title: Activation of active-site cysteine residues in the peroxiredoxin-type tryparedoxin peroxidase of Crithidia fasciculata.
abstract: Tryparedoxin peroxidase (TXNPx), recently identified as the hydroperoxide-detoxifying enzyme of trypanosomatidae [Nogoceke, E., Gommel, D. U., Kiess, M., Kalisz, H. M. & Flohé, L. (1997) Biol. Chem. 378, 827-836], is a member of the peroxiredoxin family and is characterized by two VCP motifs. Based on a consensus sequence of TXNPx and peroxiredoxin-type peroxidases, eight TXNPx variants were designed, heterologously expressed in Escherichia coli, checked for alpha-helix content by CD and kinetically analysed. The variant Q164E was fully active, C52S, W87D and R128E were inactive and C173S, W87H, W177E and W177H showed reduced activity. Wild-type TXNPx and Q164E exhibit ping-pong kinetics with infinite maximum velocities, whereas saturation kinetics were observed with C173S and W177E. The data comply with a mechanism in which C52, primarily activated by R128 and possibly by W87, is first oxidized by hydroperoxide to a sulfenic acid derivative. C173, supported by W177, then forms an intersubunit disulfide bridge with C52. If C173 is exchanged with a redox-inactive residue (Ser) or is insufficiently activated, the redox shuttle remains restricted to C52. The shift in the kinetic pattern and decrease in specific activity of C173S and W177E may result from a limited accessibility of the oxidized C52 to tryparedoxin, which in the oxidized wild-type TXNPx presumably attacks the C173 sulfur of the disulfide bridge. The proposed mechanism of action of TXNPx is consistent with that deduced for the homologous thioredoxin peroxidase of yeast [Chae, H. Z., Uhm, T. B. & Rhee, S. G. (1994) Proc. Natl Acad. Sci. USA 91, 7022-7026] and is supported by molecular modelling based on the structure of the human peroxiredoxin 'hORF6' [Choi, H.-J., Kang, S. W. Yang, C.-H., Rhee, S. G. & Ryu, S.-E. (1998) Nat. Struct. Biol. 5, 400-406].
authors.affiliation: Department of Biochemistry, Technical University of Braunschweig, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Montemartini
authors.forename: H M
authors.initials: HM
authors.lastname: Kalisz
authors.forename: H J
authors.initials: HJ
authors.lastname: Hecht
authors.forename: P
authors.initials: P
authors.lastname: Steinert
authors.forename: L
authors.initials: L
authors.lastname: Flohé
mesh_terms: D000818:Animals; D001665:Binding Sites; D002942:Circular Dichroism; D016831:Crithidia fasciculata / Q000201:enzymology*; D017931:DNA Primers; D004220:Disulfides / Q000737:chemistry; D004789:Enzyme Activation; D004926:Escherichia coli; D007700:Kinetics; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D010544:Peroxidases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D010545:Peroxides / Q000378:metabolism; D017433:Protein Structure, Secondary; D015800:Protozoan Proteins / Q000737:chemistry; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics; D013880:Thioredoxin-Disulfide Reductase / Q000737:chemistry; D015003:Yeasts / Q000201:enzymology
chemical_list: D017931:DNA Primers; D004220:Disulfides; D010545:Peroxides; D015800:Protozoan Proteins; D011994:Recombinant Proteins; D010544:Peroxidases; C110959:tryparedoxin peroxidase; D013880:Thioredoxin-Disulfide Reductase