AMT2

AMT2 (apicomplexan monocarboxylate transporter 2) is an apicoplast transporter in Toxoplasma gondii required for parasite growth and virulence (PMID:38502570). Identified through TurboID proximity labeling and genome engineering, conditional depletion of AMT2 produces critical growth defects in culture and attenuates virulence in mice (PMID:38502570). Metabolite profiling following depletion places AMT2 in the facilitation of metabolite flux linked to apicoplast isoprenoid and fatty acid biosynthesis, with loss of AMT2 causing stronger phenotypic defects than loss of its paralog AMT1 (PMID:38502570). Beyond this proximity-labeling and depletion evidence, the specific transported substrates, transport directionality, and molecular mechanism of AMT2 have not been biochemically characterized in the available corpus.

1. 2024 Medium

   Establishing that AMT2 is an apicoplast-resident transporter whose loss cripples the parasite answered whether this protein is functionally important, defining it as essential for growth and virulence.

   Evidence TurboID proximity labeling, genome engineering, and conditional protein depletion with growth and mouse virulence assays in Toxoplasma gondii

   PMID:38502570

   Open questions at the time

   • Direct transport activity and substrate specificity not demonstrated biochemically
   • Precise sub-membrane localization within the apicoplast not resolved
2. 2024 Medium

   Linking AMT2 depletion to altered metabolites of isoprenoid and fatty acid biosynthesis addressed which pathway it serves, and its stronger phenotype relative to AMT1 established functional non-redundancy between the paralogs.

   Evidence Conditional protein depletion coupled with metabolite analysis in Toxoplasma gondii

   PMID:38502570

   Open questions at the time

   • Which specific monocarboxylate metabolites are transported remains undefined
   • Whether the metabolite changes are direct transport effects or downstream consequences is unresolved
   • Mechanistic basis for the AMT2 vs AMT1 phenotypic difference not determined
3. 2024 Low

   Phylogenetic placement addressed the evolutionary origin of AMT1/AMT2, proposing derivation from the red-algal secondary endosymbiont lineage.

   Evidence Phylogenetic and genome-level analysis in Toxoplasma gondii

   PMID:38502570

   Open questions at the time

   • Evolutionary inference from genome analysis with no biochemical validation of transport mechanism or origin

• The direct transported substrate(s), transport directionality, and structural basis of AMT2 selectivity remain unknown.
• No reconstituted or heterologous transport assay establishing substrate identity
• No structural model of the transporter
• Mechanism coupling AMT2 activity to isoprenoid/fatty acid biosynthesis not resolved