Investigating the role of SCF ubiquitin ligases during sexual development of Plasmodium falciparum

Ubiquitin and Nedd8 are involved in fundamental cellular processes and are essential to all eukaryotes. As such, enzymes mediating their dynamic attachment and removal from substrates present attractive targets for therapeutic intervention for both chronic and communicable diseases. Despite being evolutionarily conserved, differences in how these pathways are controlled in higher and lower eukaryotes do exist and could potentially be exploited to generate pathogen-specific inhibitors. It is, therefore, necessary to understand the cell biological mechanisms behind how these pathways are regulated. The SCF complex comprises a group of multi-subunit enzymes that catalyse ligation of ubiquitin onto substrate proteins. The role of these ligases in controlling cell-cycle progression in eukaryotes is well-established, however neither their composition nor function have been studied in the malaria parasite, Plasmodium. We aim to characterize the SCF complex during critical transitions of Plasmodium falciparum parasite development and assess whether their activity can be selectively inhibited to block transmission. Through this work, we hope to define novel targets for the development of control strategies aimed at reducing both the clinical pathology of infected individuals and the number of malaria cases at the population level.

Ubiquitin and Nedd8 control many aspects of cell physiology in all eukaryotic organisms including the malaria parasite, Plasmodium. Importantly, these two pathways intersect in the regulation of the multi-subunit E3 ubiquitin Cullin RING ligases (CRLs). The dynamic addition of a Nedd8 moiety onto Cullin proteins mediates CRL assembly which, in turn, activates CRLs to ubiquitinate target substrates. Despite being evolutionarily conserved, human enzymatic components of the ubiquitin and Nedd8 cascades share only moderate identity with their P. falciparum orthologs. We hypothesise that these differences can be targeted to develop a new class of antimalarial therapeutics. We aim to study a subset of CRLs, the Skp1-Cullin1-Fbox ligases (SCFs), whose role in controlling cell cycle progression is well-established in eukaryotic cell biology. We have identified a subset of SCFs that are markedly upregulated during gametocytogenesis. Through proteomic approaches and parasite transgenics, we will define their substrates, function and regulation during this critical transition of Plasmodium falciparum parasite development and identify how their activity can be selectively inhibited to block transmission.