Calcium Ions Are Required for the Enhanced Thermal Stability of the Light-harvesting-Reaction Center Core Complex from Thermophilic Purple Sulfur Bacterium Thermochromatium tepidum
Calcium Ions Are Required for the Enhanced Thermal Stability of the Light-harvesting-Reaction Center Core Complex from Thermophilic Purple Sulfur Bacterium Thermochromatium tepidum
复制标题
DOI：
10.1074/jbc.m806840200
复制
发表时间：
2009-01-02
影响因子：
4.8
通讯作者：
Wang, Zheng-Yu
中科院分区：
文献类型：
--
作者：
Kimura, Yukihiro;Yu, Long-Jiang;Wang, Zheng-Yu
sThermochromatium tepidum 是一种嗜热紫色硫光合细菌，采集自黄石国家公园猛犸温泉。先前的研究表明，从该细菌中纯化的光捕获反应中心核心复合物（LH1-RC）在室温下高度稳定（Suzuki, H., Hirano, Y., Kimura, Y., Takaichi, S., Kobayashi, M., Miki, K., and Wang, Z.-Y. (2007) Biochim. Biophys. Acta 1767, 1057 - 第1063章）在这项工作中，我们证明了 Tch 的热稳定性。 tepidum LH1-RC 远高于其嗜温对应物，增强的热稳定性需要 Ca2+ 作为辅助因子。从 Tch 中去除 Ca2+。 tepidum LH1-RC 产生的复合物具有与从嗜温细菌中纯化的 LH1-RC 相同程度的热稳定性。通过向 Ca2+ 耗尽的 LH1-RC 添加 Ca2+ 可以恢复增强的热稳定性，并且该过程是完全可逆的。两种形式之间热稳定性的互换伴随着 LH1 Q(y) 跃迁在天然的 915 nm 和 Ca2+ 耗尽的 LH1-RC 的 880 nm 之间变化。差示扫描量热法测量表明，天然 LH1-RC 的降解温度比不含 Ca2+ 的 LH1-RC 高 15 摄氏度，而焓变大约 28%。用其他金属阳离子取代 Ca2+ 会导致热稳定性下降，其程度取决于阳离子的性质。这些结果表明，Ca2+离子在稳定色素膜蛋白复合物的结构和改变其光谱特性方面发挥双重作用，从而深入了解这种光合生物利用自然资源在极端环境中生存的适应性策略。
sThermochromatium tepidum is a thermophilic purple sulfur photosynthetic bacterium collected from the Mammoth Hot Springs, Yellowstone National Park. A previous study showed that the light-harvesting-reaction center core complex (LH1-RC) purified from this bacterium is highly stable at room temperature (Suzuki, H., Hirano, Y., Kimura, Y., Takaichi, S., Kobayashi, M., Miki, K., and Wang, Z.-Y. (2007) Biochim. Biophys. Acta 1767, 1057 - 1063). In this work, we demonstrate that thermal stability of the Tch. tepidum LH1-RC is much higher than that of its mesophilic counterparts, and the enhanced thermal stability requires Ca2+ as a cofactor. Removal of the Ca2+ from Tch. tepidum LH1-RC resulted in a complex with the same degree of thermal stability as that of the LH1-RCs purified from mesophilic bacteria. The enhanced thermal stability can be restored by addition of Ca2+ to the Ca2+-depleted LH1-RC, and this process is fully reversible. Interchange of the thermal stability between the two forms is accompanied by a shift of the LH1 Q(y) transition between 915 nm for the native and 880 nm for the Ca2+-depleted LH1-RC. Differential scanning calorimetry measurements reveal that degradation temperature of the native LH1-RC is 15 degrees C higher and the enthalpy change is about 28% larger than the Ca2+-depleted LH1-RC. Substitution of the Ca2+ with other metal cations caused a decrease in thermal stability of an extent depending on the properties of the cations. These results indicate that Ca2+ ions play a dual role in stabilizing the structure of the pigment-membrane protein complex and in altering its spectroscopic properties, and hence provide insight into the adaptive strategy of this photosynthetic organism to survive in extreme environments using natural resources.