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.