title: NpR3784 is the prototype for a distinctive group of red/green cyanobacteriochromes using alternative Phe residues for photoproduct tuning.
abstract: Cyanobacteriochromes (CBCRs) are photosensory proteins found in cyanobacteria and are distantly related to the widespread phytochromes. Whereas plant phytochromes exhibit responses to red and far-red light, CBCRs use the same photoisomerization of a linear tetrapyrrole (bilin) chromophore to respond to a wide range of colors. NpR6012g4 from Nostoc punctiforme and AnPixJ from Anabaena sp. PCC 7120 belong to a large subfamily of red/green CBCRs that exhibit a red-absorbing dark state similar to that of phytochrome but a green-absorbing photoproduct rather than a far-red-absorbing one. In these canonical red/green CBCRs, the photoproduct is blue-shifted relative to the orange absorption observed in the absence of native protein structure. This spectral tuning of the photoproduct requires a conserved Phe residue on the second β strand of the CBCR GAF domain, consistent with a trapped-twist mechanism in which the bilin is sterically constrained in the photoproduct. N. punctiforme also produces NpR3784, a CBCR with a similar red/green photocycle to that of NpR6012g4. NpR3784 lacks both the β2 Phe and other residues characteristic of the canonical red/green CBCRs. In the current work, we identify NpR3784 homologs with red/green photocycles in other cyanobacteria. Spectral tuning in this NpR3784 group is accomplished by a different set of conserved Phe residues, including a characteristic Phe residue on β1. This set of Phe residues cannot be interchanged with the Phe residues found in canonical red/green CBCRs such as NpR6012g4. Our results provide new insights into the flexible protein-chromophore interactions used by CBCRs to generate their remarkable spectral diversity.
authors.affiliation: Department of Molecular and Cell Biology, University of California at Davis, Davis, CA 95616, USA. jclagarias@ucdavis.edu.
authors.forename: Nathan C
authors.initials: NC
authors.lastname: Rockwell
authors.forename: Shelley S
authors.initials: SS
authors.lastname: Martin
authors.forename: Fei
authors.initials: F
authors.lastname: Gan
authors.forename: Donald A
authors.initials: DA
authors.lastname: Bryant
authors.forename: J Clark
authors.initials: JC
authors.lastname: Lagarias
mesh_terms: D017033:Anabaena; D008164:Luminescent Proteins / Q000737:chemistry* / Q000235:genetics; D046937:Nostoc; D055668:Photochemical Processes; D011487:Protein Conformation; D013057:Spectrum Analysis
chemical_list: D008164:Luminescent Proteins