Identification and characterization of Taenia solium enolase as a plasminogen-binding protein

Characterization of antigenic proteins of the Taenia solium postoncospheral form

Neurocysticercosis is the leading cause for acquired epilepsy worldwide, and it is caused by the larval stage of the parasite Taenia solium. Several proteins of this stage have been characterized and studied to understand the parasite-host interaction, however, the proteins from the early cysticercus stages (the postoncospheral form) have not yet been characterized. The study of the postoncospheral form proteins is important to understand the host-parasite relationship in the early stages of infection. The aim of this work was to identify postoncospheral form antigenic proteins using sera from neurocysticercosis patients. T. solium activated oncospheres were cultured in HCT-8 cells to obtain the postoncospheral form. Soluble total and excretory/secretory proteins were obtained from the postoncospheral form and were incubated with both pool sera and individual serum of neurocysticercosis positive human patients. Immunoblotting showed target antigenic proteins with apparent molecular weights of 23 kDa and 46-48 kDa. The 46-48 kDa antigen bands present in soluble total and excretory/secretory postoncospheral form proteins were analyzed by LC-MS/MS; proteins identified were: nuclear elongation factor 1 alpha, enolase, unnamed protein product/antigen diagnostic GP50, calcium binding protein calreticulin precursor and annexin. The postoncospheral form expresses proteins related to interaction with the host, some of these proteins are predicted to be exosomal proteins. In conclusion, postoncospheral proteins are consistent targets of the humoral immune response in human and may serve as targets for diagnosis and vaccines.

Promising immunotherapeutic targets for treating candidiasis

In the last twenty years, there has been a significant increase in invasive fungal infections, which has corresponded with the expanding population of individuals with compromised immune systems. As a result, the mortality rate linked to these infections remains unacceptably high. The currently available antifungal drugs, such as azoles, polyenes, and echinocandins, face limitations in terms of their diversity, the escalating resistance of fungi and the occurrence of significant adverse effects. Consequently, there is an urgent need to develop new antifungal medications. Vaccines and antibodies present a promising avenue for addressing fungal infections due to their targeted antifungal properties and ability to modulate the immune response. This review investigates the structure and function of cell wall proteins, secreted proteins, and functional proteins within C. albicans. Furthermore, it seeks to analyze the current advancements and challenges in macromolecular drugs to identify new targets for the effective management of candidiasis.

An alternative vaccine target for bovine Anaplasmosis based on enolase, a moonlighting protein

The discovery of new targets for preventing bovine anaplasmosis has moved away from focusing on proteins that have already been extensively studied in Anaplasma marginale, including the Major Surface Proteins, Outer Membrane Proteins, and Type IV Secretion System proteins. An alternative is moonlighting or multifunctional proteins, capable of performing various biological functions within various cellular compartments. There are several reports on the role of moonlighting proteins as virulence factors in various microorganisms. Moreover, it is known that about 25% of all moonlighting is involved in the virulence of pathogens. In this work, for the first time, we present the identification of three enolase proteins (AmEno01, AmEno15, and AmEno31) in the genome of Mexican strains of A. marginale. Using bioinformatics tools, we predicted the catalytic domains, enolase signature, and amino acids binding magnesium ion of the catalytic domain and performed a phylogenetic reconstruction. In addition, by molecular docking analysis, we found that AmEno01 would bind to erythrocyte proteins spectrin, ankyrin, and stomatin. This adhesion function has been reported for enolases from other pathogens. It is considered a promising target since blocking this function would impede the fundamental adhesion process that facilitates the infection of erythrocytes. Additionally, molecular docking predicts that AmEno01 could bind to extracellular matrix protein fibronectin, which would be significant if we consider that some proteins with fibronectin domains are localized in tick gut cells and used as an adhesion strategy to gather bacteria before traveling to salivary glands. Derived from the molecular docking analysis of AmEno01, we hypothesized that enolases could be proteins driven by the pathogen and redirected at the expense of the pathogen's needs.

High-Resolution Single-Particle Cryo-EM Hydrated Structure of Streptococcus pyogenes Enolase Offers Insights into Its Function as a Plasminogen Receptor

Cellular plasminogen (Pg) receptors (PgRs) are utilized to recruit Pg; stimulate its activation to the serine protease, plasmin (Pm); and sterically protect the surface Pm from inactivation by host inhibitors. One such PgR is the moonlighting enzyme, enolase, some of which leaves the cytoplasm and resides at the cell surface to potentially function as a PgR. Since microbes employ conscription of host Pg by PgRs as one virulence mechanism, we explored the structural basis of the ability of Streptococcus pyogenes enolase (Sen) to function in this manner. Employing single-particle cryo-electron microscopy (cryo-EM), recombinant Sen from S. pyogenes was modeled at 2.6 Å as a stable symmetrical doughnut-shaped homooctamer with point group 422 (D4) symmetry, with a monomeric subunit molecular weight of ∼49 kDa. Binding sites for hPg were reported in other studies to include an internal K^252,255 and the COOH-terminal K^434,435 residues of Sen. However, in native Sen, the latter are buried within the minor interfaces of the octamer and do not function as a Pg-binding epitope. Whereas Sen and hPg do not interact in solution, when Sen is bound to a surface, hPg interacts with Sen independently of K^{252,255,434,435}. PgRs devoid of COOH-terminal lysine utilize lysine isosteres comprising a basic residue, "i", and an anionic residue at "i + 3" around one turn of an α-helix. We highlight a number of surface-exposed potential hPg-binding lysine isosteres and further conclude that while the octameric structure of Sen is critical for hPg binding, disruption of this octamer without dissociation exposes hPg-binding epitopes.

Baicalein Acts against Candida albicans by Targeting Eno1 and Inhibiting Glycolysis

Baicalein (BE) is a promising antifungal small-molecule compound with an extended antifungal spectrum, good synergy with fluconazole, and low toxicity, but its target protein and antifungal mechanism remain elusive. In this study, we found that BE can function against Candida albicans by disrupting glycolysis through targeting Eno1 and inhibiting its function. Eno1 acts as a key therapeutic target of the drug, as BE had no antifungal activity against the eno1 null mutant in a Galleria mellonella model of C. albicans infection. To investigate the mechanism of action, we solved the crystal structure of C. albicans Eno1(CaEno1) and then compared the difference between this structure and that of Eno1 from humans. The predicted primary binding site of BE on CaEno1 is between amino acids D261 and W274, with D263, S269, and K273 playing critical roles in the interaction with BE. Both positions S269 and K273 have different residues in the human Eno1 (hEno1). This finding suggests that BE may bind selectively to CaEno1, which would limit the potential for side effects in humans. Our findings demonstrate that Eno1 is a target protein of BE and thus may serve as a novel target for the development of antifungal therapeutics acting through the inhibition of glycolysis.

IMPORTANCE Baicalein (BE) is a promising antifungal agent which has been well characterized, but its target protein is still undiscovered. The protein Eno1 plays a crucial role in the survival of Candida albicans. However, there are few antifungal agents which inhibit the functions of Eno1. Here, we found that BE can function against Candida albicans by disrupting glycolysis through targeting Eno1 and inhibiting its function. We further solved the crystal structure of C. albicans Eno1(CaEno1) and predicted that the primary binding site of BE on CaEno1 is between amino acids D261 and W274, with D263, S269, and K273 playing critical roles in the interaction with BE. Our findings will be helpful to get specific small-molecule inhibitors of CaEno1 and open the way for the development of new antifungal therapeutics targeted at inhibiting glycolysis.

A multifunctional enolase mediates cytoadhesion and interaction with host plasminogen and fibronectin in Mycoplasma hyorhinis

Mycoplasma hyorhinis may cause systemic inflammation of pigs, typically polyserositis and arthritis, and is also associated with several types of human cancer. However, the pathogenesis of M. hyorhinis colonizing and breaching the respiratory barrier to establish systemic infection is poorly understood. Glycolytic enzymes are important moonlighting proteins and virulence-related factors in various bacteria. In this study, we investigated the functions of a glycolytic critical enzyme, enolase in the infection and systemic spread of M. hyorhinis. Bacterial surface localization of enolase was confirmed by flow cytometry and colony hybridization assay. Recombinant M. hyorhinis enolase (rEno) was found to adhere to pig kidney (PK-15) cells, and anti-rEno serum significantly decreased adherence. The enzyme was also found to bind host plasminogen and fibronectin, and interactions were specific and strong, with dissociation constant (K_D) values of 1.4 nM and 14.3 nM, respectively, from surface plasmon resonance analysis. Activation of rEno-bound plasminogen was confirmed by its ability to hydrolyze plasmin-specific substrates and to degrade a reconstituted extracellular matrix. To explore key sites during these interactions, C-terminal lysine residues of enolase were replaced with leucine, and the resulting single-site and double-site mutants show significantly reduced interaction with plasminogen in far-Western blotting and surface plasmon resonance tests. The binding affinities of all mutants to fibronectin were reduced as well. Collectively, these results imply that enolase moonlights as an important adhesin of M. hyorhinis, and interacts with plasminogen and fibronectin. The two lysine residues in the C-terminus are important binding sites for its multiple binding activities.

Identification and functional characterization of the siRNA pathway in Taenia crassiceps by silencing Enolase A

A gene silencing procedure on cysticerci of the taeniid cestode Taenia crassiceps is described. This is the first time this technique is reported in this species that is widely used as an animal model for human cysticercosis. Genome database searches were performed in order to find out if relevant genes involved in gene silencing and non-coding RNA processing, Argonaute and Dicer (AGO and Dcr) are present in T. crassiceps. We found three AGO and two Dcr orthologues that were designed TcAGO1, Tc2 and Tc3, as well as TcDcr1 and TcDcr2. In order to elucidate the evolutionary relationships of T. crassiceps TcAGO and TcDcr genes, separate phylogenetic analyses were carried out for each, including AGO and Dcr orthologues of other 20 platyhelminthes. Our findings showed a close phylogenetic relationship of TcAGO and TcDcr with those previously described for Echinococcus spp. Our RT-PCR studies demonstrated expression of all TcAGO and TcDcr orthologues. Our results show that the gene silencing machinery in T. crassiceps is functionally active by inducing silencing of TcEnoA (∼90%). These results clearly show that gene silencing using siRNAs can be used as a molecular methodology to study gene function in taeniid cestodes.

PROTEOMIC ANALYSIS OF TAENIA SOLIUM CYST FLUID BY SHOTGUN LC-MS/MS

Taenia solium cysts were collected from pig skeletal muscle and analyzed via a shotgun proteomic approach to identify known proteins in the cyst fluid and to explore host-parasite interactions. Cyst fluid was aseptically collected and analyzed with shotgun liquid chromatography-tandem mass spectrometry (LC-MS/MS). Gene alignment and annotation were performed using Blast2GO software followed by gene ontology analysis of the annotated proteins. The pathways were further analyzed with the Kyoto Encyclopedia of Genes and Genomes (KEGG), and a protein-protein interaction (PPI) network map was generated using STRING software. A total of 158 known proteins were identified, most of which were low-molecular-mass proteins. These proteins were mainly involved in cellular and metabolic processes, and their molecular functions were predominantly related to catalytic activity and binding functions. The pathway enrichment analysis revealed that the known proteins were mainly enriched in the PI3K-Akt and glycolysis/gluconeogenesis signaling pathways. The nodes in the PPI network mainly consisted of enzymes involved in sugar metabolism. The cyst fluid proteins screened in this study may play important roles in the interaction between the cysticerci and the host. The shotgun LC-MS/MS, gene ontology, KEGG, and PPI network map data will be used to identify and analyze the cyst fluid proteome of cysticerci, which will provide a basis for further exploration of the invasion and activities of T. solium.

A novel, sequencing-free strategy for the functional characterization of Taenia solium proteomic fingerprint

The flatworm Taenia solium causes human and pig cysticercosis. When cysticerci are established in the human central nervous system, they cause neurocysticercosis, a potentially fatal disease. Neurocysticercosis is a persisting public health problem in rural regions of Mexico and other developing countries of Latin America, Asia, and Africa, where the infection is endemic. The great variability observed in the phenotypic and genotypic traits of cysticerci result in a great heterogeneity in the patterns of molecules secreted by them within their host. This work is aimed to identify and characterize cysticercal secretion proteins of T. solium cysticerci obtained from 5 naturally infected pigs from Guerrero, Mexico, using 2D-PAGE proteomic analysis. The isoelectric point (IP) and molecular weight (MW) of the spots were identified using the software ImageMaster 2D Platinum v.7.0. Since most secreted proteins are impossible to identify by mass spectrometry (MS) due to their low concentration in the sample, a novel strategy to predict their sequence was applied. In total, 108 conserved and 186 differential proteins were identified in five cysticercus cultures. Interestingly, we predicted the sequence of 14 proteins that were common in four out of five cysticercus cultures, which could be used to design vaccines or diagnostic methods for neurocysticercosis. A functional characterization of all sequences was performed using the algorithms SecretomeP, SignalP, and BlastKOALA. We found a possible link between signal transduction pathways in parasite cells and human cancer due to deregulation in signal transduction pathways. Bioinformatics analysis also demonstrated that the parasite release proteins by an exosome-like mechanism, which could be of biological interest.

Comparative analysis of different extracellular vesicles secreted by Echinococcus granulosus protoscoleces

Extracellular vesicles (EVs) are heterogeneous populations of different membrane-wrapped vesicles in size and encapsulated cargo and have recently emerged as a crucial carrier with the functions in intercellular communication, being involved in host-parasite interactions. However, Echinococcus granulosus EVs are not fully described. To separate EVs with a different size, the culture supernatant of E. granulosus protoscoleces (PSCs) was sequentially centrifuged at 2,000g, 10,000g and 110,000g, and the resulting precipitates were accordingly named as 2K, 10K and 110K EVs, respectively. The size and morphology of three different EVs were identified using ZETASIZER NANO and transmission electron microscopy (TEM), respectively. Then mass spectrometry was applied to define protein cargo of EVs and EV internalization was assessed using fluorescent microscopy and flow cytometry. The results showed that 2K EVs mainly ranged from 450 to 950 nm in diameter, 10K EVs ranged from 220 to 390 nm and 110K EVs from 60 to 150 nm. A total of 901 EV proteins were identified, 328 of which were commonly found in the three types of EVs. GO analysis revealed that these proteins were mainly involved in binding (44%) and catalytic activity (44%). Three types of EVs were different in biomarkers (Enolase and 14-3-3) and in reactivity with anti-echinococcosis positive serum. Moreover, 110K EVs were more easily internalized by hepatic cells than 10K EVs as well as 2K EVs (p < 0.0001). These results reveal the physical and biological discrepancy among 2K, 10K and 110K EVs, suggesting a distinct role in host-parasite interactions.

Preventing Candida albicans from subverting host plasminogen for invasive infection treatment

Candida albicans is a common fungal pathogen in humans that colonizes the skin and mucosal surfaces of the majority healthy individuals. How C. albicans disseminates into the bloodstream and causes life-threatening systemic infections in immunocompromised patients remains unclear. Plasminogen system activation can degrade a variety of structural proteins in vivo and is involved in several homeostatic processes. Here, for the first time, we characterized that C. albicans could capture and “subvert” host plasminogen to invade host epithelial cell surface barriers through cell-wall localized Eno1 protein. We found that the “subverted” plasminogen system plays an important role in development of invasive infection caused by C. albicans in mice. Base on this finding, we discovered a mouse monoclonal antibody (mAb) 12D9 targeting C. albicans Eno1, with high affinity to the ₂₅₄FYKDGKYDL₂₆₂ motif in α-helices 6, β-sheet 6 (H6S6) loop and direct blocking activity for C. albicans capture host plasminogen. mAb 12D9 could prevent C. albicans from invading human epithelial and endothelial cells, and displayed antifungal activity and synergistic effect with anidulafungin or fluconazole in proof-of-concept in vivo studies, suggesting that blocking the function of cell surface Eno1 was effective for controlling invasive infection caused by Candida spp. In summary, our study provides the evidence of C. albicans invading host by “subverting” plasminogen system, suggesting a potential novel treatment strategy for invasive fungal infections.

Effects of diclazuril on the expression of enolase in second-generation merozoites of Eimeria tenella

Eimeria tenella is an obligate intracellular parasite of the chicken cecum; it brings huge economic loss to the chicken industry. Enolase is a multifunctional glycolytic enzyme involved in many processes of parasites, such as infection and migration. In this study, the effect of diclazuril on the expression of enolase in second-generation merozoites of E. tenella (EtENO) was reported. The prokaryotic expression plasmid pET-28a-EtENO was constructed and transformed into Escherichia coli BL21 (DE3). Then, it was subjected to expression under the induction of isopropyl-β-D-1-thiogalactopyranoside. The expressed products were identified and purified. The purified EtENO protein was used for antibody preparation. The EtENO mRNA and protein expression levels were analyzed via real-time PCR and Western blotting. Localization of EtENO on the merozoites was examined by immunofluorescence technique. The mRNA and protein expression levels of EtENO were decreased by 36.3 and 40.36%, respectively, by diclazuril treatment. EtENO distributed in the surface, cytoplasm, and nucleus of the infected/control group. With diclazuril treatment, it was significantly reduced in the surface and cytoplasm and even disappeared in the nucleus of the infected/diclazuril group. These observations suggested that EtENO may play an important role in mechanism of diclazuril anticoccidial action and be a potential drug target for the intervention with E. tenella infection.

Molecular and biochemical characterization of enolase from Dermanyssus gallinae

Enolase, a multifunctional glycolytic enzyme, is known to act as a plasminogen receptor in many species, involved in the pivotal processes such as motility, adhesion, invasion, growth, and differentiation of the parasites. Knowledge on the function of enolase from Dermanyssus gallinae is very limited. Here we report on the molecular cloning, enzymatic activity, tissue distribution and plasminogen binding activity of enolase from D. gallinae (DgENO). The full-length of cDNA was 1305 bp, specifying a peptide of 434 amino acids. Bioinformatics analysis showed that DgENO was highly conserved compared with a range of organisms, indicating the potentially similar functions in D. gallinae. A recombinant DgENO (rDgENO) protein was produced and characterized, it catalyzed the dehydration of 2-phospho-D-glycerate to phosphoenolpyruvate, the optimal pH was 7.5. Polyclonal antibodies were generated in mice and western blotting indicated that antiserum specifically recognized the native enolase in the somatic extracts from D. gallinae. Immunohistochemical staining of mite sections revealed that the distribution of DgENO was ubiquitous with high level in salivary gland, mite digestive tissues and fat bodies in D. gallinae. Expression level of DgENO was observed mostly in engorged adult mites. Moreover, ELISA binding assay showed that rDgENO could bind plasminogen, and lysine analog ε-aminocaproic acid significantly inhibited this binding activity, indicating that D. gallinae enolase is a receptor of plasminogen. The present study provided foundation for understanding of the biological functions of DgENO and its application in development of vaccines against D. gallinae.

Molecular characterization of a Trichinella spiralis enolase and its interaction with the host's plasminogen

The binding and activation of host plasminogen (PLG) by worm surface enolases has been verified to participate in parasite invasion, but the role of this processes during Trichinella spiralis infection has not been clarified. Therefore, the expression and immunolocalization of a T. spiralis enolase (TsENO) and its binding activity with PLG were evaluated in this study. Based on the three-dimensional (3D) molecular model of TsENO, the protein interaction between TsENO and human PLG was analysed by the ZDOCK server. The interacting residues were identified after analysis of the protein–protein interface by bioinformatics techniques. The key interacting residues were confirmed by a series of experiments. The qPCR analysis results demonstrated that Ts-eno was transcribed throughout the whole life cycle of T. spiralis. The immunofluorescence assay (IFA) results confirmed that TsENO was distributed on the T. spiralis surface. The binding assays showed that recombinant TsENO (rTsENO) and native TsENO were able to bind PLG. Four lysine residues (90, 289, 291 and 300) of TsENO were considered to be active residues for PLG interaction. The quadruple mutant (Lys90Ala + Lys289Ala + Lys291Ala + Lys300Ala) TsENO, in which the key lysine residues were substituted with alanine (Ala) residues, exhibited a reduction in PLG binding of nearly 50% (45.37%). These results revealed that TsENO has strong binding activity with human PLG. The four lysine residues (90, 289, 291 and 300) of TsENO play an important role in PLG binding and could accelerate PLG activation and invasion of the host’s intestinal wall by T. spiralis.

Plasminogen-binding proteins as an evasion mechanism of the host's innate immunity in infectious diseases

Pathogens have developed particular strategies to infect and invade their hosts. Amongst these strategies’ figures the modulation of several components of the innate immune system participating in early host defenses, such as the coagulation and complement cascades, as well as the fibrinolytic system. The components of the coagulation cascade and the fibrinolytic system have been proposed to be interfered during host invasion and tissue migration of bacteria, fungi, protozoa, and more recently, helminths. One of the components that has been proposed to facilitate pathogen migration is plasminogen (Plg), a protein found in the host’s plasma, which is activated into plasmin (Plm), a serine protease that degrades fibrin networks and promotes degradation of extracellular matrix (ECM), aiding maintenance of homeostasis. However, pathogens possess Plg-binding proteins that can activate it, therefore taking advantage of the fibrin degradation to facilitate establishment in their hosts. Emergence of Plg-binding proteins appears to have occurred in diverse infectious agents along evolutionary history of host–pathogen relationships. The goal of the present review is to list, summarize, and analyze different examples of Plg-binding proteins used by infectious agents to invade and establish in their hosts. Emphasis was placed on mechanisms used by helminth parasites, particularly taeniid cestodes, where enolase has been identified as a major Plg-binding and activating protein. A new picture is starting to arise about how this glycolytic enzyme could acquire an entirely new role as modulator of the innate immune system in the context of the host–parasite relationship.

A novel enolase from Taenia solium metacestodes and its evaluation as an immunodiagnostic antigen for porcine cysticercosis

Cysticercosis is a worldwide parasitic disease of humans and pigs principally caused by infection with the larvae of the pork tapeworm Taenia solium. Through the use of the recently-made-available T. solium genome, we identified a gene within a novel 1448 bp ORF that theoretically encodes for a 433 amino acid-long protein and predicted to be an α-enolase closely related to enolases of other flatworms. Additional bioinformatic analyses revealed a putative plasminogen-binding region on this protein, suggesting a potential role for this protein in pathogenesis. On this basis, we isolated the mRNA encoding for this presumptive enolase from T. solium metacestodes and reverse-transcribed it into cDNA before subsequently cloning and expressing it in both E. coli (rEnoTs) and insect cells (rEnoTsBac), in a 6xHis tagged manner. The molecular weights of these two recombinant proteins were ∼48 and ∼50 kDa, respectively, with the differences likely attributable to differential glycosylation. We used spectrophotometric assays to confirm the enolase nature of rEnoTs as well as to measure its enzymatic activity. The resulting estimates of specific activity (60.000 U/mg) and K_m (0.091 mM) are quite similar to the catalytic characteristics of enolases of other flatworms. rEnoTs also exhibited high immunogenicity, eliciting a strong polyclonal antibody response in immunized rabbits. We subsequently employed rEnoTsBac for use in an ELISA aimed at discriminating between healthy pigs and those infected with T. solium. This diagnostic assay exhibited a sensitivity of 88.4% (95% CI, 74.92%-96.11%) and a specificity of 83.7% (95% CI: 69.29%-93.19%). In conclusión, this study reports on and enzymatically characterizes a novel enolase from T. solium metacestode, and shows a potential use as an immunodiagnostic for porcine cysticercosis.