Plasmodium falciparum is a protozoan parasite responsible for the most severe form of malaria. In recent years, cases of resistance to antimalarial drugs have become increasingly frequent and common. In addition to its resistance to drugs currently available, there is no vaccine available against this parasite till now. The identification of new approaches based on the specific inhibition of some of its molecular targets has become vital.The identification of the Pf-Int site specific recombinase in Plasmodium falciparum by analysis of PlasmoDB is a new opportunity to study the role of genetic variation in this parasite as it needs to adapt to its hosts. This ~ 57 kDa protein contains a C-terminal domain carrying the putative tyrosine recombinase conserved active site residues R-H-K-R-(H/W)-Y, an N-terminus with a predicted alpha-helical bundle and a mixed alpha-beta domain resembling Lambda-Int. Here, we show that the sequence is highly conserved among members of the Plasmodia. It is expressed differentially during distinct life stages as estimated by RT-PCR, namely with a peak in the schizont phase. We then tried to show the involvement of Pf-Int in the parasitic cycle. We were able to create a parasite where the Pf-Int gene was knocked-out. The comparison test showed that Pf-Int has apparently no impact on the intraerythrocytic developmental cycle of the parasite, particularly in the cycle length and the growth rate.At the molecular level, we produced two sets of anti-Pf-Int antibodies using the purified recombinant fragment C-162 (residues 162-490). Comparison of protein extracts from KO and wild parasite by Western blot technique using our antibody has failed to identify the endogenous protein in the wild type parasite.We also tried to determine the subcellular localization of Pf-Int and the role of possible alternate initiation codons by over-expressing different constructs in the parasite Plasmodium falciparum. In order to determine the impact of the N-terminal region (1-190aa) of Pf-Int on its subcellular localization, we also created a chimeric protein using a fusion of Pf-Int(1-190aa) with the GFP. We successfully expressed a variety of the recombinant form of Pf-Int in E. coli. We have first determined its secondary structure content by circular dichroism (CD) and its solution stability by thermal denaturation-CD. An 1-D NMR spectrum was also recorded. The third part of our work has involved the identification of the DNA targets of Pf-Int. Two search strategies conducted in the laboratory using a library of chemically synthesized sequences and a second library made of fragments of genomic DNA of P. falciparum. Both approaches have allowed the identification of two sets of target DNA. Secondly, electrophoretic mobility shift assays (EMSA) were used to show its affinity and specificity for DNA. The recombinant proteins were shown to be functional as they form a covalent complex with DNA. Thus Pf-Int could be a potential agent that binds to and alters DNA, either in a specific or in random fashion. Its conservation and differential expression leads us to conclude that although its role is far from being understood, Pf-Int remains a key target for P. falciparum.
Biochemical, functional and structural characterization of the Plasmodium falciparum site specific recombinase Pf-Int