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bioRxiv · 10.1101/2020.06.02.130930

Molecular Basis of Far-red Sensing in Cyanobacteriochrome

Bandara, S.·Rockwell, N. C.·Zeng, X.·Ren, Z.·Wang, C.·Shin, H.·Martin, S.·Moreno, M.·Lagarias, J. C.·Yang, X.
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Abstract

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 [A] 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 StatementPhytochromes 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.

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Bandara, S., Rockwell, N. C., Zeng, X., Ren, Z., Wang, C., Shin, H., Martin, S., Moreno, M., Lagarias, J. C., Yang, X.. 2020-06-03. Molecular Basis of Far-red Sensing in Cyanobacteriochrome. https://doi.org/10.1101/2020.06.02.130930

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