Analysis of expression of PDCP and MAL13P1.308 of Plasmodium falciparum employing a quantitative proteomics approach based on SILAC

Plasmodium falciparum is a deadly parasite that causes malaria in humans. This disease causes the death of one million people every year. To find new means to fight this parasite, it is important to learn more about its biology. As the pathways of protein expression are better understood, it becomes easier to find out how to block these mechanisms. The completion of the genome sequencing has opened new perspective of genome wide analysis. One of these studies was done by LaCount et al. who used the yeast1two1hybrid system to map the complete interaction network between proteins of P. falciparum. ¨ From this network of interaction an interesting protein was studied further by Daubenberger et al. which is PDCP. This protein is closely related to MSP11 in this protein network, a protein involved in erythrocyte invasion. PDCP is a CCCH1type zinc finger protein, a family of proteins that are involved in protein1protein interaction, nucleic acid binding and binding in small ligands. It was shown that its expression was dependant on the density of the parasites. In this study we used the SILAC technology to confirm these previous results. A culture is grown with isotopically heavy isoleucine in the medium as a control sample. After a few cell cycles, almost all the natural isoleucines are replaced with the labeled ones. Three cultures with parasitemia of 2, 5 and 10% are grown and mixed with an equal amount of the control culture. When the proteins are analyzed by mass spectrometry, the peptides that contained isoleucine will be detected as two separate peaks. After normalization of each peptide area with this internal control, the quantity of PDCP can be compared between cultures of different parasitemias. 11 peptides of PDCP have been detected by mass spectrometry, proving its existence for the first time. These peptides were labeled to more than 95%, allowing the comparison of PDCP expression between the cultures. But because of difficulty of reproducibility in in vitro cultures, the regulation of PDCP by the parasitemia has not been observed by SILAC. We wanted to study further the protein interaction network in which PDCP is involved. MAL13P1.308, a protein directly interacting with PDCP and MSP11 in the protein network map, was analyzed by IFA. It was found to be expressed during all stages of the asexual blood stage cycle and it was not imported in the host cell. The next step will be to see if it interacts with PDCP by co1localization studies