Biochemical characterization of chloroplast thioredoxin-like protein CDSP32 from Arabidopsis thaliana

Redox regulation is a post-translational modification based on the reduction/oxidation reaction of Cys residues. Thioredoxin (Trx) plays a central role in this regulatory system by serving as a mediator of reducing power. In addition to the canonical Trx subtypes, plant chloroplasts contain putative redox-regulatory factors that harbor atypical Trx motifs and are classified as Trx-like proteins. The chloroplastic drought-induced stress protein of 32 kDa (CDSP32) is a member of this group. Although some physiological implications of CDSP32 have been proposed, its molecular functions remain incompletely understood. To address this issue, we investigated the biochemical properties of recombinant CDSP32 protein from Arabidopsis thaliana. Analysis of protein redox states using thiol-labeling reagents revealed that CDSP32 can receive reducing power from ferredoxin-Trx reductase. Furthermore, CDSP32 can transfer reducing power to 2-Cys peroxiredoxin with higher efficiency than canonical Trx can, but not to other redox-sensitive enzymes examined. These findings suggest that CDSP32 functions as a specific and efficient component of the antioxidant system in a light-dependent manner.