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

• Published in: Photosynthetica 2023-01, Vol.61 (3), p.308-317
• Main Authors: Rätsep, M, Lehtmets, A, Kangur, L, Timpmann, K, Leiger, K, Wang-Otomo, Z-Y, Freiberg, A
• Format: Article
• Language: English
• Subjects: ca-containing bacteria; circular dichroism; hydrostatic high pressure; lh1-rc complex; purple bacteria
• ISSN: 0300-3604; 1573-9058; 1573-9058
• DOI: 10.32615/ps.2023.022

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 , 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.