Cyanochromes are blue/green light photoreversible photoreceptors defined by a stable double cysteine linkage to a phycoviolobilin-type chromophore
Phytochromes are a collection of bilin-containing photoreceptors that regulate a diverse array of processes in microorganisms and plants through photoconversion between two stable states, a red light-absorbing Pr form, and a far red light-absorbing Pfr form. Recently, a novel set of phytochrome-like chromoproteins was discovered in cyanobacteria, designated here as cyanochromes, that instead photoconvert between stable blue and green light-absorbing forms Pb and Pg, respectively. Here, we show that the distinctive absorption properties of cyanochromes are facilitated through the binding of phycocyanobilin via two stable cysteine-based thioether linkages within the cGMP phosphodiesterase/ adenyl cyclase/FhlA domain. Absorption, resonance Raman and infrared spectroscopy, and molecular modeling of the Te-PixJ GAF (cGMP phosphodiesterase/adenyl cyclase/FhlA) domain assembled with phycocyanobilin are consistent with attachments to the C31 carbon of the ethylidene side chain and the C4 or C5 carbons in the A-B methine bridge to generate a double thioether-linked phycoviolobilin-type chromophore. These spectroscopic methods combined with NMR data show that the bilin is fully protonated in the Pb and Pg states and that numerous conformation changes occur during Pb → Pg photoconversion. Also identified were a number of photochromically inactive mutants with strong yellow or red fluorescence that may be useful for fluorescence-based cell biological assays. Phylogenetic analyses detected cyanochromes capable of different signaling outputs in a wide range of cyanobacterial species. One unusual case is the Synechocystis cyanochrome Etr1 that also binds ethylene, suggesting that it works as a hybrid receptor to simultaneously integrate light and hormone signals. © 2009 by The American Society for Biochemistry and Molecular Biology, Inc.
Publication Source (Journal or Book title)
Journal of Biological Chemistry
Ulijasz, A., Cornilescu, G., von Stetten, D., Cornilescu, C., Escobar, F., Zhang, J., Stankey, R., Rivera, M., Hildebrandt, P., & Vierstra, R. (2009). Cyanochromes are blue/green light photoreversible photoreceptors defined by a stable double cysteine linkage to a phycoviolobilin-type chromophore. Journal of Biological Chemistry, 284 (43), 29757-29772. https://doi.org/10.1074/jbc.M109.038513