Peroxiredoxins (Prxs) constitute a family of thiol peroxidases that reduce hydrogen peroxide,peroxinitrite, and hydroperoxides using a strictly conserved cysteine. Very abundant in all organisms,Prxs are produced as diverse isoforms characterized by different catalytic mechanisms and various thiol-containing reducing agents. The oligomeric state of Prxs and the link with their functionality is a subjectof intensive research. We present here a combined X-ray and nuclear magnetic resonance (NMR) studyof a plant Prx that belongs to the D-Prx (type II) subfamily. The
Populus trichocarpa Prx is the first Prxshown to be regenerated
in vitro by both the glutaredoxin and thioredoxin systems. The crystal structureand solution NMR provide evidence that the reduced protein is a specific noncovalent homodimer bothin the crystal and in solution. The dimer interface is roughly perpendicular to the plane of the central
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sheet and differs from the interface of A- and B-Prx dimers, where proteins associate in the plane parallelto the
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sheet. The homodimer interface involves residues strongly conserved in the D (type II) Prxs,suggesting that all Prxs of this family can homodimerize. The study provides a new insight into the Prxoligomerism and the basis for protein-protein and enzyme-substrate interaction studies by NMR.