title: Structures of cyanobacteriochromes from phototaxis regulators AnPixJ and TePixJ reveal general and specific photoconversion mechanism.
abstract: Cyanobacteriochromes are cyanobacterial tetrapyrrole-binding photoreceptors that share a bilin-binding GAF domain with photoreceptors of the phytochrome family. Cyanobacteriochromes are divided into many subclasses with distinct spectral properties. Among them, putative phototaxis regulators PixJs of Anabaena sp. PCC 7120 and Thermosynechococcus elongatus BP-1 (denoted as AnPixJ and TePixJ, respectively) are representative of subclasses showing red-green-type and blue/green-type reversible photoconversion, respectively. Here, we determined crystal structures for the AnPixJ GAF domain in its red-absorbing 15Z state (Pr) and the TePixJ GAF domain in its green-absorbing 15E state (Pg). The overall structure of these proteins is similar to each other and also similar to known phytochromes. Critical differences found are as follows: (i) the chromophore of AnPixJ Pr is phycocyanobilin in a C5-Z,syn/C10-Z,syn/C15-Z,anti configuration and that of TePixJ Pg is phycoviolobilin in a C10-Z,syn/C15-E,anti configuration, (ii) a side chain of the key aspartic acid is hydrogen bonded to the tetrapyrrole rings A, B and C in AnPixJ Pr and to the pyrrole ring D in TePixJ Pg, (iii) additional protein-chromophore interactions are provided by subclass-specific residues including tryptophan in AnPixJ and cysteine in TePixJ. Possible structural changes following the photoisomerization of the chromophore between C15-Z and C15-E are discussed based on the X-ray structures at 1.8 and 2.0-Å resolution, respectively, in two distinct configurations.
authors.affiliation: Department of Life Sciences Biology, Graduate School of Art and Sciences, University of Tokyo, Komaba, Meguro, Tokyo 153-8902, Japan.
authors.forename: Rei
authors.initials: R
authors.lastname: Narikawa
authors.forename: Takami
authors.initials: T
authors.lastname: Ishizuka
authors.forename: Norifumi
authors.initials: N
authors.lastname: Muraki
authors.forename: Tomoo
authors.initials: T
authors.lastname: Shiba
authors.forename: Genji
authors.initials: G
authors.lastname: Kurisu
authors.forename: Masahiko
authors.initials: M
authors.lastname: Ikeuchi
mesh_terms: D000595:Amino Acid Sequence; D017033:Anabaena / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D018360:Crystallography, X-Ray; D000458:Cyanobacteria / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D055668:Photochemical Processes; D020283:Photoreceptors, Microbial / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011487:Protein Conformation; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D055672:Static Electricity; D045725:Tetrapyrroles / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D020283:Photoreceptors, Microbial; D045725:Tetrapyrroles