Cryptosporidium parvum vaccine candidates are incompletely modified with O-linked-N-acetylgalactosamine or contain N-terminal N-myristate and S-palmitate

Identification of the glycopeptide epitope recognized by a protective Cryptosporidium monoclonal antibody

Cryptosporidium species are a leading cause of pediatric diarrheal disease and death in low- and middle-income countries and pose a particular threat to immunocompromised individuals. As a zoonotic pathogen, Cryptosporidium can have devastating effects on the health of neonatal calves. Despite its impact on human and animal health, consistently effective drug treatments for cryptosporidiosis are lacking and no vaccine is available. We previously showed that C. parvum mucin-like glycoproteins, gp40, and gp900 express an epitope identified by a monoclonal antibody 4E9. 4E9 neutralized C. parvum infection in vitro as did glycan-binding proteins specific for the Tn antigen (GalNAc-α1-S/T). Here, we show that 4E9 ameliorates disease in vivo in a calf challenge model. The 4E9 epitope is present on C. hominis in addition to C. parvum gp40 and gp900 and localizes to the plasma membrane and dense granules of invasive and intracellular stages. To characterize the epitope recognized by 4E9, we probed a glycan array containing over 500 defined glycans together with a custom-made glycopeptide microarray containing glycopeptides from native mucins or C. parvum gp40 and gp15. 4E9 exhibited no binding to the glycan array but bound strongly to glycopeptides from native mucins or gp40 on the glycopeptide array, suggesting that the antibody epitope contains both peptide and glycan moieties. 4E9 only recognized glycopeptides with adjacent S or T residues in the motif S*/T*-X-S*/T* where X = 0 or 1. These data define the 4E9 epitope and have implications for the inclusion of the epitope in the development of vaccines or other immune-based therapies.

Specific Cryptosporidium antigens associate with reinfection immunity and protection from cryptosporidiosis

There is no vaccine to protect from cryptosporidiosis, a leading cause of diarrhea in infants in low- and middle-income countries. Here, we comprehensively identified parasite antigens associated with protection from reinfection. A Cryptosporidium protein microarray was constructed by in vitro transcription and translation of 1,761 C. parvum, C. hominis, or C. meleagridis antigens, including proteins with a signal peptide and/or a transmembrane domain. Plasma IgG and/or IgA from Bangladeshi children longitudinally followed for cryptosporidiosis from birth to 3 years of age allowed for identification of 233 seroreactive proteins. Seven of these were associated with protection from reinfection. These included Cp23, Cp17, Gp900, and 4 additional antigens - CpSMP1, CpMuc8, CpCorA and CpCCDC1. Infection in the first year of life, however, often resulted in no detectable antigen-specific antibody response, and antibody responses, when detected, were specific to the infecting parasite genotype and decayed in the months after infection. In conclusion, humoral immune responses against specific parasite antigens were associated with acquired immunity. While antibody decay over time and parasite genotype-specificity may limit natural immunity, this work serves as a foundation for antigen selection for vaccine design.

Conservation, abundance, glycosylation profile, and localization of the TSP protein family in Cryptosporidium parvum

Cryptosporidium parvum is a zoonotic apicomplexan parasite and a common cause of diarrheal disease worldwide. The development of vaccines to prevent or limit infection remains an important goal for tackling cryptosporidiosis. At present, the only approved vaccine against any apicomplexan parasite targets a conserved adhesin possessing a thrombospondin repeat domain. C. parvum possesses 12 orthologous thrombospondin repeat domain-containing proteins known as CpTSP1-12, though little is known about these potentially important antigens. Here, we explore the architecture and conservation of the CpTSP protein family, as well as their abundance at the protein level within the sporozoite stage of the life cycle. We examine the glycosylation states of these proteins using a combination of glycopeptide enrichment techniques to demonstrate that these proteins are modified with C-, O-, and N-linked glycans. Using expansion microscopy, and an antibody against the C-linked mannose that is unique to the CpTSP protein family within C. parvum, we show that these proteins are found both on the cell surface and in structures that resemble the secretory pathway of C. parvum sporozoites. Finally, we generated a polyclonal antibody against CpTSP1 to show that it is found at the cell surface and within micronemes, in a pattern reminiscent of other apicomplexan motility-associated adhesins, and is present both in sporozoites and meronts. This work sheds new light on an understudied family of C. parvum proteins that are likely to be important to both parasite biology and the development of vaccines against cryptosporidiosis.

Genomic reconstruction and features of glycosylation pathways in the apicomplexan Cryptosporidium parasites

Cryptosporidium is a genus of apicomplexan parasites infecting humans or other vertebrates. The majority of the Cryptosporidium species live in host intestines (e.g., C. parvum, C. hominis and C. ubiquitum), but there are a few gastric species (e.g., C. muris and C. andersoni). Among them, C. parvum is the most important zoonotic species, for which a number of glycoproteins have been reported for being involved in the interacting with host cells. However, little is known on the cryptosporidium glycobiology. Information on the glycosylation pathways in Cryptosporidium parasites remains sketchy and only a few studies have truly determined the glycoforms in the parasites. Here we reanalyzed the Cryptosporidium genomes and reconstructed the glycosylation pathways, including the synthesis of N- and O-linked glycans and GPI-anchors. In N-glycosylation, intestinal Cryptosporidium possesses enzymes to make a simple precursor with two terminal glucoses on the long arm (i.e., Glc2Man5GlcNAc2 vs. Glc3Man9GlcNAc2 in humans), but gastric species only makes a simpler precursor containing only the "core" structure (i.e., Man3GlcNAc2). There is an ortholog of glucosidase II (GANAB) in all Cryptosporidium species, for which the authenticity is questioned because it contains no signal peptide and exist in gastric species lacking terminal glucoses for the enzyme to act on. In O-linked glycosylation, all Cryptosporidium species may attach one-unit HexNAc (GalNAc and GlcNAc) and two-unit Fuc-type (Man-Fuc) glycans to the target proteins. Cryptosporidium lacks enzymes to further process N- and O-glycans in the Golgi. The glycosylphosphatidylinositol (GPI)-anchor in Cryptosporidium is predicted to be unbranched and unprocessed further in the Golgi. Cryptosporidium can synthesize limited nucleotide sugars, but possesses at least 12 transporters to scavenge nucleotide sugars or transport them across the ER/Golgi membranes. Overall, Cryptosporidium makes much simpler glycans than the hosts, and the N-glycoforms further differ between intestinal and gastric species. The Cryptosporidium N- and O-glycans are neutrally charged and have limited capacity to absorb water molecules in comparison to the host intestinal mucins that are negatively charged and highly expandable in waters.

The mucin-like, secretory type-I transmembrane glycoprotein GP900 in the apicomplexan Cryptosporidium parvum is cleaved in the secretory pathway and likely plays a lubrication role

BACKGROUND

Cryptosporidium parvum is a zoonotic parasite and member of the phylum Apicomplexa with unique secretory organelles, including a rhoptry, micronemes and dense granules that discharge their contents during parasite invasion. The mucin-like glycoprotein GP900 with a single transmembrane domain is an immunodominant antigen and micronemal protein. It is relocated to the surface of excysted sporozoites and shed to form trails by sporozoites exhibiting gliding motility (gliding sporozoites). However, the biological process underlying its relocation and shedding remains unclear. The primary aim of this study was to determine whether GP900 is present as a transmembrane protein anchored to the plasma membrane on the surface of sporozoites and whether it is cleaved before being shed from the sporozoites.

METHODS

Two anti-GP900 antibodies, a mouse monoclonal antibody (mAb) to the long N-terminal domain (GP900-N) and a rabbit polyclonal antibody (pAb) to the short C-terminal domain (GP900-C), were produced for the detection of intact and cleaved GP900 proteins in sporozoites and other parasite developmental stages by microscopic immunofluorescence assay and in discharged molecules by enzyme-linked immunosorbent assay.

RESULTS

Both anti-GP900 antibodies recognized the apical region of unexcysted and excysted sporozoites. However, anti-GP900-N (but not anti-GP900-C) also stained both the pellicles/surface of excysted sporozoites and the trails of gliding sporozoites. Both antibodies stained the intracellular meronts, both developing and developed, but not the macro- and microgamonts. Additionally, the epitope was recognized by anti-GP900-N (but not anti-GP900-C) and detected in the secretions of excysted sporozoites and intracellular parasites.

CONCLUSIONS

GP900 is present in sporozoites and intracellular meronts, but absent in sexual stages. It is stored in the micronemes of sporozoites, but enters the secretory pathway during excystation and invasion. The short cytoplasmic domain of GP900 is cleaved in the secretory pathway before it reaches the extracellular space. The molecular features and behavior of GP900 imply that it plays mainly a lubrication role.

Glycopeptidomics Analysis of a Cell Line Model Revealing Pathogenesis and Potential Marker Molecules for the Early Diagnosis of Gastric MALT Lymphoma

Background & Aims

Gastric mucosa-associated lymphoma (GML) is a mature B cell tumor related to Helicobacter pylori (H.pylori) infection. The clinical manifestations of GML are not specific, so GML is often misdiagnosed, leading to excessive treatment. The pathogenesis of H.pylori-induced GML is not well understood and there are no molecular markers for early GML diagnosis.

Methods

Glycopeptidomics analyses of host cell lines (a BCG823 cell line, C823) and C823 cells infected by H. pylori isolated from patients with GML (GMALT823), gastritis (GAT823), gastric ulcer (GAU823) and gastric cancer (GAC823) were carried out to clarify the host reaction mechanism against GML and to identify potential molecular criteria for the early diagnosis of GML.

Results

Thirty-three samples were analyzed and approximately 2000 proteins, 200 glycoproteins and 500 glycopeptides were detected in each sample. O-glycans were the dominant glycoforms in GMALT823 cells only. Four specific glycoforms in GMALT823 cells and 2 specific glycoforms in C823 and GMALT823 cells were identified. Eight specific glycopeptides from 7 glycoproteins were found in GMALT823 cells; of these glycopeptides, 6 and 3 specific glycopeptides had high affinity for T cell epitopes and have conformational B cell epitopes, respectively.

Conclusion

The predominant glycoforms of host cells infected by MALT H. pylori isolates differ from others, and the glycoproteins, glycosylation sites and glycoforms might be closely related to the formation of GML, which provides new insights into the pathogenic mechanisms of H. pylori infection and suggests molecular indicators for the early diagnosis of GML.

Identification and characterization of a new 34 kDa MORN motif-containing sporozoite surface-exposed protein, Cp-P34, unique to Cryptosporidium

Despite the public health impact of childhood diarrhea caused by Cryptosporidium, effective drugs and vaccines against this parasite are unavailable. Efforts to identify vaccine targets have focused on critical externally exposed virulence factors expressed in the parasite s invasive stages. However, no single surface antigen has yet been found that can elicit a significant protective immune response and it is likely that pooling multiple immune targets will be necessary. Discovery of surface proteins on Cryptosporidium sporozoites is therefore vital to this effort to develop a multi-antigenic vaccine. In this study we applied a novel single-domain camelid antibody (VHH) selection method to identify immunogenic proteins expressed on the surface of Cryptosporidium parvum sporozoites. By this approach, VHHs were identified that recognize two sporozoite surface-exposed antigens, the previously identified gp900 and an unrecognized immunogenic protein, Cp-P34. This Cp-P34 antigen, which contains multiple Membrane Occupation and Recognition Nexus (MORN) repeats, is found in excysted sporozoites as well as in the parasite s intracellular stages. Cp-P34 appears to accumulate inside the parasite and transiently appears on the surface of sporozoites to be shed in trails. Identical or nearly identical orthologs of Cp-P34 are found in the Cryptosporidium hominis and Cryptosporidium tyzzeri genomes. Except for the conserved MORN motifs, the Cp-P34 gene shares no significant homology with genes of other protozoans and thus appears to be unique to Cryptosporidium spp. Cp-P34 elicits immune responses in naturally exposed alpacas and warrants further investigation as a potential vaccine candidate.

Opportunistic parasitic infections in patients with human immunodeficiency virus/acquired immunodeficiency syndrome: A review

The number of human immunodeficiency virus (HIV) cases increases annually, and Indonesia has become the country with the fastest HIV/acquired immunodeficiency syndrome (AIDS) epidemic spread among the five Southeast Asian countries. Indonesia entered the critical phase of HIV/AIDS infections after 5 out of the 33 provinces, namely, Papua, Jakarta, Bali, West Java, and East Java, reported HIV/AIDS epidemic since 2004. In AIDS pathophysiology and immune-suppression are severe, thus, opportunistic intestinal parasitic infections that cause diarrhea in HIV infection may be fatal. Several studies have suggested that Cryptosporidium parvum, Isospora belli, and Blastocystis hominis are the most common intestinal protozoan parasites categorized as AIDS associated illness. Diarrhea caused by parasites is considerably suspected in the cases of chronic and persistent diarrhea in adults, in an era of increasing HIV/AIDS cases nowadays. The present review highlights the current advances in etiologic agents of HIV/AIDS opportunistic infections among countries, epidemiology and prevalence, lifecycle, risk factors, examination methods, and treatment.

N- and O-Glycosylation Pathways in the Microalgae Polyphyletic Group

The term microalga refers to various unicellular and photosynthetic organisms representing a polyphyletic group. It gathers numerous species, which can be found in cyanobacteria (i.e., Arthrospira) as well as in distinct eukaryotic groups, such as Chlorophytes (i.e., Chlamydomonas or Chlorella) and Heterokonts (i.e., diatoms). This phylogenetic diversity results in an extraordinary variety of metabolic pathways, offering large possibilities for the production of natural compounds like pigments or lipids that can explain the ever-growing interest of industrials for these organisms since the middle of the last century. More recently, several species have received particular attention as biofactories for the production of recombinant proteins. Indeed, microalgae are easy to grow, safe and cheap making them attractive alternatives as heterologous expression systems. In this last scope of applications, the glycosylation capacity of these organisms must be considered as this post-translational modification of proteins impacts their structural and biological features. Although these mechanisms are well known in various Eukaryotes like mammals, plants or insects, only a few studies have been undertaken for the investigation of the protein glycosylation in microalgae. Recently, significant progresses have been made especially regarding protein N-glycosylation, while O-glycosylation remain poorly known. This review aims at summarizing the recent data in order to assess the state-of-the art knowledge in glycosylation processing in microalgae.

Comparative Pathobiology of the Intestinal Protozoan Parasites Giardia lamblia, Entamoeba histolytica, and Cryptosporidium parvum

Protozoan parasites can infect the human intestinal tract causing serious diseases. In the following article, we focused on the three most prominent intestinal protozoan pathogens, namely, Giardia lamblia, Entamoeba histolytica, and Cryptosporidium parvum. Both C. parvum and G. lamblia colonize the duodenum, jejunum, and ileum and are the most common causative agents of persistent diarrhea (i.e., cryptosporidiosis and giardiasis). Entamoeba histolytica colonizes the colon and, unlike the two former pathogens, may invade the colon wall and disseminate to other organs, mainly the liver, thereby causing life-threatening amebiasis. Here, we present condensed information concerning the pathobiology of these three diseases.

Protein O- and C-Glycosylation pathways in Toxoplasma gondii and Plasmodium falciparum

Apicomplexan parasites are amongst the most prevalent and morbidity-causing pathogens worldwide. They are responsible for severe diseases in humans and livestock and are thus of great public health and economic importance. Until the sequencing of apicomplexan genomes at the beginning of this century, the occurrence of N- and O-glycoproteins in these parasites was much debated. The synthesis of rudimentary and divergent N-glycans due to lineage-specific gene loss is now well established and has been recently reviewed. Here, we will focus on recent studies that clarified classical O-glycosylation pathways and described new nucleocytosolic glycosylations in Toxoplasma gondii, the causative agents of toxoplasmosis. We will also review the glycosylation of proteins containing thrombospondin type 1 repeats by O-fucosylation and C-mannosylation, newly discovered in Toxoplasma and the malaria parasite Plasmodium falciparum. The functional significance of these post-translational modifications has only started to emerge, but the evidence points towards roles for these protein glycosylation pathways in tissue cyst wall rigidity and persistence in the host, oxygen sensing, and stability of proteins involved in host invasion.

Molecular cloning, expression, and characterization of UDP N-acetyl-α-d-galactosamine: Polypeptide N-acetylgalactosaminyltransferase 4 from Cryptosporidium parvum

Cryptosporidium spp. are the causative agents of diarrheal disease worldwide, but effective treatments are lacking. Cryptosporidium employs mucin-like glycoproteins with O-glycans to attach to and infect host intestinal epithelial cells. The Tn antigen (GalNAcα1-Ser/Thr) is an O-glycan essential for these processes, as Tn-specific lectins and a Tn-specific monoclonal antibody block attachment to and infection of host cells in vitro. The enzymes in Cryptosporidium catalyzing their synthesis, however, have not been studied. Previously, we identified four genes encoding putative UDP N-acetyl-α-d-galactosamine:polypeptide N-acetylgalactosaminyltransferases (ppGalNAc-Ts) in the genomes of three Cryptosporidium spp. Here we report the in silico analysis, cloning, expression, purification, and characterization of one of the four enzymes Cryptosporidium parvum (Cp)-ppGalNAc-T4. This enzyme contains the characteristic domains and motifs conserved in ppGalNAc-Ts and is expressed at multiple time points during in vitro infection. Recombinant soluble Cp-ppGalNAc-T4 was enzymatically active against an unmodified EA2 peptide suggesting that it may function as an "initiating" ppGalNAc-T. Cp-ppGalNAc-T4 also exhibited a strong preference for UDP-GalNAc over other nucleotide sugar donors and was active against unmodified and O-glycosylated versions of the C. parvum gp40-derived peptide, with a preference for the former, suggesting it may play a role in modifying this glycoprotein in vivo. Given the importance of mucin-type O-glycosylation in Cryptosporidium spp., the enzymes that catalyze their synthesis may serve as potential therapeutic targets.