Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt
Molecular characterisation of an expressed sequence tag locus of Toxoplasma gondii encoding the micronemal protein MIC2.
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The cloned locus encodes MIC2, a thrombospondin-repeat protein that is localized exclusively to the micronemes by cryo-immunoelectron microscopy.
"exclusively labeled the micronemes of T. gondii by cryo-immunoelectron microscopy."
Toxoplasma MIC2 is a major determinant of invasion and virulence.
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Conditional suppression of MIC2 causes M2AP mistrafficking, defective host-cell attachment and invasion, and loss of helical gliding.
"markedly defective host-cell attachment and invasion, the loss of helical gliding motility"
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The invasion defect of MIC2-depleted parasites is attributed mainly to failed adherence to the target cell.
"Therefore, the entry defect is principally due to an inability to adhere properly to the target cell, although we cannot rule out an additional defect in the penetration step that follows attachment."
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MIC2-deficient parasites were reported to be unable to support lethal murine infection, a virulence claim later contradicted by a clean knockout.
"the inability to support lethal infection in a murine model of acute toxoplasmosis"
Parasites lacking the micronemal protein MIC2 are deficient in surface attachment and host cell egress, but remain virulent in vivo.
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A clean mic2 null mutant is impaired in attachment to host cells and to collagen IV, with reduced motility and invasion traced to defective initiation.
"mic2KO parasites show impaired attachment to host cells and collagen IV."
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MIC2 is an important but non-essential attachment factor; knockout parasites remain lethal in mice and show delayed egress in vitro.
"In summary, we find here that MIC2 acts as important, but not essential, attachment factor"
Structures of the Toxoplasma gliding motility adhesin.
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MIC2 has a VWA domain and six thrombospondin repeats in its ectodomain and connects to the actomyosin system through its cytoplasmic tail; the MIC2-M2AP ectodomain complex is a 1:1 elongated monomer.
"the MIC2-M2AP ectodomain complex is a highly elongated 1:1 monomer with M2AP bound to the TSR6 domain."
The toxoplasma proteins MIC2 and M2AP form a hexameric complex necessary for intracellular survival.
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MIC2 is a type I transmembrane protein bound to M2AP; native gels and gel filtration indicate a roughly 450 kDa complex of three alpha-beta dimers.
"MIC2 and M2AP proteins form stable hexamers consisting of three alphabeta dimers."
Rapid invasion of host cells by Toxoplasma requires secretion of the MIC2-M2AP adhesive protein complex.
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Loss of M2AP traps MIC2 in the endoplasmic reticulum and Golgi, blocks its rapid secretion on contact with a target cell, and impairs host cell entry by over 80 per cent.
"M2AP knockout parasites were also unable to rapidly secrete MIC2, an event that normally accompanies parasite attachment to a target cell."
Aldolase forms a bridge between cell surface adhesins and the actin cytoskeleton in apicomplexan parasites.
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Aldolase binds the C-terminal cytoplasmic domains of TRAP-family adhesins, and the interaction requires a critical tryptophan previously shown to be essential for motility, linking adhesins to actin.
"Our findings reveal a potential role for aldolase in connecting TRAP family adhesins with the cytoskeleton, and provide a model linking adhesion with motility in apicomplexan parasites."
Two separate, conserved acidic amino acid domains within the Toxoplasma gondii MIC2 cytoplasmic tail are required for parasite survival.
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Two acidic clusters in the MIC2 cytoplasmic tail are essential for the parasite; the extreme C-terminal cluster mediates direct aldolase binding.
"two separate acidic residue clusters in the cytoplasmic domain of MIC2 that are essential for parasite survival. One region, located at the extreme C terminus, is required for the direct interaction with aldolase, whereas the second upstream acidic region is not necessary for aldolase binding but is nonetheless essential to parasite survival. Both acidic domains are conserved throughout TRAP orthologs, implicating a central role for these motifs in apicomplexan motility."
Multimerization of the Toxoplasma gondii MIC2 integrin-like A-domain is required for binding to heparin and human cells.
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The recombinant MIC2 A-domain binds heparin specifically and independently of the MIDAS motif, as a high-molecular-weight multimer that mimics native MIC2.
"the MIC2 A-domain binds specifically to heparin, a ubiquitous sulfated proteoglycan found in the extracellular matrix (ECM)"
Transepithelial migration of Toxoplasma gondii involves an interaction of intercellular adhesion molecule 1 (ICAM-1) with the parasite adhesin MIC2.
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Human ICAM-1 immunoprecipitates mature surface MIC2, and soluble ICAM-1 or ICAM-1 antibodies inhibit parasite transmigration across cellular barriers.
"human ICAM-1 immunoprecipitated the mature form of the parasite adhesin MIC2 present on the parasite surface, indicating that this interaction may contribute to cellular migration."
A spatially localized rhomboid protease cleaves cell surface adhesins essential for invasion by Toxoplasma.
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Secreted MIC2 moves from the apical surface to the posterior surface, where it colocalizes with the rhomboid protease TgROM5 and is cleaved.
"Upon microneme secretion, as occurs during invasion, the MIC2 adhesin was secreted to the apical end and translocated to the posterior, the site of cleavage, where it colocalized only with TgROM5."
The Toxoplasma adhesive protein MIC2 is proteolytically processed at multiple sites by two parasite-derived proteases.
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MPP1 removes the MIC2 C-terminal domain on release into the medium, while MPP2 trims the N terminus on the parasite surface.
"the C-terminal domain of MIC2 is removed by a protease, termed MPP1, when MIC2 is released into the culture supernatant."
Proteomic analysis of cleavage events reveals a dynamic two-step mechanism for proteolysis of a key parasite adhesive complex.
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MIC2 is shed from the parasite surface by intramembrane cleavage within its anchoring domain, consistent with a rhomboid-family sheddase.
"MIC2 is shed by intramembrane cleavage within its anchoring domain."
Conditional genome engineering in Toxoplasma gondii uncovers alternative invasion mechanisms.
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A clonal mic2 knockout line can be maintained in culture, showing MIC2 is not essential for parasite survival and that MIC2-independent invasion exists.
"we achieved isolation of a clonal mic2 KO parasite line, demonstrating for the first time that neither myoA nor mic2 are essential for parasite survival."