Effects of Calcium Ions on the Thermostability and Spectroscopic Properties of the LH1-RC Complex from a New Thermophilic Purple Bacterium Allochromatium tepidum
Effects of Calcium Ions on the Thermostability and Spectroscopic Properties of the LH1-RC Complex from a New Thermophilic Purple Bacterium Allochromatium tepidum
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DOI：
10.1021/acs.jpcb.7b03341
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发表时间：
2017-05-18
影响因子：
3.3
通讯作者：
Wang-Otomo, Zheng-Yu
中科院分区：
文献类型：
--
作者：
Kimura, Yukihiro;Lyu, Shuwen;Wang-Otomo, Zheng-Yu
研究了一株新的嗜热紫色硫细菌Allochromatium（Alc.）通过光谱和热力学分析分离并表征了tepidum。纯净的Alc tepidum LH 1-RC复合物的热稳定性与另一种嗜热紫色硫细菌Thermochromatium tepidum相当，光谱特征与中温细菌Alc相似。vinosum。通过电感耦合等离子体原子发射光谱法和等温滴定量热法检测到每个LH 1-RC约4-5个Ca 2+。去除Ca ~（2+）后，Alc. tepidum LH 1-RC复合物下降，伴随着LH 1 Q（y）吸收带的蓝移。Ca ~（2+）的影响也被观察到在共振拉曼位移的C3-乙酰vC=O带的细菌叶绿素-a，表明在色素和LH 1多肽之间的氢键相互作用的变化。Ca 2+结合Alc的热力学参数。tepidum LH 1-RC复合物的研究表明，该反应主要由抵消不利的负熵变的非常有利的静电相互作用驱动。我们的数据支持一个假设，Alc。Tepidum可能是介于嗜温和嗜热紫色细菌之间过渡生物，Ca 2+是紫色细菌LH 1-RC复合物热稳定性的关键之一。
The light harvesting-reaction center (LH1-RC) complex from a new thermophilic purple sulfur bacterium Allochromatium (Alc.) tepidum was isolated and characterized by spectroscopic and thermodynamic analyses. The purified Alc. tepidum LH1-RC complex showed a high thermostability comparable to that of another thermophilic purple sulfur bacterium Thermochromatium tepidum, and spectroscopic characteristics similar to those of a mesophilic bacterium Alc. vinosum. Approximately 4-5 Ca2+ per LH1-RC were detected by inductively coupled plasma atomic emission spectroscopy and isothermal titration calorimetry. Upon removal of Ca2+, the denaturing temperature of the Alc. tepidum LH1-RC complex dropped accompanied by a blue-shift of the LH1 Q(y) absorption band. The effect of Ca2+ was also observed in the resonance Raman shift of the C3-acetyl vC=O band of bacteriochlorophyll-a, indicating changes in the hydrogen-bonding interactions between the pigment and LH1 polypeptides. Thermodynamic parameters for the Ca2+-binding to the Alc. tepidum LH1-RC complex indicated that this reaction is predominantly driven by the largely favorable electrostatic interactions that counteract the unfavorable negative entropy change. Our data support a hypothesis that Alc. tepidum may be a transitional organism between mesophilic and thermophilic purple bacteria and that Ca2+ is one of the major keys to the thermostability of LH1-RC complexes in purple bacteria.