Crystallization and preliminary X-ray diffraction analysis of orotate phosphoribosyltransferase from the human malaria parasite Plasmodium falciparum.

Orotate phosphoribosyltransferase (OPRT) catalyzes the Mg(2+)-dependent condensation of orotic acid (OA) with 5-α-D-phosphorylribose 1-diphosphate (PRPP) to yield diphosphate (PP(i)) and the nucleotide orotidine 5'-monophosphate. OPRT from Plasmodium falciparum produced in Escherichia coli was crystallized by the sitting-drop vapour-diffusion method in complex with OA and PRPP in the presence of Mg(2+). The crystal exhibited tetragonal symmetry, belonging to space group P4(1) or P4(3), with unit-cell parameters a = b = 49.15, c = 226.94 Å. X-ray diffraction data were collected to 2.5 Å resolution at 100 K using a synchrotron-radiation source.

Catalytic mechanism of the primary human prostaglandin F2α synthase, aldo-keto reductase 1B1--prostaglandin D2 synthase activity in the absence of NADP(H).

Aldo-keto reductase 1B1 and 1B3 (AKR1B1 and AKR1B3) are the primary human and mouse prostaglandin F(2α) (PGF(2α)) synthases, respectively, which catalyze the NADPH-dependent reduction of PGH(2), a common intermediate of various prostanoids, to form PGF(2α). In this study, we found that AKR1B1 and AKR1B3, but not AKR1B7 and AKR1C3, also catalyzed the isomerization of PGH(2) to PGD(2) in the absence of NADPH or NADP(+). Both PGD(2) and PGF(2α) synthase activities of AKR1B1 and AKR1B3 completely disappeared in the presence of NADP(+) or after heat treatment of these enzymes at 100 °C for 5 min. The K(m), V(max), pK and optimum pH values of the PGD(2) synthase activities of AKR1B1 and AKR1B3 were 23 and 18 µM, 151 and 57 nmol·min(-1)·(mg protein)(-1), 7.9 and 7.6, and pH 8.5 for both AKRs, respectively, and those of PGF(2α) synthase activity were 29 and 33 µM, 169 and 240 nmol·min(-1)·(mg protein)(-1), 6.2 and 5.4, and pH 5.5 and pH 5.0, respectively, in the presence of 0.5 mm NADPH. Site-directed mutagenesis of the catalytic tetrad of AKR1B1, composed of Tyr, Lys, His and Asp, revealed that the triad of Asp43, Lys77 and His110, but not Tyr48, acts as a proton donor in most AKR activities, and is crucial for PGD(2) and PGF(2α) synthase activities. These results, together with molecular docking simulation of PGH(2) to the crystallographic structure of AKR1B1, indicate that His110 acts as a base in concert with Asp43 and Lys77 and as an acid to generate PGD(2) and PGF(2α) in the absence of NADPH or NADP(+) and in the presence of NADPH, respectively.

Structural basis for the decarboxylation of orotidine 5'-monophosphate (OMP) by Plasmodium falciparum OMP decarboxylase.

Orotidine 5'-monophoshate decarboxylase (OMPDC) catalyses the decarboxylation of orotidine 5'-monophosphate (OMP) to uridine 5'-monophosphate (UMP). Here, we report the X-ray analysis of apo, substrate or product-complex forms of OMPDC from Plasmodium falciparum (PfOMPDC) at 2.7, 2.65 and 2.65 A, respectively. The structural analysis provides the substrate recognition mechanism with dynamic structural changes, as well as the rearrangement of the hydrogen bond array at the active site. The structural basis of substrate or product binding to PfOMPDC will help to uncover the decarboxylation mechanism and facilitate structure-based optimization of antimalarial drugs.

Crystallization and preliminary crystallographic analysis of orotidine 5'-monophosphate decarboxylase from the human malaria parasite Plasmodium falciparum.

Orotidine 5'-monophosphate (OMP) decarboxylase (OMPDC; EC 4.1.1.23) catalyzes the final step in the de novo synthesis of uridine 5'-monophosphate (UMP) and defects in the enzyme are lethal in the malaria parasite Plasmodium falciparum. Active recombinant P. falciparum OMPDC (PfOMPDC) was crystallized by the seeding method in a hanging drop using PEG 3000 as a precipitant. A complete set of diffraction data from a native crystal was collected to 2.7 A resolution at 100 K using synchrotron radiation at the Swiss Light Source. The crystal exhibits trigonal symmetry (space group R3), with hexagonal unit-cell parameters a = b = 201.81, c = 44.03 A. With a dimer in the asymmetric unit, the solvent content is 46% (V(M) = 2.3 A3 Da(-1)).

Structural and mutational analysis of Trypanosoma brucei prostaglandin H2 reductase provides insight into the catalytic mechanism of aldo-ketoreductases.

Trypanosoma brucei prostaglandin F2alpha synthase is an aldo-ketoreductase that catalyzes the reduction of prostaglandin H2 to PGF2alpha in addition to that of 9,10-phenanthrenequinone. We report the crystal structure of TbPGFS.NADP+.citrate at 2.1 angstroms resolution. TbPGFS adopts a parallel (alpha/beta)8-barrel fold lacking the protrudent loops and possesses a hydrophobic core active site that contains a catalytic tetrad of tyrosine, lysine, histidine, and aspartate, which is highly conserved among AKRs. Site-directed mutagenesis of the catalytic tetrad residues revealed that a dyad of Lys77 and His110, and a triad of Tyr52, Lys77, and His110 are essential for the reduction of PGH2 and 9,10-PQ, respectively. Structural and kinetic analysis revealed that His110, acts as the general acid catalyst for PGH2 reduction and that Lys77 facilitates His110 protonation through a water molecule, while exerting an electrostatic repulsion against His110 that maintains the spatial arrangement which allows the formation of a hydrogen bond between His110 and C11 that carbonyl of PGH2. We also show Tyr52 acts as the general acid catalyst for 9,10-PQ reduction, and thus we not only elucidate the catalytic mechanism of a PGH2 reductase but also provide an insight into the catalytic specificity of AKRs.