Cloning and expression of the Plasmodium falciparum metacaspase gene PfMCA1

Abstract

Programmed cell death (PCD) is a phenomenon commonly associated with multicellular organisms. Caspases are the main mediators of PCD, and this class of proteases are responsible for many of the morphological and physiological changes observed during PCD. However, in recent years, growing evidence has suggested that PCD is not unique to metazoans; unicellular eukaryotes such as Saccharomyces cerevisiae, Trypanosoma brucei and Plasmodium spp. have also demonstrated hallmarks of apoptosis such as DNA laddering and phosphatidylserine externalization. Metacaspases are distant homologues of caspases identified through iterative PSI-BLAST searches, and they possess the same critical catalytic dyad of cysteine and histidine residues as caspases. In S. cerevisiae, a metacaspase YCA1 has been shown to be involved in the cell death pathway. Similarly, three metacaspases have been identified in P. falciparum, the most debilitating malaria parasite in humans. Of these three metacaspases, PfMCA1 bears the most similarity to YCA1, in terms of size and identity. To elucidate the role that PfMCA1 plays in plasmodial cell death, PfMCA1 will be expressed in yeast cells, and its effect on yeast cell death will be studied. However, it was found that PfMCA1 is toxic to a variety of host cells, and this toxicity is most likely due to its catalytic activity, as the non-catalytic domain could be successfully expressed while the catalytic domain could not.