Femtosecond Dynamics of Excited States of Chlorophyll Tetramer in Water-Soluble Chlorophyll-Binding Protein BoWSCP

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Dmitry A. Cherepanov^1,2,a*, Konstantin V. Neverov^3,4, Yuriy N. Obukhov³, Yulia V. Maleeva⁴, Feodor E. Gostev¹, Ivan V. Shelaev^1,2, Arseny V. Aybush¹, Michail S. Kritsky³, and Victor A. Nadtochenko^1,5,b*

¹Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, 119991 Moscow, Russia

²Belozersky Research Institute of Physical and Chemical Biology, Lomonosov Moscow State University, 119992 Moscow, Russia

³Bach Institute of Biochemistry, Federal Research Center “Fundamentals of Biotechnology” of the Russian Academy of Sciences, 119071 Moscow, Russia

⁴Faculty of Biology, Lomonosov Moscow State University, 119991 Moscow, Russia

⁵Faculty of Chemistry, Lomonosov Moscow State University, 119991 Moscow, Russia

^* To whom correspondence should be addressed.

Received June 22, 2023; Revised September 22, 2023; Accepted September 22, 2023

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The paper reports on the absorption dynamics of chlorophyll a in a symmetric tetrameric complex of the water-soluble chlorophyll-binding protein BoWSCP. It was measured by a broadband femtosecond laser pump-probe spectroscopy within the range from 400 to 750 nm and with a time resolution of 20 fs-200 ps. When BoWSCP was excited in the region of the Soret band at a wavelength of 430 nm, nonradiative intramolecular conversion S₃→S₁ was observed with a characteristic time of 83 ± 9 fs. When the complex was excited in the region of the Q_y band at 670 nm, relaxation transition between two excitonic states of the chlorophyll dimer was observed in the range of 105 ± 10 fs. Absorption spectra of the excited singlet states S₁ and S₃ of chlorophyll a were obtained. The delocalization of the excited state between exciton-coupled Chl molecules in BoWSCP tetramer changed in time and depended on the excitation energy. When BoWSCP is excited in the Soret band region, an ultrafast photochemical reaction is observed. This could result from the reduction of tryptophan in the vicinity of chlorophyll.

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KEY WORDS: chlorophyll a, WSCP proteins, femtosecond laser spectroscopy, excited state spectrum, exciton dynamics, intramolecular conversion

DOI: 10.1134/S0006297923100139

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