PLASMODIUM-FALCIPARUM S-ADENOSYLHOMOCYSTEINE HYDROLASE - CDNA IDENTIFICATION, PREDICTED PROTEIN-SEQUENCE, AND EXPRESSION IN ESCHERICHIA-COLI

Compounds that specifically inhibit S-adenosylhomocysteine hydrolase ( SAHH; EC 3.3.1.1) interfere with the proliferation of Plasmodium malar ial parasites, but efforts to identify the enzyme directly in parasite extracts have been unsuccessful. Here we report genetic and biochemic al evidence for the presence of a gene encoding P. falciparum SAHH. Th e gene is transcribed as a 2.8-kilobase mRNA in erythrocytic stage par asites. Analysis of the open reading frame predicts a 53.9-kDa protein having conserved regions thought to be involved in NAD binding. The c DNA sequence has been incorporated into an Escherichia coli expression construct to confirm the function of the sahh product. Transformed E. coli cells produce a protein with a relative molecular weight of 56,0 00 which possesses SAHH activity as evidenced by the conversion of 3-d eazaadenosine to S-3-deazaadenosylhomocysteine. Several amino acid res idues that have been suggested to be at the SAHH active site in other organisms show nonconserved replacements in P. falciparum, suggesting that some current proposals for the enzyme mechanism may need to be re vised. The structural differences between the P. falciparum and mammal ian SAHH enzymes may foster innovative strategies for drug development against malaria.