Energy transfer fluctuation observed by single-molecule spectroscopy of red-shifted bacteriochlorophyll in the homodimeric photosynthetic reaction center

Author:

Kondo Toru12ORCID,Mutoh Risa3ORCID,Arai Shun1,Kurisu Genji4ORCID,Oh-oka Hirozo5ORCID,Fujiyoshi Satoru6ORCID,Matsushita Michio6

Affiliation:

1. Department of Life Science and Technology, School of Life Science and Technology, Tokyo Institute of Technology, Meguro, Tokyo 152-8550, Japan

2. PRESTO, Japan Science and Technology Agency, Saitama 332-0012, Japan

3. Department of Applied Physics, Faculty of Science, Fukuoka University, Jyonan, Fukuoka 814-0180, Japan

4. Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan

5. Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan

6. Department of Physics, School of Science, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan

Abstract

The photosynthetic reaction center of heliobacteria (hRC) is a homodimeric chromoprotein responsible for light harvesting and photoelectric conversion. The fluorescence of the hRC is radiated from a bacteriochlorophyll (Bchl) g having the lowest energy level, called red-Bchl g. The homodimeric architecture of the hRC indicates that it includes two red-Bchls g arranged symmetrically in pairs. Red-Bchl g is a fluorescent probe useful for monitoring the energy transfer network in the RC. Here, we show the fluorescence polarization dependences of two red-Bchls g, individually measured with selective excitation of chlorophyll a serving as the primary electron acceptor. The two red-Bchls g exhibit almost the same polarization dependences. Based on the polarization dependence and structural data of the hRC, we propose a candidate molecule for red-Bchl g. The fluorescence spectra of single hRCs represent the spectral heterogeneity reflecting the local conformational inhomogeneity. A time series of the fluorescence spectra indicates occasional peak shifts between blue- and red-shifted states without significant changes in the fluorescence intensity. The spectral fluctuation is interpreted to be due to the local conformational dynamics around a Bchl g mediating the energy transfer, switching the terminal energy acceptor between two red-Bchls g. In conclusion, while the energy transfer network in the RC can be perturbed by microscopic dynamics, the total energy transfer efficiency, i.e., the light-harvesting function, is rather robust. The functional robustness may be due to multiple energy transfer pathways composed of many antenna pigments in the RC.

Funder

Grands-in-Aid for Scientific Research

JST-PRESTO

JST-CREST

JSPS Grants-in-Aid for Scientific Research on Innovative Areas

Leading Initiative for Excellent Young Researchers from MEXT

Publisher

AIP Publishing

Subject

Physical and Theoretical Chemistry,General Physics and Astronomy

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