The microneme protein MIC3 of Toxoplasma gondii is a secretory adhesin that binds to both the surface of the host cells and the surface of the parasite

Abstract

SummaryAssay of the adhesion of cultured cells on Toxoplasma gondii tachyzoite protein Western blots identified a major adhesive protein, that migrated at 90 kDa in non-reducing gels. This band comigrated with the previously described microneme protein MIC3. Cellular binding on Western blots was abolished by MIC3-specific monoclonal and polyclonal antibodies. The MIC3 protein affinity purified from tachyzoite lysates bound to the surface of putative host cells. In addition, T. gondii tachyzoites also bound to immobilized MIC3. Immunofluorescence analysis of T. gondii tachyzoite invasion showed that MIC3 was exocytosed and relocalized to the surface of the parasite during invasion. The cDNA encoding MIC3 and the corresponding gene have been cloned, allowing the determination of the complete coding sequence. The MIC3 sequence has been confirmed by affinity purification of the native protein and N-terminal sequencing. The deduced protein sequence contains five partially overlapping EGF-like domains and a chitin binding-like domain, which can be involved in protein±protein or protein± carbohydrate interactions. Taken together, these results suggest that MIC3 is a new microneme adhesin of T. gondii.

Surface Localization of the Yps3p Protein of Histoplasma capsulatum

“…Secretion followed by surface localization has been described for surface entities from a range of microbes, both prokaryotes and eukaryotes (3,4,12). Interestingly, some secreted and reattached proteins, like Blastomyces dermatitidis Bad1p and MIC3 of Toxoplasma gondii, contain EGF-like or chitin binding domains (5,12).…”

A new release on life: emerging concepts in proteolysis and parasite invasion

“…1B) whereas capping is observed for apical invasion proteins. Shaving occurs continuously as the parasite penetrates and is (Dubremetz et al ., 1985;Grimwood and Smith, 1995) Yes (Mineo and Kasper, 1994;He et al ., 2002) Unknown TgMIC1/MIC4/MIC6 (Meissner et al ., 2002b) Yes (Fourmaux et al ., 1996;Brecht et al ., 2001) MPP1 TgMIC2/M2AP Yes (Carruthers et al ., 1999;Harper et al ., 2004) MPP1 Zhou et al ., 2004) TgMIC3/MIC8 (Meissner et al ., 2002b) Yes (Garcia-Reguet et al ., 2000;Meissner et al ., 2002b) MPP1 TgAMA1 (Donahue et al ., 2000;Hehl et al ., 2000) Unknown MPP1 (S. A. Howell, M. J. Blackman and V. B. Carruthers, unpublished) Plasmodium PfTRAP and PbTRAP (Bhanot et al, 2003;Silvie et al ., 2004) Yes (McCormick et al ., 1999;Akhouri et al ., 2004) Serine protease (Silvie et al .. 2004) PfCSP (Stewart and Vanderberg, 1988; Yes (Pinzon-Ortiz et al ., 2001) Unknown PfMSP1/MSP6/MSP7 (Stafford et al ., 1994) Yes (Goel et al ., 2003;Li et al ., 2004) MESH (Howell et al ., 2003) PkAMA1 and PfAMA1 (Deans et al ., 1984;Howell et al ., 2001) Yes (Fraser et al ., 2001) MESH (Howell et al ., 2003) EBL-DBP (Camus and Hadley, 1985;Haynes et al ., 1988) Yes (Camus and Hadley, 1985;Haynes et al ., 1988) Unknown Py235 (Ogun and Holder, 1996) Yes (Ogun and Holde...…”

Apicomplexan rhomboids have a potential role in microneme protein cleavage during host cell invasion

“…Among these microneme proteins, the members of the thrombospondinrelated anonymous protein (TRAP) family, including TgMIC2 in T. gondii, are known to play an essential role in host cell invasion (Sultan et al, 1997;Yuda et al, 1999;Templeton et al, 2000;Huynh et al, 2003). In T. gondii, microneme proteins form complexes, such as TgMIC1/ MIC4/MIC6, TgMIC3/MIC8 and TgMIC2/M2AP Carruthers, 2002;Dowse and Soldati, 2004), which are composed of a transmembrane escorter protein (TgMIC6, TgMIC8 or TgMIC2) essential for the correct targeting of the complex to the micronemes, and soluble proteins, some of which exhibit host cell binding properties (TgMIC1, TgMIC4 and TgMIC3) (Fourmaux et al, 1996;Garcia-Reguet et al, 2000;Brecht et al, 2001). After discharge by the micronemes, TgMIC2 is processed by two proteolytic activities named microneme protein protease 1 and 2 (MPP1 and MPP2, respectively) .…”