Affinage · Toxoplasma gondii

AKMT

apical complex lysine methyltransferase · UniProt A0A125YQK8

Annotated
2026-09-08
5 papers in source corpus 4 papers cited in narrative 8 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

AKMT (Apical complex lysine methyltransferase) is a parasite-specific SET-domain protein lysine methyltransferase that activates the motile phase of the Toxoplasma gondii lytic cycle, with its depletion severely impairing motility activation, host-cell invasion, and egress (PMID:21909263). Its regulatory output is timed by subcellular relocation: AKMT normally resides at the apical complex but rapidly redistributes to the parasite body upon egress-stimulating Ca²⁺ elevation, coupling its activity to the signal that triggers motility (PMID:21909263). Full function requires more than the catalytic SET domain, which alone is a poor enzyme unable to complement in vivo—both N- and C-terminal domains contribute to activity, localization, and function (PMID:23685344)—and depends on homodimerization through a unique C-terminal TPR-like domain and zinc-binding motif; disrupting this interface abolishes both enzymatic activity and egress (PMID:30148980). Downstream, AKMT-mediated methylation governs a conoid-nucleated flux of F-actin initiated by the formin FRM1, acting alongside PKG and CDPK1 phosphorylation to control actin polymerization dynamics that drive motility, invasion, and egress (PMID:30753127). The physiological methylation substrate(s) of AKMT have not been identified in the available corpus.

Mechanistic history

Synthesis pass · year-by-year structured walk · 6 steps
  1. 2011 High

    Established AKMT as a lysine methyltransferase essential for switching on parasite motility, defining its place at the top of the lytic-cycle motility program rather than as a general chromatin enzyme.

    Evidence Conditional knockdown with motility, invasion, and egress phenotypic readouts in T. gondii

    PMID:21909263

    Open questions at the time
    • No methylation substrate identified
    • Molecular link between methylation and the motility machinery not defined
  2. 2011 High

    Showed that AKMT function is regulated spatially and temporally—its Ca²⁺-triggered redistribution from apical complex to parasite body ties enzyme deployment to the egress signal.

    Evidence Live fluorescence imaging of AKMT localization following Ca²⁺-elevating stimuli

    PMID:21909263

    Open questions at the time
    • Mechanism sensing Ca²⁺ and driving relocation unknown
    • Whether relocation changes catalytic activity or only substrate access not resolved
  3. 2013 High

    Demonstrated that the SET domain alone is insufficient and that flanking N- and C-terminal domains are required for activity and in vivo complementation, reframing AKMT as a multidomain enzyme.

    Evidence Truncation mutagenesis with in vitro enzymatic assays and in vivo complementation in T. gondii

    PMID:23685344

    Open questions at the time
    • Specific molecular contribution of each domain not resolved
    • Substrate binding determinants not mapped
  4. 2013 Medium

    Placed AKMT phylogenetically as the founding member of a new parasite-specific KMT subfamily, indicating a distinct evolutionary origin from host enzymes.

    Evidence Phylogenetic analysis of AKMT and related KMT sequences

    PMID:23685344

    Open questions at the time
    • Computational only; no experimental validation of the classification
    • Functional conservation across the subfamily untested
  5. 2018 High

    Solved the C-terminal crystal structure and revealed dimerization via a unique TPR-like/zinc-binding interface, explaining the multidomain activity requirement and defining a new KMT subclass related to SMYD enzymes.

    Evidence X-ray crystallography of AKMT aa289-709 at 2.1 Å with comparative structural analysis; structure-guided mutagenesis with in vitro enzyme and in vivo egress assays

    PMID:30148980

    Open questions at the time
    • Structure of full-length protein including N-terminal region not determined
    • No substrate-bound structure to define catalytic mechanism
  6. 2019 High

    Positioned AKMT in a defined motility-activation pathway, showing its methylation controls FRM1-nucleated conoidal F-actin flux in parallel with PKG and CDPK1 phosphorylation.

    Evidence Genetic epistasis with F-actin chromobodies and disruption of FRM1, myosin A, myosin H, PKG, CDPK1, and AKMT in T. gondii

    PMID:30753127

    Open questions at the time
    • Direct methylation target linking AKMT to F-actin flux not identified
    • How AKMT integrates with PKG/CDPK1 signaling mechanistically unresolved

Open questions

Synthesis pass · forward-looking unresolved questions
  • The physiological methylation substrate(s) of AKMT and the direct biochemical link between methylation and F-actin dynamics remain to be identified.
  • No validated in vivo methylation substrate
  • Mechanistic connection from methyl-mark to actin polymerization not established

Mechanism profile

Synthesis pass · controlled-vocabulary classification
Partners
CDPK1 (PARALLEL MOTILITY-ACTIVATION PATHWAY)FRM1 (FUNCTIONAL/EPISTATIC, F-ACTIN NUCLEATION)PKG (PARALLEL MOTILITY-ACTIVATION PATHWAY)
Complex memberships
AKMT homodimer (via C-terminal TPR-like/zinc-binding interface)

Evidence

Reading pass · 8 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2011 AKMT (Apical complex lysine (K) methyltransferase) is a protein lysine methyltransferase that regulates motility activation in Toxoplasma gondii; its depletion greatly inhibits activation of motility, compromises parasite invasion and egress, and severely impairs the lytic cycle. Genetic depletion (conditional knockdown) with motility, invasion, and egress phenotypic readouts PLoS pathogens High 21909263
2011 AKMT rapidly redistributes from the apical complex to the parasite body in response to egress-stimulating signals that increase cytoplasmic [Ca²⁺], indicating that its regulation of motility involves precise temporal control of its subcellular localization. Live fluorescence imaging of AKMT localization following Ca²⁺-elevating stimuli PLoS pathogens High 21909263
2013 The predicted enzymatic (SET) domain of AKMT alone is a very poor enzyme and cannot complement AKMT function in vivo; the N- and C-terminal domains have distinct impacts on enzyme activity, localization, and in vivo function, demonstrating that multiple domains are required for full AKMT activity. Systematic truncation mutagenesis with in vitro enzymatic assays and in vivo complementation Molecular and biochemical parasitology High 23685344
2013 Phylogenetic analyses established that AKMT orthologs form a new, parasite-specific subfamily of lysine methyltransferases (KMTs). Phylogenetic analysis of AKMT and related KMT sequences Molecular and biochemical parasitology Medium 23685344
2018 The crystal structure of the conserved C-terminal portion (aa289-709) of T. gondii AKMT was solved at 2.1-Å resolution, revealing that AKMT dimerizes via a unique intermolecular interface formed by a C-terminal tetratricopeptide repeat-like (TPR-like) domain together with a specific zinc-binding motif absent from all other KMTs. X-ray crystallography at 2.1-Å resolution Journal of molecular biology High 30148980
2018 Disruption of AKMT dimerization impaired both its enzyme activity in vitro and parasite egress from infected host cells in vivo, establishing that dimerization is required for AKMT function. Structure-guided mutagenesis of the dimerization interface combined with in vitro enzymatic assay and in vivo egress assay Journal of molecular biology High 30148980
2018 Structural comparisons reveal that AKMT is related to SMYD-family KMTs but possesses unique structural features (including the dimerization interface and zinc-binding motif) conserved among apicomplexan parasites and their free-living relatives but absent from animal KMTs, identifying AKMT as the founding member of a new KMT subclass. Crystal structure comparison with known KMT structures Journal of molecular biology High 30148980
2019 AKMT-mediated methylation controls a flux of F-actin initiated at the conoid by FRM1, which is crucial for motility, invasion, and egress, placing AKMT in a post-translational regulatory pathway alongside PKG and CDPK1 phosphorylation that governs actin polymerization dynamics. Genetic epistasis using F-actin chromobodies combined with gene disruption of FRM1, myosin A, myosin H, PKG, CDPK1, and AKMT eLife High 30753127

Source papers

Stage 0 corpus · 5 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2011 The motility of a human parasite, Toxoplasma gondii, is regulated by a novel lysine methyltransferase. PLoS pathogens 72 21909263
2019 Three F-actin assembly centers regulate organelle inheritance, cell-cell communication and motility in Toxoplasma gondii. eLife 68 30753127
2013 Identification of functional modules of AKMT, a novel lysine methyltransferase regulating the motility of Toxoplasma gondii. Molecular and biochemical parasitology 14 23685344
2018 Structure of a Novel Dimeric SET Domain Methyltransferase that Regulates Cell Motility. Journal of molecular biology 5 30148980
2016 Identification, production and assessment of two Toxoplasma gondii recombinant proteins for use in a Toxoplasma IgG avidity assay. Pathogens and global health 4 27697019