Affinage · Toxoplasma gondii

MIC2

microneme protein MIC2 · UniProt S8F9G8

Annotated
2026-09-07
79 papers in source corpus 35 papers cited in narrative 37 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

TgMIC2 is a transmembrane microneme adhesin that acts as the earliest effector of the Toxoplasma gondii invasion sequence, coupling host-cell recognition to the parasite's substrate-dependent gliding motility (PMID:9208224, PMID:16933991). It is stored in micronemes and discharged apically at the tight attachment zone upon a Ca2+/PKG-dependent signal, after which the adhesin treadmills posteriorly in an actomyosin-dependent manner and is capped at the posterior pole (PMID:10027960, PMID:15003497). Two conserved cytoplasmic-tail motifs (SYHYY and EIEYE) are necessary and sufficient for microneme targeting (PMID:10982850), and the same tail engages the cytoskeletal machinery: a C-terminal acidic cluster and penultimate tryptophan mediate direct aldolase binding that bridges MIC2 to F-actin, while an additional upstream acidic cluster and the glideosome-associated connector GAC provide further links to the actomyosin motor (PMID:16923803, PMID:19380114, PMID:27978434). On its extracellular face, MIC2 recognizes host ligands through its integrin-like von Willebrand A domain (which binds sulfated proteoglycan/heparin) and its thrombospondin type-1 repeats, and its mature surface form directly engages host ICAM-1 to support transepithelial migration (PMID:15003840, PMID:15760456, PMID:24639528). MIC2 forms a stable ~450 kDa heterohexameric complex of three αβ dimers with M2AP, which binds the TSR6 domain; this interaction is mutually required for correct microneme trafficking of both partners and for efficient invasion (PMID:11532123, PMID:12727875, PMID:14670959, PMID:24639528, PMID:25411252, PMID:37652989). The TSR domains are further stabilized by O-fucosylation and C-mannosylation, modifications required for efficient MIC2 processing, trafficking, and function (PMID:30538131, PMID:29432542, PMID:31862733). Cell entry requires sequential proteolysis: TgSUB1 trims the surface ectodomain, and the rhomboid intramembrane protease ROM4 sheds MIC2 from the membrane, because shedding rather than adhesion per se is the step that permits productive invasion (PMID:12471033, PMID:20421941, PMID:20678172, PMID:25336455). Functionally, MIC2 mediates a circumferential attachment zone that generates periodic inward-directed traction forces to constrain directional gliding, and its loss impairs surface attachment and delays egress while leaving core gliding and invasion machinery partly operational (PMID:24692639, PMID:28630943, PMID:36519527).

Mechanistic history

Synthesis pass · year-by-year structured walk · 21 steps
  1. 1997 High

    Establishing when MIC2 acts in invasion showed that its micronemal release is the first molecular event of host-cell entry, placing MIC2 upstream of rhoptry and dense-granule discharge.

    Evidence Immunofluorescence, immunoelectron microscopy and quantitative immunoassay during live invasion

    PMID:9208224

    Open questions at the time
    • Did not identify the trigger for release
    • Did not define the host receptor bound at the attachment zone
  2. 1999 High

    The signal controlling MIC2 discharge was unknown; pharmacological manipulation showed intracellular Ca2+ triggers apical release and actomyosin-dependent posterior capping, linking secretion to motility.

    Evidence Ca2+ ionophore and BAPTA chelation with immunofluorescence and cytoskeletal inhibitor assays

    PMID:10027960

    Open questions at the time
    • Downstream kinase effectors not yet defined
    • Molecular link between MIC2 and the actomyosin motor not identified
  3. 1999 Medium

    It was unclear whether proteolysis affected adhesion; binding assays showed only the full-length surface form of MIC2 binds host cells, establishing that shedding inactivates the adhesin, and that a staurosporine-sensitive kinase governs discharge.

    Evidence Host-cell binding assays comparing full-length vs shed MIC2, and staurosporine inhibition of secretion/invasion

    PMID:11207555

    Open questions at the time
    • Kinase identity not established
    • Single-lab binding comparison
  4. 2000 High

    The targeting signal and processing events of MIC2 were undefined; mutagenesis identified two cytoplasmic-tail motifs sufficient for micronemal delivery and mapped distinct N- and C-terminal cleavages by parasite proteases MPP1/MPP2.

    Evidence Site-directed mutagenesis, SAG1 chimera targeting, and protease inhibitor domain-mapping assays

    PMID:10982850 PMID:10799515

    Open questions at the time
    • Protease identities (MPP1/MPP2) not yet molecularly resolved
    • Trafficking machinery reading the tail motifs unknown
  5. 2001 High

    The composition of the MIC2 secretory unit was unknown; co-IP and pulse-chase showed M2AP associates with MIC2 rapidly after synthesis and remains bound through the micronemes, surface and shed forms.

    Evidence Reciprocal co-immunoprecipitation, pulse-chase labeling and orthogonal localization

    PMID:11532123

    Open questions at the time
    • Functional consequence of the association not yet tested
    • Stoichiometry of the complex not defined
  6. 2002 High

    Whether intramembrane cleavage and C-terminal shedding matter for entry was open; mapping of an intramembrane IAGG cleavage site and mutants blocking C-terminal cleavage showed shedding is required for invasion despite increased adhesion.

    Evidence Cleavage-site mutagenesis, SAG1-TMD chimeras, and invasion/adhesion assays

    PMID:11927542 PMID:12471033

    Open questions at the time
    • Rhomboid responsible for intramembrane cleavage not yet identified
    • Mechanistic reason adhesion must be released not defined
  7. 2003 High

    The functional role of the MIC2-M2AP association was untested; knockout and biochemical sizing showed the two proteins are mutually dependent for correct trafficking and form a ~450 kDa hexamer of three αβ dimers required for efficient invasion.

    Evidence M2AP gene knockout with trafficking/invasion assays, and native gel/gel filtration sizing

    PMID:12727875 PMID:14670959

    Open questions at the time
    • Structural basis of the interaction not resolved
    • Cytoplasmic C-domain shown dispensable for complex, its function unclear
  8. 2004 High

    How MIC2 recognizes host surfaces and couples to the motor was unclear; the VWA A-domain was shown to bind heparin MIDAS-independently, aldolase was shown to bridge the tail to F-actin, and PKG was placed downstream of Ca2+ controlling secretion.

    Evidence Recombinant A-domain heparin-binding assays, aldolase-tail binding with mutagenesis, and PKG pharmacology with transgenic PKG-refractory strains

    PMID:15003840 PMID:16923803 PMID:15003497

    Open questions at the time
    • In vivo relevance of heparin binding not established
    • Nature of a second tail-cytoskeleton link not defined
  9. 2005 High

    The identity of the shedding protease and a host receptor were open; TgROM5 was proposed as the posterior MIC-cleaving rhomboid, and host ICAM-1 was shown to bind mature surface MIC2 and support transmigration.

    Evidence Rhomboid cloning/cleavage assays with GFP localization, and ICAM-1 immunoprecipitation with transmigration inhibition

    PMID:15753289 PMID:15760456

    Open questions at the time
    • ROM5 assignment later revised in favor of ROM4
    • ICAM-1 co-IP from single lab without structural mapping
  10. 2006 High

    The in vivo importance and tail requirements of MIC2 were untested; conditional MIC2 suppression established the complex as a virulence determinant, tail mutagenesis defined two essential acidic clusters, and M2AP propeptide mutants revealed a trafficking checkpoint.

    Evidence Conditional MIC2 knockout with in vivo virulence, tail alanine-scanning with aldolase binding, and M2AP propeptide deletion/cleavage mutants

    PMID:16933991 PMID:16923803 PMID:16914527

    Open questions at the time
    • Identity of the second tail-binding cytoskeletal factor unknown
    • Compartment gating the propeptide-dependent exit not fully defined
  11. 2009 High

    Whether aldolase acts as a moonlighting motor bridge versus a glycolytic enzyme was ambiguous; structure-guided TgALD1 mutants separated MIC2-tail binding (needed for invasion) from glycolysis (needed for motility).

    Evidence Structure-guided TgALD1 mutagenesis with conditional-knockout complementation, in vitro tail binding, and motility/invasion assays

    PMID:19380114

    Open questions at the time
    • How force is transmitted through aldolase to actin not directly measured
  12. 2010 High

    The proteases executing MIC2 processing were reassessed; conditional knockout identified ROM4 as the primary intramembrane sheddase and gene deletion showed TgSUB1 performs surface trimming, both required for efficient attachment and invasion.

    Evidence Conditional ROM4 knockout and TgSUB1 gene deletion with shedding, motility, invasion and virulence assays

    PMID:20421941 PMID:20678172

    Open questions at the time
    • Whether ROM4 is essential during actual cell entry not resolved
    • Order of SUB1 vs ROM4 action not fully sequenced
  13. 2014 High

    The rhomboid assignment and complex architecture were clarified; systematic ROM knockouts confirmed ROM4 (not ROM5) as the main sheddase and revealed ROM-independent entry mechanisms, while crystallography defined the elongated MIC2-M2AP ectodomain, a closed VWA domain, C-mannosylation, and 1:1 M2AP binding to TSR6.

    Evidence Single/double/triple rhomboid knockouts with motility/invasion/moving-junction analysis, and X-ray crystallography with SAXS; microfluidic shear-adhesion assay

    PMID:25336455 PMID:24639528 PMID:24692639

    Open questions at the time
    • Nature of ROM-independent adhesin removal during entry unknown
    • Activation mechanism of the VWA domain inferred but not captured in an open state
  14. 2015 High

    The relative rhomboid contributions were confirmed and refined; independent knockouts established ROM4 as the primary MPP1 activity while ROM5 was dispensable for MIC2 shedding and invasion.

    Evidence Cre-recombinase and CRISPR-Cas9 knockouts of ROM4 and ROM5 with cleavage, motility and invasion assays

    PMID:25846828

    Open questions at the time
    • Residual shedding pathway during entry still unaccounted for
  15. 2014 High

    The structural basis of M2AP recognition was defined; the NMR structure of M2AP revealed a galectin fold whose hydrophobic face binds MIC2 TSR6.

    Evidence NMR structure determination with immunoprecipitation and domain mapping

    PMID:25411252

    Open questions at the time
    • Atomic detail of the TSR6 interface awaited co-crystal structure
  16. 2016 High

    A second cytoskeletal connector was sought; GAC was shown to directly bind F-actin and MIC2, and to bind phosphatidic acid via its PH domain, providing the additional motor link implied by the earlier upstream acidic-cluster requirement.

    Evidence Reciprocal Co-IP, in vitro F-actin binding, conditional GAC knockdown and TgAKMT perturbation

    PMID:27978434

    Open questions at the time
    • Whether GAC and aldolase act on the same or distinct MIC2 tail motifs not fully resolved
  17. 2017 High

    The strict essentiality of MIC2 was re-examined; a clean null mutant showed MIC2 is deficient in attachment but retains near-normal gliding speed and invasion once initiated, delays egress, and is only mildly attenuated in vivo, refining MIC2 to an attachment-focusing rather than obligatory motility factor.

    Evidence mic2 null mutant with 3D motility, shear attachment, invasion and murine infection assays

    PMID:28630943

    Open questions at the time
    • Molecular basis of functional redundancy with other adhesins not defined
    • Reconciliation with earlier conditional-knockout severe phenotype not fully explained
  18. 2018 High

    The role of TSR glycosylation was tested; MS mapping plus knockouts showed O-fucosylation (POFUT2/NST2) and C-mannosylation (DPY19) modify MIC2 TSRs, with O-fucosylation loss reducing MIC2 levels and invasion, though a second study found only modest impact of POFUT2 loss.

    Evidence MS/MS glycan mapping, Δpofut2/Δnst2 knockouts, DPY19 in vitro C-mannosyltransferase assays, and functional phenotyping

    PMID:30538131 PMID:30514763 PMID:29432542

    Open questions at the time
    • Conflicting POFUT2 functional phenotypes between labs
    • Whether glycans act on folding, stability or trafficking specifically not resolved
  19. 2019 High

    The cellular impact of C-mannosylation and micronemal dynamics were addressed; dpy19 deletion reduced MIC2 and impaired adhesion/invasion/egress beyond MIC2 alone, and imaging showed MIC2-marked micronemes are recycled from mother to daughter via an F-actin network.

    Evidence Δdpy19 knockout with functional/virulence assays, and super-resolution live imaging with F-actin perturbation

    PMID:31862733 PMID:31519913

    Open questions at the time
    • Additional C-mannosylated invasion proteins not enumerated
    • Machinery driving F-actin-dependent microneme recycling not defined
  20. 2022 High

    The biophysical role of MIC2 in directing motility was quantified; 3D traction force mapping showed MIC2 is required to form an annular attachment zone generating periodic inward forces that constrain directional gliding.

    Evidence 3D traction force microscopy with TgMIC2-null parasites and live imaging

    PMID:36519527

    Open questions at the time
    • How MIC2 organizes the circular zone molecularly not defined
  21. 2023 High

    The atomic basis of MIC2-M2AP assembly was resolved; co-crystal structures showed TSR6 hotspot His-620 and a Y602 conformational flip stabilize M2AP binding, an interaction required for complex maturation and surface transport.

    Evidence X-ray crystallography of M2AP alone and M2AP-TSR6 with H620A/Y602 mutagenesis and functional validation

    PMID:37652989

    Open questions at the time
    • Structure of the full hexamer not determined
    • Link between TSR6 binding and downstream trafficking machinery not defined

Open questions

Synthesis pass · forward-looking unresolved questions
  • The ROM-independent mechanism that removes MIC2 during actual cell entry, and the identity of the second (non-aldolase) cytoskeletal factor binding the upstream tail cluster, remain unresolved.
  • Adhesin disengagement pathway during entry in the absence of rhomboids unknown
  • Full molecular inventory of the MIC2 tail-cytoskeleton interface incomplete

Mechanism profile

Synthesis pass · controlled-vocabulary classification
Partners
ALDOLASE (TGALD1; MIC2 CYTOPLASMIC-TAIL-TO-F-ACTIN BRIDGE)DPY19 (C-MANNOSYLTRANSFERASE OF TSR DOMAINS)GAC / GLIDEOSOME-ASSOCIATED CONNECTOR (F-ACTIN AND MIC2 BINDING)HEPARIN / SULFATED PROTEOGLYCAN (VWA A-DOMAIN LIGAND)HOST ICAM-1 (HOST RECEPTOR FOR MATURE SURFACE MIC2)M2AP (MICRONEME PROTEIN, TSR6-BINDING PARTNER)PKG (CGMP-DEPENDENT KINASE REGULATING SECRETION)POFUT2/NST2 (O-FUCOSYLATION OF TSR DOMAINS)ROM4 (RHOMBOID INTRAMEMBRANE SHEDDASE)TGSUB1 (SUBTILISIN SURFACE-TRIMMING PROTEASE)
Complex memberships
MIC2-M2AP heterohexamer (~450 kDa, three αβ dimers; M2AP bound at TSR6)

Evidence

Reading pass · 37 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1997 MIC2 is sequentially released from micronemes upon host cell binding at the tight attachment zone between the parasite and host cell, prior to rhoptry and dense granule discharge, establishing MIC2 secretion as the earliest step in the invasion sequence. Immunofluorescence, immunoelectron microscopy, quantitative immunoassay during live invasion European journal of cell biology High 9208224
1999 Microneme secretion of MIC2 is regulated by parasite intracellular free Ca2+: Ca2+ ionophores trigger apical release and subsequent treadmilling/capping of MIC2 to the posterior end, while chelation of intracellular Ca2+ prevents release. This redistribution depends on the actin-myosin cytoskeleton. Ca2+ ionophore stimulation, intracellular Ca2+ chelation (BAPTA), thapsigargin/NH4Cl treatment, immunofluorescence, cytoskeletal inhibitor assays Molecular microbiology High 10027960
1999 The full-length, cell-surface form of MIC2 (but not the proteolytically shed soluble form) binds specifically to host cells, indicating that proteolytic processing inactivates the adhesive function of MIC2. Host cell binding assay comparing full-length vs. proteolytically modified secreted MIC2 Cellular microbiology Medium 11207555
1999 A staurosporine-sensitive kinase activity regulates microneme discharge (including MIC2 release) and is required for parasite invasion of host cells. Staurosporine treatment, microneme secretion assay, invasion assay Cellular microbiology Medium 11207555
2000 MIC2 is proteolytically processed at multiple sites by two parasite-derived proteases: MPP1 removes the C-terminal domain upon release into the culture supernatant, while MPP2 (a serine/cysteine protease-sensitive activity) trims the N-terminus prior to release. Biochemical protease inhibitor panel, protein secretion assays, N- and C-terminal domain mapping The Journal of biological chemistry High 10799515
2000 Two conserved cytoplasmic tail motifs (SYHYY and EIEYE) of MIC2 are both necessary and sufficient for targeting proteins to micronemes; an artificial tail containing only these two motifs in preserved spacing redirects the surface protein SAG1 to micronemes. Site-directed mutagenesis, chimeric protein (SAG1 fusion) expression, immunofluorescence and immunoelectron microscopy Molecular and cellular biology High 10982850
2001 TgM2AP physically associates with TgMIC2, forming a stable complex within 15 min of synthesis. M2AP remains associated with MIC2 in the micronemes, on the parasite surface during invasion, and in the culture medium after shedding. M2AP propeptide is removed in the Golgi, and M2AP is further processed on the parasite surface after microneme discharge. Co-immunoprecipitation, pulse-chase labeling, immunofluorescence, immunoelectron microscopy Molecular microbiology High 11532123
2002 MPP1 cleaves MIC2 within its membrane-spanning domain (intramembrane proteolysis); the cleavage site mapped to a conserved motif (IAGG) in the transmembrane domain of TgMIC2 and TgMIC6, and MPP1 is constitutively active at the parasite surface. Fusion of the SAG1 ectodomain with MIC2/MIC6 transmembrane domains showed the ectodomain is not required for cleavage recognition. Site-specific mutagenesis, chimeric SAG1-MIC2/MIC6 transmembrane domain fusions, protein secretion and surface expression assays The EMBO journal High 11927542
2002 C-terminal proteolytic processing of MIC2 (removal of the C-terminal domain upstream of the transmembrane domain) is essential for invasion: mutations preventing cleavage caused stable surface expression of MIC2 and increased host cell adhesion but severely impaired invasion, demonstrating that shedding is required for cell entry. Site-directed mutagenesis of extracellular domain, invasion and adhesion assays, surface expression quantification The Journal of biological chemistry High 12471033
2003 Disruption of M2AP (MIC2-associated protein) leads to >80% impairment in host cell entry because MIC2 accumulates in the ER/Golgi and cannot be rapidly secreted upon host cell attachment, demonstrating that the MIC2-M2AP complex is required for efficient invasion. Gene knockout, immunofluorescence, invasion assay, secretion assay The EMBO journal High 12727875
2003 MIC2 and M2AP form a stable hexameric complex of ~450 kDa consisting of three αβ dimers, as determined by native blue gels and gel filtration of parasite lysates. The cytoplasmic C-domain of MIC2 is not required for MIC2-M2AP complex formation or microneme trafficking. Native blue gel electrophoresis, gel filtration, transgenic expression of C-domain deletion mutants The Journal of biological chemistry High 14670959
2004 The integrin-like A-domain of MIC2 binds specifically to heparin (a sulfated proteoglycan of the extracellular matrix) as a high-molecular-weight multimeric species; this binding does not depend on the MIDAS divalent cation-binding motif. Recombinant A-domain fusion protein binding assays, heparin binding assay, size analysis of binding species Molecular and biochemical parasitology Medium 15003840
2004 Eimeria tenella MIC1 (the ortholog of TgMIC2) can substitute for TgMIC2 to enable the first TgMIC2 knockout clone; in TgMIC2 KO parasites, M2AP is misprocessed and mistrafficked to the parasitophorous vacuole rather than the micronemes, demonstrating mutual dependence for correct trafficking. Trans-genera complementation, gene knockout, immunofluorescence, Western blot Cellular microbiology High 15236644
2004 Aldolase bridges MIC2 to filamentous actin via the MIC2 cytoplasmic tail, coupling the adhesin to the actomyosin motor. The penultimate tryptophan and flanking acidic residues in the MIC2 cytoplasmic tail are required for aldolase binding. In vitro binding assay (aldolase-MIC2 tail interaction), homology modeling, mutagenesis Cell host & microbe (referenced in Starnes 2006); original aldolase-MIC2 interaction established in prior work cited by Starnes GL et al. Medium 16923803
2004 cGMP-dependent protein kinase (PKG) acts downstream of calcium-dependent events to regulate MIC2 secretion, gliding motility, host cell attachment, and invasion; PKG inhibition blocks MIC2 adhesin secretion even when calcium is elevated by ionophores, and PKG-refractory transgenic strains show reduced sensitivity to this inhibition. Pharmacological inhibition (compound 1/trisubstituted pyrrole), transgenic PKG mutant strains, immunofluorescence, invasion/motility assays International journal for parasitology High 15003497
2005 TgROM5, a rhomboid intramembrane serine protease localized predominantly to the posterior of the parasite, colocalizes with MIC2 at the posterior cleavage site during invasion and is the only T. gondii rhomboid able to cleave MIC adhesins in a cell-based assay, identifying it as the likely MPP1 protease responsible for MIC2 shedding. Cloning and expression of five TgROMs, GFP localization, cell-based cleavage assay Proceedings of the National Academy of Sciences of the United States of America High 15753289
2005 Human ICAM-1 immunoprecipitates the mature surface form of MIC2, indicating a direct interaction between parasite MIC2 and host ICAM-1 that contributes to transepithelial migration; soluble ICAM-1 and ICAM-1 antibodies inhibit parasite transmigration across cellular barriers. Immunoprecipitation of parasite surface MIC2 with soluble human ICAM-1, transmigration inhibition assay Cellular microbiology Medium 15760456
2006 Conditional suppression of MIC2 causes mistrafficking of M2AP, markedly defective host-cell attachment and invasion, loss of helical gliding motility, and inability to establish lethal infection in mice, establishing the MIC2-M2AP complex as a major virulence determinant. Conditional (anhydrotetracycline-regulatable) MIC2 expression system, endogenous mic2 knockout, invasion/motility/attachment assays, murine infection model PLoS pathogens High 16933991
2006 Two separate acidic residue clusters in the MIC2 cytoplasmic tail are essential for parasite survival: the C-terminal cluster is required for direct aldolase binding, while an upstream acidic cluster is essential but does not mediate aldolase binding, implying a second critical cytoskeletal interaction. Alanine point mutagenesis, in vitro aldolase binding assay, transgenic complementation, parasite survival assay The Journal of biological chemistry High 16923803
2006 The M2AP propeptide is required for the MIC2-M2AP complex to exit an early endosomal compartment; deletion of the propeptide traps the complex in the early secretory pathway, while propeptide cleavage-resistant mutants reach micronemes but cannot rapidly mobilize to the parasite surface. Both defects impair invasion and reduce virulence. Propeptide deletion and cleavage-site mutagenesis, immunofluorescence/immunoelectron microscopy, invasion assay, in vivo virulence Molecular biology of the cell High 16914527
2009 Aldolase is essential for efficient host cell invasion through its ability to bridge MIC2 cytoplasmic tail to actin filaments; mutations in TgALD1 that selectively abolish MIC2 tail binding (without affecting glycolytic activity) decrease invasion efficiency without affecting motility, while mutations affecting glycolysis reduce motility. Structure-guided mutagenesis of TgALD1, conditional knockout complementation, in vitro MIC2 tail binding assay, motility and invasion assays Cell host & microbe High 19380114
2010 TgROM4 is the primary rhomboid protease responsible for shedding of surface adhesins including MIC2; conditional knockout of TgROM4 decreases MIC2 release into supernatant, increases surface MIC2 accumulation, disrupts normal gliding (causing twirling), and severely impairs invasion despite enhanced host cell binding. Conditional knockout, surface adhesin shedding assay, supernatant MIC2 quantification, gliding motility and invasion assays PLoS pathogens High 20421941
2010 TgSUB1 (a GPI-anchored microneme subtilisin protease) is responsible for proteolytic trimming of MIC2 (and MIC4, M2AP) on the parasite surface after secretion; loss of TgSUB1 abolishes this trimming, decreases cell attachment and gliding efficiency, reduces invasion rates, and lowers virulence in mice. Gene deletion, MIC2 processing assay, attachment and invasion assays, in vivo virulence Cellular microbiology High 20678172
2014 ROM4 (not ROM5) is the primary rhomboid protease for MIC2 cleavage in T. gondii tachyzoites; ROM4 single knockout blocks MIC2 shedding and causes surface accumulation, nonproductive attachment, altered gliding, impaired moving junction formation, and reduced invasion. Triple knockout (ROM1/ROM4/ROM5) parasites are viable, demonstrating ROM-independent mechanisms for adhesin removal during actual cell entry. Single, double, and triple rhomboid knockouts, MIC2 shedding assay, motility and invasion assays, moving junction analysis mBio High 25336455
2014 Crystal structures of N-terminal proMIC2 and MIC2 fragments reveal a closed conformation of the von Willebrand A (VWA) domain, its association with the TSR1 domain, a proline-rich pigtail loop in TSR1 overlapping the VWA domain, α-C-linked mannose on Trp-276, and a mobile α5-helix with a disordered region replacing the α6-helix in a putative activation mechanism. M2AP binds as a 1:1 monomer to TSR6 in a highly elongated complex. X-ray crystallography of MIC2-M2AP ectodomain and sub-fragments, small-angle X-ray scattering Proceedings of the National Academy of Sciences of the United States of America High 24639528
2014 MIC2 contributes to initial adhesion of T. gondii tachyzoites to vascular endothelium under shear stress but is not required for adhesion strengthening, as shown by comparison of wild-type and MIC2-deficient parasites in a microfluidic system. Microfluidics, time-lapse fluorescence microscopy, MIC2-deficient parasite comparison under shear stress mBio Medium 24692639
2014 The NMR solution structure of M2AP globular domain reveals a modified galectin fold similar to MIC1 C-terminal domain; hydrophobic residues on one face of this galectin fold mediate binding to the sixth TSR domain of MIC2 (TSR6), as validated by NMR and immunoprecipitation. NMR structure determination, immunoprecipitation, domain mapping The Journal of biological chemistry High 25411252
2015 ROM4 is the primary contributor to MPP1 activity (intramembrane cleavage of MIC2 and MIC6), while ROM5 is dispensable for MIC2 shedding; ROM4 knockout parasites engage predominantly in twirling motility and show enhanced attachment but impaired invasion, whereas ROM5 knockout does not alter MIC2 shedding or invasion. Cre-recombinase and CRISPR-Cas9 knockouts of ROM4 and ROM5, MIC2/MIC6 cleavage assay, motility and invasion assays Molecular microbiology High 25846828
2016 Glideosome-associated connector (GAC), an armadillo/PH domain protein, directly binds filamentous actin and specifically associates with TgMIC2, connecting the MIC2 adhesin to the actomyosin system to mediate gliding motility, invasion, and egress. Apical localization of TgGAC depends on TgAKMT (apical lysine methyltransferase). GAC's PH domain also binds phosphatidic acid, a lipid linked to microneme exocytosis. Co-immunoprecipitation (TgGAC-TgMIC2), F-actin binding assay, localization by IFA, conditional knockdown of TgGAC, TgAKMT perturbation Cell host & microbe High 27978434
2017 MIC2 null mutant parasites are deficient in surface attachment but retain near-normal gliding speed and host cell invasion once initiated; deletion of mic2 causes delayed host cell egress in vitro, and causes only mild attenuation of virulence in vivo (slight delay, not prevention of lethal disease). Gene deletion (null mutant), 3D motility analysis, attachment under shear stress, invasion assay, in vivo murine infection Wellcome open research High 28630943
2018 MIC2 TSR domains are modified by O-fucosylation (GlcFuc disaccharide added by POFUT2/NST2) and C-mannosylation; loss of POFUT2 or NST2 markedly reduces cellular MIC2 levels, causes partial mislocalization from micronemes, and impairs host cell attachment and invasion comparable to the mic2 knockout, demonstrating that O-fucosylation is required for efficient MIC2 processing and function. Mass spectrometry glycan mapping, gene knockout (Δpofut2, Δnst2), immunofluorescence, invasion and attachment assays, anti-GlcFuc antibody detection The Journal of biological chemistry High 30538131
2018 TgPOFUT2 O-glycosylates MIC2 TSR domains (≥3 O-linked sites with >95% occupancy confirmed by MS/MS), but loss of TgPOFUT2 has only a modest impact on MIC2 levels and parasite invasion in this study, suggesting the O-glycan may be dispensable in T. gondii tachyzoites (in contrast to findings in another study). Mass spectrometry (MS/MS), enzymatic digestion, TgPOFUT2 gene knockout, plaque and invasion assay The Journal of biological chemistry Medium 30514763
2018 C-mannosylation of MIC2 TSR domains is catalyzed by apicomplexan DPY19 homologs; T. gondii and P. falciparum DPY19 enzymes modify WXXWXXC motifs in TRAP/MIC2 TSR domains when expressed in mammalian cells deficient in C-mannosylation, and can transfer mannose to WXXWXXC but not WXXW peptides in vitro. Expression of apicomplexan DPY19 in C-mannosylation-deficient mammalian cells, in vitro C-mannosyltransferase assay with peptide substrates Glycobiology High 29432542
2019 Deletion of dpy19 (C-mannosyltransferase) reduces MIC2 protein levels and impairs parasite adhesion, motility, host cell invasion, and egress; attenuation of virulence in Δdpy19 parasites cannot be fully explained by reduced MIC2 alone, suggesting C-mannosylation stabilizes additional invasion-related proteins. Gene knockout (Δdpy19), immunofluorescence, motility and invasion assays, in vivo virulence, Western blot for MIC2 levels The Journal of biological chemistry High 31862733
2019 During intracellular replication, micronemes (tracked by MIC2 labeling) are recycled from mother to daughter parasites via a highly dynamic F-actin network; this recycling is F-actin dependent, while de novo microneme synthesis is F-actin independent. The residual body acts as a storage and sorting station for micronemal vesicles. Dual labeling, super-resolution microscopy, F-actin perturbation, live imaging Nature communications High 31519913
2022 3D traction force mapping shows that a moving T. gondii parasite generates periodic, inward-directed forces at a fixed circular attachment zone on the extracellular matrix; parasites lacking TgMIC2 fail to generate these inward-directed forces and lack the constriction in the plasma membrane at this zone, and display less straight trajectories, demonstrating that TgMIC2 mediates the annular attachment zone that constrains directional motility. 3D traction force microscopy, TgMIC2-null parasites, live imaging eLife High 36519527
2023 Crystal structures of M2AP alone and in complex with MIC2 TSR6 reveal that the non-layered side of TSR6, centered on hotspot residue His-620, binds M2AP; TSR6 residue Y602 shifts from a layered to a flipped-out state upon M2AP binding, stabilizing the complex. This interaction is required for MIC2-M2AP complex maturation and transport to the parasite surface. X-ray crystallography of M2AP alone and M2AP-TSR6 complex, mutagenesis (H620A and Y602 mutants), functional validation Communications biology High 37652989

Source papers

Stage 0 corpus · 79 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
1997 Sequential protein secretion from three distinct organelles of Toxoplasma gondii accompanies invasion of human fibroblasts. European journal of cell biology 565 9208224
1999 Mobilization of intracellular calcium stimulates microneme discharge in Toxoplasma gondii. Molecular microbiology 296 10027960
1999 Secretion of micronemal proteins is associated with toxoplasma invasion of host cells. Cellular microbiology 282 11207555
2003 Rapid invasion of host cells by Toxoplasma requires secretion of the MIC2-M2AP adhesive protein complex. The EMBO journal 206 12727875
2001 Microneme proteins: structural and functional requirements to promote adhesion and invasion by the apicomplexan parasite Toxoplasma gondii. International journal for parasitology 178 11566297
2006 Toxoplasma MIC2 is a major determinant of invasion and virulence. PLoS pathogens 171 16933991
2005 A spatially localized rhomboid protease cleaves cell surface adhesins essential for invasion by Toxoplasma. Proceedings of the National Academy of Sciences of the United States of America 171 15753289
2000 The Toxoplasma adhesive protein MIC2 is proteolytically processed at multiple sites by two parasite-derived proteases. The Journal of biological chemistry 155 10799515
1997 Molecular characterisation of an expressed sequence tag locus of Toxoplasma gondii encoding the micronemal protein MIC2. Molecular and biochemical parasitology 153 9084040
2005 Transepithelial migration of Toxoplasma gondii involves an interaction of intercellular adhesion molecule 1 (ICAM-1) with the parasite adhesin MIC2. Cellular microbiology 149 15760456
2002 A family of transmembrane microneme proteins of Toxoplasma gondii contain EGF-like domains and function as escorters. Journal of cell science 135 11861763
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