Department of Chemistry, Faculty of Science and Engineering, Kindai University, Higashi-Osaka, Osaka, 577-8502, Japan.
Graduate School of Life Sciences, Ritsumeikan University, Kusatsu, Shiga, 525-8577, Japan.
Sci Rep. 2020 Nov 9;10(1):19383. doi: 10.1038/s41598-020-76540-1.
Natural chlorophylls have a D-ring reduced chlorin π-system; however, no naturally occurring photosynthetically active B-ring reduced chlorins have been reported. Here we report a B-ring reduced chlorin, 17,18-didehydro-bacteriochlorophyll (BChl) a, produced by in situ oxidation of B800 bacteriochlorophyll (BChl) a in a light-harvesting protein LH2 from a purple photosynthetic bacterium Phaeospirillum molischianum. The regioselective oxidation of the B-ring of B800 BChl a is rationalized by its molecular orientation in the protein matrix. The formation of 17,18-didehydro-BChl a produced no change in the local structures and circular arrangement of the LH2 protein. The B-ring reduced 17,18-didehydro-BChl a functions as an energy donor in the LH2 protein. The photoactive B-ring reduced Chl isomer in LH2 will be helpful for understanding the photofunction and evolution of photosynthetic cyclic tetrapyrrole pigments.
天然叶绿素具有 D 环还原的叶绿素 π-体系；然而，尚未报道过天然存在的具有光活性的 B 环还原叶绿素。在这里，我们报告了一种 B 环还原的叶绿素，17,18-二氢细菌叶绿素（BChl）a，它是通过在来自紫色光合细菌的捕光蛋白 LH2 中对 B800 细菌叶绿素（BChl）a 进行原位氧化产生的。在蛋白质基质中，B800 BChl a 的 B 环的区域选择性氧化由其分子取向合理化。B 环还原的 17,18-二氢-BChl a 的形成未改变 LH2 蛋白的局部结构和圆排列。B 环还原的 17,18-二氢-BChl a 在 LH2 蛋白中作为能量供体发挥作用。LH2 中光活性 B 环还原的 Chl 异构体将有助于理解光合作用环四吡咯色素的光功能和进化。
