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Genetic and metabolic analysis of folate salvage in the human malaria parasite Plasmodium falciparum
- Source :
- Molecular and Biochemical Parasitology. 135:77-87
- Publication Year :
- 2004
- Publisher :
- Elsevier BV, 2004.
-
Abstract
- Antifolate drugs that target the biosynthesis and processing of essential folate cofactors are widely used for treatment of chloroquine-resistant falciparum malaria. Salvage of pre-formed folate can strongly compromise the efficacy of these drugs in vitro and the availability of folate from the human host in natural infections also influences therapeutic outcomes. To investigate how different parasite lines respond to the presence of exogenous folate, we measured the effect of the latter on the susceptibility of parasites to sulfa-drug blockage of folate biosynthesis, utilising the parents and 22 progeny of the HB3-Dd2 genetic cross of Plasmodium falciparum, together with selected unrelated lines. Complete linkage of the folate utilisation phenotype was observed to a DNA sequence of 48.6 kb lying between nucleotide positions 738,489 and 787,058 of chromosome 4 and encompassing the dihydrofolate reductase-thymidylate synthase (dhfr-ts) gene locus. Examination of the putative ORFs on this fragment upstream (3) and downstream (4) of dhfr-ts revealed no plausible candidate genes for folate processing. Similarly, a marked heterogeneity in the 5'-UTR regions of Dd2 and HB3, manifest as a directly repeated 256 bp sequence in the former, also did not correlate with the folate utilisation phenotype nor apparently influence levels of dhfr-ts transcripts or protein products. By contrast, the nature of the coding sequence of the dhfr domain appeared to play a direct role, with the single mutant (S108N) HB3-type utilising folic acid much less efficiently than other allelic variants. We also compared the processing of exogenous folic acid, folinic acid and p-aminobenzoic acid (pABA) in metabolic labelling studies of HB3 and Dd2. These support the view that DHFR is likely to have a low-level folate reductase activity as well as its normal function of reducing dihydrofolate to tetrahydrofolate, and that a significant hurdle in the utilisation of exogenous folic acid is the initial reduction of fully oxidised folic acid to dihydrofolate, an activity that the single mutant enzyme found in HB3 is postulated to perform particularly poorly. This would mirror earlier studies indicating that the DHFR activity of HB3 is also compromised relative to other variants.
- Subjects :
- Candidate gene
Folate reductase activity
Genes, Protozoan
Plasmodium falciparum
Mutant
Leucovorin
Protozoan Proteins
Biology
Antimalarials
chemistry.chemical_compound
Folic Acid
Multienzyme Complexes
Sulfadoxine
parasitic diseases
medicine
Animals
Molecular Biology
Gene
Tetrahydrofolates
Dihydrofolate synthase
Genetics
Polymorphism, Genetic
Chromosome Mapping
Sequence Analysis, DNA
Thymidylate Synthase
DNA, Protozoan
biology.organism_classification
Tetrahydrofolate Dehydrogenase
Phenotype
Pyrimethamine
Amino Acid Substitution
chemistry
Biochemistry
Antifolate
biology.protein
Parasitology
5' Untranslated Regions
4-Aminobenzoic Acid
medicine.drug
Subjects
Details
- ISSN :
- 01666851
- Volume :
- 135
- Database :
- OpenAIRE
- Journal :
- Molecular and Biochemical Parasitology
- Accession number :
- edsair.doi.dedup.....b7a9fb2233a64718b4f568b8a45de7f1