AAT1

AAT1 (PF3D7_0629500) is a digestive vacuole-associated amino acid transporter of Plasmodium falciparum that participates in the export and utilisation of haemoglobin-derived peptides from the digestive vacuole (PMID:42370240). Conditional knockdown of PfAAT1 causes accumulation of Hb-derived peptides and reveals a functional overlap with PfCRT: AAT1 is largely dispensable when PfCRT is wild-type but becomes essential in a mutant PfCRT background, and restoring wild-type pfcrt abolishes the growth defect of pfaat1 knockdown (PMID:42370240). Field-selected variants act as gain-of-function alleles that compensate for impaired PfCRT peptide transport — S258L and F313S confer a fitness advantage in the mutant PfCRT background, with F313S particularly favoured under cysteine- and methionine-limiting conditions (PMID:42370240), and their selection in the field is driven by epistatic interaction with pfcrt rather than by direct effects on chloroquine transport (PMID:42370240). Consistent with a role in drug handling, heterologous expression of AAT1 in yeast produces chloroquine hypersensitivity and increased CQ and quinine uptake in an amino acid-inhibitable manner reversed by the S258L SNP (PMID:29410428), and population genomics documents temporal co-selection of pfaat1 S258L alongside pfcrt K76T (PMID:37169919).

1. 2005 Low

   Before any functional data, it was unknown whether PF3D7_0629500 encoded a transporter at all; genome annotation placed it within a candidate gene family to be tested.

   Evidence Genome-wide computational hydropathy and sequence-homology analysis of the P. falciparum genome

   PMID:15774027

   Open questions at the time

   • Computational prediction only, no experimental validation of transport
   • No substrate identified
   • No subcellular localisation determined
2. 2012 Medium

   The first evidence that an aat1 locus contributes to antimalarial drug response came from linking a mutation in the P. chabaudi orthologue to the initial step of chloroquine resistance, implicating this gene family in resistance genetics.

   Evidence Linkage group selection genetic cross and quantitative whole-genome resequencing of CQ-resistant P. chabaudi mutants

   PMID:22435897

   Open questions at the time

   • Shown in P. chabaudi ortholog, not P. falciparum PF3D7_0629500 directly
   • Mechanism of resistance not resolved
   • No transport substrate defined
3. 2018 High

   To test whether AAT1 itself handles drugs, heterologous reconstitution established it as a functional transporter capable of drug uptake and modulated by a resistance-associated SNP.

   Evidence Heterologous expression in yeast with radiolabelled drug uptake, S258L site-directed mutagenesis, tryptophan competition, and fluorescence localisation to the yeast plasma membrane

   PMID:29410428

   Open questions at the time

   • Localisation and behaviour in a heterologous yeast system may not reflect the native parasite membrane
   • Physiological substrate in the parasite not identified here
   • Direct role of drug transport in parasite resistance not demonstrated
4. 2023 High

   Combining population genomics with reciprocal genetics resolved how specific pfaat1 alleles are selected, showing S258L potentiates CQ resistance at a fitness cost while F313S restores fitness and reduces resistance, under co-selection with pfcrt K76T.

   Evidence Longitudinal population genomics (The Gambia 1984–2014), parasite genetic crosses / QTL mapping, and CRISPR editing of pfaat1 alleles with in vitro drug sensitivity and fitness assays

   PMID:37169919

   Open questions at the time

   • Molecular mechanism connecting allele to fitness not defined in this study
   • Native transported substrate not identified
   • Causal basis of epistasis with pfcrt not mechanistically explained
5. 2026 High

   Direct functional dissection in parasites established the physiological role: PfAAT1 exports/utilises haemoglobin-derived peptides from the digestive vacuole and functionally overlaps with PfCRT, explaining its conditional essentiality and the gain-of-function nature of field variants.

   Evidence Conditional pfaat1 knockdown, isogenic mutant-vs-wild-type pfcrt allele replacement, mass-spectrometry peptide accumulation assays, and growth under amino acid-limiting conditions (preprint)

   PMID:42370240

   Open questions at the time

   • Preprint, not yet peer-reviewed
   • Direct biochemical demonstration of peptide transport by purified PfAAT1 not shown
   • Structural basis of S258L/F313S gain-of-function not defined

• The direct molecular substrate specificity of PfAAT1 and the structural mechanism by which S258L and F313S enhance peptide transport remain unresolved.
• No high-resolution structure of PfAAT1
• Peptide substrate spectrum not biochemically defined
• Mechanistic basis of epistasis with PfCRT not established