page_title: Ferredoxin-thioredoxin reductase
section_title: Structure
hierarchical_section_title: Ferredoxin-thioredoxin reductase / Structure
caption_attribution_description: English: Pymol-generated image shows integral pieces of Ferredoxin-thioredoxin reductase's catalytic chain. Ferredoxin-thioredoxin reductase mechanism proceeds through redox chemistry of a 4Fe-4S cluster and surrounding Cysteine residues.
context_page_description: Ferredoxin-thioredoxin reductase EC 1.8.7.2, systematic name ferredoxin:thioredoxin disulfide oxidoreductase, is a [4Fe-4S] protein that plays an important role in the ferredoxin/thioredoxin regulatory chain. It catalyzes the following reaction:
  2 reduced ferredoxin + thioredoxin disulfide 2 oxidized ferredoxin + thioredoxin thiols + 2 H⁺
  Ferredoxin-Thioredoxin reductase converts an electron signal to a thiol signal, regulating enzymes by reduction of specific disulfide groups. It catalyses the light-dependent activation of several photosynthesis enzymes and constitutes the first historical example of a thiol/disulfide exchange cascade for enzyme regulation. It is a heterodimer of subunit alpha and subunit beta. Subunit alpha is the variable subunit, and beta is the catalytic chain. The structure of the beta subunit has been determined and found to fold around the FeS cluster.
context_section_description: Ferredoxin-Thioredoxin Reductase is an α-β heterodimer of approximately 30 kDa. FTR structure across different plant species include a conserved catalytic β subunit and a variable α subunit. The structure of FTR from Synechocystis sp. PCC6803 has been studied in detail and resolved at 1.6 Å. FTR resembles a thin concave disc, 10 Å across the center where a [4Fe-4S cluster] resides.  One side of the cluster center contains redox-active disulfide bonds that reduce Thioredoxin while the opposite docks with reduced Ferredoxin. This two sided disc structure allows FTR to simultaneously interact with Thioredoxin and Ferredoxin.
  The variable α subunit has an open β barrel structure made of five antiparallel β strands.  Its interaction with the catalytic subunit occurs mainly with two loops between β strands. The residues in these two loops are mostly conserved and are thought to stabilize the 4Fe-4S cluster in the catalytic subunit. Structurally, the α subunit is very similar to the PsaE protein, a subunit of Photosystem I, though the similarity is not seen in their sequences or functions.
  The catalytic β subunit has a general α-helical structure with an [4Fe-4S center].  The FeS center and redox-active Cysteine residues are located within the loops of these helices. Cysteine-55, 74, 76, and 85 are coordinated to the iron atoms of the cubane-type cluster.
caption: [4Fe-4S] cluster in the Ferredoxin-thioredoxin reductase catalytic β subunit is surrounded by several Cysteine residues.
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