PRMT5

PF3D7_1361000 (PRMT5) is a type II protein arginine methyltransferase in Plasmodium falciparum that couples histone arginine methylation to the regulation of red blood cell invasion (PMID:37349497). Purified recombinant PRMT5 catalyzes symmetric dimethylation of histone H3 at R2 (H3R2me2s) and R8 and of histone H4 at R3 in vitro (PMID:37349497). It operates within a methylosome-like complex, associating with the core spliceosomal Sm protein PfSmD1 and co-localizing with it, consistent with a role in cytoplasmic Sm-protein assembly (PMID:24047207), and it further associates with the invasion-related transcriptional regulators AP2-I, BDP1, and GCN5 (PMID:37349497). Functionally, disruption of PRMT5 impairs asexual growth chiefly through reduced merozoite invasion efficiency, with depletion of the active mark H3R2me2s at invasion genes, downregulation of invasion transcripts, and widespread RNA splicing anomalies including at invasion-related genes (PMID:37349497). Pharmacological inhibition with onametostat, whose primary target PRMT5 has been genetically confirmed, reduces H3R2me2s and phenocopies the invasion defect, linking PRMT5 catalytic activity to invasion gene expression (PMID:39194263).

1. 2013 Medium

   Establishing PRMT5's physical context: whether it participates in a methylosome-like assembly was unknown, and demonstrating its association with the spliceosomal Sm protein PfSmD1 placed it in a complex governing Sm-protein assembly.

   Evidence Pull-down, co-immunoprecipitation, immunofluorescence co-localization and MALDI-TOF in P. falciparum

   PMID:24047207

   Open questions at the time

   • Direct methylation of SmD1 by PRMT5 was inferred, not demonstrated enzymatically
   • Stoichiometry and full composition of the methylosome-like complex not defined
2. 2013 Medium

   Whether arginine methylation is functionally required for downstream Sm-protein interactions was open; the methylation-dependent PfSMN–PfSmD1 interaction argued that PRMT5-type methylation licenses these contacts.

   Evidence Yeast two-hybrid and in vitro pull-down assays in P. falciparum

   PMID:24047207

   Open questions at the time

   • PRMT5 itself was not shown to be the methyltransferase responsible for the SmD1 mark in this assay
   • In vivo relevance of the methylation-dependent interaction not tested
3. 2023 High

   The enzymatic identity of PRMT5 was defined by showing purified protein catalyzes symmetric dimethylation of specific histone arginines, establishing it as a type II arginine methyltransferase acting on chromatin.

   Evidence In vitro methyltransferase assay with purified recombinant PfPRMT5

   PMID:37349497

   Open questions at the time

   • Relative in vivo contribution of each histone substrate (H3R2, H3R8, H4R3) not resolved
   • Non-histone substrates beyond SmD1-type proteins not systematically mapped
4. 2023 High

   The biological consequence of PRMT5 loss was unknown; genetic disruption tied it to merozoite invasion via loss of H3R2me2s and downregulation of invasion transcripts, defining its role in the asexual cycle.

   Evidence Genetic disruption, transcriptomics, and genome-wide ChIP-seq in P. falciparum

   PMID:37349497

   Open questions at the time

   • Direct chain of causality from mark loss to specific invasion-gene silencing not dissected gene-by-gene
   • Whether transcriptional and splicing defects act independently or jointly on invasion unresolved
5. 2023 Medium

   Whether PRMT5 acts on RNA processing in addition to chromatin was addressed by showing its disruption causes RNA splicing anomalies, connecting its Sm-protein association to a functional splicing role.

   Evidence Genetic disruption with transcriptomic/splicing analysis in P. falciparum

   PMID:37349497

   Open questions at the time

   • Mechanistic link between PRMT5 methyltransferase activity and specific splicing events not established
   • Splicing defects not separated from chromatin-driven effects on invasion phenotype
6. 2023 Medium

   To connect PRMT5 to invasion regulation at the complex level, interactome analysis identified associations with the transcriptional regulators AP2-I, BDP1, and GCN5.

   Evidence Interactome/co-IP coupled with mass spectrometry in P. falciparum

   PMID:37349497

   Open questions at the time

   • Single interactome study without reciprocal validation of the partners
   • Whether these associations are direct or bridged by other factors unknown
7. 2024 High

   Whether PRMT5 is a druggable and validated target was tested; onametostat inhibited purified enzyme and showed an IC50 shift in a disruptant line, confirming PRMT5 as its primary target in P. falciparum.

   Evidence In vitro methyltransferase inhibition and IC50-shift assay in a PRMT5-disruptant parasite line

   PMID:39194263

   Open questions at the time

   • Selectivity of onametostat against other parasite methyltransferases not quantified
   • In vivo efficacy not addressed
8. 2024 Medium

   To close the loop between catalytic activity and phenotype, pharmacological inhibition was shown to reduce H3R2me2s and impair invasion, phenocopying genetic disruption.

   Evidence Onametostat treatment with western blot for H3R2me2s and invasion assay in P. falciparum

   PMID:39194263

   Open questions at the time

   • Temporal ordering of mark loss versus invasion-gene shutdown not resolved
   • Off-target contributions to the invasion phenotype not fully excluded

• How PRMT5's chromatin (H3R2me2s) and splicing functions are mechanistically integrated to control invasion, and which non-histone substrates it methylates in vivo, remain open.
• No structural model of PRMT5 or its complexes
• Direct in vivo substrate map beyond histones undefined
• Mechanism coupling arginine methylation to specific splicing outcomes unknown