Exciton Origin of Color-Tuning in Ca<sup>2+</sup>-Binding Photosynthetic Bacteria
Flexible color adaptation to available ecological niches is vital for the photosynthetic organisms to thrive. Hence, most purple bacteria living in the shade of green plants and algae apply bacteriochlorophyll <i>a</i> pigments to harvest near infra-red light around 850–875 nm. Exception...
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| Format: | Article |
| Language: | English |
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MDPI AG
2021-07-01
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| Series: | International Journal of Molecular Sciences |
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| Online Access: | https://www.mdpi.com/1422-0067/22/14/7338 |
| _version_ | 1797527070993022976 |
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| author | Kõu Timpmann Margus Rätsep Liina Kangur Alexandra Lehtmets Zheng-Yu Wang-Otomo Arvi Freiberg |
| author_facet | Kõu Timpmann Margus Rätsep Liina Kangur Alexandra Lehtmets Zheng-Yu Wang-Otomo Arvi Freiberg |
| author_sort | Kõu Timpmann |
| collection | DOAJ |
| description | Flexible color adaptation to available ecological niches is vital for the photosynthetic organisms to thrive. Hence, most purple bacteria living in the shade of green plants and algae apply bacteriochlorophyll <i>a</i> pigments to harvest near infra-red light around 850–875 nm. Exceptions are some Ca<sup>2+</sup>-containing species fit to utilize much redder quanta. The physical basis of such anomalous absorbance shift equivalent to ~5.5 kT at ambient temperature remains unsettled so far. Here, by applying several sophisticated spectroscopic techniques, we show that the Ca<sup>2+</sup> ions bound to the structure of LH1 core light-harvesting pigment–protein complex significantly increase the couplings between the bacteriochlorophyll pigments. We thus establish the Ca-facilitated enhancement of exciton couplings as the main mechanism of the record spectral red-shift. The changes in specific interactions such as pigment–protein hydrogen bonding, although present, turned out to be secondary in this regard. Apart from solving the two-decade-old conundrum, these results complement the list of physical principles applicable for efficient spectral tuning of photo-sensitive molecular nano-systems, native or synthetic. |
| first_indexed | 2024-03-10T09:37:49Z |
| format | Article |
| id | doaj.art-faff2aee250b4b239dd52341880c69a0 |
| institution | Directory Open Access Journal |
| issn | 1661-6596 1422-0067 |
| language | English |
| last_indexed | 2024-03-10T09:37:49Z |
| publishDate | 2021-07-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | International Journal of Molecular Sciences |
| spelling | doaj.art-faff2aee250b4b239dd52341880c69a02023-11-22T03:56:58ZengMDPI AGInternational Journal of Molecular Sciences1661-65961422-00672021-07-012214733810.3390/ijms22147338Exciton Origin of Color-Tuning in Ca<sup>2+</sup>-Binding Photosynthetic BacteriaKõu Timpmann0Margus Rätsep1Liina Kangur2Alexandra Lehtmets3Zheng-Yu Wang-Otomo4Arvi Freiberg5Institute of Physics, University of Tartu, W. Ostwald Str. 1, 50411 Tartu, EstoniaInstitute of Physics, University of Tartu, W. Ostwald Str. 1, 50411 Tartu, EstoniaInstitute of Physics, University of Tartu, W. Ostwald Str. 1, 50411 Tartu, EstoniaInstitute of Physics, University of Tartu, W. Ostwald Str. 1, 50411 Tartu, EstoniaFaculty of Science, Ibaraki University, Mito 310-8512, JapanInstitute of Physics, University of Tartu, W. Ostwald Str. 1, 50411 Tartu, EstoniaFlexible color adaptation to available ecological niches is vital for the photosynthetic organisms to thrive. Hence, most purple bacteria living in the shade of green plants and algae apply bacteriochlorophyll <i>a</i> pigments to harvest near infra-red light around 850–875 nm. Exceptions are some Ca<sup>2+</sup>-containing species fit to utilize much redder quanta. The physical basis of such anomalous absorbance shift equivalent to ~5.5 kT at ambient temperature remains unsettled so far. Here, by applying several sophisticated spectroscopic techniques, we show that the Ca<sup>2+</sup> ions bound to the structure of LH1 core light-harvesting pigment–protein complex significantly increase the couplings between the bacteriochlorophyll pigments. We thus establish the Ca-facilitated enhancement of exciton couplings as the main mechanism of the record spectral red-shift. The changes in specific interactions such as pigment–protein hydrogen bonding, although present, turned out to be secondary in this regard. Apart from solving the two-decade-old conundrum, these results complement the list of physical principles applicable for efficient spectral tuning of photo-sensitive molecular nano-systems, native or synthetic.https://www.mdpi.com/1422-0067/22/14/7338photosynthesisCa<sup>2+</sup>-binding bacterialight-harvestingmolecular excitonsspectral red-shift |
| spellingShingle | Kõu Timpmann Margus Rätsep Liina Kangur Alexandra Lehtmets Zheng-Yu Wang-Otomo Arvi Freiberg Exciton Origin of Color-Tuning in Ca<sup>2+</sup>-Binding Photosynthetic Bacteria International Journal of Molecular Sciences photosynthesis Ca<sup>2+</sup>-binding bacteria light-harvesting molecular excitons spectral red-shift |
| title | Exciton Origin of Color-Tuning in Ca<sup>2+</sup>-Binding Photosynthetic Bacteria |
| title_full | Exciton Origin of Color-Tuning in Ca<sup>2+</sup>-Binding Photosynthetic Bacteria |
| title_fullStr | Exciton Origin of Color-Tuning in Ca<sup>2+</sup>-Binding Photosynthetic Bacteria |
| title_full_unstemmed | Exciton Origin of Color-Tuning in Ca<sup>2+</sup>-Binding Photosynthetic Bacteria |
| title_short | Exciton Origin of Color-Tuning in Ca<sup>2+</sup>-Binding Photosynthetic Bacteria |
| title_sort | exciton origin of color tuning in ca sup 2 sup binding photosynthetic bacteria |
| topic | photosynthesis Ca<sup>2+</sup>-binding bacteria light-harvesting molecular excitons spectral red-shift |
| url | https://www.mdpi.com/1422-0067/22/14/7338 |
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