Rätsep M, Lehtmets A, Kangur L, Timpmann K, Leiger K, Wang-Otomo Z-Y, Freiberg A
Institute of Physics, University of Tartu, W. Ostwaldi 1, 50411 Tartu, Estonia.
Faculty of Science, Ibaraki University, 310-8512 Mito, Japan.
Photosynthetica. 2023 Jun 1;61(3):308-317. doi: 10.32615/ps.2023.022. eCollection 2023.
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.
颜色调谐是光合生物的一种关键生存机制。据信钙离子可增强 obligatory calcium-containing sulfur purple bacteria 的光谱调谐和热稳定性。本研究检测了两种以其极端红移光谱而闻名的含硫紫色细菌的 LH1-RC 复合物的热稳定性和压力稳定性。结果总体显示，与钙结合位点的可塑性相关的温度和压力效应的可逆性有限。虽然压力诱导的分解产物与脱钙形式的色素蛋白非常相似，但热诱导产物显示出细菌叶绿素的单体 B777 和二聚体 B820 形式，类似于在用洗涤剂处理的非硫紫色细菌中看到的形式。该研究还进一步发现蛋白质三级和二级结构几乎同时发生解链。总体而言，我们的研究结果不支持光捕获色素蛋白的颜色调节与热力学稳定性之间存在直接联系。
