Molecular Cloning and Characterization of a Putative Glutathione Reductase Gene, the PfGR2 Gene, from Plasmodium falciparum

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Abstract
Recently, glutathione reductase (GR) has emerged as a promising target for antiparasitic drugs. The central role of GR in cellular antioxidant defence, the particular susceptibility of intracellular parasites like Plasmodium falciparum to oxidative stress, and successful inhibitor studies substantiate this approach. However, more information is required on the structural and functional characteristics of GR from malarial parasites and differences from the enzyme of host erythrocytes. We have identified a putative P. falciparum GR gene coding for a polypeptide (PfGR2) of 500 ami no acids that exhibits 40–45% sequence identity with GR enzymes from other species. 18 out of 19 residues contributing to glutathione binding are identical in the putative PfGR2 and human GR. According to Southern blot analysis, the PfGR2 gene is present as a single-copy gene. It is expressed during the intraerythrocytic life cycle. Stage-specific Northern blot analysis demonstrates that the PfGR2 gene is only weakly transcribed in ring, early trophozoite, and segmenter stages; major transcription occurs in the late trophozoite/early schizont stage. This is consistent with the high glutathione reductase activity found in early schizonts. Other data also suggest that PfGR2 corresponds to the enzyme isolated from parasitized erythrocytes. These criteria include the subunit molecular mass (56.2 kDa), the N-terminal sequence (VYDLIVIGGGSGGMA), the presence of specific sequence motifs at ligand-binding sites, and, as demonstrated by Western blotting, the occurrence of a unique chain segment in the core of the central domain. In view of these data, the function(s) of PfGR2 as well as PfGR1, the product of another GR-like gene of P falciparum (Müller et al., 1995) should be carefully assessed.