Abstract
Phytochrome has an open chain tetrapyrrole (bilin) chromophore that covalently binds to a cysteine residue. We have synthesized the bilin chromophores such as phytochromobilin (PΦB), phycocyanobilin (PCB), biliverdin (BV), and their derivatives to examine the relationship among chromophore structure, assembly efficiency, and photochromism of the holoprotein. It was found that (1) each pyrrole ring of the chromophore plays a different role in chromophore assembly and the photochromic properties of PhyB, (2) a double bond on the D-ring of PΦB is crucial for PhyA function, (3) the A-ring vinyl side chain of BV is used for chromophore attachment in bacteriophytochrome Agp1.
Furthermore, investigation using sterically locked bilin chromophores revealed that (4) stereochemistry of the CD-ring component of bilin chromophore in Pr is Z-anti and Pfr E-anti, respectively.
Now a new avenue was opened to analyze the relationship between chromophore structure and phytochrome function through synthetic organic chemistry.
