Leveraging Cross-Family Catalytic Conservation for Structure-Based Virtual Screening of Leishmania Phospholipid Cyclopropane Fatty Acid Synthases

Cyclopropane fatty acid (CFA) synthases are S-adenosylmethionine-dependent enzymes that remodel microbial membrane lipids but remain an overlooked class of antiparasitic targets. In Leishmania spp., the phospholipid CFA synthases govern membrane composition, cell shape, and stress resistance. Because fatty acid cyclopropanation has no human counterpart, this enzyme represents an intrinsically parasite-selective target. Combining sequence analysis with cross-family structural superposition, we show that the catalytic machinery of Leishmania CFA synthases is conserved across both subgroups of the family: the monomeric mycobacterial mycolic-acid synthases (e.g., CmaA1) and the bacterial phospholipid CFA synthases from Escherichia coli, Aquifex aeolicus, and Lactobacillus acidophilus. Structure-based virtual screening of a library of 98,294 lipophilic compounds against CmaA1 (PDB 1KPH), followed by docking into modeled L. infantum and L. mexicana CFA synthases, 200 ns molecular dynamics simulations, and MM-PBSA binding free-energy calculations, identified several chemotypes, including an 8,16-pyranthrenedione scaffold, that bound both parasite enzymes and formed stable complexes. Although these scaffolds are predominantly lipophilic, this physicochemical profile is consistent with the membrane-associated nature of the target. Rather than identifying a single privileged scaffold, these findings indicate that the conserved CFA synthase active site can accommodate multiple chemically distinct ligands, supporting the enzyme family as a tractable, parasite-selective target class and a promising basis for synergistic, multi-target antileishmanial therapies.