Kimura Yukihiro, Hashimoto Kanako, Akimoto Seiji, Takenouchi Mizuki, Suzuki Kengo, Kishi Rikako, Imanishi Michie, Takenaka Shinji, Madigan Michael T, Nagashima Kenji V P, Wang-Otomo Zheng-Yu
Department of Agrobioscience, Graduate School of Agriculture , Kobe University , Nada, Kobe 657-8501 , Japan.
Department of Science, Graduate School of Science , Kobe University , Nada, Kobe 657-8501 , Japan.
Biochemistry. 2018 Jul 31;57(30):4496-4503. doi: 10.1021/acs.biochem.8b00644. Epub 2018 Jul 17.
The light-harvesting 1 reaction center (LH1-RC) complex from Thermochromatium tepidum exhibits a largely red-shifted LH1 Q absorption at 915 nm due to binding of Ca, resulting in an "uphill" energy transfer from LH1 to the reaction center (RC). In a recent study, we developed a heterologous expression system (strain TS2) to construct a functional hybrid LH1-RC with LH1 from Tch. tepidum and the RC from Rhodobacter sphaeroides [Nagashima, K. V. P., et al. (2017) Proc. Natl. Acad. Sci. U. S. A. 114, 10906]. Here, we present detailed characterizations of the hybrid LH1-RC from strain TS2. Effects of metal cations on the phototrophic growth of strain TS2 revealed that Ca is an indispensable element for its growth, which is also true for Tch. tepidum but not for Rba. sphaeroides. The thermal stability of the TS2 LH1-RC was strongly dependent on Ca in a manner similar to that of the native Tch. tepidum, but interactions between the heterologous LH1 and RC became relatively weaker in strain TS2. A Fourier transform infrared analysis demonstrated that the Ca-binding site of TS2 LH1 was similar but not identical to that of Tch. tepidum. Steady-state and time-resolved fluorescence measurements revealed that the uphill energy transfer rate from LH1 to the RC was related to the energy gap in an order of Rba. sphaeroides, Tch. tepidum, and strain TS2; however, the quantum yields of LH1 fluorescence did not exhibit such a correlation. On the basis of these findings, we discuss the roles of Ca, interactions between LH1 and the RC from different species, and the uphill energy transfer mechanisms.
来自嗜热栖热菌的光捕获1反应中心（LH1-RC）复合物由于钙的结合，在915nm处呈现出大幅红移的LH1 Q吸收峰，从而导致从LH1到反应中心（RC）的“上坡”能量转移。在最近的一项研究中，我们开发了一种异源表达系统（菌株TS2），以构建一种功能性杂交LH1-RC，其中LH1来自嗜热栖热菌，RC来自球形红杆菌 [长岛，K. V. P.，等人（2017年）《美国国家科学院院刊》114，10906]。在此，我们展示了来自菌株TS2的杂交LH1-RC的详细特征。金属阳离子对菌株TS2光合生长的影响表明，钙是其生长不可或缺的元素，嗜热栖热菌也是如此，但球形红杆菌并非如此。TS2 LH1-RC的热稳定性在很大程度上依赖于钙，这与天然嗜热栖热菌的情况类似，但在菌株TS2中，异源LH1和RC之间的相互作用相对较弱。傅里叶变换红外分析表明，TS2 LH1的钙结合位点与嗜热栖热菌的相似但不完全相同。稳态和时间分辨荧光测量表明，从LH1到RC的上坡能量转移速率与能量差距有关，顺序为球形红杆菌、嗜热栖热菌和菌株TS2；然而，LH1荧光的量子产率并未表现出这种相关性。基于这些发现，我们讨论了钙的作用、不同物种的LH1和RC之间的相互作用以及上坡能量转移机制。
