Reduced impact of pyrimethamine drug pressure on Plasmodium malariae dihydrofolate reductase gene.

Molecular investigations performed following the emergence of sulfadoxine-pyrimethamine (SP) resistance in Plasmodium falciparum have allowed the identification of the dihydrofolate reductase (DHFR) enzyme as the target of pyrimethamine. Although clinical cases of Plasmodium malariae are not usually treated with antifolate therapy, incorrect diagnosis and the high frequency of undetected mixed infections has probably exposed non-P. falciparum parasites to antifolate therapy in many areas. In this context, we aimed to assess the worldwide genetic diversity of the P. malariae dhfr gene in 123 samples collected in Africa and Asia, areas with different histories of SP use. Among the 10 polymorphic sites found, we have observed 7 new mutations (K55E, S58R, S59A, F168S, N194S, D207G, and T221A), which led us to describe 6 new DHFR proteins. All isolates from African countries were classified as wild type, while new mutations and haplotypes were recognized as exclusive to Madagascar (except for the double mutations at nucleotides 341 and 342 [S114N] found in one Cambodian isolate). Among these nonsynonymous mutations, two were likely related to pyrimethamine resistance: S58R (corresponding to C59R in P. falciparum and S58R in Plasmodium vivax; observed in one Malagasy sample) and S114N (corresponding to S108N in P. falciparum and S117N in P. vivax; observed in three Cambodian samples).

Evaluation of the intra- and inter-specific genetic variability of Plasmodium lactate dehydrogenase.

BACKGROUND: Malaria diagnosis is vital to efficient control programmes and the recent advent of malaria rapid diagnostic tests (RDTs) provides a reliable and simple diagnostic method. However a characterization of the efficiency of these tests and the proteins they detect is needed to maximize RDT sensitivity. METHODS: Plasmodial lactate dehydrogenase (pLDH) gene of wild isolates of the four human species of Plasmodium from a variety of malaria endemic settings were sequenced and analysed. RESULTS: No variation in nucleotide was found within Plasmodium falciparum, synonymous mutations were found for Plasmodium malariae and Plasmodium. vivax; and three different types of amino acid sequence were found for Plasmodium ovale. Conserved and variable regions were identified within each species. CONCLUSION: The results indicate that antigen variability is unlikely to explain variability in performance of RDTs detecting pLDH from cases of P. falciparum, P. vivax or P. malariae malaria, but may contribute to poor detection of P. ovale.

Active-site specificity of digestive aspartic peptidases from the four species of Plasmodium that infect humans using chromogenic combinatorial peptide libraries.

Two targeted chromogenic octapeptide combinatorial libraries, comprised of 38 pools each containing 361 different peptides, were used to analyze the enzyme/substrate interactions of five plasmepsins. The first library (P1 library) was based on a good synthetic aspartic peptidase substrate [Westling, J., Cipullo, P., Hung, S. H., Saft, H., Dame, J. B., and Dunn, B. M. (1999) Protein Sci. 8, 2001-2009; Scarborough, P. E., and Dunn, B. M. (1994) Protein Eng. 7, 495-502] and had the sequence Lys-Pro-(Xaa)-Glu-P1*Nph-(Xaa)-Leu. The second library (P1' library) incorporated results with the plasmepsins from the first library and had the sequence Lys-Pro-Ile-(Xaa)-Nph*P1'-Gln-(Xaa). In both cases, P1 and P1' were fixed residues for a given peptide pool, where Nph was a para-nitrophenylalanine chromogenic reporter and Xaa was a mixture of 19 different amino acids. Kinetic assays monitoring the rates of cleavage of these libraries revealed the optimal P1 and P1' residues for the five plasmepsins as hydrophobic substitutions. Extended specificity preferences were obtained utilizing liquid chromatography-mass spectrometry (LC-MS) to analyze the cleavage products produced by enzyme-catalyzed digestion of the best pools of each peptide library. LC-MS analysis of the P1-Phe and P1'-Phe pools revealed the favored amino acids at the P3, P2, P2', and P3' positions. These analyses have provided new insights on the binding preferences of malarial digestive enzymes that were used to design specific methyleneamino peptidomimetic inhibitors of the plasmepsins. Some of these compounds were potent inhibitors of the five plasmepsins, and their possible binding modes were analyzed by computational methods.

Crystallization and preliminary X-ray analysis of the aspartic protease plasmepsin 4 from the malarial parasite Plasmodium malariae.

Plasmepsin 4 from the malarial parasite Plasmodium malariae (PmPM4) is a member of the plasmepsins (Plasmodium pepsins), a subfamily of the pepsin-like aspartic proteases whose ortholog in the malarial parasite P. falciparum is involved in hemoglobin digestion in its digestive vacuole. Crystals of PmPM4 in complex with the small-molecule inhibitor AG1776 have been grown from a precipitant of 15% PEG 4000 and 200 mM ammonium sulfate in 100 mM sodium acetate pH 4.5. X-ray diffraction data were collected on a Rigaku rotating-anode generator from a single crystal under cryoconditions, with a maximal useful diffraction pattern to 3.3 A resolution. The crystals are shown to be orthorhombic and have been assigned to space group P2(1)2(1)2, with unit-cell parameters a = 95.88, b = 112.58, c = 90.40 A and a scaling Rsym of 0.104 for 14,334 unique reflections. Packing consideration and self-rotation function results indicate that there are two molecules per asymmetric unit. It is expected that in the near future the structure of PmPM4 will be obtained using molecular-replacement methods, obtaining phases from previously determined plasmepsin structures. Elucidation of the structure of PmPM4 in complex with inhibitors may be paramount to producing new antimalarial therapeutic agents.

Cloning and characterization of iron-containing superoxide dismutase from the human malaria species Plasmodium ovale, P. malariae and P. vivax.

The iron-containing superoxide dismutase (FeSOD) gene from three human malaria species, namely Plasmodium ovale, P. malariae and P. vivax, was amplified by polymerase chain reaction, cloned and then sequenced. Comparisons of their deduced amino acid sequences with that of the FeSOD from P. falciparum revealed a very low polymorphism at the FeSOD locus in human malaria species. One P. ovale and the P. vivax FeSOD genes presented the same nucleotide sequence as that of the P. falciparum strain HB3 whereas the second P. ovale and the P. malariae genes exhibited two punctual mutations. These mutations did not affect the function and structure of the enzyme. The FeSOD polymorphism was so low that no phylogenetic relationship among human malaria species could be proposed, but this conservative structure strengthened the potentiality of this enzyme as a possible target for antimalarial drugs.

Plasmodium falciparum, P. vivax, and P. malariae: a comparison of the active site properties of plasmepsins cloned and expressed from three different species of the malaria parasite.

Aspartic endopeptidases (plasmepsins) have been implicated in the degradation of hemoglobin in the erythrocytic stage of infection by Plasmodium falciparum. To develop new targets for drug development, these enzymes have been isolated and cloned, expressed, and studied structurally and enzymatically. This study expands this approach to two other species of the malarial parasite, P. vivax and P. malariae. Expression of cloned genes from these species, utilizing methodology similar to that employed in the original reports on the enzymes from P. falciparum, has provided active enzymes for analysis by kinetic methods. We describe here studies of three enzymes, plasmepsin II from P. falciparum, and one plasmepsin from both P. vivax and P. malariae, utilizing oligopeptide substrates and low-molecular-weight inhibitors. These analyses provide new information on the properties of distinct regions of the active site cleft; such data can suggest strategies for drug design to inhibit these critical enzymes of the parasite.

Electrophoretic variants of enzymes in isolates of Plasmodium falciparum, P. malariae and P. vivax from Thailand.

A new electrophoretic variant of glucose phosphate isomerase (GPI), which we now denote GPI-3, has been found in isolates of Plasmodium falciparum from 6 patients, all of whom acquired the infection in the same region (in or near Prachinburi province) of Thailand. In other regions, from which 453 isolates have been tested, only GPI-1 and/or GPI-2 have been found. Two isolates of P. malariae from patients at Kanchanaburi showed a band of GPI activity on cellulose acetate gels at a cathodal position quite distinct from that of any previously known GPI variants in other human malaria parasites. Thirty-nine isolates of P. vivax from 3 regions of Thailand have been examined for variants of GPI and lactate dehydrogenase (LDH). Three forms of GPI were found, corresponding approximately in band positions to GPI-1, 2 and 3 of P. falciparum. The position of the band of LDH activity in P. vivax was the same in all the isolates examined, and different from that of LDH-1 in P. falciparum.

Malaria parasites of rodents of the Congo (Brazzaville): Plasmodium chabaudi adami subsp. nov. and Plasmodium vinckei lentum Landau, Michel, Adam and Boulard, 1970.

Descriptions are given of the blood forms, sporogonic stages and enzyme forms of Plasmodium chabaudi adami subsp.-nov. and P. vinckei lentum, malaria parasites of the thicket-rat Thamnomys rutilans of the Brazzaville region. The two species differ from each other in both morphological and enzymic characters. P.c. adami and P. v. lentum differ from the other subspecies of P. chabaudi and P. vinckei principally by their enzyme forms.