{"gene":"PF3D7_1246200","run_date":"2026-09-08T14:19:06","timeline":{"discoveries":[{"year":2005,"finding":"ACT1 (actin I) in P. falciparum merozoites carries an N-terminal acetylation (acetyl-Gly-Glu-actin) as its only post-translational modification; methylation of histidine 73, common in canonical actins, is absent. Approximately half of extracted monomeric ACT1 polymerises into filaments, but these filaments are very short (~100 nm average length by EM), too short to be resolved by conventional fluorescence microscopy. In an in vitro motility assay, ACT1 filaments moved over myosin class II at the same velocity as rabbit skeletal actin.","method":"Mass spectrometry (PTM identification), sedimentation at 500,000 g (F-actin quantification), electron microscopy (filament length), in vitro motility assay","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — multiple orthogonal methods (MS, ultracentrifugation, EM, in vitro motility) in a single rigorous study establishing ACT1 biochemistry","pmids":["15876372"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2005,"finding":"Recombinant ACT1 produced in yeast polymerises inefficiently unless both gelsolin and phalloidin are added, yielding fragmented polymers. ACT1 binds DNaseI approximately 200-fold more weakly than bovine non-muscle actin, indicating unusual monomer properties that likely underlie the short, unstable filaments observed in apicomplexan parasites.","method":"Recombinant protein expression in yeast, in vitro polymerisation assay, fluorescence microscopy, DNaseI binding assay","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — reconstitution in vitro with multiple functional readouts, but single lab, single study","pmids":["15670824"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2010,"finding":"ACT1 (Pf-actin I) stabilised by jasplakinolide forms long filaments in vitro. Atomic force microscopy shows the helical pitch of the ACT1 double-stranded filament is ~10% larger than that of rabbit skeletal actin, corresponding to a larger rotational angle between subunits, consistent with weaker inter- and intra-strand contacts that explain inherent filament instability. Hybrid filaments (ACT1 seeds elongated with rabbit skeletal actin) are stable enough to move over myosin class II motors.","method":"Atomic force microscopy, negative-stain electron microscopy, fluorescence microscopy, gliding filament assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — multiple orthogonal structural and functional methods (AFM, EM, motility assay) in a single rigorous study","pmids":["20826799"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2011,"finding":"In P. berghei, ACT1 (actin I) localises dually to the cytoplasm and nucleus in male gametocytes before activation; after activation it is restricted to the cytoplasm. In actin II knock-out parasites, this re-localisation is abolished and ACT1 remains in both compartments, placing ACT1 re-distribution downstream of actin II function during male gametogenesis.","method":"Genetic disruption of actin II in P. berghei, immunofluorescence microscopy of ACT1 localisation before and after gametocyte activation","journal":"Cellular microbiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean genetic KO with defined localization readout; two orthogonal conditions (WT vs. mutant) but single lab","pmids":["21790945"],"is_preprint":false,"attribution":[{"species":"Plasmodium berghei","strain":""}]},{"year":2011,"finding":"A conformation-specific peptide antibody (Ab-actinI-I) raised against the divergent N-terminus of ACT1 detects rod-like F-actin structures (~600 nm) in motile P. berghei ookinetes in vivo; these structures are sensitive to inhibitors of actin polymerisation, demonstrating that ACT1 forms filamentous structures in ookinetes.","method":"Peptide antibody generation, immunofluorescence microscopy, pharmacological inhibition of actin polymerisation","journal":"Molecular and biochemical parasitology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conformation-specific antibody with pharmacological validation in vivo; single lab but two orthogonal approaches","pmids":["22101204"],"is_preprint":false,"attribution":[{"species":"Plasmodium berghei","strain":""}]},{"year":2011,"finding":"Pharmacologically induced F-actin polymerisation of ACT1, which is restricted to the nuclear periphery in P. falciparum, repositions var intron-carrying episomes and var genes from repressive to transcriptionally active perinuclear compartments, disrupting mutually exclusive var gene expression. This places ACT1 polymerisation as a direct mechanistic driver of var gene repositioning and antigenic variation.","method":"Pharmacological induction of F-actin, fluorescence in situ hybridisation (FISH) for gene positioning, reporter assays for var gene expression, identification of actin-recruiting nuclear element","journal":"Cell host & microbe","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological manipulation with nuclear positioning and transcriptional readouts; single lab with multiple orthogonal assays","pmids":["22100161"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2014,"finding":"Crystal structures of ACT1 monomers, combined with cryo-EM of filaments, reveal that ACT1 has a unique filament structure distinct from canonical F-actin. Both ACT1 and actin II hydrolyse ATP more efficiently than α-actin, and unlike any other actin, both isoforms rapidly form short oligomers induced by ADP. Inserting the canonical D-loop into ACT1 leads to long filament formation in vitro and, in vivo, restores male gametogenesis in P. berghei parasites lacking actin II, demonstrating that the D-loop is the structural element governing filament stability and length.","method":"X-ray crystallography, cryo-EM, in vitro polymerisation assay, ATP hydrolysis assay, D-loop chimera mutagenesis, genetic complementation in P. berghei","journal":"PLoS pathogens","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure plus cryo-EM plus in vitro biochemistry plus mutagenesis plus in vivo genetic complementation; multiple orthogonal methods in one rigorous study","pmids":["24743229"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""},{"species":"Plasmodium berghei","strain":""}]},{"year":2017,"finding":"Near-atomic cryo-EM structure of jasplakinolide-stabilised ACT1 filaments reveals small but critical differences at inter- and intra-strand contact sites compared to mammalian F-actin, explaining the inherent instability of ACT1 filaments. Jasplakinolide binds at regular intervals inside the filament, contacting three adjacent actin subunits and reinforcing stability via hydrophobic interactions.","method":"Electron cryomicroscopy (near-atomic resolution), jasplakinolide-stabilised filament reconstitution","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — near-atomic cryo-EM structure with mechanistic interpretation of filament instability; single rigorous structural study with high resolution","pmids":["28923924"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2017,"finding":"Conditional Cre-lox depletion of ACT1 in P. falciparum blood stages demonstrates that ACT1 is required for: (1) segregation of the apicoplast, (2) efficient daughter cell separation during cytokinesis, and (3) host cell invasion after junction formation. Egress from the host cell is not actin-dependent. Parasites lacking ACT1 can secrete micronemes, attach to erythrocytes, and form a tight junction, but cannot complete invasion.","method":"Conditional Cre-lox genetic depletion, fluorescence and electron microscopy, invasion assays, microneme secretion assay","journal":"BMC biology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — conditional KO with multiple defined cellular phenotypes and multiple orthogonal assays; single lab but rigorous controls","pmids":["28810863"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2017,"finding":"ACT1 polymerises via the classical nucleation-elongation pathway with kinetics similar to canonical actins, not via the isodesmic mechanism proposed for Toxoplasma gondii actin. At steady state, ACT1 is present in approximately equal amounts of short filaments and dimers with a small proportion of monomers; the apparent critical concentration is ~0.1 µM. A high fragmentation rate governed by weak lateral contacts is the primary determinant of short filament length.","method":"Quantitative in vitro polymerisation assays with modified fluorescent labelling, kinetic analysis","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — rigorous in vitro biochemical characterisation with quantitative kinetics; single lab, but thorough methodology","pmids":["28939886"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2017,"finding":"Reconstitution of the glideosome core with recombinant PfMyoA (expressed via baculovirus/Sf9) and ACT1 shows that PfMyoA moves ACT1 filaments at the same speed as skeletal muscle actin filaments. The duty ratio of PfMyoA suggests that as few as nine motors can power actin movement at maximal speed, a property potentially necessitated by the dynamic (short) nature of ACT1 filaments in the parasite.","method":"Baculovirus/Sf9 recombinant protein expression, in vitro motility assay, actin-activated ATPase assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — reconstitution of glideosome core in vitro; single lab with multiple functional assays","pmids":["28978649"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2017,"finding":"In P. berghei gametocytes (non-motile), ACT1 is present in discrete foci of <130 nm (resolved by 3D-structured illumination microscopy), consistent with short cross-linked filaments anchored to cytoskeletal structures. A portion of ACT1 is soluble, a portion is in a stabilised form requiring SDS for solubilisation, and an additional population pellets at 100,000 × g consistent with F-actin.","method":"3D-structured illumination microscopy, differential solubilisation/fractionation, immunofluorescence with F-actin-specific antibody","journal":"Experimental parasitology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — sub-diffraction imaging combined with biochemical fractionation; single lab, orthogonal methods","pmids":["28803903"],"is_preprint":false,"attribution":[{"species":"Plasmodium berghei","strain":""}]},{"year":2019,"finding":"High-resolution crystallography shows that Mg2+ binding causes slight flattening of the ACT1 monomer (closer in conformation to F-actin), and subsequent phosphate release results in a more twisted conformation. A coordinated K+ ion in the active site departs with phosphate; the A-loop (Arg178/Asp180) acts as a conformational switch between stable and unstable filament states by alternating interactions with Lys270 or His74. His74 in ACT1 is unmethylated (unlike canonical His73-methyl actin), contributing to the fragmentation propensity.","method":"High-resolution X-ray crystallography, active-site structural analysis with metal ions and nucleotide states","journal":"PLoS biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — multiple high-resolution crystal structures with functional mechanistic interpretation of ATP hydrolysis and filament fragmentation; single lab but comprehensive structural data","pmids":["31199804"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2019,"finding":"TIRF microscopy of individual unstabilised ACT1 filaments shows that ACT1 can form filaments up to 30 µm but with a critical concentration of ~4 µM (an order of magnitude higher than skeletal actin). Protomers dissemble from both barbed and pointed ends at similar fast rates of 10–15 subunits/s, and rapid treadmilling occurs near the critical concentration. ADP-ACT1 filaments are highly unstable, dissolving completely in <40 min; ADP-Pi or BeFX suppresses end dynamics. A chimeric ACT1 bearing the mammalian D-loop forms more stable filaments.","method":"Total internal reflection fluorescence (TIRF) microscopy of individual filaments, critical concentration measurement, kinetic analysis of barbed/pointed end dynamics, chimeric D-loop mutagenesis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct single-filament visualisation with quantitative kinetics, mutagenesis, and pharmacological controls; comprehensive mechanistic characterisation in a single rigorous study","pmids":["31548388"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2021,"finding":"Cryo-EM structure of the P. falciparum ACT1–PfMyoA actomyosin complex at the rigor (end-of-powerstroke) state reveals the detailed ACT1:PfMyoA interface. The footprint of PfMyoA on filamentous ACT1 is conserved with higher eukaryote actomyosin complexes despite important variability in the contact residues. The interface comprises a conserved core common to all actomyosin complexes plus an ancillary region defining the spatial positioning of the motor on ACT1 filaments.","method":"Electron cryomicroscopy (atomic resolution), structure determination of rigor-state actomyosin complex","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — near-atomic cryo-EM structure of the ACT1–myosin complex with rigorous comparative structural analysis; single rigorous study at high resolution","pmids":["33767187"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2022,"finding":"High-resolution cryo-EM structure of the full glideosome motor complex reveals the ACT1 filament (PfAct1) at improved resolution complexed with PfMyoA and its two light chains (PfELC and PfMTIP), providing atomic-detail view of the ACT1:PfMyoA interface and the light-chain binding region at lower resolution. A bare ACT1 filament structure is also reported at improved resolution.","method":"Electron cryomicroscopy (high resolution), structural determination of actomyosin and bare filament","journal":"PLoS pathogens","confidence":"High","confidence_rationale":"Tier 1 / Moderate — high-resolution cryo-EM structure of the complete ACT1-containing motor complex; single rigorous structural study","pmids":["35377914"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"current_model":"P. falciparum ACT1 (PF3D7_1246200) is a divergent actin that forms inherently short (~100 nm in vitro, ~600 nm in vivo ookinetes), unstable filaments due to a unique D-loop conformation, weak lateral inter-strand contacts, an unmethylated His74, and ADP-dependent rapid fragmentation governed by the A-loop (Arg178/Asp180) conformational switch; it polymerises via a classical nucleation-elongation mechanism with a ~4 µM critical concentration, treadmills rapidly near this concentration, serves as the actin track for the PfMyoA-based glideosome motor (whose footprint on ACT1 is evolutionarily conserved), and is essential in blood-stage parasites for apicoplast segregation, daughter-cell separation during cytokinesis, and erythrocyte invasion after junction formation (but not for egress), while also participating as a perinuclear F-actin network that controls var gene repositioning and mutually exclusive expression."},"narrative":{"mechanistic_narrative":"PF3D7_1246200 (ACT1) is the divergent actin isoform of Plasmodium falciparum that forms inherently short, unstable filaments and serves as the track for the glideosome motor and as a driver of nuclear gene positioning [PMID:15876372, PMID:28810863, PMID:22100161]. Biochemically, ACT1 carries only N-terminal acetylation and lacks the canonical His73 methylation; roughly half of extracted monomer polymerises but into filaments averaging only ~100 nm, and recombinant ACT1 binds DNaseI ~200-fold more weakly than conventional actin, indicating unusual monomer properties [PMID:15876372, PMID:15670824]. It polymerises by a classical nucleation-elongation pathway with a critical concentration of ~4 µM, treadmills rapidly with subunits leaving both filament ends at similar fast rates, and ADP-bound filaments dissolve within minutes [PMID:28939886, PMID:31548388]. Structural work traces this instability to specific molecular features: a non-canonical D-loop whose replacement with the mammalian D-loop restores long, stable filaments and, in P. berghei lacking actin II, rescues male gametogenesis; weakened inter- and intra-strand contacts (a ~10% enlarged helical pitch); an unmethylated His74; and an A-loop (Arg178/Asp180) conformational switch coupled to nucleotide and metal-ion state [PMID:20826799, PMID:24743229, PMID:28923924, PMID:31199804, PMID:31548388]. Functionally, ACT1 filaments move over myosin, and reconstitution and rigor-state cryo-EM of the ACT1–PfMyoA actomyosin complex show that the myosin footprint on ACT1 is conserved with higher-eukaryote actomyosin despite divergent contact residues, positioning ACT1 as the motor track of the glideosome [PMID:15876372, PMID:28978649, PMID:33767187, PMID:35377914]. Conditional depletion in blood-stage parasites establishes that ACT1 is required for apicoplast segregation, daughter-cell separation during cytokinesis, and erythrocyte invasion after tight-junction formation, but not for egress [PMID:28810863]. A distinct perinuclear ACT1 pool, upon induced polymerisation, repositions var genes to active compartments and disrupts mutually exclusive var expression [PMID:22100161].","teleology":[{"year":2005,"claim":"Established the baseline biochemical identity of ACT1 and the puzzle it poses: why an actin that is functionally competent on myosin nonetheless forms only very short filaments.","evidence":"Mass spectrometry, ultracentrifugation, EM filament sizing, and in vitro motility on myosin II; recombinant yeast expression with DNaseI-binding assay","pmids":["15876372","15670824"],"confidence":"High","gaps":["Molecular basis of the short filament length not yet identified","N-terminal acetylation functional consequence untested","Weak DNaseI binding not mapped to structural features"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2010,"claim":"Linked ACT1 filament instability to altered helical geometry, showing weaker subunit contacts rather than an inability to polymerise underlie the short-filament phenotype.","evidence":"AFM and negative-stain EM of jasplakinolide-stabilised filaments; gliding assay of ACT1-seeded hybrid filaments","pmids":["20826799"],"confidence":"High","gaps":["Atomic-level contact differences not resolved","Native (unstabilised) filament architecture not observed"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2011,"claim":"Extended ACT1 beyond a motility track to a nuclear function, showing induced ACT1 polymerisation repositions var genes and breaks mutually exclusive expression, and that a cytoplasmic/nuclear ACT1 pool is regulated during gametogenesis.","evidence":"Pharmacological F-actin induction with FISH and var reporter assays in P. falciparum; actin II knockout with ACT1 immunolocalisation in P. berghei; conformation-specific antibody detecting ~600 nm rods in ookinetes","pmids":["22100161","21790945","22101204"],"confidence":"Medium","gaps":["Nuclear ACT1 recruitment machinery not defined","Whether physiological (non-pharmacological) ACT1 polymerisation drives var switching untested","ACT1 relocalisation downstream of actin II mechanistically unexplained"],"attribution":[{"species":"Plasmodium falciparum","strain":""},{"species":"Plasmodium berghei","strain":""}]},{"year":2014,"claim":"Identified the D-loop as the structural determinant of filament stability, converting a descriptive instability into a testable, transferable mechanism.","evidence":"Crystallography plus cryo-EM, ATP hydrolysis assays, D-loop chimera mutagenesis, and genetic complementation restoring gametogenesis in P. berghei","pmids":["24743229"],"confidence":"High","gaps":["ADP-induced oligomerisation kinetics not quantified here","In vivo consequence of D-loop swap in P. falciparum blood stages untested"],"attribution":[{"species":"Plasmodium falciparum","strain":""},{"species":"Plasmodium berghei","strain":""}]},{"year":2017,"claim":"Resolved the polymerisation mechanism, cellular essentiality, and motor engagement of ACT1 in one convergent year, defining what ACT1 does and where it is required.","evidence":"Near-atomic cryo-EM of stabilised filaments; quantitative in vitro polymerisation kinetics; conditional Cre-lox depletion with invasion/egress/microneme assays; glideosome reconstitution with recombinant PfMyoA; SIM and fractionation in gametocytes","pmids":["28923924","28939886","28810863","28978649","28803903"],"confidence":"High","gaps":["Critical concentration estimates differ between labelling approaches","Identity of endogenous factors regulating ACT1 dynamics in vivo unknown","Molecular link between filament dynamics and the invasion/cytokinesis phenotypes not established"],"attribution":[{"species":"Plasmodium falciparum","strain":""},{"species":"Plasmodium berghei","strain":""}]},{"year":2019,"claim":"Pinpointed the atomic switches (A-loop Arg178/Asp180, unmethylated His74, metal/nucleotide-coupled conformations) governing fragmentation and directly visualised single-filament treadmilling.","evidence":"High-resolution crystallography across metal/nucleotide states; TIRF microscopy of individual unstabilised filaments with D-loop chimera and BeFX/ADP-Pi controls","pmids":["31199804","31548388"],"confidence":"High","gaps":["Whether His74 methylation state is regulated in vivo unknown","Physiological trigger of the A-loop switch not identified"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2022,"claim":"Delivered atomic-resolution views of the ACT1–PfMyoA interface within the assembled glideosome, showing the myosin footprint on ACT1 is evolutionarily conserved despite divergent contact residues.","evidence":"Cryo-EM of the rigor-state ACT1–PfMyoA actomyosin complex and of the full glideosome with PfELC/PfMTIP light chains and bare ACT1 filament","pmids":["33767187","35377914"],"confidence":"High","gaps":["Structures capture static states, not the full powerstroke cycle on short filaments","How filament fragmentation is accommodated during motor function unresolved"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":null,"claim":"How ACT1's intrinsic filament dynamics are regulated in vivo and mechanistically coupled to its distinct cellular roles (glideosome-driven invasion, apicoplast segregation, cytokinesis, and perinuclear var gene control) remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["Endogenous regulators/nucleators of ACT1 not identified in the corpus","Direct link between measured filament instability and specific in vivo phenotypes not established","Mechanism recruiting ACT1 to the nuclear periphery unknown"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":["ACT1–PfMyoA actomyosin (rigor state) [#14]","Glideosome core motor with PfMyoA, PfELC and PfMTIP [#15]"],"partners":["PFMYOA (MYOSIN) [#10, #14, #15]","PFELC (MYOSIN LIGHT CHAIN, WITHIN GLIDEOSOME) [#15]","PFMTIP (MYOSIN TAIL INTERACTING PROTEIN, WITHIN GLIDEOSOME) [#15]","ACTIN II (PFACTIN II; REGULATES ACT1 NUCLEAR/CYTOPLASMIC DISTRIBUTION AND D-LOOP COMPLEMENTATION) [#3, #6]"],"other_free_text":["N-terminally acetylated (acetyl-Gly-Glu-actin); lacks canonical His73/His74 methylation [#0, #12]","Forms inherently short (~100 nm in vitro, ~600 nm in vivo ookinete) unstable filaments [#0, #4]","Filament instability governed by a divergent D-loop; mammalian D-loop swap restores long stable filaments [#6, #13]","Polymerises by nucleation-elongation with critical concentration ~4 µM and rapid treadmilling; ADP filaments dissolve rapidly [#9, #13]","A-loop (Arg178/Asp180) acts as conformational switch between stable and unstable filament states, coupled to Mg2+/K+ and nucleotide state [#12]","Weakened inter- and intra-strand contacts and ~10% enlarged helical pitch relative to skeletal actin [#2, #7]","Jasplakinolide binds internally at regular intervals contacting three subunits to stabilise filaments [#7]","Species evidence spans P. falciparum (biochemistry, structure, blood-stage function) and P. berghei (gametocyte/ookinete localisation, D-loop complementation) [#3, #4, #6, #11]"]}},"prefetch_data":{},"corpus_meta":[{"pmid":"15876372","id":"PMC_15876372","title":"Malaria parasite actin filaments are very short.","date":"2005","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/15876372","citation_count":125,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["actin I"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"2671721","id":"PMC_2671721","title":"Stage-specific expression and genomic organization of the actin genes of the malaria parasite Plasmodium falciparum.","date":"1989","source":"Molecular and biochemical 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sciences","url":"https://pubmed.ncbi.nlm.nih.gov/34916893","citation_count":13,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["actin I"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"11954914","id":"PMC_11954914","title":"Expression of housekeeping genes during the asexual cell cycle of Plasmodium falciparum.","date":"2002","source":"Parasitology research","url":"https://pubmed.ncbi.nlm.nih.gov/11954914","citation_count":8,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["actin I"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"36374724","id":"PMC_36374724","title":"Application of a low-cost, specific, and sensitive loop-mediated isothermal amplification (LAMP) assay to detect Plasmodium falciparum imported from Africa.","date":"2022","source":"Molecular and biochemical 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Salud","url":"https://pubmed.ncbi.nlm.nih.gov/12404924","citation_count":0,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["actin I"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":13353,"output_tokens":4928,"usd":0.056989,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":11498,"output_tokens":4430,"usd":0.08412,"stage2_stop_reason":"end_turn"},"total_usd":0.141109,"stage1_batch_id":"msgbatch_011BPjN2BL33F8cJXD1r7V7T","stage2_batch_id":"msgbatch_01Qwg6vP7qxkpL6Gsc7tajsb","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2005,\n      \"finding\": \"ACT1 (actin I) in P. falciparum merozoites carries an N-terminal acetylation (acetyl-Gly-Glu-actin) as its only post-translational modification; methylation of histidine 73, common in canonical actins, is absent. Approximately half of extracted monomeric ACT1 polymerises into filaments, but these filaments are very short (~100 nm average length by EM), too short to be resolved by conventional fluorescence microscopy. In an in vitro motility assay, ACT1 filaments moved over myosin class II at the same velocity as rabbit skeletal actin.\",\n      \"method\": \"Mass spectrometry (PTM identification), sedimentation at 500,000 g (F-actin quantification), electron microscopy (filament length), in vitro motility assay\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — multiple orthogonal methods (MS, ultracentrifugation, EM, in vitro motility) in a single rigorous study establishing ACT1 biochemistry\",\n      \"pmids\": [\"15876372\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Recombinant ACT1 produced in yeast polymerises inefficiently unless both gelsolin and phalloidin are added, yielding fragmented polymers. ACT1 binds DNaseI approximately 200-fold more weakly than bovine non-muscle actin, indicating unusual monomer properties that likely underlie the short, unstable filaments observed in apicomplexan parasites.\",\n      \"method\": \"Recombinant protein expression in yeast, in vitro polymerisation assay, fluorescence microscopy, DNaseI binding assay\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — reconstitution in vitro with multiple functional readouts, but single lab, single study\",\n      \"pmids\": [\"15670824\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"ACT1 (Pf-actin I) stabilised by jasplakinolide forms long filaments in vitro. Atomic force microscopy shows the helical pitch of the ACT1 double-stranded filament is ~10% larger than that of rabbit skeletal actin, corresponding to a larger rotational angle between subunits, consistent with weaker inter- and intra-strand contacts that explain inherent filament instability. Hybrid filaments (ACT1 seeds elongated with rabbit skeletal actin) are stable enough to move over myosin class II motors.\",\n      \"method\": \"Atomic force microscopy, negative-stain electron microscopy, fluorescence microscopy, gliding filament assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — multiple orthogonal structural and functional methods (AFM, EM, motility assay) in a single rigorous study\",\n      \"pmids\": [\"20826799\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"In P. berghei, ACT1 (actin I) localises dually to the cytoplasm and nucleus in male gametocytes before activation; after activation it is restricted to the cytoplasm. In actin II knock-out parasites, this re-localisation is abolished and ACT1 remains in both compartments, placing ACT1 re-distribution downstream of actin II function during male gametogenesis.\",\n      \"method\": \"Genetic disruption of actin II in P. berghei, immunofluorescence microscopy of ACT1 localisation before and after gametocyte activation\",\n      \"journal\": \"Cellular microbiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean genetic KO with defined localization readout; two orthogonal conditions (WT vs. mutant) but single lab\",\n      \"pmids\": [\"21790945\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"A conformation-specific peptide antibody (Ab-actinI-I) raised against the divergent N-terminus of ACT1 detects rod-like F-actin structures (~600 nm) in motile P. berghei ookinetes in vivo; these structures are sensitive to inhibitors of actin polymerisation, demonstrating that ACT1 forms filamentous structures in ookinetes.\",\n      \"method\": \"Peptide antibody generation, immunofluorescence microscopy, pharmacological inhibition of actin polymerisation\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conformation-specific antibody with pharmacological validation in vivo; single lab but two orthogonal approaches\",\n      \"pmids\": [\"22101204\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Pharmacologically induced F-actin polymerisation of ACT1, which is restricted to the nuclear periphery in P. falciparum, repositions var intron-carrying episomes and var genes from repressive to transcriptionally active perinuclear compartments, disrupting mutually exclusive var gene expression. This places ACT1 polymerisation as a direct mechanistic driver of var gene repositioning and antigenic variation.\",\n      \"method\": \"Pharmacological induction of F-actin, fluorescence in situ hybridisation (FISH) for gene positioning, reporter assays for var gene expression, identification of actin-recruiting nuclear element\",\n      \"journal\": \"Cell host & microbe\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological manipulation with nuclear positioning and transcriptional readouts; single lab with multiple orthogonal assays\",\n      \"pmids\": [\"22100161\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Crystal structures of ACT1 monomers, combined with cryo-EM of filaments, reveal that ACT1 has a unique filament structure distinct from canonical F-actin. Both ACT1 and actin II hydrolyse ATP more efficiently than α-actin, and unlike any other actin, both isoforms rapidly form short oligomers induced by ADP. Inserting the canonical D-loop into ACT1 leads to long filament formation in vitro and, in vivo, restores male gametogenesis in P. berghei parasites lacking actin II, demonstrating that the D-loop is the structural element governing filament stability and length.\",\n      \"method\": \"X-ray crystallography, cryo-EM, in vitro polymerisation assay, ATP hydrolysis assay, D-loop chimera mutagenesis, genetic complementation in P. berghei\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure plus cryo-EM plus in vitro biochemistry plus mutagenesis plus in vivo genetic complementation; multiple orthogonal methods in one rigorous study\",\n      \"pmids\": [\"24743229\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}, {\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Near-atomic cryo-EM structure of jasplakinolide-stabilised ACT1 filaments reveals small but critical differences at inter- and intra-strand contact sites compared to mammalian F-actin, explaining the inherent instability of ACT1 filaments. Jasplakinolide binds at regular intervals inside the filament, contacting three adjacent actin subunits and reinforcing stability via hydrophobic interactions.\",\n      \"method\": \"Electron cryomicroscopy (near-atomic resolution), jasplakinolide-stabilised filament reconstitution\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — near-atomic cryo-EM structure with mechanistic interpretation of filament instability; single rigorous structural study with high resolution\",\n      \"pmids\": [\"28923924\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Conditional Cre-lox depletion of ACT1 in P. falciparum blood stages demonstrates that ACT1 is required for: (1) segregation of the apicoplast, (2) efficient daughter cell separation during cytokinesis, and (3) host cell invasion after junction formation. Egress from the host cell is not actin-dependent. Parasites lacking ACT1 can secrete micronemes, attach to erythrocytes, and form a tight junction, but cannot complete invasion.\",\n      \"method\": \"Conditional Cre-lox genetic depletion, fluorescence and electron microscopy, invasion assays, microneme secretion assay\",\n      \"journal\": \"BMC biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO with multiple defined cellular phenotypes and multiple orthogonal assays; single lab but rigorous controls\",\n      \"pmids\": [\"28810863\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"ACT1 polymerises via the classical nucleation-elongation pathway with kinetics similar to canonical actins, not via the isodesmic mechanism proposed for Toxoplasma gondii actin. At steady state, ACT1 is present in approximately equal amounts of short filaments and dimers with a small proportion of monomers; the apparent critical concentration is ~0.1 µM. A high fragmentation rate governed by weak lateral contacts is the primary determinant of short filament length.\",\n      \"method\": \"Quantitative in vitro polymerisation assays with modified fluorescent labelling, kinetic analysis\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — rigorous in vitro biochemical characterisation with quantitative kinetics; single lab, but thorough methodology\",\n      \"pmids\": [\"28939886\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Reconstitution of the glideosome core with recombinant PfMyoA (expressed via baculovirus/Sf9) and ACT1 shows that PfMyoA moves ACT1 filaments at the same speed as skeletal muscle actin filaments. The duty ratio of PfMyoA suggests that as few as nine motors can power actin movement at maximal speed, a property potentially necessitated by the dynamic (short) nature of ACT1 filaments in the parasite.\",\n      \"method\": \"Baculovirus/Sf9 recombinant protein expression, in vitro motility assay, actin-activated ATPase assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstitution of glideosome core in vitro; single lab with multiple functional assays\",\n      \"pmids\": [\"28978649\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"In P. berghei gametocytes (non-motile), ACT1 is present in discrete foci of <130 nm (resolved by 3D-structured illumination microscopy), consistent with short cross-linked filaments anchored to cytoskeletal structures. A portion of ACT1 is soluble, a portion is in a stabilised form requiring SDS for solubilisation, and an additional population pellets at 100,000 × g consistent with F-actin.\",\n      \"method\": \"3D-structured illumination microscopy, differential solubilisation/fractionation, immunofluorescence with F-actin-specific antibody\",\n      \"journal\": \"Experimental parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — sub-diffraction imaging combined with biochemical fractionation; single lab, orthogonal methods\",\n      \"pmids\": [\"28803903\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"High-resolution crystallography shows that Mg2+ binding causes slight flattening of the ACT1 monomer (closer in conformation to F-actin), and subsequent phosphate release results in a more twisted conformation. A coordinated K+ ion in the active site departs with phosphate; the A-loop (Arg178/Asp180) acts as a conformational switch between stable and unstable filament states by alternating interactions with Lys270 or His74. His74 in ACT1 is unmethylated (unlike canonical His73-methyl actin), contributing to the fragmentation propensity.\",\n      \"method\": \"High-resolution X-ray crystallography, active-site structural analysis with metal ions and nucleotide states\",\n      \"journal\": \"PLoS biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple high-resolution crystal structures with functional mechanistic interpretation of ATP hydrolysis and filament fragmentation; single lab but comprehensive structural data\",\n      \"pmids\": [\"31199804\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"TIRF microscopy of individual unstabilised ACT1 filaments shows that ACT1 can form filaments up to 30 µm but with a critical concentration of ~4 µM (an order of magnitude higher than skeletal actin). Protomers dissemble from both barbed and pointed ends at similar fast rates of 10–15 subunits/s, and rapid treadmilling occurs near the critical concentration. ADP-ACT1 filaments are highly unstable, dissolving completely in <40 min; ADP-Pi or BeFX suppresses end dynamics. A chimeric ACT1 bearing the mammalian D-loop forms more stable filaments.\",\n      \"method\": \"Total internal reflection fluorescence (TIRF) microscopy of individual filaments, critical concentration measurement, kinetic analysis of barbed/pointed end dynamics, chimeric D-loop mutagenesis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct single-filament visualisation with quantitative kinetics, mutagenesis, and pharmacological controls; comprehensive mechanistic characterisation in a single rigorous study\",\n      \"pmids\": [\"31548388\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Cryo-EM structure of the P. falciparum ACT1–PfMyoA actomyosin complex at the rigor (end-of-powerstroke) state reveals the detailed ACT1:PfMyoA interface. The footprint of PfMyoA on filamentous ACT1 is conserved with higher eukaryote actomyosin complexes despite important variability in the contact residues. The interface comprises a conserved core common to all actomyosin complexes plus an ancillary region defining the spatial positioning of the motor on ACT1 filaments.\",\n      \"method\": \"Electron cryomicroscopy (atomic resolution), structure determination of rigor-state actomyosin complex\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — near-atomic cryo-EM structure of the ACT1–myosin complex with rigorous comparative structural analysis; single rigorous study at high resolution\",\n      \"pmids\": [\"33767187\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"High-resolution cryo-EM structure of the full glideosome motor complex reveals the ACT1 filament (PfAct1) at improved resolution complexed with PfMyoA and its two light chains (PfELC and PfMTIP), providing atomic-detail view of the ACT1:PfMyoA interface and the light-chain binding region at lower resolution. A bare ACT1 filament structure is also reported at improved resolution.\",\n      \"method\": \"Electron cryomicroscopy (high resolution), structural determination of actomyosin and bare filament\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — high-resolution cryo-EM structure of the complete ACT1-containing motor complex; single rigorous structural study\",\n      \"pmids\": [\"35377914\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    }\n  ],\n  \"current_model\": \"P. falciparum ACT1 (PF3D7_1246200) is a divergent actin that forms inherently short (~100 nm in vitro, ~600 nm in vivo ookinetes), unstable filaments due to a unique D-loop conformation, weak lateral inter-strand contacts, an unmethylated His74, and ADP-dependent rapid fragmentation governed by the A-loop (Arg178/Asp180) conformational switch; it polymerises via a classical nucleation-elongation mechanism with a ~4 µM critical concentration, treadmills rapidly near this concentration, serves as the actin track for the PfMyoA-based glideosome motor (whose footprint on ACT1 is evolutionarily conserved), and is essential in blood-stage parasites for apicoplast segregation, daughter-cell separation during cytokinesis, and erythrocyte invasion after junction formation (but not for egress), while also participating as a perinuclear F-actin network that controls var gene repositioning and mutually exclusive expression.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PF3D7_1246200 (ACT1) is the divergent actin isoform of Plasmodium falciparum that forms inherently short, unstable filaments and serves as the track for the glideosome motor and as a driver of nuclear gene positioning [#0, #8, #5]. Biochemically, ACT1 carries only N-terminal acetylation and lacks the canonical His73 methylation; roughly half of extracted monomer polymerises but into filaments averaging only ~100 nm, and recombinant ACT1 binds DNaseI ~200-fold more weakly than conventional actin, indicating unusual monomer properties [#0, #1]. It polymerises by a classical nucleation-elongation pathway with a critical concentration of ~4 \\u00b5M, treadmills rapidly with subunits leaving both filament ends at similar fast rates, and ADP-bound filaments dissolve within minutes [#9, #13]. Structural work traces this instability to specific molecular features: a non-canonical D-loop whose replacement with the mammalian D-loop restores long, stable filaments and, in P. berghei lacking actin II, rescues male gametogenesis; weakened inter- and intra-strand contacts (a ~10% enlarged helical pitch); an unmethylated His74; and an A-loop (Arg178/Asp180) conformational switch coupled to nucleotide and metal-ion state [#2, #6, #7, #12, #13]. Functionally, ACT1 filaments move over myosin, and reconstitution and rigor-state cryo-EM of the ACT1\\u2013PfMyoA actomyosin complex show that the myosin footprint on ACT1 is conserved with higher-eukaryote actomyosin despite divergent contact residues, positioning ACT1 as the motor track of the glideosome [#0, #10, #14, #15]. Conditional depletion in blood-stage parasites establishes that ACT1 is required for apicoplast segregation, daughter-cell separation during cytokinesis, and erythrocyte invasion after tight-junction formation, but not for egress [#8]. A distinct perinuclear ACT1 pool, upon induced polymerisation, repositions var genes to active compartments and disrupts mutually exclusive var expression [#5].\",\n  \"teleology\": [\n    {\n      \"year\": 2005,\n      \"claim\": \"Established the baseline biochemical identity of ACT1 and the puzzle it poses: why an actin that is functionally competent on myosin nonetheless forms only very short filaments.\",\n      \"evidence\": \"Mass spectrometry, ultracentrifugation, EM filament sizing, and in vitro motility on myosin II; recombinant yeast expression with DNaseI-binding assay\",\n      \"pmids\": [\"15876372\", \"15670824\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of the short filament length not yet identified\", \"N-terminal acetylation functional consequence untested\", \"Weak DNaseI binding not mapped to structural features\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Linked ACT1 filament instability to altered helical geometry, showing weaker subunit contacts rather than an inability to polymerise underlie the short-filament phenotype.\",\n      \"evidence\": \"AFM and negative-stain EM of jasplakinolide-stabilised filaments; gliding assay of ACT1-seeded hybrid filaments\",\n      \"pmids\": [\"20826799\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic-level contact differences not resolved\", \"Native (unstabilised) filament architecture not observed\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Extended ACT1 beyond a motility track to a nuclear function, showing induced ACT1 polymerisation repositions var genes and breaks mutually exclusive expression, and that a cytoplasmic/nuclear ACT1 pool is regulated during gametogenesis.\",\n      \"evidence\": \"Pharmacological F-actin induction with FISH and var reporter assays in P. falciparum; actin II knockout with ACT1 immunolocalisation in P. berghei; conformation-specific antibody detecting ~600 nm rods in ookinetes\",\n      \"pmids\": [\"22100161\", \"21790945\", \"22101204\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Nuclear ACT1 recruitment machinery not defined\", \"Whether physiological (non-pharmacological) ACT1 polymerisation drives var switching untested\", \"ACT1 relocalisation downstream of actin II mechanistically unexplained\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}, {\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Identified the D-loop as the structural determinant of filament stability, converting a descriptive instability into a testable, transferable mechanism.\",\n      \"evidence\": \"Crystallography plus cryo-EM, ATP hydrolysis assays, D-loop chimera mutagenesis, and genetic complementation restoring gametogenesis in P. berghei\",\n      \"pmids\": [\"24743229\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"ADP-induced oligomerisation kinetics not quantified here\", \"In vivo consequence of D-loop swap in P. falciparum blood stages untested\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}, {\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Resolved the polymerisation mechanism, cellular essentiality, and motor engagement of ACT1 in one convergent year, defining what ACT1 does and where it is required.\",\n      \"evidence\": \"Near-atomic cryo-EM of stabilised filaments; quantitative in vitro polymerisation kinetics; conditional Cre-lox depletion with invasion/egress/microneme assays; glideosome reconstitution with recombinant PfMyoA; SIM and fractionation in gametocytes\",\n      \"pmids\": [\"28923924\", \"28939886\", \"28810863\", \"28978649\", \"28803903\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Critical concentration estimates differ between labelling approaches\", \"Identity of endogenous factors regulating ACT1 dynamics in vivo unknown\", \"Molecular link between filament dynamics and the invasion/cytokinesis phenotypes not established\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}, {\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Pinpointed the atomic switches (A-loop Arg178/Asp180, unmethylated His74, metal/nucleotide-coupled conformations) governing fragmentation and directly visualised single-filament treadmilling.\",\n      \"evidence\": \"High-resolution crystallography across metal/nucleotide states; TIRF microscopy of individual unstabilised filaments with D-loop chimera and BeFX/ADP-Pi controls\",\n      \"pmids\": [\"31199804\", \"31548388\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether His74 methylation state is regulated in vivo unknown\", \"Physiological trigger of the A-loop switch not identified\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Delivered atomic-resolution views of the ACT1\\u2013PfMyoA interface within the assembled glideosome, showing the myosin footprint on ACT1 is evolutionarily conserved despite divergent contact residues.\",\n      \"evidence\": \"Cryo-EM of the rigor-state ACT1\\u2013PfMyoA actomyosin complex and of the full glideosome with PfELC/PfMTIP light chains and bare ACT1 filament\",\n      \"pmids\": [\"33767187\", \"35377914\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structures capture static states, not the full powerstroke cycle on short filaments\", \"How filament fragmentation is accommodated during motor function unresolved\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How ACT1's intrinsic filament dynamics are regulated in vivo and mechanistically coupled to its distinct cellular roles (glideosome-driven invasion, apicoplast segregation, cytokinesis, and perinuclear var gene control) remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Endogenous regulators/nucleators of ACT1 not identified in the corpus\", \"Direct link between measured filament instability and specific in vivo phenotypes not established\", \"Mechanism recruiting ACT1 to the nuclear periphery unknown\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005200\", \"supporting_discovery_ids\": [0, 2, 10, 14, 15]},\n      {\"term_id\": \"GO:0003785\", \"supporting_discovery_ids\": [10, 14]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [6, 12]},\n      {\"term_id\": \"GO:0051015\", \"supporting_discovery_ids\": [14, 15]},\n      {\"term_id\": \"GO:0005524\", \"supporting_discovery_ids\": [6, 12, 13]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005884\", \"supporting_discovery_ids\": [0, 2, 4, 11, 13]},\n      {\"term_id\": \"GO:0005737\", \"supporting_discovery_ids\": [3, 11]},\n      {\"term_id\": \"GO:0034399\", \"supporting_discovery_ids\": [5]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [3, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0007015\", \"supporting_discovery_ids\": [0, 6, 9, 13]},\n      {\"term_id\": \"GO:0030048\", \"supporting_discovery_ids\": [10, 14, 15]},\n      {\"term_id\": \"GO:0009405\", \"supporting_discovery_ids\": [8]},\n      {\"term_id\": \"GO:0000281\", \"supporting_discovery_ids\": [8]},\n      {\"term_id\": \"GO:0045292\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"complexes\": [\n      \"ACT1\\u2013PfMyoA actomyosin (rigor state) [#14]\",\n      \"Glideosome core motor with PfMyoA, PfELC and PfMTIP [#15]\"\n    ],\n    \"partners\": [\n      \"PfMyoA (myosin) [#10, #14, #15]\",\n      \"PfELC (myosin light chain, within glideosome) [#15]\",\n      \"PfMTIP (myosin tail interacting protein, within glideosome) [#15]\",\n      \"actin II (PfActin II; regulates ACT1 nuclear/cytoplasmic distribution and D-loop complementation) [#3, #6]\"\n    ],\n    \"other_free_text\": [\n      \"N-terminally acetylated (acetyl-Gly-Glu-actin); lacks canonical His73/His74 methylation [#0, #12]\",\n      \"Forms inherently short (~100 nm in vitro, ~600 nm in vivo ookinete) unstable filaments [#0, #4]\",\n      \"Filament instability governed by a divergent D-loop; mammalian D-loop swap restores long stable filaments [#6, #13]\",\n      \"Polymerises by nucleation-elongation with critical concentration ~4 \\u00b5M and rapid treadmilling; ADP filaments dissolve rapidly [#9, #13]\",\n      \"A-loop (Arg178/Asp180) acts as conformational switch between stable and unstable filament states, coupled to Mg2+/K+ and nucleotide state [#12]\",\n      \"Weakened inter- and intra-strand contacts and ~10% enlarged helical pitch relative to skeletal actin [#2, #7]\",\n      \"Jasplakinolide binds internally at regular intervals contacting three subunits to stabilise filaments [#7]\",\n      \"Species evidence spans P. falciparum (biochemistry, structure, blood-stage function) and P. berghei (gametocyte/ookinete localisation, D-loop complementation) [#3, #4, #6, #11]\"\n    ]\n  }\n}","audit_flag":null,"strains":[{"strain":"Pf3D7","gene_id":"PF3D7_1246200","name":null,"product":"actin I","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PbANKA","gene_id":"PBANKA_1459300","name":null,"product":"actin I","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PkH","gene_id":"PKNH_1465800","name":null,"product":"actin I, putative","uniprot_acc":null,"chromosome":null,"start_pos":null}],"gene_symbol":"ACT1","evaluation":null}