The surface antigen SAG3 mediates the attachment of Toxoplasma gondii to cell-surface proteoglycans

Jacquet, Alain; Coulon, Laurent; Nève, Joël De; Daminet, Véronique; Haumont, Michèle; Garcia, Lida; Bollen, Alex; Jurado, Margarita; Biemans, Ralph

doi:10.1016/s0166-6851(01)00297-3

Cited by 102 publications

(79 citation statements)

References 33 publications

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“…In studies of cells lacking all N sulfation due to combined deficiency in NDST1 and NDST2, no further diminution of T. gondii infection has been observed (data not shown). These results show that NDST1 generates a specific pattern of sulfation required for efficient T. gondii expresses a surface antigen (SAG3) that binds to heparan sulfate, which originally suggested that it might act as a ligand involved in heparan sulfate-dependent attachment (25). Mutants lacking SAG3 exhibited reduced infectivity, a finding consistent with this idea.…”

Section: Discussionsupporting

confidence: 75%

Cell Surface Heparan Sulfate Promotes Replication of Toxoplasma gondii

2005

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Previous work suggests that cell surface heparan sulfate acts as a receptor for the Apicomplexan parasite Toxoplasma gondii. Using Chinese hamster ovary cell mutants defective in heparan sulfate biosynthesis, we show that heparan sulfate is necessary and sufficient for infectivity. Further, we demonstrate that the parasite requires N sulfation of heparan sulfate initiated by N-deacetylase/N-sulfotransferase-1, but 2-O sulfation and 6-O sulfation appear to be dispensable. In order to study the role of heparan sulfate in other cell types, we created a conditional allele for N-deacetylase/N-sulfotransferase-1 by using Cre-loxP technology. Mammary tumor cells lacking N-deacetylase/N-sulfotransferase-1 exhibited reduced toxoplasma infectivity like Chinese hamster ovary cell mutants. Surprisingly, heparin, chemically modified heparinoids, and monoclonal antibodies to heparan sulfate had no effect on toxoplasma infection. T. gondii attachment and invasion were unchanged in N-deacetylase/N-sulfotransferase-1-inactivated cells as well, but replication was reduced. Thus, heparan sulfate does not appear to function as a receptor for T. gondii but instead facilitates parasite replication postinvasion.

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Section: Discussionsupporting

confidence: 75%

Cell Surface Heparan Sulfate Promotes Replication of Toxoplasma gondii

2005

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“…The ratio of bound parasites is then determined using the laser scanning cytometer, yielding a highly reproducible measure of relative attachment (Mital et al, manuscript in preparation). Both fixed and unfixed host cells (Mineo et al, 1993;Ortega-Barria and Boothroyd, 1999;Jacquet et al, 2001;Kieschnick et al, 2001) were tested in the assay, because there appear to be subtle differences in the way parasites attach to live versus fixed host cells (Mital et al., manuscript in preparation). Figure 6 shows that the conditional knockout parasites, grown with or without Atc, attach to either fixed or unfixed host cells in a 1:1 ratio, indicating equivalent binding.…”

Section: A Tgama1 Deficiency Does Not Affect the Early Steps Of Invasionmentioning

confidence: 99%

Conditional Expression ofToxoplasma gondiiApical Membrane Antigen-1 (TgAMA1) Demonstrates That TgAMA1 Plays a Critical Role in Host Cell Invasion

Mital

Meissner

Soldati

et al. 2005

MBoC

231

250

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Toxoplasma gondii is an obligate intracellular parasite and an important human pathogen. Relatively little is known about the proteins that orchestrate host cell invasion by T. gondii or related apicomplexan parasites (including Plasmodium spp., which cause malaria), due to the difficulty of studying essential genes in these organisms. We have used a recently developed regulatable promoter to create a conditional knockout of T. gondii apical membrane antigen-1 (TgAMA1). TgAMA1 is a transmembrane protein that localizes to the parasite's micronemes, secretory organelles that discharge during invasion. AMA1 proteins are conserved among apicomplexan parasites and are of intense interest as malaria vaccine candidates. We show here that T. gondii tachyzoites depleted of TgAMA1 are severely compromised in their ability to invade host cells, providing direct genetic evidence that AMA1 functions during invasion. The TgAMA1 deficiency has no effect on microneme secretion or initial attachment of the parasite to the host cell, but it does inhibit secretion of the rhoptries, organelles whose discharge is coupled to active host cell penetration. The data suggest a model in which attachment of the parasite to the host cell occurs in two distinct stages, the second of which requires TgAMA1 and is involved in regulating rhoptry secretion. INTRODUCTIONToxoplasma gondii is one of the one most common protozoan parasites of humans, infecting approximately one-third of the world's population. The disease caused by an acute T. gondii infection, toxoplasmosis, can be life threatening in the congenitally infected fetus and immunocompromised hosts. Like all members of the Phylum Apicomplexa, including Plasmodium spp. (the causative agents of malaria) and Cryptosporidium parvum (a significant worldwide cause of waterborne illness), T. gondii is an obligate intracellular parasite. Host cell invasion is a critical step in the pathogenesis of the diseases caused by apicomplexan parasites, including toxoplasmosis. T. gondii represents an excellent model system for studying the relatively conserved process of apicomplexan invasion, because of the ease with which this parasite can be cultured and genetically manipulated (Roos et al., 1994;Black and Boothroyd, 2000;Kim and Weiss, 2004).Host cell invasion by apicomplexan parasites is a complex, multistep process (reviewed in Black and Boothroyd, 2000;Chitnis and Blackman, 2000). In T. gondii, the asexual stage tachyzoites move over solid surfaces, including cells, by an unusual form of substrate-dependent gliding motility (Sibley et al., 1998;Hakansson et al., 1999). After the apical end of a parasite comes in contact with the host cell membrane, apical secretory organelles (micronemes and rhoptries) sequentially discharge their contents (Dubremetz et al., 1993;Carruthers and Sibley, 1997) and a zone of tight interaction forms between the two cells (Nichols and O'Connor, 1981;Dubremetz et al., 1985;Grimwood and Smith, 1995). An invagination in the host cell plasma membrane develops at the point ...

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“…Interactions with the host cell at this stage may involve parasite surface antigens (SAGs) as well as basal levels of micronemal adhesins. (Jacquet et al, 2001) By definition, parasites in the contact stage, are well enough attached to the host that they are not dislodged during the buffer switch at t=0, but fail to bind tightly enough to resist the wash at t=T.…”

Section: Mathematical Modelingmentioning

confidence: 99%

“…gondii invasion involves a series of highly coordinated events. Initial attachment through one or more of the parasite's abundant surface proteins (Dzierszinski et al, 2000, Jacquet et al, 2001) leads to tighter apical attachment upon release of proteins from secretory granules called micronemes. At least one of these microneme proteins associates with other proteins released from the neck of a second set of secretory organelles, the rhoptries, to the form of a structure called the moving junction (Alexander et al, 2005.…”

Section: Introductionmentioning

confidence: 99%

Kinetic modeling of Toxoplasma gondii invasion

Kafsack

Carruthers

Pineda

2007

Journal of Theoretical Biology

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The phylum Apicomplexa includes parasites responsible for global scourges such as malaria, cryptosporidiosis, and toxoplasmosis. Parasites in this phylum reproduce inside the cells of their hosts, making invasion of host cells an essential step of their life cycle. Characterizing the stages of host-cell invasion, has traditionally involved tedious microscopic observations of individual parasites over time. As an alternative, we introduce the use of compartment models for interpreting data collected from snapshots of synchronized populations of invading parasites. Parameters of the model are estimated via a maximum negative log-likelihood principle. Estimated parameter values and their 95% confidence intervals (95% CI), are consistent with reported observations of individual parasites. For RH-strain parasites, our model yields that: 1) penetration of the host cell plasma membrane takes 26 sec (95% CI: 22-30 sec), 2) parasites that ultimately invade, remained attached 3 times longer than parasites that eventually detach from the host cells, and 3) 25% (95% CI: 19-33%) of parasites invade while 75% (95% CI: 67-81%) eventually detach from their host cells without progressing to invasion. A key feature of the model is the incorporation of invastion stages that cannot be directly observed. This allows us to characterize the phenomenon, of parasite detachment from host cells. The properties of this phenomenon would be difficult to quantify without a mathematical model. We conclude that mathematical modeling provides a powerful new tool for characterizing the stages of host-cell invasion by intracellular parasites.

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The surface antigen SAG3 mediates the attachment of Toxoplasma gondii to cell-surface proteoglycans

Cited by 102 publications

References 33 publications

Cell Surface Heparan Sulfate Promotes Replication of Toxoplasma gondii

Cell Surface Heparan Sulfate Promotes Replication of Toxoplasma gondii

Conditional Expression ofToxoplasma gondiiApical Membrane Antigen-1 (TgAMA1) Demonstrates That TgAMA1 Plays a Critical Role in Host Cell Invasion

Kinetic modeling of Toxoplasma gondii invasion

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