Steve Ealick's Research Group
Leishmania donovani OMP Decarboxylase
The final two steps of de novo uridine 5′-monophosphate (UMP) biosynthesis are catalyzed by orotate phosphoribosyltransferase (OPRT) and orotidine 5′-monophosphate decarboxylase (OMPDC). In most prokaryotes and simple eukaryotes these two enzymes are encoded by separate genes, while in mammals they are expressed as a bifunctional gene product called UMP synthase (UMPS), with OPRT at the N-terminus and OMPDC at the C-terminus. Leishmania and some closely related organisms also express a bifunctional enzyme for these two steps, but the domain order is reversed relative to mammalian UMPS. We subcloned, expressed, purified and crystallized the monofunctional Leishmania donovani OMPDC (LdOMPDC). Its structure was solved by molecular replacement using Plasmodium falciparum OMPDC (PDB ID 2F84) and in turn used to determine the structure of bifunctional Leishmania donovani UMPS (LdUMPS).
The overall structure of the protomer of LdOMPDC uses a triose phosphate isomerase fold that is similar to that of other bacterial OMPDCs such as Bacillus subtilis OMPDC, whose structure was solved previously by our laboratory.
|As in the case of the other bacterial OMPDCs, a dimer was found in the crystal structure and confirmed by size exclusion chromatography.|
The LdOMPDC active site is near the dimer interface and is comprised of residues from both chains. UMP was present in the purification and crystallization of LdUMPS and was found in the LdOMPDC active site in the bifunctional enzyme.
French JB, Yates PA, Soysa DR, Boitz JM, Carter NS, Chang B, Ullman B, and Ealick SE. The Leishmania donovani UMP synthase is essential for promastigote viability and has an unusual tetrameric structure that exhibits substrate-controlled oligomerization. J. Biol. Chem. 296:20930-20941 (2011). PubMed