Electrostatic charge controls the lowest LH1 Qy transition energy in the triply extremophilic purple phototrophic bacterium, Halorhodospira halochloris
Electrostatic charge controls the lowest LH1 Qy transition energy in the triply extremophilic purple phototrophic bacterium, Halorhodospira halochloris
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DOI：
10.1016/j.bbabio.2021.148473
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发表时间：
2021-08-03
影响因子：
4.3
通讯作者：
Yu, Long-Jiang
中科院分区：
文献类型：
--
作者：
Kimura, Yukihiro;Nojima, Shingo;Yu, Long-Jiang
Halorhodspira(HLR.)盐氯菌是一种独特的光养紫色细菌，因为它是一种三重极端细菌--该有机体是嗜热、嗜碱和嗜盐的。HLR最显著的光合作用特征。盐生绿藻是指围绕在其反应中心(RC)周围的含细菌叶绿素(BCHL)b的核心捕光(LH1)复合体，在1016 nm处有最大吸收，是光养生物中最低的跃迁能。在这里，我们报道了HLR的这个异常红移的LH1q(Y)带。根据BCHL b分子周围的静电电荷分布，卤代氯离子表现出可相互转换的光谱位移。HLR的1016 nm波段。卤氯菌LH1-RC复合体在脱盐或pH降低时蓝移到958 nm，但在加盐或pH升高时又恢复到原来的位置。共振拉曼分析表明，这些可相互转换的光谱位移与BCHL b和LH1多肽之间的氢键相互作用的强度无关。此外，还得到了HLR的LH1q(Y)跃迁的圆二色信号。卤代氯菌出现阳性信号(如在含Bchl b的布拉斯托氯菌物种中)，而与含Bchl a的紫色细菌相反，可能是由于Bchl a和Bchl b之间的跃迁偶极矩略有差异以及相邻BChl之间的相互作用在其组装状态下的共同作用。根据这些发现和LH1的氨基酸序列，提出了HLR。为了进行光合作用并在其严酷的高盐和碱性生境中茁壮成长，卤氯藻进化出了其独特的、可调的静电捕光系统。
Halorhodospira (Hlr.) halochloris is a unique phototrophic purple bacterium because it is a triple extremophile-the organism is thermophilic, alkalophilic, and halophilic. The most striking photosynthetic feature of Hlr. halochloris is that the bacteriochlorophyll (BChl) b-containing core light-harvesting (LH1) complex surrounding its reaction center (RC) exhibits its LH1 Q(y) absorption maximum at 1016 nm, which is the lowest transition energy among phototrophic organisms. Here we report that this extraordinarily red-shifted LH1 Q(y) band of Hlr. halochloris exhibits interconvertible spectral shifts depending on the electrostatic charge distribution around the BChl b molecules. The 1016 nm band of the Hlr. halochloris LH1-RC complex was blue-shifted to 958 nm upon desalting or pH decrease but returned to its original position when supplemented with salts or pH increase. Resonance Raman analysis demonstrated that these interconvertible spectral shifts are not associated with the strength of hydrogen-bonding interactions between BChl b and LH1 polypeptides. Furthermore, circular dichroism signals for the LH1 Q(y) transition of Hlr. halochloris appeared with a positive sign (as in BChl b-containing Blastochloris species) and opposite those of BChl a-containing purple bacteria, possibly due to a combined effect of slight differences in the transition dipole moments between BChl a and BChl b and in the interactions between adjacent BChls in their assembled state. Based on these findings and LH1 amino acid sequences, it is proposed that Hlr. halochloris evolved its unique and tunable light-harvesting system with electrostatic charges in order to carry out photosynthesis and thrive in its punishing hypersaline and alkaline habitat.