AP2-LT

AP2-LT (PF3D7_0802100) is an AP2-domain transcription factor of Plasmodium falciparum that functions as an integral subunit of a divergent PfGCN5 histone acetyltransferase complex, which additionally contains the plant homeodomain proteins PfPHD1 and PfPHD2 (PMID:34403450). Chromatin mapping by CUT&Tag-seq places AP2-LT together with PfGCN5 and the active mark H3K9ac at gene promoters in asexual blood stages, consistent with a role in recruiting the acetyltransferase complex to its target promoters (PMID:40558503). Its binding motif is enriched at merozoite invasion genes that are down-regulated when the PfGCN5 bromodomain or the PfPHD1 PHD domain is deleted, indicating that AP2-LT, alongside AP2-I and BDP1, directs the complex to activate erythrocyte invasion genes (PMID:34403450). Beyond its role within the PfGCN5 complex and its promoter co-localization, no further mechanistic detail specific to AP2-LT has been characterized in the available corpus.

1. 2016 Low

   Whether AP2-LT is subject to post-translational regulation was addressed by proteome-wide acetylome profiling, which detected AP2-LT as a lysine-acetylated protein and established acetylation as a candidate switch on ApiAP2 DNA binding.

   Evidence Mass spectrometry acetylome profiling plus in vitro DNA-binding assays on acetylated AP2 domains

   PMID:26813983

   Open questions at the time

   • The DNA-binding ablation was shown for ApiAP2 domains generally, not demonstrated specifically for the AP2-LT domain
   • No in vivo consequence of AP2-LT acetylation established
   • Acetylation site occupancy and the enzyme responsible not defined for AP2-LT
2. 2021 Medium

   The functional context of AP2-LT was resolved by defining it as an integral subunit of a divergent PfGCN5 acetyltransferase complex and linking that complex to activation of merozoite invasion genes bearing the AP2-LT motif.

   Evidence Co-IP/mass spectrometry complex identification with ΔBrd/ΔPHD domain-deletion mutants, transcriptomics, and binding-motif analysis in P. falciparum

   PMID:34403450

   Open questions at the time

   • The specific contribution of AP2-LT versus AP2-I and BDP1 to recruitment was not dissected by AP2-LT loss-of-function
   • Direct binding of AP2-LT to invasion-gene promoters not demonstrated in this study
   • Complex identification from a single lab, not independently replicated
3. 2025 Medium

   Whether AP2-LT physically occupies promoters with the PfGCN5 complex on chromatin was tested by direct in vivo mapping, showing co-localization with PfGCN5 and H3K9ac at promoters and supporting a promoter-recruitment role.

   Evidence CUT&Tag-seq chromatin localization mapping and co-localization analysis in P. falciparum asexual blood stages

   PMID:40558503

   Open questions at the time

   • Causal test of whether AP2-LT is required for PfGCN5 or H3K9ac deposition at promoters not performed
   • Genome-wide direct DNA sequence recognition by AP2-LT not resolved
   • Single-lab dataset

• It remains unknown whether AP2-LT is functionally required for PfGCN5 complex recruitment and invasion-gene activation, and how its acetylation modulates DNA binding in vivo.
• No AP2-LT-specific knockout or knockdown phenotype reported
• Direct in vitro DNA-binding specificity of the AP2-LT domain not characterized
• Mechanism connecting acetylation of AP2-LT to its chromatin occupancy unestablished