JmjC1

PF3D7_0809900 (JmjC1) is a predicted JmjC-domain histone lysine demethylase of P. falciparum that conserves the iron- and 2-oxoglutarate-binding and substrate-binding residues characteristic of the mammalian Jumonji enzyme family (PMID:18299133, PMID:32272012). It is one of three JmjC-domain proteins in the parasite, and pharmacological inhibition of the P. falciparum Jumonji demethylases as a group with pan-JmjC inhibitors killed asexual blood-stage parasites and blocked gametocyte development, accompanied by increased trimethylated histone lysine marks consistent with loss of demethylase activity (PMID:32272012). Comparative genomics places JmjC1 in primate and avian malaria parasites (P. falciparum, P. vivax, P. knowlesi, P. gallinaceum) but not in rodent malaria parasites, an evolutionary distribution linked to its functional coupling with PfSET2-deposited H3K36me3 (PMID:24391504, PMID:34238209). Its own locus is repressed in stage II gametocytes through stage-specific H3K36me2/3 enrichment upstream of the transcription start site, integrating JmjC1 into the H3K36-methylation regulatory circuit during early gametocyte development (PMID:33794978). Direct in vitro enzymatic characterization of JmjC1 specifically — including biochemical confirmation of its substrate specificity — has not been reported in the available corpus; catalytic activity was demonstrated for the sibling PfJmj3, not for JmjC1 (PMID:32272012).

1. 2008 Low

   The question of whether P. falciparum encodes enzymes capable of removing histone lysine methylation was first addressed by identifying JmjC1 as a candidate JmjC-domain demethylase, establishing that active histone demethylation was plausible in the parasite.

   Evidence Bioinformatic/phylogenetic analysis of the P. falciparum genome; no direct enzymatic assay of JmjC1 performed

   PMID:18299133

   Open questions at the time

   • Computational prediction only; no in vitro demethylase assay of JmjC1
   • No substrate identified experimentally
   • No cellular localization or expression data
2. 2014 Low

   To connect JmjC1 to a defined chromatin pathway, comparative genomics proposed it as the cognate demethylase counteracting PfSET2-deposited H3K36me3 and showed it is restricted to primate malaria parasites, implicating it in var gene regulation.

   Evidence Comparative genomics across six Plasmodium species; functional link to PfSET2/H3K36me3 inferred from orthology, not direct assay of JmjC1

   PMID:24391504

   Open questions at the time

   • Enzyme-substrate link to H3K36me3 inferred from orthology, not demonstrated for JmjC1
   • No loss-of-function evidence for a role in var gene regulation
   • Functional consequence of primate-specific distribution untested
3. 2020 Medium

   Whether the parasite Jumonji enzymes are catalytically competent and druggable was tested; JmjC1 was shown to conserve the catalytic iron/2-OG residues, and pan-JmjC inhibition killed asexual parasites and blocked gametocytes with rising histone trimethylation, though direct catalysis was proven only for the sibling PfJmj3.

   Evidence Sequence alignment for JmjC1 catalytic residues; asexual growth (3D7, Dd2) and gametocyte assays with pan-JmjC inhibitors; histone trimethylation immunoassay; in vitro 2-OG-to-succinate assay of PfJmj3 only

   PMID:32272012

   Open questions at the time

   • JmjC1-specific enzymatic activity not directly measured; catalysis shown for PfJmj3 only
   • Inhibitor phenotypes apply to the JmjC family collectively, not JmjC1 alone
   • No genetic knockout to attribute phenotypes to JmjC1
4. 2021 Medium

   How JmjC1 itself is regulated across the life cycle was addressed by mapping histone marks at its locus, revealing stage II gametocyte-specific H3K36me2/3 enrichment upstream of its TSS correlating with transcriptional repression, embedding JmjC1 within a self-referential H3K36 regulatory circuit.

   Evidence ChIP-seq for H3K36me2/me3 in stage-specific gametocytes correlated with expression data

   PMID:33794978

   Open questions at the time

   • Repression inferred from mark association, not confirmed by loss-of-function
   • Mechanism depositing H3K36me2/3 at jmjc1 not defined
   • Functional consequence of jmjc1 repression for gametocytes untested
5. 2021 Low

   The evolutionary breadth of JmjC1 was refined by synteny analysis showing conservation across Laverania, P. vivax, and the avian parasite P. gallinaceum but loss in rodent parasites, arguing its origin predates the Plasmodium root and its functions extend beyond var gene regulation.

   Evidence Comparative genomic synteny analysis across Plasmodium species and Laverania members

   PMID:34238209

   Open questions at the time

   • Comparative genomics only; no functional experiment
   • Additional (non-var) functions proposed but not defined
   • No mechanistic basis for loss in rodent parasites
6. 2022 Low

   Reviews consolidated JmjC1's presumed substrate specificity, citing prior work that it acts on H3K9me2/3 and H3K36me3 and grouping it with the JMJD/KDM4-related demethylases to rationalize antimalarial inhibitor design, without adding new experimental evidence on JmjC1.

   Evidence Substrate specificity cited from prior literature in review and medicinal-chemistry contexts; no new experiment on JmjC1

   PMID:35433676 PMID:36106425

   Open questions at the time

   • Substrate specificity attributed to cited studies, not independently demonstrated in this corpus
   • No structural model of JmjC1
   • No direct enzyme kinetics or inhibitor selectivity data for JmjC1

• The central open question is direct biochemical demonstration of JmjC1's own demethylase activity and substrate specificity, and genetic dissection of its role in var gene regulation and gametocyte development independent of its sibling Jumonji enzymes.
• No purified-enzyme demethylase assay for JmjC1
• No JmjC1-specific loss-of-function phenotype
• No structure or defined interaction partners for JmjC1