possible perspectives to improve drug development. Based on all findings, proteases could be considered potential targets against leishmaniasis.

Asymmetric peptidomimetics containing L-tartaric acid core inhibit the aspartyl peptidase activity and growth of Leishmania amazonensis promastigotes

Aspartyl-type peptidases are promising chemotherapeutic targets in protozoan parasites. In the present work, we identified an aspartyl peptidase activity from the soluble extract of Leishmania amazonensis promastigotes, which cleaved the fluorogenic peptide 7-methoxycoumarin-4-acetyl-Gly-Lys-Pro-Ile-Leu-Phe-Phe-Arg-Leu-Lys(DNP)-D-Arg-amide (cathepsin D substrate) under acidic pH conditions at 37°C, showing a KM of 0.58 μM and Vmax of 129.87 fluorescence arbitrary units/s mg protein. The leishmanial aspartyl peptidase activity was blocked by pepstatin A (IC50 = 6.8 μM) and diazo-acetyl-norleucinemetilester (IC50 = 10.2 μM), two classical aspartyl peptidase inhibitors. Subsequently, the effects of 6 asymmetric peptidomimetics, containing L-tartaric acid core, were tested on both aspartyl peptidase and growth of L. amazonensis promastigotes. The peptidomimetics named 88, 154 and 158 promoted a reduction of 50% on the leishmanial aspartyl peptidase activity at concentrations ranging from 40 to 85 μM, whereas the peptidomimetic 157 was by far the most effective, presenting IC50 of 0.04 μM. Furthermore, the peptidomimetics 157 and 154 reduced the parasite proliferation in a dose-dependent manner, displaying IC50 values of 33.7 and 44.5 μM, respectively. Collectively, the peptidomimetic 157 was the most efficient compound able to arrest both aspartyl peptidase activity and leishmanial proliferation, which raises excellent perspectives regarding its use against this human pathogenic protozoan.

New compounds identified through in silico approaches reduce the α-synuclein expression by inhibiting prolyl oligopeptidase in vitro

Prolyl oligopeptidase (POP) is a serine protease that is responsible for the maturation and degradation of short neuropeptides and peptide hormones. The inhibition of POP has been demonstrated in the treatment of α-synucleinopathies and several neurological conditions. Therefore, ligand-based and structure-based pharmacophore models were generated and validated in order to identify potent POP inhibitors. Pharmacophore-based and docking-based virtual screening of a drug-like database resulted in 20 compounds. The in vitro POP assays indicated that the top scoring compounds obtained from virtual screening, Hit 1 and Hit 2 inhibit POP activity at a wide range of concentrations from 0.1 to 10 µM. Moreover, treatment of the hit compounds significantly reduced the α-synuclein expression in SH-SY5Y human neuroblastoma cells, that is implicated in Parkinson’s disease. Binding modes of Hit 1 and Hit 2 compounds were explored through molecular dynamics simulations. A detailed investigation of the binding interactions revealed that the hit compounds exhibited hydrogen bond interactions with important active site residues and greater electrostatic and hydrophobic interactions compared to those of the reference inhibitors. Finally, our findings indicated the potential of the identified compounds for the treatment of synucleinopathies and CNS related disorders.

Prolyl oligopeptidase and its role in the organism: attention to the most promising and clinically relevant inhibitors

Prolyl oligopeptidase (POP), also called prolyl endopeptidase, is a cytosolic enzyme investigated by several research groups. It has been proposed to play an important role in physiological processes such as modulation of the levels of several neuronal peptides and hormones containing a proline residue. Due to its proteolytic activity and physiological role in cell signaling pathways, inhibition of POP offers an emerging approach for the treatment of Alzheimer's and Parkinson's diseases as well as other diseases related to cognitive impairment. Furthermore, it may also represent an interesting target for treatment of neuropsychiatric disorders, and as an antiangiogenesis or antineoplastic agent. In this review paper, we summarized naturally occurring POP inhibitors together with peptide-like inhibitors and their biological effects. Some of them have shown promising results and interesting pharmacological profiles. However, to date, there is no POP inhibitor available on the market although several clinical trials have been undertaken.

Insight into the Exoproteome of the Tissue-Derived Trypomastigote form of Trypanosoma cruzi

The protozoan parasite Trypanosoma cruzi causes Chagas disease, one of the major neglected infectious diseases. It has the potential to infect any nucleated mammalian cell. The secreted/excreted protein repertoire released by T. cruzi trypomastigotes is crucial in host-pathogen interactions. In this study, mammalian tissue culture-derived trypomastigotes (Y strain) were used to characterize the exoproteome of the infective bloodstream life form. Proteins released into the serum-free culture medium after 3 h of incubation were harvested and digested with trypsin. NanoLC-MS/MS analysis resulted in the identification of 540 proteins, the largest set of released proteins identified to date in Trypanosoma spp. Bioinformatic analysis predicted most identified proteins as secreted, predominantly by non-classical pathways, and involved in host-cell infection. Some proteins possess predicted GPI-anchor signals, these being mostly trans-sialidases, mucin associated surface proteins and surface glycoproteins. Moreover, we enriched phosphopeptides and glycopeptides from tryptic digests. The majority of identified glycoproteins are trans-sialidases and surface glycoproteins involved in host-parasite interaction. Conversely, most identified phosphoproteins have no Gene Ontology classification. The existence of various proteins related to similar functions in the exoproteome likely reflects this parasite's enhanced mechanisms for adhesion, invasion, and internalization of different host-cell types, and escape from immune defenses.

The genome ofStrongyloidesspp. gives insights into protein families with a putative role in nematode parasitism

Parasitic nematodes are important and abundant parasites adapted to live a parasitic lifestyle, with these adaptations all aimed at facilitating their survival and reproduction in their hosts. The recently sequenced genomes of fourStrongyloidesspecies, gastrointestinal parasites of humans and other animals, alongside transcriptomic and proteomic analysis of free-living and parasitic stages of their life cycles have revealed a number of protein families with a putative role in their parasitism. Many of these protein families have also been associated with parasitism in other parasitic nematode species, suggesting that these proteins may play a fundamental role in nematode parasitism more generally. Here, we review key protein families that have a putative role inStrongyloides’ parasitism – acetylcholinesterases, astacins, aspartic proteases, prolyl oligopeptidases, proteinase inhibitors (trypsin inhibitors and cystatins), SCP/TAPS and transthyretin-like proteins – and the evidence for their key, yet diverse, roles in the parasitic lifestyle.

[Prospects for the design of new therapeutically significant protease inhibitors based on knottins and sunflower seed trypsin inhibitor (SFTI 1)]

Plant seed knottins, mainly from the Cucurbitacea family, and sunflower seed trypsin inhibitor (SFTI 1) are the most low-molecular canonical peptide inhibitors of serine proteases. High efficiency of inhibition of various serine proteases, structure rigidity together with the possibility of limited variations of amino acid sequences, high chemical stability, lack of toxic properties, opportunity of production by either chemical synthesis or use of heterologous expression systems make these inhibitors attractive templates for design of new compounds for regulation of therapeutically significant serine protease activities. Hence the design of such compounds represents a prospective research field. The review considers structural characteristics of these inhibitors, their properties, methods of preparation and design of new analogs. Examples of successful employment of natural serine protease inhibitors belonging to knottin family and SFTI 1 as templates for the design of highly specific inhibitors of certain proteases are given.

Prolyl Oligopeptidase from the Blood Fluke Schistosoma mansoni: From Functional Analysis to Anti-schistosomal Inhibitors

Background

Blood flukes of the genus Schistosoma cause schistosomiasis, a parasitic disease that infects over 240 million people worldwide, and for which there is a need to identify new targets for chemotherapeutic interventions. Our research is focused on Schistosoma mansoni prolyl oligopeptidase (SmPOP) from the serine peptidase family S9, which has not been investigated in detail in trematodes.

Methodology/Principal Findings

We demonstrate that SmPOP is expressed in adult worms and schistosomula in an enzymatically active form. By immunofluorescence microscopy, SmPOP is localized in the tegument and parenchyma of both developmental stages. Recombinant SmPOP was produced in Escherichia coli and its active site specificity investigated using synthetic substrate and inhibitor libraries, and by homology modeling. SmPOP is a true oligopeptidase that hydrolyzes peptide (but not protein) substrates with a strict specificity for Pro at P1. The inhibition profile is analogous to those for mammalian POPs. Both the recombinant enzyme and live worms cleave host vasoregulatory, proline-containing hormones such as angiotensin I and bradykinin. Finally, we designed nanomolar inhibitors of SmPOP that induce deleterious phenotypes in cultured schistosomes.

Conclusions/Significance

We provide the first localization and functional analysis of SmPOP together with chemical tools for measuring its activity. We briefly discuss the notion that SmPOP, operating at the host-parasite interface to cleave host bioactive peptides, may contribute to the survival of the parasite. If substantiated, SmPOP could be a new target for the development of anti-schistosomal drugs.

Schistosomiasis (bilharzia) is a major global health problem caused by the schistosome flatworm which lives in the bloodstream. Treatment and control of the disease relies on a single drug, and should resistance emerge, there would be increased pressure to discover new drug targets. Proteolytic enzymes are fundamental to the survival of parasites, and, hence, are attractive targets for drug intervention. Oligopeptidases from the S9 family are known virulence factors for protozoan trypanosomatids but have yet to be studied in parasitic flukes. We, therefore, investigated prolyl oligopeptidase in Schistosoma mansoni (SmPOP) and found that it is expressed in those developmental stages that infect humans. We provide a comprehensive analysis of the peptidase’s expression, localization and functional biochemical properties. Interestingly, SmPOP, which is found in the tegument and parenchyma of the parasite, can cleave blood peptides involved in vasoregulation and we discuss how this ability may aid the parasite’s survival. Finally, we designed potent inhibitors of SmPOP that cause deleterious changes in cultured parasites. We conclude that SmPOP is important for parasite survival and may be a potential target for the development of anti-schistosomal drugs.

An essential signal peptide peptidase identified in an RNAi screen of serine peptidases of Trypanosoma brucei

The serine peptidases of Trypanosoma brucei have been viewed as potential drug targets. In particular, the S9 prolyl oligopeptidase subfamily is thought to be a good avenue for drug discovery. This is based on the finding that some S9 peptidases are secreted and active in the mammalian bloodstream, and that they are a class of enzyme against which drugs have successfully been developed. We collated a list of all serine peptidases in T. brucei, identifying 20 serine peptidase genes, of which nine are S9 peptidases. We screened all 20 serine peptidases by RNAi to determine which, if any, are essential for bloodstream form T. brucei survival. All S9 serine peptidases were dispensable for parasite survival in vitro, even when pairs of similar genes, coding for oligopeptidase B or prolyl oligopeptidase, were targeted simultaneously. We also found no effect on parasite survival in an animal host when the S9 peptidases oligopeptidase B, prolyl oligopeptidase or dipeptidyl peptidase 8 were targeted. The only serine peptidase to emerge from the RNAi screen as essential was a putative type-I signal peptide peptidase (SPP1). This gene was essential for parasite survival both in vitro and in vivo. The growth defect conferred by RNAi depletion of SPP1 was rescued by expression of a functional peptidase from an RNAi resistant SPP1 gene. However, expression of catalytically inactive SPP1 was unable to rescue cells from the SPP1 depleted phenotype, demonstrating that SPP1 serine peptidase activity is necessary for T. brucei survival.

The endothelin system has a significant role in the pathogenesis and progression of Mycobacterium tuberculosis infection

Tuberculosis (TB) remains a major global health problem, and although multiple studies have addressed the relationship between Mycobacterium tuberculosis and the host on an immunological level, few studies have addressed the impact of host physiological responses. Proteases produced by bacteria have been associated with important alterations in the host tissues, and a limited number of these enzymes have been characterized in mycobacterial species. M. tuberculosis produces a protease called Zmp1, which appears to be associated with virulence and has a putative action as an endothelin-converting enzyme. Endothelins are a family of vasoactive peptides, of which 3 distinct isoforms exist, and endothelin 1 (ET-1) is the most abundant and the best-characterized isoform. The aim of this work was to characterize the Zmp1 protease and evaluate its role in pathogenicity. Here, we have shown that M. tuberculosis produces and secretes an enzyme with ET-1 cleavage activity. These data demonstrate a possible role of Zmp1 for mycobacterium-host interactions and highlights its potential as a drug target. Moreover, the results suggest that endothelin pathways have a role in the pathogenesis of M. tuberculosis infections, and ETA or ETB receptor signaling can modulate the host response to the infection. We hypothesize that a balance between Zmp1 control of ET-1 levels and ETA/ETB signaling can allow M. tuberculosis adaptation and survival in the lung tissues.

Cell surface proteome analysis of human-hosted Trypanosoma cruzi life stages

Chagas' disease is a neglected infectious illness, caused by the protozoan Trypanosoma cruzi. It remains a challenging health issue in Latin America, where it is endemic, and so far there is no immunoprophylatic vaccine or satisfactory chemotherapic treatment for its chronic stage. The present work addressed the analysis of the plasma membrane (PM) subproteome from T. cruzi human-hosted life stages, trypomastigote and axenic amastigote, by two complementary PM protein enrichment techniques followed by identification using an LC-MS/MS approach. The results revealed an extensive repertoire of proteins in the PM subproteomes, including enzymes that might be suitable candidates for drug intervention. The comparison of the cell surface proteome among the life forms revealed some potentially stage-specific enzymes, although the majority was shared by both stages. Bioinformatic analysis showed that the vast majority of the identified proteins are membrane-derived and/or possess predicted transmembrane domains. They are mainly involved in host cell infection, protein adhesion, cell signaling, and the modulation of mammalian host immune response. Several virulence factors and proteins potentially capable of acting at a number of metabolic pathways of the host and also to regulate cell differentiation of the parasite itself were also found.