The structure of reduced tryparedoxin peroxidase reveals a decamer and insight into reactivity of 2Cys-peroxiredoxins

Tryparedoxin peroxidase (TryP) is a recently discovered 2Cys-peroxiredoxin involved in defence against oxidative stress in parasitic trypanosomatids. The crystal structure of recombinant Crithidia fasciculata TryP, in the red uced state, has been determined using multi-wavelength anomalous dispersion methods applied to a selenomethionyl derivative. The model comprises a dec amer with 52 symmetry, ten chloride ions with 23 water molecules and has be en refined, using data to 3.2 Angstrom resolution (1 Angstrom = 0.1 nm), to an R-factor and R-free of 27.3 and 28.6 %, respectively. Secondary structu re topology places TryP along with tryparedoxin and glutathione peroxidase in a distinct subgroup of the thioredoxin superfamily. The molecular detail s at the active site support ideas about the enzyme mechanism and compariso ns with an oxidised 2Cys-peroxiredoxin reveal structural alterations induce d by the change in oxidation state. These include a difference in quaternar y structure from dimer (oxidised form) to decamer (reduced form). The 2Cys- peroxiredoxin assembly may prevent indiscriminate oligomerisation, localise ten peroxidase active sites and contribute to both the specificity of redu ction by the redox partner tryparedoxin and attraction of peroxides into th e active site. (C) 2000 Academic Press.