Covalent inhibition of Plasmodium falciparum Ubc13 impairs global protein synthesis

Abstract

The ubiquitin-conjugating enzyme 13 (Ubc13) has an essential function and putative role in artemisinin activity against Plasmodium falciparum. Ubc13 conjugates lysine 63-linked ubiquitin (K63-Ub) to proteins, but the role of this modification in Plasmodium remains largely unknown. Herein, we characterize and deploy NSC697923 to interrogate PfUbc13 function. We demonstrate that NSC697923 covalently targets the PfUbc13 catalytic cysteine and exhibits nanomolar inhibitory potency. NSC697923 inhibits multiple life stages and synergizes with the malaria drug dihydroartemisinin. NSC697923 specifically reduces K63-Ub in blood stage parasites, and subsequent chemoproteomic studies identified 31 putative PfUbc13 substrates. These proteins were enriched in transcription, translation, and proteasome processes, and 90% overlapped with previous Plasmodium ubiquitinome studies. Nascent protein synthesis was reduced following NSC697923 exposure, supporting a role for PfUbc13 and K63-Ub in mediating protein translation. These findings expand our knowledge of PfUbc13-dependent processes in these pathogenic parasites and highlight this enzyme as a potential antimalarial drug target.