Green/red light-sensing mechanism in the chromatic acclimation photosensor

• Published in: Science advances Vol. 10; no. 24; p. eadn8386
• Main Authors: Nagae, Takayuki, Fujita, Yuya, Tsuchida, Tatsuya, Kamo, Takanari, Seto, Ryoka, Hamada, Masako, Aoyama, Hiroshi, Sato-Tomita, Ayana, Fujisawa, Tomotsumi, Eki, Toshihiko, Miyanoiri, Yohei, Ito, Yutaka, Soeta, Takahiro, Ukaji, Yutaka, Unno, Masashi, Mishima, Masaki, Hirose, Yuu
• Format: Journal Article
• Language: English
• Published: United States American Association for the Advancement of Science 14.06.2024
• Subjects: Acclimatization; Bacterial Proteins - chemistry; Bacterial Proteins - metabolism; Bile Pigments - chemistry; Bile Pigments - metabolism; Biomedicine and Life Sciences; Cyanobacteria - metabolism; Cyanobacteria - physiology; Light; Models, Molecular; Photosynthesis; Phytochrome - chemistry; Phytochrome - metabolism; Red Light; SciAdv r-articles; Structural Biology
• ISSN: 2375-2548; 2375-2548
• DOI: 10.1126/sciadv.adn8386

Certain cyanobacteria alter their photosynthetic light absorption between green and red, a phenomenon called complementary chromatic acclimation. The acclimation is regulated by a cyanobacteriochrome-class photosensor that reversibly photoconverts between green-absorbing (Pg) and red-absorbing (Pr) states. Here, we elucidated the structural basis of the green/red photocycle. In the Pg state, the bilin chromophore adopted the extended C15- Z , anti structure within a hydrophobic pocket. Upon photoconversion to the Pr state, the bilin is isomerized to the cyclic C15- E , syn structure, forming a water channel in the pocket. The solvation/desolvation of the bilin causes changes in the protonation state and the stability of π-conjugation at the B ring, leading to a large absorption shift. These results advance our understanding of the enormous spectral diversity of the phytochrome superfamily. The structure of the cyanobacterial chromatic acclimation photosensor revealed a unique mechanism for green and red light sensing.