ARP4

ARP4 (PF3D7_1422800) is a nuclear actin-related protein of Plasmodium falciparum that couples chromatin remodeling to blood-stage cell-cycle progression (PMID:32552779). It localizes to the parasite nucleus, where it co-localizes with and directly binds ARP6 (PMID:32552779), and it is a component of the P. falciparum NuA4 (PfNuA4) histone acetyltransferase complex, identified through tandem affinity purification of PfMYST (PMID:38564734). At intergenic/upstream regions of euchromatic genes ARP4 co-occupies chromatin with the histone variant H2A.Z and the active mark H3K9ac; conditional knockdown depletes H2A.Z and reduces H3K9ac at these regions and represses transcription of H2A.Z-dependent genes, linking ARP4 to maintenance of euchromatic promoter states (PMID:32552779). Conditional knockdown blocks intraerythrocytic development, establishing ARP4 as essential for the blood-stage cell cycle (PMID:32552779). Beyond these findings, the biochemical activity of ARP4 within PfNuA4 has not been characterized in the available corpus.

1. 2020 Medium

   Whether ARP4 has a required function in the malaria parasite was unknown; conditional depletion established it as essential for intraerythrocytic development.

   Evidence glmS ribozyme conditional knockdown with growth curves and western blot in P. falciparum blood stages

   PMID:32552779

   Open questions at the time

   • Does not define the cell-cycle stage at which arrest occurs
   • Does not distinguish direct chromatin roles from indirect effects on growth
2. 2020 Medium

   The subcellular context and physical partners of ARP4 were undefined; imaging and pulldown placed it in the nucleus in complex with ARP6.

   Evidence Co-immunofluorescence and co-immunoprecipitation of epitope-tagged ARP4 and ARP6 in transgenic parasites

   PMID:32552779

   Open questions at the time

   • Single co-IP without reciprocal validation for the ARP4-ARP6 pair
   • Stoichiometry and directness of the interaction not resolved
3. 2020 Medium

   How ARP4 acts on chromatin was unknown; genome-wide profiling tied it to H2A.Z deposition, H3K9ac maintenance, and transcription of H2A.Z-dependent genes.

   Evidence ChIP-seq for H2A.Z and H3K9ac plus RNA-seq comparing ARP4 knockdown and control parasites

   PMID:32552779

   Open questions at the time

   • Whether ARP4 directly drives H2A.Z deposition or acts through a remodeling complex is not established
   • Enzymatic contribution of ARP4 itself not defined
4. 2024 Medium

   The complex membership of ARP4 was clarified by placing it within the PfNuA4 histone acetyltransferase complex.

   Evidence Tandem affinity purification of PfMYST with LC-MS/MS and reciprocal PfEAF2::GFP pulldown in P. falciparum 3D7

   PMID:38564734

   Open questions at the time

   • Does not resolve whether ARP4 also partitions into a SWR1-type complex in the parasite
   • Functional contribution of ARP4 to PfNuA4 acetyltransferase activity not tested

• The biochemical role of ARP4 within PfNuA4 and its mechanistic link between ARP6/H2A.Z chromatin function and NuA4 remain unresolved.
• No structural model of ARP4 within PfNuA4
• Whether ARP4 bridges NuA4 and an H2A.Z-depositing remodeler is untested
• No defined enzymatic or scaffolding activity for ARP4 itself