Abstract
In higher plants, red algae, and cyanobacteria, phytobilins are utilized for photoreceptor and/or light harvesting pigments. Phytobilins are synthesized by ferredoxin-dependent bilin reductases (FDBRs) from biliverdin ΙΧα (BV). Phycocyanobilin:ferredoxin oxidoreductase (PcyA), one such FDBR, successively reduces two sites of BV, the vinyl group of D-ring and the A-ring, to produce phycocyanobilin. This indicates that PcyA recognizes the slight difference between the vinyl and methyl groups, and controls the sequence of the reductions.
We have determined the crystal structure of PcyA from Synechocystis sp. PCC 6803 in complex with BV at 1.51 Å resolution, revealing the first tertiary structure of an FDBR family member. The binding site of ferredoxin, and the mechanisms of recognition and reduction of BV will be discussed. Additionally, the features of molecular surfaces and active sites of other FDBRs, which were derived by homology modeling, were compared with those of PcyA.
