MUTATIONS IN DIHYDROPTEROATE SYNTHASE ARE RESPONSIBLE FOR SULFONE ANDSULFONAMIDE RESISTANCE IN PLASMODIUM-FALCIPARUM

Plasmodium falciparum causes the most severe form of malaria in humans . An important class of drugs in malaria treatment is the sulfone/sulf onamide group, of which sulfadoxine is the most commonly used, The tar get of sulfadoxine is the enzyme dihydropteroate synthase (DHPS), and sequencing of the DHPS gene has identified amino acid differences that may be involved in the mechanism of resistance to this drug. In this study we have sequenced the DHPS gene in 10 isolates from Thailand and identified a new allele of DHPS that has a previously unidentified am ino acid difference. We have expressed eight alleles of P. falciparum PPPK-DHPS in Escherichia coli and purified the functional enzymes to h omogeneity. Strikingly the K-i for sulfadoxine varies by almost three orders of magnitude from 0.14 mu M for the DHPS allele from sensitive isolates to 112 mu M for an enzyme expressed in a highly resistant iso late. Comparison of the K-i of different sulfonamides and the sulfone dapsone has suggested that the amino acid differences in DHPS would co nfer cross-resistance to these compounds, These results show that the amino acid differences in the DHPS enzyme of sulfadoxine-resistant iso lates of P. falciparum are central to the mechanism of resistance to s ulfones and sulfonamides,