title: The Toxoplasma gondii protein MIC3 requires pro-peptide cleavage and dimerization to function as adhesin.
abstract: Attachment and invasion of host cells by apicomplexan parasites involve the exocytosis of the micronemal proteins (MICs). Most MICs are adhesins, which show homology with adhesive domains from higher eukaryote proteins and undergo proteolytic processing of unknown biological significance during their transport to micronemes. In Toxoplasma gondii, the micronemal homodimeric protein MIC3 is a potent adhesin that displays features shared by most Apicomplexa MICs. We have developed an original MIC3-binding assay by transfection of mammalian cells with complete or truncated MIC3 gene sequences and demonstrated that the receptor binding site of MIC3 is located in the N-terminal chitin-binding-like domain, which remains poorly accessible until the adjacent pro-peptide has been cleaved, and that binding requires dimerization. We have localized the dimerization domain in the C-terminal end of the protein and shown that it is able to convert MIC8, a monomeric micronemal protein sharing the MIC3 lectin-like domain, into a dimer able to interact with host cell receptors. These findings shed new light on molecular mechanisms that control functional maturation of MICs.
authors.affiliation: UMR Université-INRA d'Immunologie Parasitaire, Faculté des Sciences Pharmaceutiques et Biologiques, 31 Avenue Monge, F-37200 Tours, France.
authors.forename: Odile
authors.initials: O
authors.lastname: Cérède
authors.forename: Jean François
authors.initials: JF
authors.lastname: Dubremetz
authors.forename: Daniel
authors.initials: D
authors.lastname: Bout
authors.forename: Maryse
authors.initials: M
authors.lastname: Lebrun
mesh_terms: D018829:Adhesins, Bacterial; D020816:Amino Acid Motifs; D000818:Animals; D019921:Biotinylation; D015153:Blotting, Western; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D002448:Cell Adhesion; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002686:Chitin / Q000378:metabolism; D019281:Dimerization; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D037102:Lectins / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008861:Microsomes / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D016366:Open Reading Frames; D010455:Peptides / Q000737:chemistry; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D015800:Protozoan Proteins / Q000737:chemistry / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D014122:Toxoplasma / Q000378:metabolism*; D014162:Transfection
chemical_list: D018829:Adhesins, Bacterial; D002352:Carrier Proteins; D037102:Lectins; C421382:MIC3 protein, Toxoplasma gondii; D010455:Peptides; D015800:Protozoan Proteins; D011994:Recombinant Proteins; D002686:Chitin