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Green/red light-sensing mechanism in the chromatic acclimation photosensor
Takayuki Nagae1, Yuya Fujita2, Tatsuya Tsuchida3
1Department of Molecular Biophysics, School of Pharmacy, Tokyo University of Pharmacy and Life Sciences, Hachioji, Tokyo 192-0392, Japan.
Science Advances
|June 12, 2024
Summary
Certain cyanobacteria adjust light absorption using cyanobacteriochromes, which switch between green-absorbing (Pg) and red-absorbing (Pr) states. This study reveals the structural changes in the bilin chromophore driving this complementary chromatic acclimation.
Area of Science:
- Biochemistry
- Photobiology
- Microbiology
Background:
- Cyanobacteria exhibit complementary chromatic acclimation, altering light absorption between green and red wavelengths.
- This process is mediated by cyanobacteriochrome (Cbc) photosensors that reversibly switch between green-absorbing (Pg) and red-absorbing (Pr) states.
Purpose of the Study:
- To elucidate the structural mechanisms underlying the green/red photocycle of cyanobacteriochromes.
- To understand how structural changes in the bilin chromophore lead to spectral shifts.
Main Methods:
- X-ray crystallography to determine the structure of the cyanobacteriochrome in different states.
- Spectroscopic analysis to characterize the bilin chromophore and its environment.
Main Results:
- In the Pg state, the bilin chromophore adopts an extended C15-Z,anti structure within a hydrophobic pocket.
- Upon photoconversion to the Pr state, the bilin isomerizes to a cyclic C15-E,syn structure, creating a water channel.
- Solvation/desolvation of the bilin alters its protonation state and π-conjugation stability, causing a significant spectral shift.
Conclusions:
- The structural transformation of the bilin chromophore is the key to the reversible green/red spectral shift in cyanobacteriochromes.
- This work provides fundamental insights into the spectral diversity and photocycle mechanisms within the phytochrome superfamily.
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