Affinage · Plasmodium

ACP

PF3D7_0208500 · acyl carrier protein

Annotated
2026-09-07
41 papers in source corpus 16 papers cited in narrative 16 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

PF3D7_0208500 (ACP) is a nuclear-encoded apicoplast acyl carrier protein of P. falciparum that serves as the central acyl-chain scaffold of the organellar type II fatty acid synthesis (FASII) pathway (PMID:9770490, PMID:12270624). It is imported into the apicoplast via an N-terminal bipartite presequence sufficient to target reporters to the organelle, whose transit peptide must remain intrinsically disordered for productive import and is proteolytically removed inside the apicoplast (PMID:9770490, PMID:21668595, PMID:17074076). ACP is activated to its holo form by addition of a 4'-phosphopantetheine prosthetic group derived from coenzyme A (PMID:12270624), and its NMR/crystal structures reveal a three-helix fold whose hydrophobic core sequesters acyl chains up to twelve carbons and expands via defined helix II/III interactions to accommodate longer chains, with a conformational switch of the prosthetic group linked to activation (PMID:16734426, PMID:19520851). In blood-stage parasites ACP is maintained predominantly in a reduced, monomeric holo state, reflecting a reducing apicoplast environment (PMID:19768685). Mechanistically, ACP accepts malonyl groups from MCAT to form malonyl-ACP and donates acyl intermediates to KASIII for decarboxylative condensation (PMID:12270624, PMID:12549938), and it additionally displays intrinsic self-acylation and malonyl transferase activities dependent on identified catalytic residues (PMID:17656314, PMID:19462023); its functional interchangeability with bacterial ACP underscores the conservation of these roles (PMID:17522044, PMID:19462023). Beyond FASII, ACP is essential in blood stages independently of fatty acid synthesis: it binds and stabilizes apicoplast pyruvate kinase II (PKII), and ACP loss depletes PKII, impairs isoprenoid precursor biosynthesis, and blocks apicoplast biogenesis, rendering ACP knockdown lethal (PMID:41959251).

Mechanistic history

Synthesis pass · year-by-year structured walk · 13 steps
  1. 1998 High

    Established where ACP acts and implicated apicoplast fatty acid biosynthesis as an essential organellar function, framing all subsequent mechanistic work.

    Evidence Immunolocalization of endogenous ACP in P. falciparum plus GFP presequence-targeting reporter in transgenic T. gondii

    PMID:9770490

    Open questions at the time
    • Did not test whether FASII/ACP is essential in blood stages
    • No biochemical activity demonstrated
  2. 2002 High

    Demonstrated that ACP requires 4'-phosphopantetheine activation to function as the acyl carrier that feeds KASIII, defining its core biochemical role in FASII.

    Evidence Recombinant expression, in vitro 4'-PP modification, and transacylase assay with PfKASIII

    PMID:12270624

    Open questions at the time
    • In vitro reconstitution only
    • Identity of the physiological PPTase not established here
  3. 2003 High

    Placed ACP within the FASII enzyme cascade by showing it accepts malonyl from MCAT and that the transit peptide blocks enzyme recognition, indicating processing is required for function.

    Evidence In vitro malonyl transfer with recombinant pfMCAT and pfACP, kinetics with pfKASIII, and negative control with transit-peptide-containing construct

    PMID:12549938

    Open questions at the time
    • Used recombinant proteins outside the organelle
    • Did not resolve when/where the transit peptide is cleaved in vivo
  4. 2005 Medium

    Tested the depth of functional conservation of ACP, showing the Plasmodium protein can substitute for bacterial ACP in vivo.

    Evidence In vivo complementation of an E. coli acpP temperature-sensitive mutant with PfACP

    PMID:17522044

    Open questions at the time
    • Single-method genetic assay
    • Does not address Plasmodium-specific partner interactions
  5. 2005 Low

    Proposed the enzyme responsible for generating holo-ACP, addressing how apo-ACP is activated in the apicoplast.

    Evidence Bioinformatic identification of PfACPS-PPT with functional characterization performed on the C. parvum homolog, not PfACPS-PPT itself

    PMID:16002647

    Open questions at the time
    • PfACPS-PPT never directly assayed on PfACP
    • Apicoplast targeting only predicted
    • No in vivo demonstration of holo-ACP synthesis by this enzyme
  6. 2006 High

    Provided the atomic structure of holo-ACP and linked a prosthetic-group conformational switch to activation, explaining how the carrier presents its cargo.

    Evidence High-resolution NMR solution structures of two holo-PfACP conformers with 4'-PP-protein NOEs

    PMID:16734426

    Open questions at the time
    • Functional role of the two states not tested by mutation
    • No acyl-loaded structure in this study
  7. 2007 Medium

    Revealed an intrinsic self-acylation activity of ACP using dicarboxylic acids, expanding its catalytic repertoire beyond passive carrier function.

    Evidence In vitro self-acylation assay with recombinant PfACP plus site-directed mutagenesis of key residues

    PMID:17656314

    Open questions at the time
    • Physiological relevance of self-acylation in vivo unclear
    • Single in vitro system
  8. 2009 High

    Defined the structural basis for accommodating growing acyl chains, explaining how one carrier handles substrates of increasing length during FASII elongation.

    Evidence NMR of acyl-ACP intermediates (CSP, double-filtered NOESY, pKa) identifying core expansion mechanism

    PMID:19520851

    Open questions at the time
    • Behavior with the full complement of FAS enzymes not tested
    • Upper limit of chain capacity in vivo not established
  9. 2009 High

    Showed ACP itself carries intrinsic malonyl transferase activity with identified catalytic residues, further blurring the carrier/enzyme boundary.

    Evidence In vitro malonyl transferase assay, mutagenesis, and in vivo complementation of a fabD(Ts) E. coli strain

    PMID:19462023

    Open questions at the time
    • Contribution of this activity relative to MCAT in vivo unclear
    • No parasite genetic test of the catalytic residues
  10. 2011 High

    Established that intrinsic disorder of the ACP transit peptide is a functional requirement for apicoplast import, defining the biophysical rule governing its targeting.

    Evidence NMR of the isolated transit peptide plus in vivo import assays with proline-disorder and helix-stabilizing mutants in P. falciparum

    PMID:21668595

    Open questions at the time
    • Import receptor recognizing the disordered peptide not identified
    • Sequence-specific determinants not mapped
  11. 2010 High

    Determined that ACP is kept in a reduced monomeric holo state in blood stages, establishing the redox environment of the functional carrier.

    Evidence X-ray crystallography of reduced and disulfide-linked forms plus non-reducing PAGE and diamide treatment of blood-stage parasites

    PMID:19768685

    Open questions at the time
    • Functional role of the disulfide-linked dimer, if any, undefined
    • Redox state in other life-cycle stages not examined
  12. 2013 Medium

    Used ACP to define the FASII pathway's stage-specific requirement, showing FAS enzymes act in the apicoplast and are needed for mosquito-stage but not blood-stage growth.

    Evidence Immunofluorescence colocalization of FabI with ACP and targeted deletion of fabI and fabB/F across life-cycle stages in P. falciparum

    PMID:24297444

    Open questions at the time
    • ACP itself not deleted here
    • Does not address why ACP is essential in blood stages if FASII is dispensable
  13. 2026 High

    Resolved the paradox of blood-stage essentiality by showing ACP acts independently of FASII, stabilizing PKII and supporting isoprenoid precursor synthesis and apicoplast biogenesis.

    Evidence CRISPR knockout, ligand-dependent knockdown, BioID proximity biotinylation, co-IP, isoprenoid and apicoplast biogenesis assays in P. falciparum (preprint)

    PMID:41959251

    Open questions at the time
    • Molecular basis of ACP-PKII binding not structurally defined
    • Whether ACP stabilizes additional apicoplast proteins not established
    • Preprint, not yet peer-reviewed

Open questions

Synthesis pass · forward-looking unresolved questions
  • How ACP's canonical FASII carrier role is mechanistically coupled to its FASII-independent PKII-stabilizing function within the same molecule remains unresolved.
  • No structure of the ACP-PKII complex
  • Unknown whether the acyl-carrier and PKII-binding surfaces overlap
  • Identity of the endogenous apicoplast PPTase remains bioinformatic

Mechanism profile

Synthesis pass · controlled-vocabulary classification
Partners
APICOPLAST PYRUVATE KINASE II (PKII) [#15]FABI (ENOYL-ACP REDUCTASE) [#12]FALCILYSIN (FLN, TRANSIT PEPTIDE CLEAVAGE) [#5]PFACPS-PPT (PREDICTED PHOSPHOPANTETHEINYL TRANSFERASE) [#14]PFKASIII (BETA-KETOACYL-ACP SYNTHASE III) [#1, #2]PFMCAT (MALONYL-COA:ACP TRANSACYLASE) [#2]
Complex memberships
ACP-PKII (apicoplast pyruvate kinase II) complex [#15]

Evidence

Reading pass · 16 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1998 ACP (PF3D7_0208500) is a nuclear-encoded protein that localizes to the apicoplast in P. falciparum, as verified by immunolocalization; the ACP N-terminal presequence is sufficient to target a recombinant GFP reporter to the apicoplast in transgenic T. gondii, implicating ACP and apicoplast fatty acid biosynthesis as an essential function of the organelle. Immunolocalization of endogenous ACP; GFP reporter targeting assay in transgenic T. gondii Proceedings of the National Academy of Sciences of the United States of America High 9770490
2002 Purified recombinant P. falciparum ACP is activated by addition of a 4'-phosphopantetheine (4'-PP) prosthetic group derived from coenzyme A to generate holo-PfACP; holo-PfACP is an effective substrate for the transacylase activity of PfKASIII in vitro, establishing ACP's role as acyl group carrier in the type II FAS pathway. Recombinant protein expression, in vitro 4'-PP modification assay, transacylase activity assay with PfKASIII Molecular and biochemical parasitology High 12270624
2003 Pure recombinant pfMCAT catalyzes malonyl transfer from malonyl-CoA to pfACP in vitro, generating malonyl-pfACP; this product is then a substrate for pfKASIII, which catalyzes decarboxylative condensation. Notably, pfACP(trans), a construct containing the N-terminal apicoplast transit peptide, was NOT a substrate for pfMCAT, demonstrating that the transit peptide interferes with enzyme recognition. In vitro malonyl transfer assay with recombinant pfMCAT and pfACP; kinetic characterization of pfKASIII with malonyl-pfACP Biochemistry High 12549938
2005 P. falciparum ACP (apicoplast form) can functionally replace E. coli AcpP in vivo, restoring growth to an E. coli temperature-sensitive acpP mutant strain, demonstrating that PfACP is functionally interchangeable with bacterial ACP despite evolutionary distance. In vivo complementation of E. coli acpP temperature-sensitive mutant with recombinant PfACP The Journal of biological chemistry Medium 17522044
2006 High-resolution NMR solution structures of holo-PfACP reveal two conformational equilibrium states arising from different orientations of the 4'-phosphopantetheine (4'-PP) prosthetic group; the 4'-PP interacts with the polypeptide backbone, and a conformational switch between the two states is proposed to be essential for ACP activation. The structures consist of three tightly packed helices stabilized by hydrophobic interactions. High-resolution NMR structure determination (20 structures each form, >1200 NOEs including 4'-PP-protein NOEs, backbone dihedral angles, hydrogen bonds) Biochemistry High 16734426
2006 Falcilysin (FLN), a zinc metalloprotease found in the P. falciparum apicoplast, cleaves the transit peptide from apicoplast-resident ACP in vitro, supporting a role for FLN in transit peptide degradation after proteolytic release from ACP precursor protein. In vitro cleavage assay of ACP transit peptide by recombinant falcilysin; GFP-FLN transgenic parasite localization Molecular microbiology Medium 17074076
2007 PfACP exhibits self-acylation activity intrinsic to the individual protein, selectively using dicarboxylic acids as substrates; mutational analysis identified key residues required for this self-acylation. This demonstrates that self-acylation is not restricted to ACPs in polyketide biosynthesis but extends to type II FAS ACPs. In vitro self-acylation assay with recombinant PfACP; site-directed mutagenesis of key residues Chemistry & biology Medium 17656314
2009 NMR structural studies on acyl-ACP intermediates of P. falciparum show that the hydrophobic core of ACP can sequester acyl chains up to 12 carbons; additional carbons protrude from the hydrophobic cavity. A unique side chain-to-backbone hydrogen bond between Ile-55 HN and Glu-48 O, combined with charge-charge repulsion between helix II and helix III, provides the molecular mechanism for ACP core expansion to accommodate longer acyl chains. NMR (chemical shift perturbation, 13C,15N-double-filtered NOESY, pKa measurement) on acyl-ACP intermediates The Journal of biological chemistry High 19520851
2009 Recombinant PfACP from P. falciparum exhibits malonyl transferase activity intrinsic to the individual ACP; mutational analysis identifies an arginine/lysine in loop II and an arginine/glutamine in helix III as catalytic residues essential for the malonyl transferase reaction, and this activity can complement a fabD(Ts) E. coli strain. In vitro malonyl transferase assay; site-directed mutagenesis; in vivo complementation of fabD(Ts) E. coli Molecular bioSystems High 19462023
2009 The ACP targeting sequence is used to drive GFP to the apicoplast in live P. berghei parasites; live imaging shows the apicoplast remains as a single branched organelle until nuclear division is complete, then rapidly segregates into daughter cells across all three asexual replication phases. Live fluorescence microscopy of P. berghei expressing GFP fused to ACP targeting sequence; FRAP and time-lapse imaging Biology of the cell Medium 19143588
2010 Crystal structures of P. falciparum ACP in both reduced (monomer) and disulfide-linked (dimer) forms reveal the disulfide in the cross-linked dimer is sequestered from bulk solvent at a tight molecular interface. Biochemical analysis of blood-stage parasites shows monomeric (reduced, holo) PfACP predominates; the disulfide-linked form is not detected even under oxidative stress, indicating the apicoplast maintains a reducing environment during blood-stage growth. X-ray crystallography of reduced and disulfide-linked ACP; solvent accessibility assays with reducing agents; non-reducing SDS-PAGE of parasite lysates; diamide treatment of blood-stage parasites Proteins High 19768685
2011 NMR analysis of the P. falciparum ACP transit peptide shows it is intrinsically disordered (unstructured) in vitro; in vivo mutagenesis studies demonstrate that increased helical content in the transit peptide disrupts apicoplast import, while transit peptides with proline-enforced disorder support robust apicoplast localization, establishing that structural disorder is a functional requirement for ACP transit peptide-mediated apicoplast targeting. NMR structural analysis of isolated transit peptide; in vivo apicoplast import assay with proline-substitution and helix-stabilizing mutants in P. falciparum Traffic (Copenhagen, Denmark) High 21668595
2013 FabI (enoyl-ACP reductase) colocalizes with apicoplast-targeted ACP in P. falciparum oocyst sporozoites, confirming FabI functions in the apicoplast as part of the type II FAS pathway; targeted deletion of fabI and fabB/F abolishes sporozoite development within the midgut oocyst without affecting asexual blood-stage replication. Immunofluorescence colocalization of FabI with ACP; targeted gene deletion and phenotypic analysis across life cycle stages Eukaryotic cell Medium 24297444
2021 ACP knockdown leads to loss of ACP immunofluorescence signal and loss of the apicoplast genome in P. falciparum PfΔGyrA parasites, indicating ACP is an established marker for apicoplast integrity used to confirm organelle loss. CRISPR/Cas9 gene editing of PfGyrA; ACP immunofluorescence as readout for apicoplast presence Antimicrobial agents and chemotherapy Low 34152814
2005 A P. falciparum ACPS-type phosphopantetheinyl transferase (PfACPS-PPT) is responsible for synthesizing holo-ACP from apo-ACP; PfACPS-PPT is bifunctional (fused to a metal-dependent hydrolase domain), is predicted to be targeted to the apicoplast, and is more closely related to proteobacterial PPTases than to animal or SFP-type PPTases. Bioinformatic identification; functional characterization of homologous CpSFP-PPT by in vitro and in vivo assays in E. coli (PfACPS-PPT not directly assayed in vitro) Eukaryotic cell Low 16002647
2026 Knockout or ligand-dependent knockdown of apicoplast ACP (PF3D7_0208500) is lethal to blood-stage P. falciparum independently of type II fatty acid synthesis activity; loss of ACP impairs biosynthesis of essential isoprenoid precursors and blocks apicoplast biogenesis. Proximity biotinylation and biochemical interaction studies show ACP binds and stabilizes apicoplast pyruvate kinase II (PKII), the only known source of NTPs in the apicoplast; ACP knockdown causes loss of PKII, which is sufficient to explain ACP essentiality at this stage. CRISPR/Cas9 knockout; ligand-dependent knockdown (conditional expression); proximity biotinylation (BioID); co-immunoprecipitation/biochemical interaction studies; isoprenoid biosynthesis assay; apicoplast biogenesis imaging bioRxivpreprint High 41959251

Source papers

Stage 0 corpus · 41 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
1998 Nuclear-encoded proteins target to the plastid in Toxoplasma gondii and Plasmodium falciparum. Proceedings of the National Academy of Sciences of the United States of America 600 9770490
2013 Type II fatty acid biosynthesis is essential for Plasmodium falciparum sporozoite development in the midgut of Anopheles mosquitoes. Eukaryotic cell 120 24297444
2003 The initiating steps of a type II fatty acid synthase in Plasmodium falciparum are catalyzed by pfACP, pfMCAT, and pfKASIII. Biochemistry 75 12549938
2007 In vivo functional analyses of the type II acyl carrier proteins of fatty acid biosynthesis. The Journal of biological chemistry 66 17522044
2009 GFP-targeting allows visualization of the apicoplast throughout the life cycle of live malaria parasites. Biology of the cell 65 19143588
2006 Kinetic, inhibition and structural studies on 3-oxoacyl-ACP reductase from Plasmodium falciparum, a key enzyme in fatty acid biosynthesis. The Biochemical journal 63 16225460
2005 Synthesis, biological activity, and X-ray crystal structural analysis of diaryl ether inhibitors of malarial enoyl acyl carrier protein reductase. Part 1: 4'-substituted triclosan derivatives. Bioorganic & medicinal chemistry letters 63 16198563
2006 Solution structures of conformationally equilibrium forms of holo-acyl carrier protein (PfACP) from Plasmodium falciparum provides insight into the mechanism of activation of ACPs. Biochemistry 61 16734426
2006 A role for falcilysin in transit peptide degradation in the Plasmodium falciparum apicoplast. Molecular microbiology 61 17074076
2004 Slow-tight-binding inhibition of enoyl-acyl carrier protein reductase from Plasmodium falciparum by triclosan. The Biochemical journal 60 15086316
2003 Apicoplast fatty acid biosynthesis as a target for medical intervention in apicomplexan parasites. International journal for parasitology 59 12906873
2010 Plasmodium falciparum acyl carrier protein crystal structures in disulfide-linked and reduced states and their prevalence during blood stage growth. Proteins 58 19768685
2007 X-ray structural analysis of Plasmodium falciparum enoyl acyl carrier protein reductase as a pathway toward the optimization of triclosan antimalarial efficacy. The Journal of biological chemistry 56 17567585
2006 Novel diphenyl ethers: design, docking studies, synthesis and inhibition of enoyl ACP reductase of Plasmodium falciparum and Escherichia coli. Bioorganic & medicinal chemistry 55 16893651
2005 Anti-protozoal and plasmodial FabI enzyme inhibiting metabolites of Scrophularia lepidota roots. Phytochemistry 54 15680992
2005 The crystal structure of PfFabZ, the unique beta-hydroxyacyl-ACP dehydratase involved in fatty acid biosynthesis of Plasmodium falciparum. Protein science : a publication of the Protein Society 54 15930004
2002 Functional characterization of the acyl carrier protein (PfACP) and beta-ketoacyl ACP synthase III (PfKASIII) from Plasmodium falciparum. Molecular and biochemical parasitology 52 12270624
2006 Synthesis and biological activity of diaryl ether inhibitors of malarial enoyl acyl carrier protein reductase. Part 2: 2'-substituted triclosan derivatives. Bioorganic & medicinal chemistry letters 47 16466916
2007 Green tea catechins potentiate triclosan binding to enoyl-ACP reductase from Plasmodium falciparum (PfENR). Journal of medicinal chemistry 45 17263522
2007 Studies of Toxoplasma gondii and Plasmodium falciparum enoyl acyl carrier protein reductase and implications for the development of antiparasitic agents. Acta crystallographica. Section D, Biological crystallography 42 17327670
2004 Mutational analysis of the triclosan-binding region of enoyl-ACP (acyl-carrier protein) reductase from Plasmodium falciparum. The Biochemical journal 41 15139852
2013 In vitro and in silico antimalarial activity of 2-(2-hydrazinyl)thiazole derivatives. European journal of pharmaceutical sciences : official journal of the European Federation for Pharmaceutical Sciences 39 24231338
2021 Natural biflavonoids as potential therapeutic agents against microbial diseases. The Science of the total environment 36 33493916
2011 Plasmodium falciparum apicoplast transit peptides are unstructured in vitro and during apicoplast import. Traffic (Copenhagen, Denmark) 34 21668595
2016 Overexpression of Plasmodium berghei ATG8 by Liver Forms Leads to Cumulative Defects in Organelle Dynamics and to Generation of Noninfectious Merozoites. mBio 32 27353755
2012 Lipoic acid metabolism of Plasmodium--a suitable drug target. Current pharmaceutical design 31 22607141
2007 Self-acylation properties of type II fatty acid biosynthesis acyl carrier protein. Chemistry & biology 27 17656314
2005 The plastid of Plasmodium spp.: a target for inhibitors. Current topics in microbiology and immunology 27 16265894
2009 Structural insights into the acyl intermediates of the Plasmodium falciparum fatty acid synthesis pathway: the mechanism of expansion of the acyl carrier protein core. The Journal of biological chemistry 25 19520851
2005 Plasmodium falciparum possesses organelle-specific alpha-keto acid dehydrogenase complexes and lipoylation pathways. Biochemical Society transactions 25 16246025
2008 Inhibiting enoyl-ACP reductase (FabI) across pathogenic microorganisms by linear sesquiterpene lactones from Anthemis auriculata. Phytomedicine : international journal of phytotherapy and phytopharmacology 24 18424102
2006 Analyses of co-operative transitions in Plasmodium falciparum beta-ketoacyl acyl carrier protein reductase upon co-factor and acyl carrier protein binding. The FEBS journal 24 16934037
2005 Functional characterization of an evolutionarily distinct phosphopantetheinyl transferase in the apicomplexan Cryptosporidium parvum. Eukaryotic cell 24 16002647
2006 Recombinant expression and biochemical characterization of the unique elongating beta-ketoacyl-acyl carrier protein synthase involved in fatty acid biosynthesis of Plasmodium falciparum using natural and artificial substrates. The Journal of biological chemistry 23 16467310
2007 Mass spectrometry-based systems approach for identification of inhibitors of Plasmodium falciparum fatty acid synthase. Antimicrobial agents and chemotherapy 21 17485508
2021 Divergent acyl carrier protein decouples mitochondrial Fe-S cluster biogenesis from fatty acid synthesis in malaria parasites. eLife 18 34612205
2008 Mechanical features of Plasmodium falciparum acyl carrier protein in the delivery of substrates. Journal of chemical information and modeling 17 19007113
2005 A novel approach for over-expression, characterization, and isotopic enrichment of a homogeneous species of acyl carrier protein from Plasmodium falciparum. Biochemical and biophysical research communications 17 15823545
2009 Catalysis and mechanism of malonyl transferase activity in type II fatty acid biosynthesis acyl carrier proteins. Molecular bioSystems 15 19462023
2021 Properties of Plasmodium falciparum with a Deleted Apicoplast DNA Gyrase. Antimicrobial agents and chemotherapy 11 34152814
2026 Acyl Carrier Protein is Essential for Apicoplast Biogenesis in Malaria Parasites Independent of Fatty Acid Synthesis. bioRxiv : the preprint server for biology 1 41959251