Structural Basis of Redox Signaling in Photosynthesis: Structure and Function of Ferredoxin:thioredoxin Reductase and Target Enzymes

Abstract

The role of the ferredoxin:thioredoxin system in the reversible light activation of chloroplast enzymes by thioldisulfide interchange with thioredoxins is now well established. Recent fruitful collaboration between biochemists and structural biologists, reflected by the shared authorship of the paper, allowed to solve the structures of all of the components of the system, including several target enzymes, thus providing a structural basis for the elucidation of the activation mechanism at a molecular level. In the present Review, these structural data are analyzed in conjunction with the information that was obtained previously through biochemical and site-directed mutagenesis approaches. The unique 4Fe-4S cluster enzyme ferredoxin:thioredoxin reductase (FTR) uses photosynthetically reduced ferredoxin as an electron donor to reduce the disulfide bridge of different thioredoxin isoforms. Thioredoxins in turn reduce regulatory disulfides of various target enzymes. This process triggers conformational changes on these enzymes, allowing them to reach optimal activity. No common activation mechanism can be put forward for these enzymes, as every thioredoxin-regulated protein undergoes specific structural modifications. It is thus important to solve the structures of the individual target enzymes in order to fully understand the molecular mechanism of the redox regulation of each of them.Abbreviations: FBPase -fructose-

Chloroplast NADPH-Thioredoxin Reductase Interacts with Photoperiodic Development in Arabidopsis

“…Plants possess two main types of thioredoxin reductases, the universal NTRs and the plastidial FTR, which is unique for photosynthetic organisms (Hirt et al, 2002;Dai et al, 2004). The family of NTRs includes NTRA and NTRB, dually localized in cytosol and mitochondria, and chloroplastic NTRC (Hirt et al, 2002).…”

“…A particularly divergent composition of thioredoxin systems is found in plastids, in which four types of thioredoxins (m, f, x, and y), several thioredoxin-like proteins, and two distinct types of thioredoxin reductases have been identified (Meyer et al, 2005;Perez-Ruiz et al, 2006). The classical ferredoxin-dependent thioredoxin reductase (FTR) is an iron-sulfur protein unique to chloroplasts and cyanobacteria (Dai et al, 2004). The second type, NADPH-dependent thioredoxin reductase (NTR), be-longs to the flavoprotein family of pyridine nucleotide disulfide oxidoreductases present in all living cells (Hirt et al, 2002).…”

HCF164 Receives Reducing Equivalents from Stromal Thioredoxin across the Thylakoid Membrane and Mediates Reduction of Target Proteins in the Thylakoid Lumen

“…In the light, photosynthetic electron transport via ferredoxin and ferredoxin-NADP ϩ reductase (FNR) 2 results in the synthesis of NADPH, which is used as a source of reducing equivalents for carbon fixation. However, a portion of the electrons produced by the photosynthetic electron transport is transferred to thioredoxin (Trx) through ferredoxin and ferredoxin-thioredoxin reductase (1)(2)(3). The two stromal thioredoxin isoforms Trx-f and Trx-m were originally identified for this pathway (4, 5); they have been extensively characterized and are known to regulate the activity of a number of thiol enzymes by alteration of their redox state.…”

Reconstitution and Properties of the Recombinant Glyceraldehyde-3-Phosphate Dehydrogenase/CP12/Phosphoribulokinase Supramolecular Complex of Arabidopsis

“…Signals involved in the maintenance of such balance include thioredoxins and a number of biochemical factors, including pyridine nucleotides, several metabolites, as well as pH and magnesium ions (Wolosiuk et al, 1993). In the Calvin cycle, five out of 11 enzymes are prominently sensitive to these signals (glyceraldehyde-3-phosphate dehydrogenase [GAPDH], Fru bisphosphate and sedoheptulose bisphosphate phosphatases, phosphoribulokinase [PRK], and Rubisco via Rubisco activase), and their activities are strongly regulated in vivo by light/dark conditions (Ruelland and MiginiacMaslow, 1999;Schü rmann and Jacquot, 2000;Dai et al, 2004;Buchanan and Balmer, 2005). Moreover, redox regulation in chloroplasts is not restricted to carbon reduction, and the whole plastid metabolism seems to be controlled by the redox status of thioredoxins, as suggested by redox proteomic analysis (for review, see Buchanan and Balmer, 2005).…”