Plasmodium falciparum DNA helicase 60 is a schizont stage specific, bipolar and dual helicase stimulated by PKC phosphorylation

The fundamental biology and the biochemical processes at different developmental stages of the malaria parasite Plasmodium falciparum have not been explored in detail. As a step toward understanding the various mechanisms engaged in nucleic acid metabolism of this pathogen, particularly the essential enzymes involved in nucleic acid unwinding, recently, we have reported the isolation of the first P. falciparum DEAD-box DNA helicase 60 (PfDH60), which contained striking homology with p68 protein [Pradhan A, Chauhan VS, Tuteja R. A novel 'DEAD-box' DNA helicase from Plasmodium falciparum is homologous to p68. Mol Biochem Parasitol 2005;140:55-60]. In this study, we show novel important properties of PfDH60. Immunofluorescence assay studies revealed that the peak expression of PfDH60 is mainly in the schizont stages of the development of P. falciparum, where DNA replication is active. Interestingly, this is a bipolar DNA helicase, which unwinds dsDNA in both the directions. PfDH60 can also unwind RNA-DNA and RNA-RNA duplexes. PfDH60 is phosphorylated by protein kinase C at the Ser and Thr residues. The helicase and ATPase activities of PfDH60 were stimulated after this phosphorylation. The cell-cycle dependent expression, bipolar translocation and dual nature collectively suggest that PfDH60 may be involved in the process of DNA replication and distinct cellular processes in the parasite and this study should make an important contribution in our better understanding of DNA metabolic pathways such as repair, recombination and replication.