Structural and functional roles of Ca2+ in the light-harvesting 1 complex from thermophilic purple sulfur bacterium Thermochromatium tepidum

紫色硫光合细菌Thermochromatiumtepidum是一种中等嗜热菌，生长温度最高，对LH 1 Q_y的吸收不寻常。目前的光谱和热力学分析表明，Ca^<2+>-结合对LH 1蛋白的二级结构影响不大，但精确地调节BChl a的构象和LH 1-RC复合物的热稳定性。此外，我们发现，Sr离子是一个替代的辅因子生物功能可替代的钙离子在这个嗜热生物。

Ca ions are responsible for unique properties of the purple sulfur photosynthetic bacterium Thermochromatium tepidum which is a moderate thermophile grown at the highest temperature among purple bacteria and shows an unusual LH1 Q_y absorption. The present spectroscopic and thermodynamic analyses revealed that the Ca^<2+>-binding little affects secondary structures of the LH1 proteins but precisely modulates conformation of BChl a and thermal stability of the LH1-RC complex. Furthermore, we discovered that Sr ion is an alternative cofactor biofunctionally replaceable with Ca ion in this thermophilic organism.