Alternative Protein Secretion in the Malaria Parasite Plasmodium falciparum

PLoS One. 2015 Apr 24;10(4):e0125191. doi: 10.1371/journal.pone.0125191. eCollection 2015.


Plasmodium falciparum invades human red blood cells, residing in a parasitophorous vacuole (PV), with a parasitophorous vacuole membrane (PVM) separating the PV from the host cell cytoplasm. Here we have investigated the role of N-myristoylation and two other N-terminal motifs, a cysteine potential S-palmitoylation site and a stretch of basic residues, as the driving force for protein targeting to the parasite plasma membrane (PPM) and subsequent translocation across this membrane. Plasmodium falciparum adenylate kinase 2 (Pf AK2) contains these three motifs, and was previously proposed to be targeted beyond the parasite to the PVM, despite the absence of a signal peptide for entry into the classical secretory pathway. Biochemical and microscopy analyses of PfAK2 variants tagged with green fluorescent protein (GFP) showed that these three motifs are involved in targeting the protein to the PPM and translocation across the PPM to the PV. It was shown that the N-terminal 37 amino acids of PfAK2 alone are sufficient to target and translocate GFP across the PPM. As a control we examined the N-myristoylated P. falciparum ADP-ribosylation factor 1 (PfARF1). PfARF1 was found to co-localise with a Golgi marker. To determine whether or not the putative palmitoylation and the cluster of lysine residues from the N-terminus of PfAK2 would modulate the subcellular localization of PfARF1, a chimeric fusion protein containing the N-terminus of PfARF1 and the two additional PfAK2 motifs was analysed. This chimeric protein was targeted to the PPM, but not translocated across the membrane into the PV, indicating that other features of the N-terminus of PfAK2 also play a role in the secretion process.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • ADP-Ribosylation Factor 1 / metabolism
  • Adenylate Kinase / metabolism
  • Amino Acid Motifs / physiology
  • Animals
  • Cell Membrane / metabolism
  • Cysteine / metabolism
  • Erythrocytes / parasitology
  • Golgi Apparatus / metabolism
  • Green Fluorescent Proteins / metabolism
  • Humans
  • Lysine / metabolism
  • Malaria, Falciparum / parasitology*
  • Parasites / metabolism
  • Parasites / physiology*
  • Plasmodium falciparum / metabolism
  • Plasmodium falciparum / physiology*
  • Protein Sorting Signals / physiology
  • Protein Transport / physiology
  • Protozoan Proteins / metabolism*
  • Secretory Pathway / physiology*
  • Vacuoles / metabolism


  • Protein Sorting Signals
  • Protozoan Proteins
  • Green Fluorescent Proteins
  • Adenylate Kinase
  • adenylate kinase 2
  • ADP-Ribosylation Factor 1
  • Lysine
  • Cysteine

Grant support

This work was funded by the European Community's FP7 grant agreement 242095 (EVIMalaR; through a PhD studentship to TT, and by Sonder forschungs bereich 593 ( to KL. AAH is funded through the MRC (U117532067; The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.