SRPK1

SRPK1 (PF3D7_0302100) is a serine/threonine protein kinase that couples RNA processing and translation to developmental transitions across the Plasmodium life cycle (PMID:20870716, PMID:36094218). In P. falciparum, PfSRPK1 phosphorylates the putative splicing factor PfSR1, with which it co-localizes in the nucleus early in development, and it inhibits pre-mRNA splicing in parasite nuclear extracts while modulating PfSR1's RNA-binding activity (PMID:20870716). Genetic deletion in P. falciparum reduces merozoite formation during asexual schizogony and completely blocks male gamete differentiation, abolishing transmission to mosquitoes; transcriptomic analysis of knockout stage V gametocytes shows altered splicing and transcript abundance for genes governing microtubule/cilium morphogenesis, cyclic nucleotide metabolism, and signaling, consistent with a role in transcript homeostasis (PMID:36094218). In P. berghei, the ortholog acts within the first minute of male gametocyte activation, generating a distinct phosphoproteomic signature during the rapid cell cycle of gametogenesis (PMID:29141230); there it localizes to the cytoplasm (unlike the nuclear CDPK4 and MAP2), interacts with partners implicated in RNA translation, and its loss produces severe axoneme defects, placing SRPK1 in a cytoplasmic translational control pathway during endomitosis (PMID:40127922). Beyond these findings, the kinase's direct substrate repertoire outside PfSR1 has not been characterized in the available corpus.

1. 2010 Medium

   Establishing what molecular process SRPK1 acts on: the finding that PfSRPK1 phosphorylates the splicing factor PfSR1 and inhibits splicing defined SRPK1 as a regulator of RNA processing rather than an uncharacterized kinase.

   Evidence In vitro splicing inhibition and kinase assays with parasite nuclear extracts, plus RNA-binding and co-localization assays, in P. falciparum

   PMID:20870716

   Open questions at the time

   • single lab, single study without independent replication
   • no in-cell demonstration that SRPK1-dependent PfSR1 phosphorylation controls specific transcripts
   • substrate repertoire beyond PfSR1 unaddressed
2. 2017 Medium

   Placing SRPK1 temporally and functionally in male gametogenesis: phosphoproteomics of a P. berghei mutant showed SRPK1 drives specific phosphorylation events within the first minute of activation, linking it to the rapid gametogenesis cell cycle.

   Evidence Time-course phosphoproteomics comparing SRPK1 mutant and wild-type P. berghei gametocytes

   PMID:29141230

   Open questions at the time

   • direct kinase-substrate relationships not resolved from phosphoproteome correlation
   • single lab
   • does not distinguish direct from indirect phosphorylation targets
3. 2017 Low

   Testing SRPK1 dispensability in laboratory culture: convergent selection of a nonsense mutation during in vitro adaptation indicated loss-of-function confers a fitness advantage under culture, implying SRPK1's essential roles lie outside asexual culture growth.

   Evidence Longitudinal genome sequencing of cultured P. falciparum clinical isolates tracking emergent SNPs

   PMID:28117431

   Open questions at the time

   • genomic observation only, no direct functional assay of the mutant allele
   • mechanism of the fitness advantage unknown
   • does not establish SRPK1's normal function
4. 2022 High

   Defining the cellular consequences of SRPK1 loss in P. falciparum: knockout phenotyping showed reduced merozoite formation and a complete transmission block via failed male gametogenesis, tying SRPK1 to transcript homeostasis of morphogenesis and signaling genes.

   Evidence Gene knockout, mosquito transmission assays, and RNA-seq of stage V gametocytes in P. falciparum NF54

   PMID:36094218

   Open questions at the time

   • RNA-seq changes do not distinguish direct splicing targets from downstream effects
   • kinase substrates mediating the phenotype not identified
   • single lab
5. 2023 Low

   Confirming convergent culture selection of SRPK1 loss-of-function: independent emergence of nonsense mutations across multiple West African isolates reproduced the earlier observation that SRPK1 is a repeatable target of culture adaptation.

   Evidence Longitudinal genome sequencing of independent cultured P. falciparum clinical isolates

   PMID:37204422

   Open questions at the time

   • genomic observation only, no functional assay
   • does not clarify the mechanistic basis of the fitness cost of intact SRPK1 in culture
6. 2025 Medium

   Refining the subcellular context and pathway of SRPK1 in gametogenesis: cytoplasmic localization, Co-IP with translation-associated partners, and axoneme defects in knockouts placed P. berghei SRPK1 in a cytoplasmic RNA-translation pathway during endomitosis.

   Evidence Live-cell imaging, immunoprecipitation of interactors, and ultrastructure expansion microscopy/TEM of P. berghei knockout parasites

   PMID:40127922

   Open questions at the time

   • Co-IP interactors not reciprocally validated or functionally tested
   • how a cytoplasmic kinase controls translation mechanistically is unresolved
   • relationship between the nuclear splicing role and cytoplasmic translation role not reconciled

• The direct in vivo substrate set of SRPK1 beyond PfSR1, and how its distinct nuclear (splicing) and cytoplasmic (translation) activities are coordinated across developmental stages, remain unresolved.
• no comprehensive direct-substrate map
• mechanism switching kinase between nuclear and cytoplasmic roles unknown
• structural basis of substrate recognition uncharacterized