title: A novel enzyme complex of orotate phosphoribosyltransferase and orotidine 5'-monophosphate decarboxylase in human malaria parasite Plasmodium falciparum: physical association, kinetics, and inhibition characterization.
abstract: Human malaria parasite, Plasmodium falciparum, can only synthesize pyrimidine nucleotides using the de novo pathway, whereas mammalian cells obtain pyrimidine nucleotides from both the de novo and salvage pathways. The parasite's orotate phosphoribosyltransferase (PfOPRT) and orotidine 5'-monophosphate decarboxylase (PfOMPDC) of the de novo pyrimidine pathway are attractive targets for antimalarial drug development. Previously, we have reported that the two enzymes in P. falciparum exist as a multienzyme complex containing two subunits each of 33-kDa PfOPRT and 38-kDa PfOMPDC. In this report, the gene encoding PfOPRT has been cloned and expressed in Escherichia coli. An open reading frame of PfOMPDC gene was identified in the malaria genome database, and PfOMPDC was cloned from P. falciparum cDNA, functionally expressed in E. coli, purified, and characterized. The protein sequence has <20% identity with human OMPDC and four microbial OMPDC for which crystal structures are known. Recombinant PfOMPDC was catalytically active in a dimeric form. Both recombinant PfOPRT and PfOMPDC monofunctional enzymes were kinetically different from the native multienzyme complex purified from P. falciparum. Oligomerization of PfOPRT and PfOMPDC cross-linked by dimethyl suberimidate indicated that they were tightly associated as the heterotetrameric 140-kDa complex, (PfOPRT)2(PfOMPDC)2. Kinetic analysis of the PfOPRT-PfOMPDC associated complex was similar to that of the native P. falciparum enzymes and was different from that of the bifunctional human enzymes. Interestingly, a nanomolar inhibitor of the yeast OMPDC, 6-thiocarboxamido-uridine 5'-monophosphate, was about 5 orders of magnitude less effective on the PfOMPDC than on the yeast enzyme. Our results support that the malaria parasite has unique structural and functional properties, sharing characteristics of the monofunctional pyrimidine-metabolizing enzymes in prokaryotes and bifunctional complexes in eukaryotes.
authors.affiliation: Department of Biochemistry, Faculty of Medicine, Chulalongkorn University, Rama 4 Road, Bangkok 10330, Thailand.
authors.forename: Sudaratana R
authors.initials: SR
authors.lastname: Krungkrai
authors.forename: Brian J
authors.initials: BJ
authors.lastname: DelFraino
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Smiley
authors.forename: Phisit
authors.initials: P
authors.lastname: Prapunwattana
authors.forename: Toshihide
authors.initials: T
authors.lastname: Mitamura
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Horii
authors.forename: Jerapan
authors.initials: J
authors.lastname: Krungkrai
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D003001:Cloning, Molecular; D004791:Enzyme Inhibitors / Q000737:chemistry; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000235:genetics; D009962:Orotate Phosphoribosyltransferase / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000235:genetics; D009964:Orotidine-5'-Phosphate Decarboxylase / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000235:genetics; D010963:Plasmodium falciparum / Q000201:enzymology* / Q000235:genetics; D011485:Protein Binding; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014542:Uridine Monophosphate / Q000737:chemistry
chemical_list: D004791:Enzyme Inhibitors; D009097:Multienzyme Complexes; D011994:Recombinant Proteins; D014542:Uridine Monophosphate; D009962:Orotate Phosphoribosyltransferase; D009964:Orotidine-5'-Phosphate Decarboxylase