title: The thioredoxin system of the malaria parasite Plasmodium falciparum. Glutathione reduction revisited.
abstract: In most living cells, redox homeostasis is based both on the glutathione and the thioredoxin system. In the malaria parasite Plasmodium falciparum antioxidative proteins represent promising targets for the development of antiparasitic drugs. We cloned and expressed a thioredoxin of P. falciparum (pftrx), and we improved the stable expression of the thioredoxin reductase (PfTrxR) of the parasite by multiple silent mutagenesis. Both proteins were biochemically characterized and compared with the human host thioredoxin system. Intriguingly, the 13-kDa protein PfTrx is a better substrate for human TrxR (K(m) = 2 microm, k(cat) = 3300 min(-)(1)) than for P. falciparum TrxR (K(m) = 10.4 microm, k(cat) = 3100 min(-)(1)). Possessing a midpoint potential of -270 mV, PfTrx was found to reduce the disease-related metabolites S-nitrosoglutathione and GSSG. The rate constant k(2) for the reaction between reduced P. falciparum thioredoxin and GSSG was determined to be 0.039 microm(-)(1) min(-)(1) at 25 degrees C and pH 7.4. The k(2) for thioredoxins from man, Drosophila melanogaster, and Escherichia coli was approximately 5 times lower. Our data suggest that GSSG reduction can be supported at a high rate by the TrxR/Trx system in glutathione reductase-deficient cells; this may be relevant for certain stages of the malarial parasite but also for cells containing high [GSSG] of other organisms like dormant forms of Neurospora, glutathione reductase-deficient yeast mutants, or CD4(+) lymphocytes of AIDS patients.
authors.affiliation: Center of Biochemistry, Heidelberg University, D-69120 Heidelberg, Research Center for Infectious Diseases, Würzburg University, D-97070 Würzburg, Germany.
authors.forename: S M
authors.initials: SM
authors.lastname: Kanzok
authors.forename: R H
authors.initials: RH
authors.lastname: Schirmer
authors.forename: I
authors.initials: I
authors.lastname: Turbachova
authors.forename: R
authors.initials: R
authors.lastname: Iozef
authors.forename: K
authors.initials: K
authors.lastname: Becker
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000962:Antimalarials / Q000494:pharmacology; D001483:Base Sequence; D003001:Cloning, Molecular; D016054:DNA, Protozoan; D005978:Glutathione / Q000378:metabolism*; D019803:Glutathione Disulfide / Q000378:metabolism; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D010963:Plasmodium falciparum / Q000187:drug effects / Q000378:metabolism*; D013879:Thioredoxins / Q000235:genetics / Q000378:metabolism*
chemical_list: D000962:Antimalarials; D016054:DNA, Protozoan; D013879:Thioredoxins; D005978:Glutathione; D019803:Glutathione Disulfide