Schistosomiasis, caused by a parasitic blood fluke of the genus Schistosoma, is a global health problem for which new chemotherapeutic options are needed. We explored the scaffold of gallinamide A, a natural peptidic metabolite of marine cyanobacteria that has previously been shown to inhibit cathepsin L-type proteases. We screened a library of 19 synthetic gallinamide A analogs and identified nanomolar inhibitors of the cathepsin B-type protease SmCB1, which is a drug target for the treatment of schistosomiasis mansoni. Against cultured S. mansoni schistosomula and adult worms, many of the gallinamides generated a range of deleterious phenotypic responses. Imaging with a fluorescent-activity-based probe derived from gallinamide A demonstrated that SmCB1 is the primary target for gallinamides in the parasite. Furthermore, we solved the high-resolution crystal structures of SmCB1 in complex with gallinamide A and its two analogs and describe the acrylamide covalent warhead and binding mode in the active site. Quantum chemical calculations evaluated the contribution of individual positions in the peptidomimetic scaffold to the inhibition of the target and demonstrated the importance of the P1' and P2 positions. Our study introduces gallinamides as a powerful chemotype that can be exploited for the development of novel antischistosomal chemotherapeutics.

• Keywords
• Schistosoma mansoni, acrylamide inhibitor, cathepsin B, cysteine protease, drug target, parasite,
• MeSH
• Cathepsin B * antagonists & inhibitors   metabolism   MeSH
• Crystallography, X-Ray MeSH
• Models, Molecular MeSH
• Schistosoma mansoni * enzymology   drug effects   MeSH
• Schistosomicides pharmacology   chemistry   MeSH
• Protein Binding MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Cathepsin B * MeSH
• Schistosomicides MeSH

The structure and biochemical properties of protease inhibitors from the thyropin family are poorly understood in parasites and pathogens. Here, we introduce a novel family member, Ir-thyropin (IrThy), which is secreted in the saliva of Ixodes ricinus ticks, vectors of Lyme borreliosis and tick-borne encephalitis. The IrThy molecule consists of two consecutive thyroglobulin type-1 (Tg1) domains with an unusual disulfide pattern. Recombinant IrThy was found to inhibit human host-derived cathepsin proteases with a high specificity for cathepsins V, K, and L among a wide range of screened cathepsins exhibiting diverse endo- and exopeptidase activities. Both Tg1 domains displayed inhibitory activities, but with distinct specificity profiles. We determined the spatial structure of one of the Tg1 domains by solution NMR spectroscopy and described its reactive center to elucidate the unique inhibitory specificity. Furthermore, we found that the inhibitory potency of IrThy was modulated in a complex manner by various glycosaminoglycans from host tissues. IrThy was additionally regulated by pH and proteolytic degradation. This study provides a comprehensive structure-function characterization of IrThy-the first investigated thyropin of parasite origin-and suggests its potential role in host-parasite interactions at the tick bite site.

• Keywords
• cathepsin, cysteine protease, parasite, protease inhibitor, protein structure, saliva, thyropin, tick,
• MeSH
• Cysteine MeSH
• Glycosaminoglycans MeSH
• Cathepsins metabolism   MeSH
• Ixodes * metabolism   MeSH
• Humans MeSH
• Magnetic Resonance Spectroscopy MeSH
• Saliva * metabolism   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Cysteine MeSH
• Glycosaminoglycans MeSH
• Cathepsins MeSH

Fasciola hepatica is a global parasite of livestock which also causes a neglected zoonosis in humans. The parasite's communication with the host during its complicated lifecycle is based on an ingenious enzymatic apparatus which includes a variety of peptidases. These enzymes are implicated in parasite migration, pathogenesis of the disease, and modification of host immune response. Although the dynamics of proteolytic machinery produced by intra-mammalian F. hepatica life stages has been previously investigated in great detail, peptidases of the eggs so far received little scientific attention. In this study, we performed a comparative RNA-seq analysis aimed at identification of peptidases expressed in F. hepatica eggs, cultured at 37 °C to represent gall bladder retained eggs, for different time periods and employed mass spectrometry in order to identify and quantify peptidases translated in F. hepatica egg lysates. We demonstrated that F. hepatica eggs undergo significant molecular changes when cultured at the physiological temperature of the definitive host. Egg transcriptome is subject to numerous subtle changes while their proteome is even more variable. The peptidase profile is considerably modified on both transcriptome and proteome level. Finally, we measured and classified proteolytic activities in extracts from F. hepatica eggs using a library of fluorogenic substrates and peptidase class-selective inhibitors. Activities of threonine peptidases were detected constantly, while the cysteine peptidases prevailing in freshly laid eggs are substituted by aspartic peptidase and metallopeptidase activities in the later stages of egg development.

• MeSH
• Fasciola hepatica * enzymology   MeSH
• Ovum * enzymology   MeSH
• Peptide Hydrolases * metabolism   MeSH
• Proteome * MeSH
• Proteomics MeSH
• Mammals parasitology   MeSH
• Body Temperature MeSH
• Transcriptome * MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Peptide Hydrolases * MeSH
• Proteome * MeSH

BACKGROUND: The blood flukes of genus Schistosoma are the causative agent of schistosomiasis, a parasitic disease that infects more than 200 million people worldwide. Proteases of schistosomes are involved in critical steps of host-parasite interactions and are promising therapeutic targets. We recently identified and characterized a group of S1 family Schistosoma mansoni serine proteases, including SmSP1 to SmSP5. Expression levels of some SmSPs in S. mansoni are low, and by standard genome sequencing technologies they are marginally detectable at the method threshold levels. Here, we report their spatial gene expression patterns in adult S. mansoni by the high-sensitivity localization assay. METHODOLOGY: Highly sensitive fluorescence in situ RNA hybridization (FISH) was modified and used for the localization of mRNAs encoding individual SmSP proteases (including low-expressed SmSPs) in tissues of adult worms. High sensitivity was obtained due to specifically prepared tissue and probes in combination with the employment of a signal amplification approach. The assay method was validated by detecting the expression patterns of a set of relevant reference genes including SmCB1, SmPOP, SmTSP-2, and Sm29 with localization formerly determined by other techniques. RESULTS: FISH analysis revealed interesting expression patterns of SmSPs distributed in multiple tissues of S. mansoni adults. The expression patterns of individual SmSPs were distinct but in part overlapping and were consistent with existing transcriptome sequencing data. The exception were genes with significantly low expression, which were also localized in tissues where they had not previously been detected by RNA sequencing methods. In general, SmSPs were found in various tissues including reproductive organs, parenchymal cells, esophagus, and the tegumental surface. CONCLUSIONS: The FISH-based assay provided spatial information about the expression of five SmSPs in adult S. mansoni females and males. This highly sensitive method allowed visualization of low-abundantly expressed genes that are below the detection limits of standard in situ hybridization or by RNA sequencing. Thus, this technical approach turned out to be suitable for sensitive localization studies and may also be applicable for other trematodes. The results suggest that SmSPs may play roles in diverse processes of the parasite. Certain SmSPs expressed at the surface may be involved in host-parasite interactions.

• Keywords
• Blood fluke, Fluorescence RNA in situ hybridization, Platyhelminthes, Schistosoma mansoni, Serine proteases, Transcript, mRNA detection,
• MeSH
• Gene Expression * MeSH
• In Situ Hybridization, Fluorescence methods   standards   MeSH
• Helminth Proteins genetics   MeSH
• RNA metabolism   MeSH
• Schistosoma mansoni enzymology   genetics   MeSH
• Serine Proteases genetics   MeSH
• Gene Expression Profiling MeSH
• Animals MeSH
• Check Tag
• Male MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Helminth Proteins MeSH
• RNA MeSH
• Serine Proteases MeSH

Schistosomiasis, a parasitic disease caused by blood flukes of the genus Schistosoma, is a global health problem with over 200 million people infected. Treatment relies on just one drug, and new chemotherapies are needed. Schistosoma mansoni cathepsin B1 (SmCB1) is a critical peptidase for the digestion of host blood proteins and a validated drug target. We screened a library of peptidomimetic vinyl sulfones against SmCB1 and identified the most potent SmCB1 inhibitors reported to date that are active in the subnanomolar range with second order rate constants (k2nd) of ∼2 × 105 M-1 s-1. High resolution crystal structures of the two best inhibitors in complex with SmCB1 were determined. Quantum chemical calculations of their respective binding modes identified critical hot spot interactions in the S1' and S2 subsites. The most potent inhibitor targets the S1' subsite with an N-hydroxysulfonic amide moiety and displays favorable functional properties, including bioactivity against the pathogen, selectivity for SmCB1 over human cathepsin B, and reasonable metabolic stability. Our results provide structural insights for the rational design of next-generation SmCB1 inhibitors as potential drugs to treat schistosomiasis.

• Keywords
• Schistosoma mansoni, cathepsin B, cysteine peptidase, drug target, parasite, vinyl sulfone inhibitor,
• MeSH
• Cathepsin B * MeSH
• Humans MeSH
• Schistosoma mansoni MeSH
• Schistosomiasis * drug therapy   MeSH
• Sulfones pharmacology   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH
• Names of Substances
• divinyl sulfone MeSH Browser
• Cathepsin B * MeSH
• Sulfones MeSH

Azapeptide nitriles are postulated to reversibly covalently react with the active-site cysteine residue of cysteine proteases and form isothiosemicarbazide adducts. We investigated the interaction of azadipeptide nitriles with the cathepsin B1 drug target (SmCB1) from Schistosoma mansoni, a pathogen that causes the global neglected disease schistosomiasis. Azadipeptide nitriles were superior inhibitors of SmCB1 over their parent carba analogs. We determined the crystal structure of SmCB1 in complex with an azadipeptide nitrile and analyzed the reaction mechanism using quantum chemical calculations. The data demonstrate that azadipeptide nitriles, in contrast to their carba counterparts, undergo a change from E- to Z-configuration upon binding, which gives rise to a highly favorable energy profile of noncovalent and covalent complex formation. Finally, azadipeptide nitriles were considerably more lethal than their carba analogs against the schistosome pathogen in culture, supporting the further development of this chemotype as a treatment for schistosomiasis.

• Keywords
• azapeptide inhibitors, cysteine proteases, protein structures, schistosomiasis, structure−activity relationships,
• MeSH
• Cathepsin B MeSH
• Peptide Hydrolases * MeSH
• Schistosoma mansoni * MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH
• Names of Substances
• Cathepsin B MeSH
• Peptide Hydrolases * MeSH

BACKGROUND: Serine proteases are important virulence factors for many pathogens. Recently, we discovered a group of trypsin-like serine proteases with domain organization unique to flatworm parasites and containing a thrombospondin type 1 repeat (TSR-1). These proteases are recognized as antigens during host infection and may prove useful as anthelminthic vaccines, however their molecular characteristics are under-studied. Here, we characterize the structural and proteolytic attributes of serine protease 2 (SmSP2) from Schistosoma mansoni, one of the major species responsible for the tropical infectious disease, schistosomiasis. METHODOLOGY/PRINCIPAL FINDINGS: SmSP2 comprises three domains: a histidine stretch, TSR-1 and a serine protease domain. The cleavage specificity of recombinant SmSP2 was determined using positional scanning and multiplex combinatorial libraries and the determinants of specificity were identified with 3D homology models, demonstrating a trypsin-like endopeptidase mode of action. SmSP2 displayed restricted proteolysis on protein substrates. It activated tissue plasminogen activator and plasminogen as key components of the fibrinolytic system, and released the vasoregulatory peptide, kinin, from kininogen. SmSP2 was detected in the surface tegument, esophageal glands and reproductive organs of the adult parasite by immunofluorescence microscopy, and in the excretory/secretory products by immunoblotting. CONCLUSIONS/SIGNIFICANCE: The data suggest that SmSP2 is secreted, functions at the host-parasite interface and contributes to the survival of the parasite by manipulating host vasodilatation and fibrinolysis. SmSP2 may be, therefore, a potential target for anti-schistosomal therapy.

• MeSH
• Fibrinolysis drug effects   MeSH
• Blood Coagulation drug effects   MeSH
• Hemostatics antagonists & inhibitors   MeSH
• Blood Pressure drug effects   MeSH
• Models, Molecular MeSH
• Plasminogen drug effects   MeSH
• Protein Domains MeSH
• Helminth Proteins chemistry   genetics   pharmacology   MeSH
• Proteolysis drug effects   MeSH
• Recombinant Proteins MeSH
• Schistosoma mansoni enzymology   MeSH
• Schistosomiasis mansoni parasitology   MeSH
• Amino Acid Sequence MeSH
• Serine Endopeptidases chemistry   genetics   pharmacology   MeSH
• Tissue Plasminogen Activator drug effects   MeSH
• Vasodilation drug effects   MeSH
• Animals MeSH
• Check Tag
• Male MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Hemostatics MeSH
• Plasminogen MeSH
• Helminth Proteins MeSH
• Recombinant Proteins MeSH
• Serine Endopeptidases MeSH
• Tissue Plasminogen Activator MeSH
• trypsin-like serine protease MeSH Browser

Schistosomiasis is one of a number of chronic helminth diseases of poverty that severely impact personal and societal well-being and productivity. Peptidases (proteases) are vital to successful parasitism, and can modulate host physiology and immunology. Interference of peptidase action by specific drugs or vaccines can be therapeutically beneficial. To date, research on peptidases in the schistosome parasite has focused on either the functional characterization of individual peptidases or their annotation as part of global genome or transcriptome studies. We were interested in functionally characterizing the complexity of peptidase activity operating at the host-parasite interface, therefore the excretory-secretory products of key developmental stages of Schistosoma mansoni that parasitize the human were examined. Using class specific peptidase inhibitors in combination with a multiplex substrate profiling assay, a number of unique activities derived from endo- and exo-peptidases were revealed in the excretory-secretory products of schistosomula (larval migratory worms), adults and eggs. The data highlight the complexity of the functional degradome for each developmental stage of this parasite and facilitate further enquiry to establish peptidase identity, physiological and immunological function, and utility as drug or vaccine candidates.

• Keywords
• Excretion, Fluke, Inhibitor, Parasite, Protease, Secretion,
• MeSH
• Host-Pathogen Interactions MeSH
• Humans MeSH
• Molecular Sequence Data MeSH
• Ovum metabolism   MeSH
• Peptide Hydrolases metabolism   MeSH
• Helminth Proteins metabolism   MeSH
• Proteolysis MeSH
• Schistosoma mansoni growth & development   metabolism   physiology   MeSH
• Schistosomiasis mansoni parasitology   MeSH
• Amino Acid Sequence MeSH
• Life Cycle Stages MeSH
• Substrate Specificity MeSH
• Binding Sites MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH
• Names of Substances
• Peptide Hydrolases MeSH
• Helminth Proteins MeSH

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.

• MeSH
• DNA Primers genetics   MeSH
• Escherichia coli MeSH
• Microscopy, Fluorescence MeSH
• Hydrolysis MeSH
• Immunoblotting MeSH
• Catalytic Domain genetics   MeSH
• Real-Time Polymerase Chain Reaction MeSH
• Models, Molecular * MeSH
• Prolyl Oligopeptidases MeSH
• Gene Expression Regulation, Enzymologic physiology   MeSH
• Recombinant Proteins genetics   metabolism   MeSH
• Schistosoma mansoni enzymology   MeSH
• Serine Endopeptidases genetics   metabolism   MeSH
• Gene Expression Profiling MeSH
• Substrate Specificity MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• DNA Primers MeSH
• Prolyl Oligopeptidases MeSH
• Recombinant Proteins MeSH
• Serine Endopeptidases MeSH