A large scale Plasmodium vivax trophozoite-schizont transition proteome.

Background: Plasmodium vivax is an apicomplexan organism with ca. 5459 genes (Salvador-1 strain) with differential stage-specific expression, which poses a significant public health threat. Examination of its unique biology, biochemistry, and pathogenesis at the molecular level will be important for the development of diagnostics, therapeutics, and vaccines that can reduce disease burden. Examination of expressed blood stage proteomes may complement metabolome and transcriptome data, and also give insights into cellular function. Materials and Methods: Two biological replicates of Percoll gradient-purified iRBC with late stage trophozoite: early stage (2-4 nucleated) schizont ratios of 44:56 and 40:60 were isolated from Saimiri boliviensis monkeys infected with P. vivax (Sal-1). Proteins were purified and digested by trypsin with the FASP-II protocol, and analyzed on an Orbitrap mass spectrometer using 4 separate 2D lc/ms/ms runs per proteome. Protein set enrichment analysis of P. vivax proteins, identified at least twice by a search engine, utilized PlasmoDB GO annotations and InterPro domain assignments with P=0.05. Results and Conclusions: Two biological replicates contained over 5000 identified host plus parasite proteins, making this the most comprehensive Plasmodium vivax iRBC proteome to date. Three of the top five enriched P. vivax protein molecular function categories included oxidoreductases acting on peroxide, peroxidases, and antioxidant activity. P. vivax proteins involved in the response to oxidative stress were enriched 3.55 fold over background. Both observations are concordant with our direct observation of significant protein oxidation in this protome as well as in a P. vivax trophozoite stage proteome. Other P. vivax protein enrichment included a) protein-DNA complex, DNA packaging, nucleosome and chromatin proteins, consistent with gene expression and/or ongoing epigenomic processes; b) proteins regulating intracellular pH and proton transport; c) vacuolar and vesicle-associated proteins; d) proteasome and ribosomal subunits; and e) proteins important for nuclear localization or nuclear import. We also identify, at least twice by a search engine, 31 Vir or Vir-related proteins, which may be important for antigenic variation or iRBC adhesion to other cells. The results suggest the potential biological prominence of these areas.