RT Journal Article
SR Electronic
T1 Molecular Basis of Far-red Sensing in Cyanobacteriochrome
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 2020.06.02.130930
DO 10.1101/2020.06.02.130930
A1 Sepalika Bandara
A1 Nathan Rockwell
A1 Xiaoli Zeng
A1 Zhong Ren
A1 Cong Wang
A1 Heewhan Shin
A1 Shelley S. Martin
A1 Marcus V. Moreno
A1 J. Clark Lagarias
A1 Xiaojing Yang
YR 2020
UL http://biorxiv.org/content/early/2020/06/03/2020.06.02.130930.abstract
AB Cyanobacteriochromes are small, panchromatic photoreceptors in the phytochrome superfamily that regulate diverse light-mediated adaptive processes in cyanobacteria. The molecular basis of far-red (FR) light perception by cyanobacteriochromes is currently unknown. Here we report the crystal structure of a far-red-sensing cyanobacteriochrome from Anabaena cylindrica PCC 7122, which exhibits a reversible far-red/orange photocycle. The 2.7 Å structure of its FR-absorbing dark state, determined by room temperature serial crystallography and cryo-crystallography, reveals an all-Z,syn configuration of its bound linear tetrapyrrole (bilin) chromophore that is less extended than the bilin chromophores of all known phytochromes. Based on structural comparisons with other bilin-binding proteins and extensive spectral analyses on mutants, we identify key protein-chromophore interactions that enable far-red sensing in bilin-binding proteins. We propose that FR-CBCRs employ two distinct tuning mechanisms, which work together to produce a large batho-chromatic shift. Findings of this work have important implications for development and improvement of photoproteins with far-red absorption and fluorescence.Significance Statement Phytochromes are well known far-red-light sensors found in plants that trigger adaptive responses to facilitate competition for light capture with neighboring plants. Red- and far-red-sensing are critical to cyanobacteria living in the far-red-enriched shade of plants. Here we report the crystal structure of a far-red-sensing cyanobacteriochrome, a distant cyanobacterial relative of phytochrome. These studies shed insight into the poorly understood molecular basis of far-red-sensing by phytobilin-based photoreceptors. Owing to the deep tissue penetration of far-red light, far-red-sensing photoreceptors offer promising protein scaffolds for developing gene-based photoswitches, optoacoustic contrast agents and fluorescent probes for in situ imaging and optogenetic applications.Competing Interest StatementThe authors have declared no competing interest.