KDAC4

TgKDAC4 is a class IV lysine deacetylase of Toxoplasma gondii that localizes to the periphery of the apicoplast, where it is the only lysine deacetylase identified in this organelle to date (PMID:37375060). Beyond this localization, mechanistic characterization is limited: phylogenetic analysis and immunoprecipitation-mass spectrometry point to a KDAC domain of putative prokaryotic origin and to apicoplast-resident candidate substrates TgCPN60 and TgGAPDH2, but these remain uncharacterized biochemically in the available corpus (PMID:37375060). No enzymatic activity, catalytic mechanism, or functional consequence of deacetylation has been experimentally established.

1. 2023 Medium

   Establishing where a candidate deacetylase acts defined TgKDAC4 as the first lysine deacetylase associated with the Toxoplasma apicoplast, implicating acetylation control in this metabolic organelle.

   Evidence Transmission electron microscopy and subcellular localization/fractionation assays in Toxoplasma gondii

   PMID:37375060

   Open questions at the time

   • Localization does not demonstrate deacetylase enzymatic activity
   • Whether TgKDAC4 sits inside the apicoplast lumen or is peripherally attached is not resolved
   • Functional role of the enzyme in apicoplast biology is untested
2. 2023 Low

   Phylogenetic classification addressed the evolutionary origin of the enzyme, assigning it to class IV with a KDAC domain of putative prokaryotic origin unique to apicomplexans.

   Evidence Phylogenetic analysis of the KDAC domain (computational)

   PMID:37375060

   Open questions at the time

   • Computational prediction only, no in vitro enzymatic validation
   • Only a portion of the canonical KDAC domain is shared, leaving catalytic competence unconfirmed
   • No structural model of the domain
3. 2023 Low

   Interaction proteomics began to define candidate substrates, nominating apicoplast-resident acetylated proteins TgCPN60 and TgGAPDH2 as putative partners or substrates.

   Evidence Co-immunoprecipitation followed by mass spectrometry in Toxoplasma gondii

   PMID:37375060

   Open questions at the time

   • Single Co-IP/MS experiment without reciprocal pull-down or functional validation
   • Direct deacetylation of these substrates by TgKDAC4 not demonstrated
   • Cannot distinguish stable interactors from transient enzyme-substrate contacts

• Whether TgKDAC4 has catalytic deacetylase activity, which apicoplast substrates it deacetylates, and how this regulates apicoplast metabolism remain unresolved.
• No in vitro or in vivo demonstration of deacetylase activity
• No genetic loss-of-function phenotype reported
• Candidate substrate deacetylation not biochemically confirmed