The role of vibronic modes in formation of red antenna states of cyanobacterial PSI
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ORIGINAL ARTICLE
The role of vibronic modes in formation of red antenna states of cyanobacterial PSI Roman Y. Pishchalnikov1 · Vladimir. V. Shubin2 · Andrei. P. Razjivin3 Received: 30 January 2020 / Accepted: 29 July 2020 © Springer Nature B.V. 2020
Abstract Cyanobacterial photosystem I (PSI) constitutes monomeric and trimeric pigment–protein complexes whose optical properties are marked by the presence of long-wavelength absorption bands. In spite of numerous experimental studies, the nature of these bands is still under debate and requires intensive theoretical analysis. Collecting together the data of linear spectroscopy and single-molecule spectroscopy (SMS) of PSI from Arthrospira platensis, we performed quantum modeling of the optical response based on molecular exciton theory (ET) and the multimode Brownian oscillator model (MBOM). Applying MBOM, the spectra of the red antenna state were calculated considering a particular for each red state adjustment of the low-frequency vibronic modes. Within the framework of our PSI exciton model it was shown that the coupling energy between antenna chlorophylls cannot be a factor of the red states formation, thus the long-wavelength bands are calculated without attribution to so-called antenna red chlorophylls. By the fitting of Huang–Rhys factors and frequencies for the lowest vibronic modes, we were able to reproduce the effects of strong and weak electron–phonon coupling experimentally observed in SMS spectra of red antenna states. Based on our theoretical calculations and also analysis of existing crystal structures of cyanobacterial PSI, we assumed that long-wavelength Chls can be localized in the peripheral protein subunits containing one or two pigment molecules. Keywords Photosystem I · Long-wavelength states · PSI monomer · PSI trimer · Energy transfer · Absorption · Singlemolecule fluorescence spectroscopy · Multimode Brownian oscillator model Abbreviations PSI Photosystem I ET Exciton theory MBOM The multimode Brownian oscillator model Chl Chlorophyll P700 PSI reaction center LWCs Long-wavelength Chls SMS Single-molecule spectroscopy SD Spectral density function CD Circular dichroism FWHM Full width at half maximum * Roman Y. Pishchalnikov [email protected] 1
Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, Russia
2
Bach Institute of Biochemistry, Research Center of Biotechnology of the Russian Academy of Sciences, Moscow, Russia
3
Lomonosov Moscow State University, Belozersky Institute of Physico-Chemical Biology, Moscow, Russia
Introduction The photosynthetic apparatus of cyanobacteria, higher plants, and algae contains two types of light-harvesting pigment–protein complexes, photosystem II and I (PSI), functioning in tandem to support the light induced reactions of water oxidation and carbon dioxide reduction (Blankenship 2014; Shevela et al. 2013). The structure of PSI, the largest of them, varies in different organisms. In cyanobacteria it exists in a trimeric form (Grotjohann and Fromme
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