1YNT

Structure of the monomeric form of T. gondii SAG1 surface antigen bound to a human Fab

Summary for 1YNT

• Entry DOI: 10.2210/pdb1ynt/pdb
• Related: 1KZQ
• Descriptor: 4F11E12 Fab variable light chain region, 4F11E12 Fab variable heavy chain region, protein L, ... (5 entities in total)
• Functional Keywords: toxoplasma gondii, recombinant sag1, conformational epitope, immune system
• Biological source: Finegoldia magna; More
• Total number of polymer chains: 7
• Total formula weight: 154548.07

Authors

Graille, M.,Stura, E.A.,Bossus, M.,Muller, B.H.,Letourneur, O.,Battail-Poirot, N.,Sibai, G.,Rolland, D.,Le Du, M.H.,Ducancel, F. (deposition date: 2005-01-25, release date: 2005-12-27, Last modification date: 2024-11-13)

Primary citation

Graille, M.,Stura, E.A.,Bossus, M.,Muller, B.H.,Letourneur, O.,Battail-Poirot, N.,Sibai, G.,Gauthier, M.,Rolland, D.,Le Du, M.H.,Ducancel, F.
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
J.Mol.Biol., 354:447-458, 2005

PubMed Abstract: Toxoplasma gondii, the intracellular parasite responsible for toxoplasmosis infects more than one-third of the world population and can be life-threatening for fetuses and immunocompromised patients. The surface protein SAG1 is an important immune target, which provides a strong immune response against the invasive tachyzoite while the other forms of the parasite, devoid of SAG1 at their surface, are multiplying. In addition to this role as a "hot spot" decoy, SAG1 is predicted to act as an adhesin during host-cell attachment through its binding to proteoglycans. To begin to understand the relationships between SAG1 epitopes and the ligand-binding site, we have solved the crystal structure of the monomeric form of T.gondii SAG1 complexed to a Fab derived from a monoclonal antibody raised against tachyzoite particles. This antibody competes strongly with human Toxoplasma-specific sera, suggesting that its epitope is part of an immunodominant region present on the surface of SAG1. The structure reveals that this conformational epitope, located within the SAG1 N-terminal domain, does not overlap with the proposed ligand-binding pocket. This study provides the first structural description of the monomeric form of SAG1, and significant insights into its dual role of adhesin and immune target during parasite infection.

PubMed: 16242717
DOI: 10.1016/j.jmb.2005.09.028

Experimental method

X-RAY DIFFRACTION (3.1 Å)