Molecular Origin of Photoprotection in Cyanobacteria Probed by Watermarked Femtosecond Stimulated Raman Spectroscopy

Yusaku Hontani, Miroslav Kloz, Tomáš Polívka, Mahendra K. Shukla, Roman Sobotka, John T.M. Kennis*

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

Photoprotection is fundamental in photosynthesis to avoid oxidative photodamage upon excess light exposure. Excited chlorophylls (Chl) are quenched by carotenoids, but the precise molecular origin remains controversial. The cyanobacterial HliC protein belongs to the Hlip family ancestral to plant light-harvesting complexes, and binds Chl a and β-carotene in 2:1 ratio. We analyzed HliC by watermarked femtosecond stimulated Raman spectroscopy to follow the time evolution of its vibrational modes. We observed a 2 ps rise of the C=C stretch band of the 2Ag - (S1) state of β-carotene upon Chl a excitation, demonstrating energy transfer quenching and fast excess-energy dissipation. We detected two distinct β-carotene conformers by the C=C stretch frequency of the 2Ag - (S1) state, but only the β-carotene whose 2Ag - energy level is significantly lowered and has a lower C=C stretch frequency is involved in quenching. It implies that the low carotenoid S1 energy that results from specific pigment-protein or pigment-pigment interactions is the key property for creating a dissipative energy channel. We conclude that watermarked femtosecond stimulated Raman spectroscopy constitutes a promising experimental method to assess energy transfer and quenching mechanisms in oxygenic photosynthesis.

Original languageEnglish
Pages (from-to)1788-1792
Number of pages5
JournalJournal of Physical Chemistry Letters
Volume9
Issue number7
Early online date23 Mar 2018
DOIs
Publication statusPublished - 5 Apr 2018

Funding

Y.H. and J.T.M.K. were supported by the Chemical Sciences Council of The Netherlands Organization for Scientific Research (NWO) through a VICI grant and a Middelgroot investment grant to J.T.M.K. M.K. was supported by the Czech Science Foundation project number 17-01137S. R.S. and M.K.S. were supported by the project 17-08755S of the Czech Science Foundation and by the Czech Ministry of Education (project LO1416). T.P. was supported by the project P501/12/G055 from the Czech Science Foundation.

FundersFunder number
Chemical Sciences Council of The Netherlands Organization for Scientific Research
Ministerstvo Školství, Mládeže a TělovýchovyP501/12/G055, LO1416
Grantová Agentura České Republiky17-01137S, 17-08755S
Nederlandse Organisatie voor Wetenschappelijk Onderzoek

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