A Chinese Cabbage cDNA with High Sequence Identity to Phospholipid Hydroperoxide Glutathione Peroxidases Encodes a Novel Isoform of Thioredoxin-dependent Peroxidase

Abstract

A cDNA, PHCC-TPx, specifying a protein highly homologous to known phospholipid hydroperoxide glutathione peroxidases was isolated from a Chinese cabbage cDNA library.

Structural Basis for a Distinct Catalytic Mechanism in Trypanosoma brucei Tryparedoxin Peroxidase

“…In TxP, the glutamine residue of the catalytic triad is replaced by a glutamate (Glu 79 ), but the structural arrangement is comparable with that in the selenocysteine enzymes. A respective mutation in GPX4 severely affected the catalytic efficiency of the protein (13,42), but in the TxP of Chinese cabbage (19), a glutamine to glycine mutation resulted in a fully active enzyme species.…”

“…Despite a number of known structures and detailed biochemical studies, it is still not clear why the N-terminal Cys of the CXXC motif in glutaredoxins has a pK value significantly lower than that of a free cysteine, whereas the pK value of the C-terminal active site Cys has a pK value higher than that of free cysteine (53). A common hypothesis is that conserved basic residues (Arg 26 and Lys 19 in pig glutaredoxin) (54) or an arginine in peroxiredoxins (55) stabilize the thiolate of the more N-terminal cysteine (54). However, a recent molecular dynamics simulation suggests that cationic side chains contribute little to the activation.…”

“…Interestingly, in a related enzyme from Chinese cabbage, the respective glutamine to glycine mutation had no effect on peroxidase activity (19). Nearly all of the cysteine homologues, but not the selenoenzymes, possess a second cysteine (Cys 95 in T. brucei Px III) that is essential for peroxidase activity (18,19). In the first half reaction of catalysis, the thiolate form of Cys 47 (reduced enzyme) reacts with the hydroperoxide substrate, resulting in the respective alcohol and probably a sulfenate at Cys 47 .…”

“…Substitution of Cys 47 or Gln 82 by a glycine residue resulted in inactive protein species, and the glycine mutant of Trp 137 had only 12% wild type activity (18), which seemed to confirm the presence of the catalytic triad. Interestingly, in a related enzyme from Chinese cabbage, the respective glutamine to glycine mutation had no effect on peroxidase activity (19). Nearly all of the cysteine homologues, but not the selenoenzymes, possess a second cysteine (Cys 95 in T. brucei Px III) that is essential for peroxidase activity (18,19).…”

Differential expression of resistance to powdery mildew at the early stage of development in wheat line N0308

“…Trxh is involved in multiple processes, and its best documented function is its implication in reserve breakdown that sustains early seedling growth of germinating cereal seeds (Wong et al, 2002). These proteins are electron donors in several enzymes involved in the protection against oxidative stress, such as peroxiredoxin, methionine sulfoxide reductase, and glutathione reductase (Jung et al, 2002;Gelhaye et al, 2003).…”