Cloning and characterization of a plasminogen-binding surface-associated enolase from Schistosoma bovis

Extracellular vesicles from parasitic helminths contain specific excretory/secretory proteins and are internalized in intestinal host cells

The study of host-parasite interactions has increased considerably in the last decades, with many studies focusing on the identification of parasite molecules (i.e. surface or excretory/secretory proteins (ESP)) as potential targets for new specific treatments and/or diagnostic tools. In parallel, in the last few years there have been significant advances in the field of extracellular vesicles research. Among these vesicles, exosomes of endocytic origin, with a characteristic size ranging from 30–100 nm, carry several atypical secreted proteins in different organisms, including parasitic protozoa. Here, we present experimental evidence for the existence of exosome-like vesicles in parasitic helminths, specifically the trematodes Echinostoma caproni and Fasciola hepatica. These microvesicles are actively released by the parasites and are taken up by host cells. Trematode extracellular vesicles contain most of the proteins previously identified as components of ESP, as confirmed by proteomic, immunogold labeling and electron microscopy studies. In addition to parasitic proteins, we also identify host proteins in these structures. The existence of extracellular vesicles explains the secretion of atypical proteins in trematodes, and the demonstration of their uptake by host cells suggests an important role for these structures in host-parasite communication, as described for other infectious agents.

Cloning and characterization of a plasminogen-binding enolase from the saliva of the argasid tick Ornithodoros moubata

Significant amounts of enolase have recently been found in the saliva of the argasid tick Ornithodoros moubata, raising the question as to what the function of enolase in the tick-host interface is. Enolase is a multifunctional glycolytic enzyme known to act as a plasminogen receptor on cellular surfaces, promoting fibrinolysis and extracellular matrix degradation. Fibrinolysis could be important for ticks to dissolve clots that might be formed during feeding as well as to prevent clotting of the ingested blood meal in the tick midgut. Additionally, enolase-mediated extracellular matrix degradation could contribute to the tick feeding lesion. Moreover, previous observations suggested an additional antihaemostatic role for O. moubata enolase as a P-selectin antagonist ligand. Accordingly, the aim of the present study was to investigate the potential role of the O. moubata salivary enolase as a plasminogen receptor and P-selectin ligand, and to evaluate its potential as an antigen target for anti-O. moubata vaccines. The study included the cloning, sequencing and recombinant production of the O. moubata enolase, plasminogen binding and activation assays, P-selectin binding assays, animal immunization trials, and RNAi knockdown of the enolase gene. Here we confirmed that enolase is secreted to the saliva of the tick and provide convincing evidence for a role of this salivary enolase as a plasminogen receptor, most likely stimulating host fibrinolysis and maintaining blood fluidity during tick feeding. The RNAi experiments and immunization trials indicated that enolase could be also involved in the regulation of tick reproduction, suggesting new potential control strategies. Finally, the P-selectin binding experiments demonstrated that this enolase is not a P-selectin ligand.

Fructose-bisphosphate aldolase and enolase from Echinococcus granulosus: genes, expression patterns and protein interactions of two potential moonlighting proteins

Glycolytic enzymes, such as fructose-bisphosphate aldolase (FBA) and enolase, have been described as complex multifunctional proteins that may perform non-glycolytic moonlighting functions, but little is known about such functions, especially in parasites. We have carried out in silico genomic searches in order to identify FBA and enolase coding sequences in Echinococcus granulosus, the causative agent of cystic hydatid disease. Four FBA genes and 3 enolase genes were found, and their sequences and exon-intron structures were characterized and compared to those of their orthologs in Echinococcus multilocularis, the causative agent of alveolar hydatid disease. To gather evidence of possible non-glycolytic functions, the expression profile of FBA and enolase isoforms detected in the E. granulosus pathogenic larval form (hydatid cyst) (EgFBA1 and EgEno1) was assessed. Using specific antibodies, EgFBA1 and EgEno1 were detected in protoscolex and germinal layer cells, as expected, but they were also found in the hydatid fluid, which contains parasite's excretory-secretory (ES) products. Besides, both proteins were found in protoscolex tegument and in vitro ES products, further suggesting possible non-glycolytic functions in the host-parasite interface. EgFBA1 modeled 3D structure predicted a F-actin binding site, and the ability of EgFBA1 to bind actin was confirmed experimentally, which was taken as an additional evidence of FBA multifunctionality in E. granulosus. Overall, our results represent the first experimental evidences of alternative functions performed by glycolytic enzymes in E. granulosus and provide relevant information for the understanding of their roles in host-parasite interplay.

The interaction of canine plasminogen with Streptococcus pyogenes enolase: they bind to one another but what is the nature of the structures involved?

For years it has been clear that plasminogen from different sources and enolase from different sources interact strongly. What is less clear is the nature of the structures required for them to interact. This work examines the interaction between canine plasminogen (dPgn) and Streptococcus pyogenes enolase (Str enolase) using analytical ultracentrifugation (AUC), surface plasmon resonance (SPR), fluorescence polarization, dynamic light scattering (DLS), isothermal titration calorimetry (ITC), and simple pull-down reactions. Overall, our data indicate that a non-native structure of the octameric Str enolase (monomers or multimers) is an important determinant of its surface-mediated interaction with host plasminogen. Interestingly, a non-native structure of plasminogen is capable of interacting with native enolase. As far as we can tell, the native structures resist forming stable mixed complexes.

Molecular and functional characterization of a Schistosoma bovis annexin: fibrinolytic and anticoagulant activity

Annexins belong to an evolutionarily conserved multigene family of proteins expressed throughout the animal and plant kingdoms. Although they are soluble cytosolic proteins that lack signal sequences, they have also been detected in extracellular fluids and have been associated with cell surface membranes, where they could be involved in anti-haemostatic and anti-inflammatory functions. Schistosome annexins have been identified on the parasite's tegument surface and excretory/secretory products, but their functions are still unknown. Here we report the cloning, sequencing, in silico analysis, and functional characterization of a Schistosoma bovis annexin. The predicted protein has typical annexin secondary and tertiary structures. Bioassays with the recombinant protein revealed that the protein is biologically active in vitro, showing fibrinolytic and anticoagulant properties. Finally, the expression of the native protein on the tegument surface of S. bovis schistosomula and adult worms is demonstrated, revealing the possibility of exposure to the host's immune system and thus offering a potential vaccine target for the control of schistosomiasis in ruminants.

Enolase: a key player in the metabolism and a probable virulence factor of trypanosomatid parasites-perspectives for its use as a therapeutic target

Glycolysis and glyconeogenesis play crucial roles in the ATP supply and synthesis of glycoconjugates, important for the viability and virulence, respectively, of the human-pathogenic stages of Trypanosoma brucei, Trypanosoma cruzi, and Leishmania spp. These pathways are, therefore, candidate targets for antiparasite drugs. The glycolytic/gluconeogenic enzyme enolase is generally highly conserved, with similar overall fold and identical catalytic residues in all organisms. Nonetheless, potentially important differences exist between the trypanosomatid and host enzymes, with three unique, reactive residues close to the active site of the former that might be exploited for the development of new drugs. In addition, enolase is found both in the secretome and in association with the surface of Leishmania spp. where it probably functions as plasminogen receptor, playing a role in the parasite's invasiveness and virulence, a function possibly also present in the other trypanosomatids. This location and possible function of enolase offer additional perspectives for both drug discovery and vaccination.

Clonorchis sinensis enolase: identification and biochemical characterization of a glycolytic enzyme from excretory/secretory products

Enolase plays a key role in energy metabolism and development of most organisms. We isolated a gene encoding enolase from Clonorchis sinensis (C. sinensis) adult cDNA library and expressed the recombinant protein in Escherichia coli. C. sinensis enolase (Csenolase) was identified as both an excretory/secretory product and a tegumental component of C. sinensis by western blot analysis. The transcriptional level of Csenolase was examined at adult worm, metacercaria, cercaria and egg of C. sinensis, and results showed that Csenolase is transcribed at the four life stages of C. sinensis while showing a significant higher expression level at the stage of adult worm. Immunohistochemical localization indicated that Csenolase was specifically deposited on the tegument of adult worm and cyst wall of metacercaria. Ligand blot assay revealed a specific characteristic of dose-dependent plasminogen-binding activity of Csenolase and kinetic parameters were explored using 2-phospho-D-glycerate (2-PGA) as the primary substrate by monitoring the conversion of nicotinamide-adenine dinucleotide (NADH) into nicotinamide adenine dinucleotide (NAD). In addition, Csenolase exhibited active enzyme activity in catalytic reactions while the anti-Csenolase serum inhibited the enzyme activity. In vitro incubation experiments revealed that Csenolase might play key roles in the growth of the parasites. In conclusion, Csenolase is an important glycolytic enzyme required for the development of C. sinensis, and may be a potential vaccine candidate and drug target against C. sinensis infection.