Abstract
Phytochromes are red and far-red light receptors in plants. Cyanobacteriochromes, which are distantly related to phytochromes and present only in cyanobacteria, show various spectral properties. Of these, the putative phototactic photoreceptor, AnPixJ, covalently binds phycocyanobilin and shows reversible photoconversion between green-absorbing (Pg) and red-absorbing (Pr) forms. It is suggested that unorthodox green-red reversible photoconversion of AnPixJ undergoes the same Z/E isomerization as phytochromes. In this study, we obtained blue crystals of Pr form of AnPixJ by hanging-drop vapor diffusion method. The crystal structure was solved at 1.8 Å resolution by SAD method using anomalous scattering of iodide. The configuration of chromophore of AnPixJ is quite similar to that of bacteriophytochrome, although the local environment surrounding chromophore of AnPixJ is clearly distinct from that of bacteriophytochrome. This is consistent with the previous spectral studies. Possible photoconversion mechanism from phytochrome-like Pr form to unusual Pg form will be discussed.
