SAP18

PF3D7_0711400 (SAP18) is a putative histone deacetylase complex subunit in Plasmodium whose only direct biochemical characterization to date is its lactate-induced lysine lactylation: in P. knowlesi trophozoites treated with lactate, SAP18 acquires a lysine lactylation mark at a site unique to the lactylome (absent from the acetylome), and in this context it is described as associated with HDAC1 (PMID:41417877). Beyond this association and PTM, the protein has not been functionally or structurally characterized in the available corpus, and no direct experiment establishes its role within the deacetylase complex. At the transcript level in P. falciparum, SAP18 mRNA shows dynamic regulation across cell-cycle and developmental transitions—downregulated as an early responder at the G1/S transition following DFMO-induced arrest and polyamine rescue (PMID:30409996), and upregulated during gametocyte development where it is implicated in reduced DNA synthesis and a proliferative block accompanying sexual differentiation (PMID:31795940)—but these are transcriptomic correlations rather than protein-level or mechanistic evidence for SAP18 function.

1. 2018 Low

   To ask whether SAP18 participates in cell-cycle control, its transcript behavior was tracked through a controlled arrest-and-re-entry protocol, establishing it as an early transcriptional responder downregulated at the G1/S transition.

   Evidence Transcriptomics during DFMO-induced G1 arrest and polyamine-rescued cell-cycle re-entry in P. falciparum

   PMID:30409996

   Open questions at the time

   • Single transcriptomic study with no protein-level or functional validation of SAP18 in cell-cycle control
   • No evidence that the transcript change reflects a causal role rather than a downstream correlate
   • No link established between this transcript regulation and SAP18's role in a deacetylase complex
2. 2019 Low

   To probe SAP18's involvement in sexual differentiation, its expression was profiled across gametocyte development, showing upregulation coincident with decreased DNA synthesis and a proliferative block.

   Evidence High-resolution transcriptome profiling across gametocyte developmental stages in P. falciparum

   PMID:31795940

   Open questions at the time

   • Correlative transcriptomics only; no direct experiment tests SAP18's role in the proliferation block
   • No protein-level or mechanistic validation for SAP18 specifically
   • Causal contribution to sexual differentiation not demonstrated
3. 2025 Medium

   To determine whether SAP18 is a direct target of lactate-driven modification, PTM proteomics identified a unique lysine lactylation site on SAP18 in lactate-treated trophozoites, providing the first direct protein-level evidence for the gene and linking it to HDAC1 association.

   Evidence Mass spectrometry-based PTM proteomics of P. knowlesi trophozoite cultures +/- 25 mM lactate

   PMID:41417877

   Open questions at the time

   • No functional validation of the lactylation mark on SAP18 itself
   • The HDAC1 association is described but not biochemically mapped or reciprocally validated for SAP18
   • Functional consequence of the modification for deacetylase complex activity is unknown

• Whether SAP18 has a defined biochemical activity, a mapped role within a Plasmodium HDAC complex, or a causal function in the cell-cycle and gametocyte phenotypes it correlates with remains unresolved.
• No knockout, knockdown, or complementation study of SAP18
• No structural or reconstitution data for SAP18 or its complex membership
• No demonstration that transcript-level correlations reflect protein-level SAP18 function