Evidence for glycosyl-phosphatidylinositol anchoring of Toxoplasma gondii major surface antigens.

Tomavo, Stanislas; Schwarz, Ralph Τ.; Dubremetz, Jean François

doi:10.1128/mcb.9.10.4576

Cited by 104 publications

(56 citation statements)

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“…The four SnSAGs were all found to be membrane associated and displayed on the merozoite surface, consistent with their homology to surface antigens in related parasites. Sequence predictions suggested the presence of glycolipid anchors, as observed for the SAGs of T. gondii (49,60) and N. caninum (32,55). Although the SnSAGs could not be liberated from the merozoite surface by treatment with phosphatidylinositol-specific phospholipase C (data not shown), it is likely that this was due to inositol modification in the S. neurona GPI anchors, as observed previously for N. caninum tachyzoites (54,55).…”

Section: Fig 3 (A)supporting

confidence: 75%

Sarcocystis neuronaMerozoites Express a Family of Immunogenic Surface Antigens That Are Orthologues of theToxoplasma gondiiSurface Antigens (SAGs) and SAG-Related Sequences

et al. 2005

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Sarcocystis neurona is a member of the Apicomplexa that causes myelitis and encephalitis in horses but normally cycles between the opossum and small mammals. Analysis of an S. neurona expressed sequence tag (EST) database revealed four paralogous proteins that exhibit clear homology to the family of surface antigens (SAGs) and SAG-related sequences of Toxoplasma gondii. The primary peptide sequences of the S. neurona proteins are consistent with the two-domain structure that has been described for the T. gondii SAGs, and each was predicted to have an amino-terminal signal peptide and a carboxyl-terminal glycolipid anchor addition site, suggesting surface localization. All four proteins were confirmed to be membrane associated and displayed on the surface of S. neurona merozoites. Due to their surface localization and homology to T. gondii surface antigens, these S. neurona proteins were designated SnSAG1, SnSAG2, SnSAG3, and SnSAG4. Consistent with their homology, the SnSAGs elicited a robust immune response in infected and immunized animals, and their conserved structure further suggests that the SnSAGs similarly serve as adhesins for attachment to host cells. Whether the S. neurona SAG family is as extensive as the T. gondii SAG family remains unresolved, but it is probable that additional SnSAGs will be revealed as more S. neurona ESTs are generated. The existence of an SnSAG family in S. neurona indicates that expression of multiple related surface antigens is not unique to the ubiquitous organism T. gondii. Instead, the SAG gene family is a common trait that presumably has an essential, conserved function(s).Sarcocystis neurona is an apicomplexan parasite and the primary cause of equine protozoal myeloencephalitis (EPM). EPM is a serious debilitating disease and is the most commonly diagnosed neurologic disorder of horses. Although seroprevalence studies have indicated that approximately 30 to 50% of horses have been exposed to S. neurona, the incidence of EPM is estimated to be less than 1% (15, 46). Thus, S. neurona infection clearly does not equate directly with clinical illness, and it is not clear what factors influence the progression from simple infection to severe neurologic disease. The normal life cycle of S. neurona alternates between the definitive host, the opossum (20), and various small mammal intermediate hosts, including skunks (9), raccoons (17), armadillos (8), and cats (16). Although S. neurona readily infects equids, these animals are currently believed to be aberrant hosts for this parasite species since latent forms (sarcocysts) have not been found in infected horses.Like other members of the Apicomplexa, S. neurona is an obligate intracellular parasite that requires a number of unique molecules (i.e., virulence factors) to support its parasitic lifestyle. Apicomplexan surface molecules are important virulence factors that are responsible for the pathogen's initial interactions with the host cell surface and components of the host immune response. A broad family of more than 20 relate...

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Section: Fig 3 (A)supporting

confidence: 75%

Sarcocystis neuronaMerozoites Express a Family of Immunogenic Surface Antigens That Are Orthologues of theToxoplasma gondiiSurface Antigens (SAGs) and SAG-Related Sequences

et al. 2005

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“…GPIs of Plasmodium falciparum, Trypanosoma brucei, Leishmania mexicana, and Trypanosoma cruzi are inducers of TNF␣ production in macrophages (23)(24)(25)(26). Free GPIs as well as GPI-anchored proteins are present in T. gondii (27). We show that isolated T. gondii GPIs induce the production of TNF␣ in macrophages, involving the activation of NF-B p65, a member of the NF-B/c-rel family of transcription factors.…”

mentioning

confidence: 78%

Roles of Glycosylphosphatidylinositols of Toxoplasma gondii

Debierre‐Grockiego¹,

Azzouz²,

Schmidt³

et al. 2003

Journal of Biological Chemistry

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Toxoplasma gondii is a ubiquitous parasitic protozoan, which causes congenital infectious diseases as well as severe encephalitis, a major cause of death among immune-deficient persons, such as AIDS patients. T. gondii is normally controlled by the immune system of healthy individuals, leading to an asymptomatic infection. T. gondii triggers early cytokine production, which, to a certain extent, protects the host against replication of tachyzoites, the infective form of the parasite. Glycosylphosphatidylinositols (GPIs) constitute a class of glycolipids that have various functions, the most fundamental being to link proteins to eucaryotic cell membranes. GPIs are involved in the pathogenicity of other protozoan parasites and are known to induce tumor necrosis factor-␣ (TNF␣) production. We show that GPIs highly purified from T. gondii tachyzoites, as well as their core glycans, induce TNF␣ production in macrophages. A chemically synthesized GPI of T. gondii lacking its lipid moiety, GPIa, has the same effect as the natural GPIs, whereas a chemically synthesized molecule with dialkylglycerol instead of diacylglycerol as lipid moiety, GPIb, does not induce TNF␣ production. Moreover, GPIb inhibits the TNF␣ production induced by T. gondii GPI or by GPIa. The core glycan prepared from the two chemically synthesized molecules activates macrophages, showing that the lipid moiety may regulate signaling. Stimulation of macrophages with GPIs of T. gondii results in activation of the transcription factor NF-B, which is inhibited by the chemically synthesized GPIb, suggesting the involvement of NF-B in TNF␣ gene expression. Our results support the idea that T. gondii GPIs are bioactive factors that participate in the production of TNF␣ during toxoplasmal pathogenesis.

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“…In this regard, several other GRA proteins that are secreted within the PV also contain central hydrophobic domains that are predicted to mediate their interactions with membranes, including GRA4 and GRA6 (reviewed in Cesbron-Delauw, 1994). In contrast, all of the abundant cell surface proteins of Toxoplasma are linked in the membrane via glycosylphosphate inositol anchors at their C termini (Tomavo et al, 1989), an addition that may mark proteins for export to the plasma membrane (Seeber et al, 1998). The insertion or translocation of proteins across membranes does not normally occur spontaneously but requires accessory proteins to mediate the passage of large hydrophilic protein domains across the impermeant phospholipid barrier.…”

Section: Discussionmentioning

confidence: 99%

Transmembrane Insertion of theToxoplasma gondiiGRA5 Protein Occurs after Soluble Secretion into the Host Cell

Lecordier

Mercier

Sibley

et al. 1999

MBoC

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The intracellular parasite Toxoplasma gondii resides within a specialized compartment, the parasitophorous vacuole (PV), that resists fusion with host cell endocytic and lysosomal compartments. The PV is extensively modified by secretion of parasite proteins, including the dense granule protein GRA5 that is specifically targeted to the delimiting membrane of the PV (PVM). We show here that GRA5 is present both in a soluble form and in hydrophobic aggregates. GRA5 is secreted as a soluble form into the PV after which it becomes stably associated with the PVM. Topological studies demonstrated that GRA5 was inserted into the PVM as a transmembrane protein with its N-terminal domain extending into the cytoplasm and its C terminus in the vacuole lumen. Deletion of 8 of the 18 hydrophobic amino acids of the single predicted transmembrane domain resulted in the failure of GRA5 to associate with the PVM; yet it remained correctly packaged in the dense granules and was secreted as a soluble protein into the PV.Collectively, these studies demonstrate that the secretory pathway in Toxoplasma is unusual in two regards; it allows soluble export of proteins containing typical transmembrane domains and provides a mechanism for their insertion into a host cell membrane after secretion from the parasite. INTRODUCTIONAmong the varied lifestyles adopted by intracellular parasites is the residence in host cell vacuoles that do not fuse with lysosomes, a strategy exhibited by the protozoan parasite Toxoplasma and the bacterial pathogens Legionella, Chlamydia, and Mycobacteria (Garcia delPortillo and Finlay, 1995). The Toxoplasma-containing vacuole, called the parasitophorous vacuole (PV) 1 , forms by active penetration of the parasite causing invagination of the plasma membrane bilayer (Suss-Toby et al., 1996). This compartment subsequently resists fusion with endosomes and lysosomes by a mechanism that is poorly understood; however, it is clear that the fate of the vacuole is determined at the time of formation (Sibley et al., 1985;Joiner, 1991;Mordue and Sibley, 1997). As the parasite grows and replicates within the cell, it forms a network of tubular membranes that are continuous with the delimiting membrane of the vacuole (Nichols et al., 1983;Sibley et al., 1995).Secretion of proteins stored in apical organelles (micronemes, rhoptries, and dense granules) is a prominent feature of Toxoplasma invasion and presumably contributes both to the nonfusigenic status of the PV and subsequent nutrient uptake by the parasite (Carruthers and Sibley, 1997). Segregated from the endocytic system and cut off from the extracellular fluid, § Corresponding author. E-mail address: mcesbron@infobiogen. fr. † Present address: Laboratory of Molecular Parasitology, Université Libre de Bruxelles, Rhode Saint Genese, Belgium. 1 Abbreviations used: EM, electron microscopy; FBS, fetal bovine serum; F/T, freeze/thaw; HFF, human foreskin fibroblasts; HSP, high-speed pellet; HSS, high-speed supernatant; LSP, lowspeed pellet; LSS, low-speed supernatant; NP-40...

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Evidence for glycosyl-phosphatidylinositol anchoring of Toxoplasma gondii major surface antigens.

Cited by 104 publications

References 30 publications

Sarcocystis neuronaMerozoites Express a Family of Immunogenic Surface Antigens That Are Orthologues of theToxoplasma gondiiSurface Antigens (SAGs) and SAG-Related Sequences

Sarcocystis neuronaMerozoites Express a Family of Immunogenic Surface Antigens That Are Orthologues of theToxoplasma gondiiSurface Antigens (SAGs) and SAG-Related Sequences

Roles of Glycosylphosphatidylinositols of Toxoplasma gondii

Transmembrane Insertion of theToxoplasma gondiiGRA5 Protein Occurs after Soluble Secretion into the Host Cell

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