Open AccessSequence Variation of the Hydroxymethyldihydropterin Pyrophosphokinase: Dihydropteroate Synthase Gene in Lines of the Human Malaria Parasite, Plasmodium falciparum , with Differing Resistance to Sulfadoxine
Author(s) -
Brooks Darren R.,
Wang Ping,
Read Martin,
Watkins William M.,
Sims Paul F. G.,
Hyde John E.
Publication year - 1994
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1994.00397.x
Subject(s) - dihydropteroate synthase , plasmodium falciparum , dhps , biology , point mutation , genetics , gene , dihydrofolate reductase , coding region , peptide sequence , microbiology and biotechnology , pyrimethamine , mutation , malaria , immunology
Dihydropteroate synthase (H 2 Pte synthase) is the target of the sulfur‐based antimalarial drugs, which are frequently used in synergistic combination with inhibitors of dihydrofolate reductase (H 2 folate reductase) to combat chloroquine‐resistant malaria. We have isolated the H 2 Pte synthase coding sequence of the most pathogenic human parasite Plasmodium falciparum. It forms part of a longer coding sequence, located on chromosome 8, that also specifies 6‐hydroxymethyl‐7,8‐dihydropterin pyrophosphokinase (CH 2 OH‐H 2 pterin PP kinase) at its 5′ proximal end. This domain is unusually large, with two long insertions relative to other CH 2 OH‐H 2 pterin PP kinase molecules. To investigate a possible genetic basis for clinical resistance to sulfa drugs, we sequenced the complete H 2 Pte synthase domains from eleven isolates of P. falciparum with diverse geographical origins and levels of sulfadoxine resistance. Overall, point mutations in five positions were observed, affecting four codons. Parasite lines exhibiting high‐level resistance were found to carry either a double mutation, altering both Ser436 and Ala613, or a single mutation affecting Ala581. The mutations at positions 436 and 581 have the same location relative to each of two degenerate repeated amino acid motifs that are conserved across all other known H 2 Pte synthase molecules. The amino acid alteration at residue 613 is identically positioned relative to a different conserved motif. The fourth amino acid residue (437) affected by mutation, though adjacent to the apparently crucial residue 436, shows no obvious correlation with resistance. Although these mutations have no exact counterparts in any other organism, that at position 581 falls within a region of three amino acids where H 2 Pte synthase is modified in various ways in a number of sulfonamide‐resistant pathogenic bacteria. Copy‐number analysis indicated that there was no amplification of the H 2 Pte synthase domain in resistant parasite lines of P. falciparum , compared to sensitive lines.