Abstract
Phytochromes are red and far-red light receptors in plants. The GAF domain of phytochromes is essential for chromophore holding. A distinct but related subgroup of the GAF domain is abundantly present only in cyanobacteria (denoted cyanobacteriochrome). Recently, our group reported that one of cyanobacteriochrome GAF domains (TePixJ) bound phycocyanobilin (PCB) and showed blue-green photoreversibility. In this study, we focused on the PixJ homolog (AnPixJ) in Anabaena sp. PCC 7120 whose GAF domain is distinct from that of TePixJ.
We expressed the second GAF domain of AnPixJ as a His-tagged protein (H6AnPixJ-GAF2) in PCB-producing Escherichia coli and purified it. H6AnPixJ-GAF2 showed photoreversibility between green-absorbing form (543 nm) and red-absorbing form (648 nm). Acidic denaturation analysis suggested that the chromophore photoreaction of H6AnPixJ-GAF2 is essentially the same as that of orthodox phytochrome. From these, possible light-sensing mechanism of AnPixJ will be discussed. Finally, we will discuss about the perspective of diverse cyanobacteriochromes.
