Ferredoxin-NADP(+) oxydoreductase (FNR) (EC 1.18.1.2) transfers electrons from ferredoxin (or flavodoxin) to NADP(+) to generate NADPH. In eucaryotes, the nuclear-encoded, chloroplast-targeted enzyme contains two domains: an FAD-binding domain and an NADP(+)-binding domain. With the exception of Gloeobacter violaceus PCC 7421, the predicted sequences of all cyanobacterial petH genes, encoding FNR, correspond to a protein containing three domains. Two domains at the C terminus correspond to the FAD- and NADP(+)-binding domains of higher plants FNR protein, which compose the catalytic domains of the enzyme. The N-terminal domain is similar to phycobilisome (PBS)-associated linker proteins from numerous cyanobacteria [(PUBMED:1554697), (PUBMED:2040095), (PUBMED:4636046)] and is associated with:

• - CpcD, the phycocyanin (PC)-associated, rod-capping, linker polypeptide of PBS. The similarity spans nearly the entire sequence of this linker class.
• - CpcC, the PC-associated rod linker polypeptide. The similarity is confined only to the C terminus of this linker class.
• - ApcC, the allophycocyanin (APC)-associated, core linker polypeptide. The similarity only correspond to about half of the molecule.

The CpcD-like domain has an elongated shape and consists of a three-stranded beta-sheet, two alpha-helices, one of which has only about one turn, and the connecting random coil segments [(PUBMED:9990029)].