Crystallization and preliminary X-ray studies of the chromophore-binding domain of cyanobacteriochrome AnPixJ from Anabaena sp. PCC 7120

Cyanobacteriochromes form a recently defined superfamily of tetrapyrrole-based photoreceptors that are distantly related to conventional red/far-red photoreceptor phytochromes. Among these molecules, AnPixJ from Anabaena sp. PCC 7120 is a novel photoreceptor that shows reversible photoconversion between green-absorbing and red-absorbing forms, which is in contrast to the properties of conventional phytochromes. In order to better understand the structural basis of this unique photoconversion mechanism, the chromophore-binding domain of AnPixJ (AnPixJ-GAF2) was heterologously overproduced and purified, and crystallization of both forms was attempted. Blue crystals of the red-absorbing form of AnPixJ-GAF2 were successfully obtained; they belonged to space group P4₃2₁2 and contained one monomer per asymmetric unit. Diffraction data were collected to a resolution of 1.8 Å using synchrotron-radiation beamline BL-5A at the Photon Factory.