Photosynthetica 2023, 61(3):308-317 | DOI: 10.32615/ps.2023.022

Evaluation of the relationship between color-tuning of photosynthetic excitons and thermodynamic stability of light-harvesting chromoproteins

M. RÄTSEP1, A. LEHTMETS1, L. KANGUR1, K. TIMPMANN1, K. LEIGER1, Z.-Y. WANG-OTOMO2, A. FREIBERG1, 3
1 Institute of Physics, University of Tartu, W. Ostwaldi 1, 50411 Tartu, Estonia
2 Faculty of Science, Ibaraki University, 310-8512 Mito, Japan
3 Estonian Academy of Sciences, Kohtu 6, 10130 Tallinn, Estonia

Color-tuning is a critical survival mechanism for photosynthetic organisms. Calcium ions are believed to enhance both spectral tuning and thermostability in obligatory calcium-containing sulfur purple bacteria. This study examined the thermo- and piezo stability of the LH1-RC complexes from two calcium-containing sulfur purple bacteria notable for their extreme red-shifted spectra. The results generally show limited reversibility of both temperature and pressure effects related to the malleability of calcium-binding sites. While the pressure-induced decomposition product closely resembles the calcium-depleted form of the chromoproteins, the thermally induced products reveal monomeric B777 and dimeric B820 forms of bacteriochlorophyll a, similar to those seen in non-sulfur purple bacteria treated with detergent. The study further found nearly unison melting of the protein tertiary and secondary structures. Overall, our findings do not support a direct link between color adjustment and thermodynamic stability in light-harvesting chromoproteins.

Additional key words: Ca-containing bacteria; circular dichroism; hydrostatic high pressure; LH1-RC complex; purple bacteria.

Received: April 17, 2023; Revised: April 17, 2023; Accepted: May 17, 2023; Prepublished online: June 1, 2023; Published: October 5, 2023  Show citation

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RÄTSEP, M., LEHTMETS, A., KANGUR, L., TIMPMANN, K., LEIGER, K., WANG-OTOMO, Z.-Y., & FREIBERG, A. (2023). Evaluation of the relationship between color-tuning of photosynthetic excitons and thermodynamic stability of light-harvesting chromoproteins. Photosynthetica, 61(3), 308-317. doi: 10.32615/ps.2023.022
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