Organelle autonomy: Protein turnover and biogenesis of the apicoplast in malaria parasites

P. falciparum contains a unique organelle known as the apicoplast, a distinctive endosymbiont with essential metabolic functions. The apicoplast has its own DNA but most of its proteins are encoded by the cell nucleus, and it is unclear how the apicoplast controls its metabolic functions and biogenesis without being able to regulate its own protein synthesis.

In our research we discovered a proteolytic system residing within the apicoplast, that functions as a key regulator of the organelle’s biology. Using advanced molecular genetics and a plethora of cellular assays, we have shown that the plastid uses Clp-mediated degradation as the main mechanism to control protein levels and the consequent organellar functions. We identified and characterized several components of the Clp complex, including a ClpP protease, a ClpR inactive subunit, a ClpC chaperone and a ClpS adaptor molecule. We used multiple affinity assays to reveal the Clp interactome, a network of positive and negative regulators which determine proteostasis in the organelle. We analyze the organellar functions of these regulators, while working towards decoding the molecular rules governing degradation in the organelle. Finally, we developed high resolution, time-lapse imaging protocols to investigate how do degradation, turnover and translation affect organelle biogenesis. This work identified Plasmodium Clp’s as potential drug targets and suggest the repurposing of anti-bacterial Clp inhibitors as anti-malarials. Furthermore, our studies demonstrate how conserved mechanisms evolved to facilitate unique cellular function in these deeply branched eukaryotic parasites.