Fes kinase structure reveals cooperative interactions between SH2-kinase domains and substrate

Phytochromes of plants, fungi, algae and bacteria are the photoreceptors that bind linear tetrapyrroles and show reversible photoconversion between red-absorbing form (Pr) and far-redabsorbing form.Cyanobacteriochromes with various spectral properties are the recently emerged photoreceptors that are distinctive relative of the phytochromes.Among them, AnPixJ-GAF2 from cyanobacterium Anabaena sp.PCC 7120 is a novel photoreceptor that covalently binds phycocyanobilin and shows green/red reversible photoconversion.It is suggested that the Pr form of AnPixJ-GAF2, which corresponds to that of phytochrome, is photoconverted to unusual blue-shifted green-absorbing form (Pg) via phytochromelike intermediate states.To get structural insights into this unique photoconversion mechanism, we tried to crystallize AnPixJ-GAF2 in both forms.As a result, we obtained blue crystals of the Pr form by hanging-drop vapor diffusion method.The crystals belong to space group P43212 and contain one monomer in an asymmetric unit.The crystal structure was solved at 1.8 Å resolution by iodide-SAD method.The overall structure and the chromophore structure of the Pr form are very similar to those of the Pr forms of bacterial phytochromes, although relative position of the chromophore to the apoprotein is significantly deviated.In correspondence with the deviation, amino acid residues surrounding the chromophore are quite diverged.Nevertheless, we can point out a common structural feature conserved between the two Pr forms.Moreover, some residues unique to AnPixJ-GAF2 are suggested to be crucial for the formation of the unusual Pg form.These results shed light on the universal and unique aspects of photosensory mechanism of phytochromes and cyanobacteriochromes.