H4

Plasmodium falciparum histone H4 (PF3D7_1105000) is a core nucleosomal histone whose gene is transcribed in a replication-coupled manner, with mRNA peaking in late-stage asexual (trophozoite/schizont) parasites and an amino acid sequence that is fully conserved across P. falciparum, P. berghei, and P. yoelii (PMID:12739134). Its N-terminal tail is a hub for dynamic post-translational modification that reads out into transcriptional control and genome organization. H4 is acetylated at K5, K8, K12, and K16, marks written in vitro by the acetyltransferase PfMYST and reversed by HDAC activity that maintains H4 in a hypoacetylated state (PMID:16410041, PMID:20807207, PMID:28107750); among these, H4K8 acetylation is the rate-limiting acetylation and redistributes genome-wide from intergenic to coding regions in association with active transcription (PMID:28830512). The tail is additionally methylated at R3—asymmetrically by PfPRMT1 and symmetrically by PfPRMT5, the latter promoting active chromatin and invasion-gene expression—and at K20 by SET-domain HKMTs (PMID:19344311, PMID:37349497, PMID:18299133). Within the globular domain, K31 acetylation associates with active promoters while monomethyl-K31 demarcates pericentromeric heterochromatin, establishing H4K31 modifications as determinants of genome organization (PMID:29101771). These modification states are decoded and propagated by dedicated machinery: PfSir2 enforces H4 hypoacetylation at telomere-proximal loci to silence var genes and is displaced upon var activation (PMID:15820676), while tetra-acetylated H4 is bound by the PfBDP1 bromodomain and recruits the BDP1/BDP2 reader complex in an acetylation-level-dependent manner (PMID:36328269, PMID:31728527). The chromatin-assembly chaperone PfRbAp46/48 directly binds H4 in vitro (PMID:32363442).

1. 2003 Medium

   Establishing when H4 is made addressed whether its expression is coupled to DNA replication, framing H4 supply as part of the asexual cell cycle program.

   Evidence RT-PCR developmental transcription profiling and comparative sequence analysis across three Plasmodium species

   PMID:12739134

   Open questions at the time

   • Does not measure protein-level abundance or nucleosome deposition timing
   • Does not address which chaperones deposit H4
2. 2005 High

   Linking H4 acetylation state to var gene silencing showed that reversible H4 hypoacetylation is a mechanism of mutually exclusive antigenic variation.

   Evidence ChIP with acetylation-specific antibodies and PfSir2 localization across var loci

   PMID:15820676

   Open questions at the time

   • Does not resolve which specific H4 lysines PfSir2 targets
   • Does not establish how PfSir2 removal is triggered
3. 2006 Medium

   Cataloguing H4 acetyl and methyl marks and their cell-cycle timing defined the modifiable residues and showed that individual marks differ in dynamics (steady K5/K8/K12 vs. trophozoite-peaking K16).

   Evidence Mass spectrometry and acetylation-specific immunoblotting across the erythrocytic cycle

   PMID:16410041

   Open questions at the time

   • Does not assign enzymes to each mark
   • Does not map genomic distribution of the marks
4. 2008 Medium

   Detecting H4K20 methylation and SET-domain HKMT activity toward H4 extended the modification repertoire beyond acetylation to lysine methylation.

   Evidence Methyl-lysine-specific immunoblotting and in vitro HKMT assay from a eukaryotic expression system

   PMID:18299133

   Open questions at the time

   • Does not identify which SET protein deposits K20me in vivo
   • Functional consequence of H4K20 methylation not established
5. 2009 High

   Identifying PfPRMT1 as the H4R3 methyltransferase assigned a writer to an arginine mark and connected it to transcriptional activation.

   Evidence In vitro methyltransferase assay with peptide MS site mapping and developmental immunoblotting

   PMID:19344311

   Open questions at the time

   • In vivo requirement of PfPRMT1 for H4R3me not tested here
   • Downstream effectors reading H4R3me not identified
6. 2010 High

   Demonstrating that PfMYST acetylates H4 at K5/K8/K12/K16 assigned the writer for the H4 acetyl marks and linked H4 acetylation to cell-cycle progression.

   Evidence In vitro HAT assay with parasite-purified recombinant PfMYST plus GFP-tagged overexpression in parasites

   PMID:20807207

   Open questions at the time

   • Does not distinguish PfMYST from other HATs at each site
   • Overexpression phenotype not resolved to specific H4 residues
7. 2016 Medium

   Showing that HDAC inhibitors hyperacetylate H4 confirmed that HDAC enzymes actively maintain H4 hypoacetylation, closing the write/erase loop for the acetyl marks (in P. knowlesi).

   Evidence In situ anti-acetyl-H4 immunoblotting after treatment with four clinical HDAC inhibitors

   PMID:28107750

   Open questions at the time

   • Shown in P. knowlesi, not P. falciparum
   • Does not identify which specific HDAC erases which H4 site
8. 2017 High

   Genome-wide mapping identified H4K8ac as the rate-limiting acetylation and showed it redistributes with transcription, elevating H4K8ac to a principal regulatory mark of the intraerythrocytic cycle.

   Evidence Dominant-negative transgenic overexpression, ChIP-seq, and HDAC inhibitor treatment

   PMID:28830512

   Open questions at the time

   • Mechanism coupling H4K8ac shifts to transcription machinery unresolved
   • Reader specific for H4K8ac not defined
9. 2017 High

   Discovering globular-domain H4K31 modifications revealed that H4 shapes genome organization directly, with K31ac at active promoters and K31me1 marking an HP1/H3K9me3-independent pericentromeric heterochromatin.

   Evidence ChIP-seq, MS identification of H4K31 modifications, and comparative genomics with Toxoplasma gondii

   PMID:29101771

   Open questions at the time

   • Writers/erasers of H4K31 modifications not identified
   • How K31me1 recruits or defines heterochromatin without HP1 unresolved
10. 2019 Medium

    Quantitative reader proteomics established that H4 acetylation level, not just presence, dictates recruitment of the BDP1/BDP2 complex and a set of other reader proteins.

    Evidence Histone peptide pull-down with quantitative mass spectrometry and interaction proteomics

    PMID:31728527

    Open questions at the time

    • In vivo occupancy of readers on H4-marked chromatin not confirmed
    • Functional consequence of each reader binding not tested
11. 2020 Low

    Detecting a direct PfRbAp46/48–H4 interaction implicated a chromatin-assembly chaperone in H4 handling.

    Evidence Pull-down with purified recombinant PfRbAp46/48 and H4 plus nuclear localization by fractionation/IF

    PMID:32363442

    Open questions at the time

    • Single pull-down without reciprocal validation
    • In vivo role in H4 deposition not demonstrated
    • Binding interface not mapped
12. 2021 Low

    Cyclic tetrapeptide HDAC inhibitors hyperacetylating H4 in P. falciparum reinforced that PfHDACs act on H4 in this species.

    Evidence In situ hyperacetylation immunoblot and PfHDAC1 catalytic inhibition assay

    PMID:34491031

    Open questions at the time

    • Single immunoblot readout, pharmacological not genetic
    • Does not map which H4 residues are deacetylated by which HDAC
13. 2022 High

    Structural characterization proved that the PfBDP1 bromodomain preferentially binds tetra-acetylated H4, defining H4 multi-acetylation as a discrete reader-binding platform.

    Evidence Crystal structure of PfBDP1-BRD, solution NMR, and ITC with acetylated H4 peptides

    PMID:36328269

    Open questions at the time

    • Cellular consequence of BDP1 binding to tetra-acetyl H4 not tested here
    • Combinatorial specificity relative to single-acetyl marks not fully resolved
14. 2023 High

    Identifying PfPRMT5 as the H4R3 symmetric dimethyltransferase distinguished symmetric from asymmetric R3 methylation and tied it to active chromatin and invasion-gene regulation.

    Evidence In vitro methyltransferase assay, conditional knockdown, ChIP-seq, and transcriptomics

    PMID:37349497

    Open questions at the time

    • Direct causal link between H4R3sme2 and specific invasion genes not isolated from other PfPRMT5 activities
    • Reader of symmetric H4R3me not identified

• How the many H4 marks are integrated combinatorially to specify a given chromatin state, and which erasers act on the methyl and globular-domain marks, remains unresolved.
• Writers/erasers for H4K20me and H4K31 modifications not fully assigned
• Combinatorial cross-talk among acetyl/methyl marks not mapped
• In vivo requirement of most individual H4 marks for parasite viability untested