Journal
JOURNAL OF CHEMICAL PHYSICS
Volume 156, Issue 10, Pages -Publisher
AIP Publishing
DOI: 10.1063/5.0077290
Keywords
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Funding
- JST-PRESTO [JPMJPR18G7]
- JST-CREST [JPMJCR20E1]
- JSPS [19H04724]
- Leading Initiative for Excellent Young Researchers (LEADER) from MEXT
- [26810003]
- [19H02665]
- [15K21122]
- [T18K061530]
- [T21K061120]
- Grants-in-Aid for Scientific Research [19H04724] Funding Source: KAKEN
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This study investigates the polarization dependence and role of red-Bchl g in the photosynthetic reaction center. A candidate molecule for red-Bchl g is proposed based on fluorescence spectra and structural data. The study finds that while the energy transfer network in the reaction center can be perturbed by local conformational dynamics, the overall energy transfer efficiency remains relatively stable.
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. Published under an exclusive license by AIP Publishing.
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