Ralph Biemans
Université libre de Bruxelles
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Featured researches published by Ralph Biemans.
Molecular and Biochemical Parasitology | 2001
Alain Jacquet; Ludivine Coulon; Joël De Nève; Véronique Daminet; Michèle Haumont; Lida Garcia; Alex Bollen; Margarita Jurado; Ralph Biemans
The attachment of Toxoplasma gondii to target cells is mediated by recognition of cellular heparan sulfate proteoglycans (HSPGs). The present study was performed to determine whether SAG1 and SAG3, two of the parasite surface antigens anchored to the membrane via glycosylphosphatidylinositol groups (GPIs), are involved in the tachyzoite binding to proteoglycans. The use of recombinant soluble forms of these proteins allowed us to demonstrate that SAG3, but not SAG1, interacts specifically with cellular HSPGs. Indeed, soluble recombinant SAG3 protein (recSAG3) was found to bind to immobilized heparin, whereas recSAG1 did not interact with this glycoaminoglycan. The specific adherence of recSAG3 to CHO cells was inhibited by soluble glycoconjugates, of which heparin, fucoidan and dextran sulfate were the most effective. Moreover, binding of recSAG3 to two HSPGs-deficient cell mutants was reduced by up to 80%. Proteoglycan sulfation was critical for SAG3 adherence to HSPGs as incubation of cells in the presence of sodium chlorate drastically reduced the recSAG3 binding. Finally, preincubation of CHO cells with recSAG3 blocked the adsorption of radiolabelled Toxoplasma tachyzoites. Taken together, these results indicate that SAG3 is a first glycoaminoglycan-binding protein associated with Toxoplasma, and SAG3-HSPGs interactions are involved in the parasite attachment to target cells.
Infection and Immunity | 2000
Michèle Haumont; Louis Delhaye; Lida Garcia; Margarita Jurado; Pasqualina Mazzu; Véronique Daminet; Vincent Verlant; Alex Bollen; Ralph Biemans; Alain Jacquet
ABSTRACT Primary infection with Toxoplasma gondii during pregnancy can induce fetal pathology and abortion in both humans and animals. The present study describes the development of an experimental model of congenital toxoplasmosis in the guinea pig. In this animal model, we evaluated the protective effect of vaccination with a recombinant form of SAG1 against maternofetal transmission of tachyzoites. The presence of parasites in fetuses was determined by nested PCRs and by an in vivo readout after fetal brain homogenate injections in mice. The absence of parasites was demonstrated in 66 to 86% of fetuses derived from adult guinea pigs immunized with SAG1 and challenged with the mildly virulent T. gondii strain C56. In contrast, more than 80% of fetuses from mock-immunized guinea pigs were infected. The protection was not correlated with titers of antibody to SAG1. Our results indicated that this experimental model constitutes a relevant model for evaluation of vaccine candidates against congenital toxoplasmosis and that SAG1 elicits significant protection against maternofetal transmission.
Journal of Biotechnology | 1998
Ralph Biemans; Diane Grégoire; Michèle Haumont; Alain Bosseloir; Lida Garcia; Alain Jacquet; Christine Dubeaux; Alex Bollen
A truncated form of SAG1, the immunodominant surface antigen of Toxoplasma gondii, has been produced in the methylotrophic yeast, Pichia pastoris. By construction, the recombinant protein lacks C-terminal residues 308-336 which, in native SAG1, encompass the glycosylphosphatidylinositol anchorage site. Secretion of anchor-less SAG1 proceeded via the yeast prepro alpha-mating factor signal peptide and yielded two immunoreactive protein species having apparent molecular masses of 31.5 and 34.5 kDa, respectively, and differing only by N-glycosylation of the single Asn-X-Ser site present in the molecule. Purification of the anchor-less SAG1 was achieved by a combination of ion-exchange and size-exclusion chromatographies. N-terminal amino acid sequencing of the products indicated the presence of additional residues glutamic acid--alanine at the N-terminal end of the products. Despite incomplete processing and unnatural glycosylation, anchor-less SAG1 proteins apparently adopted a suitable conformation recognized by monoclonal and human serum-derived antibodies, specific for the native SAG1. In addition, the recombinant anchor-less SAG1 proved competent for inducing proliferation, in vitro, of mononuclear cells from seropositive individuals. Finally, properly adjuvanted anchor-less SAG1 was able to induce protection of mice against a lethal challenge with T. gondii tachyzoites.
Acta Crystallographica Section D-biological Crystallography | 2000
Margarida Archer; Maria Luisa Rodrigues; M. Aurélio; Ralph Biemans; Alfredo Cravador; Mariaarménia Carrondo
Cinnamomin (CIN) belongs to a family of 10 kDa proteins designated as elicitins. Some of these proteins induce a hypersensitive response in diverse plant species, leading to resistance against fungal and bacterial plant pathogens. CIN was crystallized by the vapour-diffusion method using either ammonium sulfate or polyethyleneglycol (PEG) as precipitants in solutions buffered at around pH 7. These crystals are isomorphous and belong to the triclinic space group, with unit-cell parameters a = 31.69, b = 36. 99, c = 44.09 A, alpha = 76.86, beta = 84.41, gamma = 80.26 degrees. A frozen crystal diffracted X-rays beyond 1.45 A resolution on a synchrotron-radiation source.
European Journal of Histochemistry | 2010
D. Ehirchiou; Wuly Zorzi; Ralph Biemans; A. Vanderbeeke; Michèle Haumont; Bernard Coumans; Sarah Collin; Olivier Jolois; Alex Bollen; Ernst Heinen; Nadine Antoine
Splenic germinal center reactions were measured during primary response to a plasmidic DNA intramuscular injection. Cardiotoxin-pretreated Balb/c mice were immunized with DNA plasmids encodmg or not the SAG1 protein, a membrane antigen of Toxoplasma gondii. Specific anti-SAG1 antibodies were detected on days 16 and 36 after injection of coding plasmids. The results of ELISAs showed that the SAG1-specific antibodies are of the IgG2a class. Morphometric analyses were done on serial immunostained cryosections of spleen and draining or non-draining lymph nodes. This new approach made it possible to evaluate the chronological changes induced by DNA immunisation in the germinal centres (in number and in size). Significant increases in the number of germinal centres were measured in the spleen and only in draining lymph nodes after plasmid injection, the measured changes of the germinal centers appeared to result from the adjuvant stimulatory effect of the plasmidic DNA since both the coding and the noncoding plasmid DNA induced them. No measurable changes were recorded in the T-dependent zone of lymph organs.
Protein Expression and Purification | 1999
Alain Jacquet; Véronique Daminet; Michèle Haumont; Lida Garcia; Sylvie Chaudoir; Alex Bollen; Ralph Biemans
Archive | 1999
Ralph Biemans; Alex Bollen; Michèle Haumont
Archive | 2000
Ralph Biemans; Alex Bollen; Neve Joel De; Michèle Haumont; Alain Jacquet
Identification of an elicitn gene cluster in Phytophthora cinnamomi and analysis of the necrotic activity of a purified recombinant beta-cinnamomin | 1998
J. Duclos; M. Aurélio; José Graça; Ana Cristina Coelho; Alain Fauconnier; Alain Jacquet; Alex Bollen; Alfredo Cravador; Ralph Biemans; Edmond Godfroid
Acta Crystallographica | 2000
Margarida Archer; Maria Luisa Rodrigues; M. Aurélio; Ralph Biemans; Alfredo Cravador; Maria Arménia Carrondo