Isolation and characterization of a new peroxiredoxin from poplar sieve tubes that uses either glutaredoxin or thioredoxin as a proton donor

A sequence coding for a peroxiredoxin (Prx) was isolated from a xylem/phloe m cDNA library from Populus trichocarpa and subsequently inserted into an e xpression plasmid yielding the construction pET-Prx. The recombinant protei n was produced in Escherichia coli cells and purified to homogeneity with a high yield. The poplar Prx is composed of 162 residues, a property that ma kes it the shortest plant Prx sequence isolated so far. It was shown that t he protein is monomeric and possesses two conserved cysteines (Cys). The Pr x degrades hydrogen peroxide and alkyl hydroperoxides in the presence of an exogenous proton donor that can be either thioredoxin or glutaredoxin (Grx ). Based on this finding, we propose that the poplar protein represents a n ew type of Prx that differs from the so-called 2-Cys and 1-Cys Prx, a sugge stion supported by the existence of natural fusion sequences constituted of a Prx motif coupled to a Grx motif. The protein was shown to be highly exp ressed in sieve tubes where thioredoxin h and Grx are also major proteins.