ARFGEF

PF3D7_1442900 is the single Sec7 domain-containing ARF-GEF encoded in the P. falciparum genome and functions as the primary target of the secretory-pathway inhibitor brefeldin A in the parasite (PMID:11555294). A conserved methionine in helix H of its Sec7 domain governs brefeldin A sensitivity: allelic replacement of the endogenous locus with a construct carrying a single Met-to-Ile substitution at this residue is sufficient to render parasites brefeldin A-resistant, establishing PF3D7_1442900 as the drug's molecular target (PMID:11555294, PMID:15500915). The Sec7 domain is structurally atypical, with two conserved subdomains separated by a 146-amino-acid insertion not found in other eukaryotic ARF-GEFs; gene-replacement constructs lacking this insertion failed to yield viable resistant parasites, indicating the insertion is required for the protein's function (PMID:11555294, PMID:15500915). Direct GDP/GTP exchange activity of PF3D7_1442900 on its presumptive substrate PfArf1 has not been demonstrated in the available corpus; in vitro activation of PfArf1 has only been shown using a heterologous human ARNO Sec7 domain as a surrogate (PMID:32144363).

1. 2001 Medium

   Establishing whether Plasmodium encodes an ARF-GEF and linking it to drug action, the identification of a single Sec7-domain ARF-GEF and a helix H point mutation in a brefeldin A-resistant line first implicated PF3D7_1442900 as the parasite's brefeldin A target.

   Evidence drug-selection of a brefeldin A-resistant parasite line followed by Sec7-domain sequencing

   PMID:11555294

   Open questions at the time

   • Causality inferred by correlation, not yet by genetic replacement
   • Enzymatic ARF-GEF activity of the protein not tested
2. 2001 Low

   Defining the domain architecture, sequence analysis revealed an unusual 146-amino-acid insertion splitting the two conserved subdomains of the Sec7 domain, distinguishing PF3D7_1442900 from other eukaryotic ARF-GEFs.

   Evidence sequence and structural comparison of the plasmodial Sec7 domain against other eukaryotic Sec7 domains

   PMID:11555294

   Open questions at the time

   • Structural inference from sequence only, no biochemical or structural validation
   • Functional role of the insertion untested at this stage
3. 2004 High

   Converting correlation into causation, targeted allelic replacement showed the single Met-to-Ile helix H mutation is sufficient for brefeldin A resistance, and that constructs lacking the 146-aa insertion fail, establishing the insertion as required for function.

   Evidence double cross-over gene replacement of the endogenous Sec7 domain with mutant transgenic sequences followed by brefeldin A selection

   PMID:15500915

   Open questions at the time

   • Does not demonstrate the protein's GDP/GTP exchange activity
   • Molecular basis of insertion requirement not resolved
   • Substrate ARF and downstream secretory role not directly assayed
4. 2020 Low

   Testing whether the ARF-GEF activates PfArf1, an in vitro study established that PfArf1 can be activated by a Sec7 domain but used the human ARNO domain as a surrogate, leaving PF3D7_1442900's own catalytic activity undemonstrated.

   Evidence in vitro colorimetric GTPase assay with truncated PfArf1 and heterologous Sec7/GAP domains

   PMID:32144363

   Open questions at the time

   • The Sec7 domain used was heterologous (human ARNO), not PF3D7_1442900
   • No direct enzymatic demonstration of PF3D7_1442900 activity on PfArf1

• The intrinsic ARF-GEF catalytic activity of PF3D7_1442900, its authentic parasite ARF substrate, its subcellular localization, and the mechanistic function of its 146-amino-acid Sec7 insertion remain undetermined in the available corpus.
• No direct measurement of PF3D7_1442900-mediated nucleotide exchange
• Localization within the secretory pathway not experimentally established
• Function of the 146-aa insertion at the molecular level unknown