Computational approaches and experimental investigation for identification of potential inhibitors targeting cysteine synthase in Leishmania donovani.

Visceral leishmaniasis poses a significant health challenge due to limited treatment options, drug resistance, and lack of vaccine. Targeting essential proteins of Leishmania parasites, either absent or distinct from human, is imperative for developing new chemotherapeutic strategies. The cysteine synthase (CS) and serine O-acetyltransferase (SAT) involved in the de novo cysteine biosynthetic pathway of L. donovani may represent an attractive drug target. This pathway is absent in humans and controls the trypanothione-based redox metabolism; crucial for parasite survival and drug resistance. The C-terminal SAT-peptides strongly bind to CS creating a regulatory CS-SAT complex, leading to partial or complete inhibition of CS activity. In this study, CS in complex with SAT was utilized as a framework to screen inhibitors against LdCS. Structure-based virtual screening and molecular docking against LdCS protein with varying precisions (SP and XP modes) were performed to identify potential novel inhibitors. We have identified 17 top-ranked hits exhibiting inhibitory activity based on docking score against LdCS. Four of these compounds were further evaluated through molecular dynamics simulations and biological assays. Compounds (ASN05106249) and (ASN03069898) showed significant inhibitory effect on CS enzymatic activity and growth of parasite that highlight the potential of LdCS to develop new therapies against Leishmaniasis.