Journal of Vector Borne Diseases (Mar 2007)
‘DEAD-box’ helicase from Plasmodium falciparum is active at wide pH and is schizont stage-specific
Abstract
Background & objectives: DNA helicases catalyse unwinding of duplex DNA in an ATP-dependentmanner and are involved in all the basic genetic processes. In order to study these important enzymesin the human malaria parasite we have recently cloned the first full-length ‘DEAD-box’ helicasegene from Plasmodium falciparum (3D7). In the present study, we report some of the importantactivities of the encoded protein.Methods: We have expressed the P. falciparum helicase in Escherichia coli and characterised theencoded biochemically active helicase protein. The characterisation of the protein was carried outusing radioactively labeled substrate and the standard strand displacement assay. The localisation ofthe enzyme was studied using immunofluorescence assay.Results & conclusion: P. falciparum helicase gene is 1551 bp in length and encodes for a proteinconsisting of 516 amino acid residues with a predicted molecular mass of 59.8 kDa. The protein isdesignated as Plasmodium falciparum DEAD-box helicase 60 kDa in size (PfDH60). Purified PfDH60showed ATP and Mg2+ dependent DNA unwinding, ssDNA-dependent ATPase and ATP-bindingactivities. Interestingly, this is a unique helicase because it works at a wide pH range (from5.0–10.0). The peak expression of PfDH60 is mainly in schizont stages of the development of P.falciparum, where DNA replication is active. The cell-cycle dependent expression suggests thatPfDH60 may be involved in the process of DNA replication and distinct cellular processes in theparasite and this study should make an important contribution in our better understanding of DNAmetabolic pathways in the parasite.
