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Multistep 11-cis to All-trans Retinal Photoisomerization in Bestrhodopsin, an Unusual Microbial Rhodopsin.
Matthias Broser1, Spyridon Kaziannis2,3, Ivo H M van Stokkum4
1Institut für Biologie, Experimentelle Biophysik, Humboldt Universität zu Berlin, Invalidenstrasse 42, Berlin D-10115, Germany.
Journal of the American Chemical Society
|July 10, 2025
Summary
This study reveals the unique 11-cis to all-trans photoisomerization in P. antarctica bestrhodopsin. It details ultrafast isomerization pathways and proposes bicycle pedal models for retinal chromophore transformations.
Area of Science:
- Biochemistry
- Photochemistry
- Structural Biology
Background:
- Rhodopsins are photoreceptors with diverse photoisomerization mechanisms.
- Bestrhodopsins exhibit bistable states (D661 and P540) with unusual isomerization.
- Understanding P. antarctica bestrhodopsin's photochemistry is key to microbial rhodopsin function.
Purpose of the Study:
- To elucidate the 11-cis to all-trans photoreaction mechanism of P. antarctica bestrhodopsin.
- To characterize the primary photoproducts and their subsequent transformations.
- To propose molecular models for the observed photoisomerization events.
Main Methods:
- Femtosecond-to-submillisecond transient absorption spectroscopy.
- Femtosecond stimulated Raman spectroscopy.
- Flash-photolysis spectroscopy.
Main Results:
- Ultrafast isomerization (240 fs) yields a mixture of all-trans and 13-cis retinal.
- The 13-cis fraction thermally isomerizes to all-trans retinal in 120 ps.
- Branched photoisomerization pathways are proposed, involving bicycle pedal motions.
Conclusions:
- P. antarctica bestrhodopsin utilizes a distinct 11-cis to all-trans isomerization pathway.
- Bicycle pedal models explain the formation of different retinal isomers.
- The photoreaction involves ultrafast primary steps followed by slower thermal relaxations.
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