Characterisation of the plasmodium falciparum HSP70-HSP90 organising protein
Malaria is caused by Plasmodium falciparum (P. falciparum) parasite and accounts for approximately more than half a million deaths yearly. P. falciparum survives under various physiological conditions during its life cycle. The parasite employs its molecular chaperones machinery particularly heat shock proteins (Hsps) to protect its protein constituents. This enables it to circumvent the effects of the stress linked to its life cycle. P. falciparum Hsp70-1 (PfHsp70-1; PF3D7_0818900) and P. falciparum Hsp90 (PfHsp90; PF3D7_0708400) are some of the major Hsps involved in the cytoprotection of the parasite and therefore pathogenesis of malaria. Hsp70 and Hsp90 are brought into close proximity by Hsp70-Hsp90 organising protein (Hop), allowing Hsp70 to pass partially folded substrates such as kinases to Hsp90 for further folding. Although a Hop homologue in P. falciparum (PfHop; PF3D7_1434300) is represented on the parasite genome, it is yet to be characterised. The objective of the study was to characterise the role of PfHop in mediating the functional partnership between PfHsp70-1 and PfHsp90. Structural domains and motifs such as the tetratricopeptide repeat (TPR) that are conserved across Hop homologues were identified in the PfHop. Data suggested that PfHop is a canonical Hop homologue of the P. falciparum. Recombinant PfHop was heterologously expressed in Escherichia coli (E. coli) XL1 Blue cells and subsequently purified using nickel-chelating Sepharose beads. Using surface plasmon resonance spectroscopy (SPR) analysis, recombinant PfHop was shown to bind to PfHsp70-1 in a concentration dependent manner. Based on immunofluorescence assay (IFA), it was demonstrated that PfHop is predominantly cytosolic and it tended to co-localise with PfHsp70-1 and PfHsp90. Co-immunoprecipitation studies suggested that PfHop and PfHsp70-1 interact. It was also demonstrated that PfHop was concominantly upregulated with PfHsp70-1 during the intraerythrocytic cycle. These findings suggest possible cytoprotective roles of PfHop and PfHsp70-1 during parasite host invasion and development in the erythrocyte. In conclusion, the study provides evidence that PfHop mediates the function of PfHsp70-1 and in particular its functional interaction with PfHsp90.
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