NEK1

PF3D7_1228300 (NEK1) is a NIMA-related protein kinase that governs cell-cycle progression and mitotic apparatus organization in Plasmodium (PMID:11322879, PMID:39255311). It is catalytically active as a recombinant protein, autophosphorylating and phosphorylating exogenous substrates with a specificity typical of NIMA/Nek-family kinases; activity depends on a single essential serine within a variant SMAHS motif that substitutes for the canonical FXXT (PMID:11322879). Among defined substrates, NEK1 phosphorylates the atypical P. falciparum MAPK homologue Pfmap-2 in vitro, and co-incubation of the two kinases synergistically increases substrate labelling, placing NEK1 upstream of or coordinate with MAPK-pathway output (PMID:11322879). In P. falciparum, NEK1 is non-redundantly required to complete the asexual erythrocytic cycle and is expressed in male but not female gametocytes (PMID:21757488). Its function is epistatically linked to the Aurora-related kinase PfArk1: mutations abolishing NEK1 catalytic activity confer resistance to the Aurora inhibitor Hesperadin, connecting NEK1 to PfArk1-dependent control of proliferation (PMID:33219324). During P. berghei male gametogenesis NEK1 localizes to the microtubule organising centre and is essential for spindle formation, kinetochore attachment, and chromosome segregation through the rapid closed endomitosis of gamete formation (PMID:39255311).

1. 2001 High

   Establishing whether PF3D7_1228300 encodes a functional kinase and defining its catalytic requirements answered the basic question of biochemical activity and revealed an atypical active-site motif.

   Evidence Bacterially expressed recombinant protein tested by in vitro autophosphorylation and substrate kinase assays with active-site mutagenesis

   PMID:11322879

   Open questions at the time

   • In vitro activity does not define physiological substrates or regulation in the parasite
   • The relevance of the variant SMAHS motif to cellular signalling was not tested
2. 2001 Medium

   Identifying Pfmap-2 as an in vitro substrate began to place NEK1 within a signalling relationship to the MAPK pathway.

   Evidence In vitro kinase assay with recombinant NEK1 and Pfmap-2 showing specific phosphorylation and synergistic substrate labelling

   PMID:11322879

   Open questions at the time

   • Phosphorylation shown only in vitro, not demonstrated in vivo
   • Functional consequence of Pfmap-2 phosphorylation for MAPK signalling not established
   • No reciprocal or cellular validation of the interaction
3. 2011 High

   Reverse genetics resolved whether NEK1 is dispensable relative to sibling Nek kinases, establishing a non-redundant essential role in asexual replication and a sex-specific expression pattern.

   Evidence Gene disruption/knockdown and immunofluorescence in P. falciparum

   PMID:21757488

   Open questions at the time

   • The molecular process NEK1 controls in the asexual cycle was not defined
   • Basis of male-restricted gametocyte expression not explained
4. 2020 High

   A drug-resistance selection connected NEK1 catalytic activity to the Aurora-related kinase PfArk1, defining a functional epistatic link controlling proliferation.

   Evidence Hesperadin resistance selection, whole-genome sequencing, and genetic epistasis analysis in P. falciparum

   PMID:33219324

   Open questions at the time

   • Direct biochemical interaction or phospho-relationship between NEK1 and PfArk1 not demonstrated
   • Mechanism by which loss of NEK1 activity confers drug protection unresolved
5. 2024 High

   High-resolution imaging and conditional knockdown assigned NEK1 a spatiotemporal role at the MTOC in male gametogenesis, linking it to spindle and kinetochore-mediated chromosome segregation.

   Evidence Live imaging, U-ExM, electron microscopy, conditional knockdown, and proteomics in P. berghei

   PMID:39255311

   Open questions at the time

   • Substrates NEK1 phosphorylates at the MTOC not identified
   • Whether the asexual essential role reflects the same MTOC/spindle function is untested
   • Relationship of MTOC role to PfArk1 epistasis not integrated

• The in vivo substrates and regulatory logic that couple NEK1 catalytic activity to PfArk1, MTOC organisation, and asexual-cycle progression remain undefined.
• No physiological substrate identified beyond in vitro Pfmap-2
• Mechanistic basis of NEK1–PfArk1 epistasis unknown
• Whether asexual and gametogenesis roles share a common molecular mechanism unresolved