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The Toxoplasma gondii protein MIC3 requires pro-peptide cleavage and dimerization to function as adhesin
Odile Cérède1, Jean François Dubremetz, Daniel Bout
1UMR Université-INRA d'Immunologie Parasitaire, Faculté des Sciences Pharmaceutiques et Biologiques, 31 Avenue Monge, F-37200 Tours, France.
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.
Insights
Toxoplasma gondii micronemal protein MIC3, an adhesin, requires dimerization and pro-peptide cleavage for host cell binding. This dimerization domain can induce dimerization in other proteins, impacting parasite invasion.
Area of Science:
- Parasitology
- Molecular Biology
- Cell Biology
Background:
- Apicomplexan parasite invasion relies on micronemal protein (MIC) exocytosis.
- MICs function as adhesins, often undergoing proteolytic processing.
- MIC3 in Toxoplasma gondii is a homodimeric adhesin with conserved features.
Purpose of the Study:
- To elucidate the molecular mechanisms of MIC3-mediated host cell attachment.
- To identify the receptor binding site and dimerization domain of MIC3.
- To investigate the role of proteolytic processing in MIC3 function.
Main Methods:
- Development of a novel MIC3-binding assay using transfected mammalian cells.
- Expression of full-length and truncated MIC3 gene sequences.
- Localization of the MIC3 dimerization domain and its functional transfer to MIC8.
Main Results:
- The MIC3 receptor binding site is in the N-terminal chitin-binding-like domain.
- Pro-peptide cleavage is necessary for receptor binding site accessibility.
- Protein binding requires MIC3 dimerization, mediated by a C-terminal domain.
- This domain can induce dimerization in the monomeric MIC8 protein.
Conclusions:
- MIC3 functional maturation involves pro-peptide cleavage and dimerization.
- The C-terminal dimerization domain is crucial for MIC3 function and can be transferred to other MICs.
- These findings provide insights into the regulation of MICs for parasite invasion.