Conserved phenylalanine residues are required for blue-shifting of cyanobacteriochrome photoproducts.
Cyanobacteriochromes (CBCRs) are cyanobacterial photosensory proteins distantly related to phytochromes. Both phytochromes and CBCRs reversibly convert between dark-stable and photoproduct states upon photoisomerization of their linear tetrapyrrole (bilin) chromophores. While most phytochromes convert between a red-absorbing dark state and a far-red-absorbing photoproduct, CBCRs exhibit spectral responses spanning the entire near-ultraviolet and visible spectrum. For example, red/green CBCRs such as AnPixJ and NpR6012g4 exhibit a red-absorbing dark state similar to that of phytochrome, but photoconversion yields a green-absorbing photoproduct. "Teal-DXCF" CBCRs convert from blue- or green-absorbing dark states to yield photoproducts with very narrow absorption in the teal region of the spectrum (approximately 500 nm). The recent determination of a crystal structure of AnPixJ in its red-absorbing dark state led to the proposal that movement of a Trp residue (the "lid Trp") upon photoconversion would allow solvation of the photoproduct, thereby producing a large blue-shift. We find that substitution of the lid Trp has little effect on the NpR6012g4 photoproduct. Instead, two Phe residues conserved in red/green and teal-DXCF CBCRs are essential for determining photoproduct absorption in both CBCR groups with no significant influence on the dark-adapted state. We propose that these Phe residues constrain chromophore movement after primary photoisomerization. This work supports a trapped-twist mechanism for generating both red/green and teal-DXCF photoproducts.
Department of Molecular and Cellular Biology, University of California , Davis, California 95616, United States.
Nathan C
NC
Rockwell
Shelley S
SS
Martin
Alexander G
AG
Gulevich
J Clark
JC
Lagarias
D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics; D018360:Crystallography, X-Ray; D000458:Cyanobacteria / Q000737:chemistry* / Q000235:genetics; D010649:Phenylalanine / Q000737:chemistry* / Q000235:genetics; D010860:Pigments, Biological / Q000737:chemistry* / Q000235:genetics; D011487:Protein Conformation
D001426:Bacterial Proteins; D010860:Pigments, Biological; D010649:Phenylalanine