title: Intramembrane cleavage of microneme proteins at the surface of the apicomplexan parasite Toxoplasma gondii.
abstract: Apicomplexan parasites actively secrete proteins at their apical pole as part of the host cell invasion process. The adhesive micronemal proteins are involved in the recognition of host cell receptors. Redistribution of these receptor-ligand complexes toward the posterior pole of the parasites is powered by the actomyosin system of the parasite and is presumed to drive parasite gliding motility and host cell penetration. The microneme protein protease termed MPP1 is responsible for the removal of the C-terminal domain of TgMIC2 and for shedding of the protein during invasion. In this study, we used site-specific mutagenesis to determine the amino acids essential for this cleavage to occur. Mapping of the cleavage site on TgMIC6 established that this processing occurs within the membrane-spanning domain, at a site that is conserved throughout all apicomplexan microneme proteins. The fusion of the surface antigen SAG1 with these transmembrane domains excluded any significant role for the ectodomain in the cleavage site recognition and provided evidence that MPP1 is constitutively active at the surface of the parasites, ready to sustain invasion at any time.
authors.affiliation: Zentrum für Molekulare Biologie, Universität Heidelberg, INF282, D-69120 Heidelberg, Germany.
authors.forename: Corinna
authors.initials: C
authors.lastname: Opitz
authors.forename: Manlio
authors.initials: M
authors.lastname: Di Cristina
authors.forename: Matthias
authors.initials: M
authors.lastname: Reiss
authors.forename: Thomas
authors.initials: T
authors.lastname: Ruppert
authors.forename: Andrea
authors.initials: A
authors.lastname: Crisanti
authors.forename: Dominique
authors.initials: D
authors.lastname: Soldati
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D017124:Conserved Sequence; D003593:Cytoplasm / Q000378:metabolism; D010450:Endopeptidases / Q000378:metabolism; D004789:Enzyme Activation; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010449:Peptide Mapping; D017354:Point Mutation; D011499:Protein Processing, Post-Translational; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D014122:Toxoplasma / Q000235:genetics / Q000378:metabolism*
chemical_list: C408878:MIC2 protein, Toxoplasma gondii; D008565:Membrane Proteins; D015800:Protozoan Proteins; D010450:Endopeptidases