A molecular docking strategy identifies Eosin B as a non-active site inhibitor of protozoal bifunctional thymidylate synthase-dihydrofolate reductase.

Chloé E Atreya, Eric F Johnson, John J Irwin, Antonia Dow, Kristen M Massimine, Isabelle Coppens, Valeska Stempliuk, Stephen Beverley, Keith A Joiner, Brian K Shoichet, Karen S Anderson

Index: J. Biol. Chem. 278(16) , 14092-100, (2003)

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Abstract

Protozoal parasites are unusual in that their thymidylate synthase (TS) and dihydrofolate reductase (DHFR) enzymes exist on a single polypeptide. In an effort to probe the possibility of substrate channeling between the TS and DHFR active sites and to identify inhibitors specific for bifunctional TS-DHFR, we used molecular docking to screen for inhibitors targeting the shallow groove connecting the two active sites. Eosin B is a 100 microm non-active site inhibitor of Leishmania major TS-DHFR identified by molecular docking. Eosin B slows both the TS and DHFR reaction rates. When Arg-283, a key residue to which eosin B is predicted to bind, is mutated to glutamate, however, eosin B only minimally inhibits the TS-DHFR reaction. Additionally, eosin B was found to be a 180 microm inhibitor of Toxoplasma gondii in both biochemical and cell culture assays.