Drug resistance-associated mutations in Plasmodium UBP-1 disrupt its essential deubiquitinating activity.

Deubiquitinating enzymes function to cleave ubiquitin (Ub) moieties from modified proteins, serving to maintain the pool of free Ub in the cell while simultaneously impacting the fate and function of a target protein. Like all eukaryotes, Plasmodium parasites rely on the dynamic addition and removal of Ub for their own growth and survival. While humans possess around 100 deubiquitinases, Plasmodium contains ∼20 putative Ub hydrolases, many of which bear little to no resemblance to those of other organisms. In this study, we characterize Plasmodium falciparum UBP-1, a large Ub hydrolase unique to Plasmodium spp., which has been linked to endocytosis and drug resistance. We demonstrate its Ub activity, linkage specificity, and assess the repercussions of point mutations associated with drug resistance on catalytic activity and parasite fitness. We confirm that the deubiquitinating activity of UBP-1 is essential for parasite survival, implicating an important role for Ub signaling in endocytosis.