Ferredoxine

Ferredoxins are a family of small iron–sulfur proteins that mediate electron transfer in a wide range of biological processes. They are typically acidic and contain one or more iron–sulfur clusters coordinated by conserved cysteine residues, with the exact cluster type influencing redox potential and partner specificity. The clusters most commonly encountered are [2Fe-2S], [3Fe-4S], and [4Fe-4S], and their presence enables efficient single-electron transfer between enzymes in metabolic pathways.

Functions and roles: In photosynthesis, plastid ferredoxins receive electrons from photosystem I and donate them to ferredoxin-NADP+ reductase to reduce NADP+ to NADPH, a key step in carbon fixation. In bacteria and archaea, ferredoxins participate in anaerobic respiration and fermentation, nitrogen fixation, sulfate assimilation, and various hydrogen- or carbon- metabolism pathways. They often serve as electron donors or acceptors for oxidoreductases, hydrogenases, and other reductases, linking metabolic steps that would otherwise be energetically separated.

Distribution and structure: Ferredoxins are found across bacteria, archaea, and plants. Plant-type ferredoxins are typically located in chloroplasts and photosynthetic tissues, whereas bacterial and archaeal ferredoxins can be cytosolic or associated with membranes. Their size generally ranges from about 60 to 120 amino acids, and their structure centers on a compact fold that surrounds the iron–sulfur cluster to enable rapid electron transfer.

Biotechnological relevance: Ferredoxins are valuable model systems for studying electron transfer mechanisms. Engineered ferredoxins are explored for applications in bioenergy, biosynthesis, and synthetic biology as components of designed electron transfer chains.