Crystal Structure of the Complex between the Monomeric Form of Toxoplasma gondii Surface Antigen 1 (SAG1) and a Monoclonal Antibody that Mimics the Human Immune Response

Graille, Marc; Stura, E.A.; Bossus, Marc; Müller, Bruno; Letourneur, Odile; Battail-Poirot, Nicole; Sibai, G.; Gauthier, Marie; Rolland, Dominique; Du, Marie-Hélène Le; Ducancel, Frédéric

doi:10.1016/j.jmb.2005.09.028

Cited by 56 publications

(58 citation statements)

References 50 publications

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“…This family of surface antigens from T. gondii is defined by the presence of an N-terminal secretion signal, a GPI anchor, and a set of conserved amino acids, among which are six cysteines involved in the formation of three disulfide bonds important in maintaining the structure of the SRS fold (40). To date, more than 160 DNA sequences from T. gondii have been identified as belonging to the SRS superfamily (45), but only the structures for SAG1, SporoSAG, and BSR4 have been solved (39,40,46,47). Although there is some structural divergence among these three proteins, and within each protein the N-terminal (D1) and C-terminal (D2) domains are also structurally distinct, the SRS fold is observed as a common feature in the domains of all three (40) (Fig.…”

Section: Discussionmentioning

confidence: 99%

Structure of thePlasmodium6-cysteine s48/45 domain

Arredondo

Cai²,

Takayama³

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

107

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The s48/45 domain was first noted in Plasmodium proteins more than 15 y ago. Previously believed to be unique to Plasmodium , the s48/45 domain is present in other aconoidasidans. In Plasmodium , members of the s48/45 family of proteins are localized on the surface of the parasite in different stages, mostly by glycosylphosphatydylinositol-anchoring. Members such as P52 and P36 seem to play a role in invasion of hepatocytes, and Pfs230 and Pfs48/45 are involved in fertilization in the sexual stages and have been consistently studied as targets of transmission-blocking vaccines for years. In this report, we present the molecular structure for the s48/45 domain corresponding to the C-terminal domain of the blood-stage protein Pf12 from Plasmodium falciparum , obtained by NMR. Our results indicate that this domain is a β-sandwich formed by two sheets with a mixture of parallel and antiparallel strands. Of the six conserved cysteines, two pairs link the β-sheets by two disulfide bonds, and the third pair forms a bond outside the core. The structure of the s48/45 domain conforms well to the previously defined surface antigen 1 (SAG1)-related-sequence (SRS) fold observed in the SAG family of surface antigens found in Toxoplasma gondii . Despite extreme sequence divergence, remarkable spatial conservation of one of the disulfide bonds is observed, supporting the hypothesis that the domains have evolved from a common ancestor. Furthermore, a homologous domain is present in ephrins, raising the possibility that the precursor of the s48/45 and SRS domains emerged from an ancient transfer to Apicomplexa from metazoan hosts.

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Section: Discussionmentioning

confidence: 99%

Structure of thePlasmodium6-cysteine s48/45 domain

Arredondo

Cai²,

Takayama³

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

107

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“…An inhibition ELISA, as described elsewhere (7,9), with some modifications was carried out in order to evaluate the immunodominant properties of the epitopes recognized by A3A4, A4D12, and 1B8 MAbs. A panel of 20 human sera (10 seropositive and 10 seronegative to T. gondii) was used, and the serological statuses of the samples were determined by indirect ELISA for IgG to T. gondii, using STAg.…”

Section: Methodsmentioning

confidence: 99%

Reverse Enzyme-Linked Immunosorbent Assay Using Monoclonal Antibodies against SAG1-Related Sequence, SAG2A, and p97 Antigens fromToxoplasma gondiiTo Detect Specific Immunoglobulin G (IgG), IgM, and IgA Antibodies in Human Sera

Carvalho

Silva

Cunha-Júnior

et al. 2008

Clin Vaccine Immunol

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The present study aimed to evaluate the performance of three monoclonal antibodies (MAbs) in reverse enzyme-linked immunosorbent assays (ELISAs) for detecting immunoglobulin G (IgG), IgM, and IgA antibodies against Toxoplasma gondii in 175 serum samples from patients at different stages of T. gondii infection, as defined by both serological and clinical criteria, as follows: recent (n ‫؍‬ 45), transient (n ‫؍‬ 40), and chronic (n ‫؍‬ 55) infection as well as seronegative subjects (n ‫؍‬ 35). The results were compared with those obtained by indirect ELISA using soluble Toxoplasma total antigen (STAg). Our data demonstrated that MAb A3A4 recognizes a conformational epitope in SAG1-related-sequence (SRS) antigens, while A4D12 and 1B8 recognize linear epitopes defined as SAG2A surface antigen and p97 cytoplasmatic antigen, respectively. Reverse ELISA for IgG with A3A4 or A4D12 MAbs was highly correlated with indirect ELISA for anti-STAg IgG, whereas only A4D12 reverse ELISA showed high correlation with indirect ELISA for IgM and IgA isotypes. To our knowledge, this is the first report analyzing the performance of a reverse ELISA for simultaneous detection of IgG, IgM, and IgA isotypes active toward native SAG2A, SRS, and p97 molecules from STAg, using a panel of human sera from patients with recent and chronic toxoplasmosis. Thus, reverse ELISA based on the capture of native SAG2A and SRS antigens of STAg by MAbs could be an additional approach for strengthening the helpfulness of serological tests assessing the stage of infection, particularly in combination with highly sensitive and specific assays that are frequently used nowadays for diagnosis of toxoplasmosis during pregnancy or congenital infection in newborns.

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“…Although this has not been confirmed biochemically for SAG1, elution studies showed that the SRS adhesin SAG3 was selectively retained on a heparin column, suggesting a direct interaction (20). More recently SAG1 was co-crystallized with a monoclonal antibody that binds a major epitope on SAG1 (18). This latter study shows that the SAG1-antibody complex is a monomer in solution and that the mapped immunogenic epitope does not overlap with the putative ligand-binding groove (19).…”

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confidence: 93%

“…To date, the highly immunogenic surface adhesin SAG1 is the only SRS antigen for which a crystal structure has been determined (18,19). In the original, seminal study, Garcia and co-workers (19) established that SAG1 assembled into a dimer with the monomer adopting a novel SRS fold.…”

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confidence: 99%

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Structural Characterization of the Bradyzoite Surface Antigen (BSR4) from Toxoplasma gondii, a Unique Addition to the Surface Antigen Glycoprotein 1-related Superfamily

Crawford

Grujic

Bruic

et al. 2009

Journal of Biological Chemistry

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Toxoplasma gondii is an obligate intracellular protozoan parasite that infects nearly one-third of the human population. The success of T. gondii is based on its complex life cycle; a lytic tachyzoite form disseminates infection, whereas an encysted bradyzoite form establishes a latent, chronic infection. Persistence and transmissibility is central to the survival of the parasite and is, in part, mediated by a family of antigenically distinct surface antigen glycoprotein (SAG)-related sequences (SRS) adhesins that play a dual role in host cell attachment and host immune evasion. More than 160 members of the SRS family have been identified with only the tachyzoite-expressed SAG1 structurally characterized. Here we report the first structural description of the bradyzoite adhesin BSR4 using x-ray crystallography and small angle x-ray scattering. The 1.90-Å crystal structure of BSR4 reveals an architecture comprised of tandem ␤ sandwich domains organized in a head to tail fashion with the N-terminal domain responsible for dimer formation. A restructured topology in BSR4 results in a ligand-binding site that is significantly reorganized in both structure and chemistry relative to SAG1, consistent with BSR4 binding a distinct physiological ligand. The small angle x-ray scattering solution structure of BSR4 highlights a potentially important structural role for the interdomain polymorphic linker that imparts significant flexibility that may promote structural adaptation during ligand binding. This study reveals an unexpected level of structural diversity within the SRS superfamily and provides important insight into the role of these virulence factors.The protozoan parasite Toxoplasma gondii, the causative agent of toxoplasmosis, is a serious global pathogen that infects nearly one-third of the human population (1-3). T. gondii infections can be lethal to a developing fetus and immunocompromised, cancer, AIDS, and organ transplant patients. Clinical features range from asymptomatic infection to lymphadenopathy, ileitis, encephalitis, and/or blinding ocular infections in both children and adults with the severity of symptoms tending to increase with age (1, 4 -9). During infection, T. gondii cycles between the rapidly growing, lytic tachyzoite stage and the slow growing, cyst-forming bradyzoite stage. Upon challenge by the immune system, the tachyzoites, which are responsible for rapid dissemination of the parasite, differentiate into encysted bradyzoites that promote chronic infection. The molecular switches that regulate interconversion of the two parasitic stages in the host remain largely undefined. Despite the complex life cycle of T. gondii, it exists as a single species and has been referred to as one of the most, if not the most, successful protozoan parasite of animals on this planet (3).The success of T. gondii is largely due to its ability to infect a broad range of host cells (10), which is, in part, mediated by a family of developmentally expressed, antigenically distinct surface antigen glycoprotein (SAG)...

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Crystal Structure of the Complex between the Monomeric Form of Toxoplasma gondii Surface Antigen 1 (SAG1) and a Monoclonal Antibody that Mimics the Human Immune Response

Cited by 56 publications

References 50 publications

Structure of thePlasmodium6-cysteine s48/45 domain

Structure of thePlasmodium6-cysteine s48/45 domain

Reverse Enzyme-Linked Immunosorbent Assay Using Monoclonal Antibodies against SAG1-Related Sequence, SAG2A, and p97 Antigens fromToxoplasma gondiiTo Detect Specific Immunoglobulin G (IgG), IgM, and IgA Antibodies in Human Sera

Structural Characterization of the Bradyzoite Surface Antigen (BSR4) from Toxoplasma gondii, a Unique Addition to the Surface Antigen Glycoprotein 1-related Superfamily

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