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Pfnek3 functions as an atypical MAPKK in Plasmodium falciparum

Huiyu Low1, Yu Min Lye, Tiow-Suan Sim

  • 1Department of Microbiology, Yong Loo Lin School of Medicine, National University of Singapore, MD4A, 5 Science Drive 2, Singapore 117597, Singapore.

Biochemical and Biophysical Research Communications
|July 31, 2007
PubMed

Insights

Plasmodium falciparum may use Pfnek3, a malarial protein kinase, to activate signaling pathways. Pfnek3 phosphorylates Pfmap2 at residue T290, suggesting a non-conventional mitogen-activated protein kinase (MAPK) cascade.

Area of Science:

  • Molecular parasitology
  • Signal transduction pathways
  • Protein kinase function

Background:

  • Eukaryotic cells utilize mitogen-activated protein kinases (MAPKs) for regulatory pathway activation.
  • The malaria parasite Plasmodium falciparum lacks canonical MAPK cascade components, including known MAPK kinase (MAPKK) sequences.
  • Two Plasmodium falciparum MAPK homologues (Pfmap1 and Pfmap2) have been identified, but their upstream activators are unknown.

Purpose of the Study:

  • To biochemically and molecularly characterize the role of Pfnek3 as a potential upstream MAPKK in Plasmodium falciparum.
  • To investigate the phosphorylation site and activation mechanism of Pfmap2 by Pfnek3.

Main Methods:

  • Homology PCR to identify plasmodial MAPK homologues.
  • Site-directed mutagenesis of Pfmap2 (T290A, S291A, H292K) based on a proposed TSH activation motif.
  • Kinase assays to assess Pfnek3's phosphorylation activity on Pfmap2 and its mutants.
  • Liquid chromatography-mass spectrometry to confirm phosphorylation sites.

Main Results:

  • Pfnek3 was confirmed as an unusual activator of Pfmap2.
  • Residue T290 of Pfmap2 was identified as the primary site of phosphorylation by Pfnek3.
  • Mutagenesis studies supported the role of T290 in Pfnek3-mediated activation of Pfmap2.
  • Mass spectrometry validated T290 as the phosphorylation site.

Conclusions:

  • Plasmodium falciparum may employ non-conventional kinases like Pfnek3 to mediate signaling pathway activation, mimicking MAPK cascade functions.
  • Pfnek3 acts as an upstream kinase, phosphorylating Pfmap2 at T290, suggesting a unique signaling mechanism in the parasite.
  • This study elucidates a novel aspect of signal transduction in Plasmodium falciparum, despite the absence of a canonical MAPK pathway.

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