NEK3

PF3D7_1201600 (NEK3/Pfnek3) is a Plasmodium falciparum NIMA-related kinase that acts as an atypical MAPKK-like upstream activator of the malarial MAP kinase Pfmap2, phosphorylating it specifically at residue T290 within its TSH activation motif while sparing Pfmap1 and human MAPK1, establishing substrate selectivity for Pfmap2 (PMID:17064692, PMID:17662247). NEK3's own catalytic output is controlled by activation-loop phosphorylation at S221 and S226 (an SSEQSS MAPKK-consensus motif) together with T82 (PMID:19644735), and the enzyme displays dual-specificity serine/threonine and tyrosine kinase activity, with divalent-cation-dependent tyrosine autophosphorylation stimulating its activity despite a catalytic-loop motif resembling classical Ser/Thr kinases (PMID:22116321). NEK3 is expressed in late asexual and gametocyte stages and is phylogenetically divergent from mammalian NIMA kinases (PMID:17064692). In P. berghei, nek3 transcript is downregulated upon PP6 disruption, placing it within the PKG-Ca2+ signaling cascade during gametogenesis (PMID:40623036). Beyond these findings, the in vivo genetic requirements and structural basis of NEK3 function have not been characterized in the available corpus.

1. 2006 Medium

   Establishing that a Plasmodium NIMA-related kinase could serve as an upstream MAPK activator answered whether malarial MAPKs are controlled by a canonical MAPKK, showing instead an atypical activator with strict substrate selectivity.

   Evidence In vitro kinase assays with recombinant NEK3 against Pfmap2, Pfmap1, and human MAPK1

   PMID:17064692

   Open questions at the time

   • Substrate specificity shown only in vitro, not in parasite
   • No demonstration that endogenous NEK3 activates Pfmap2 in vivo
2. 2007 High

   Pinpointing the exact residue NEK3 phosphorylates on Pfmap2 defined the molecular basis of the MAPKK-like relationship, moving from bulk activation to a mapped phosphosite.

   Evidence Site-directed mutagenesis (T290A, S291A, H292K), in vitro kinase assays, and LC-MS confirmation

   PMID:17662247

   Open questions at the time

   • Does not establish stoichiometry or kinetics of Pfmap2 activation in vivo
   • No confirmation this phosphorylation event occurs at a specific parasite stage
3. 2009 High

   Identifying NEK3's own regulatory phosphosites answered how the kinase itself is switched on, revealing activation-loop and additional phosphocontrol upstream of Pfmap2.

   Evidence Site-directed mutagenesis, tandem mass spectrometry, and in vitro kinase assays mapping S221, S226, and T82

   PMID:19644735

   Open questions at the time

   • Upstream kinase(s) responsible for these phosphorylations not identified
   • Whether these sites are phosphorylated in vivo not shown
4. 2011 Medium

   Demonstrating dual serine/threonine and tyrosine kinase activity addressed the enzymatic character of NEK3, showing an unexpected tyrosine-phosphorylation-dependent activation mode not predicted by its catalytic-loop sequence.

   Evidence Immunoblot autophosphorylation analysis, in vitro kinase assays with MBP, cation dependence, and biocomputational site prediction

   PMID:22116321

   Open questions at the time

   • Tyrosine sites Y117/Y122/Y172/Y238 identified partly computationally, not fully validated
   • Physiological substrate of the tyrosine activity unknown
5. 2023 Medium

   Screening human PLK1 inhibitors against parasite kinases flagged NEK3 as a druggable target but showed it is unlikely to be the sole target of these compounds, informing inhibitor selectivity considerations.

   Evidence Kinase panel binding screen and phosphoproteomics comparing two structurally distinct PLK1 inhibitors

   PMID:36919909

   Open questions at the time

   • Does not establish NEK3 as the causal antimalarial target
   • No NEK3-specific inhibitor characterized
6. 2025 Low

   Linking nek3 transcription to PP6 disruption placed the kinase within a defined signaling cascade during gametogenesis, extending its role from an in vitro biochemical activity to a pathway context in P. berghei.

   Evidence PP6 genetic knockout in P. berghei with transcriptomics and cGMP/Ca2+ measurements in activated gametocytes

   PMID:40623036

   Open questions at the time

   • NEK3 downregulation is a secondary transcriptomic consequence, not a direct manipulation of NEK3
   • Does not establish that NEK3 itself is required for the observed phenotypes

• Whether NEK3 is genetically required for asexual growth or gametogenesis and how it is positioned relative to PKG-Ca2+ signaling at the protein level remain unresolved.
• No direct NEK3 knockout/knockdown phenotype reported
• No structural model of NEK3 or its Pfmap2 complex
• Upstream activating kinase of NEK3 unidentified