Department of Chemistry, Faculty of Science and Engineering, Kindai University, Higashi-Osaka, Osaka, 577-8502, Japan.
Graduate School of Agricultural Science, Kobe University, Kobe, 657-8501, Japan.
Sci Rep. 2019 Mar 6;9(1):3636. doi: 10.1038/s41598-019-40082-y.
Engineering chlorophyll (Chl) pigments that are bound to photosynthetic light-harvesting proteins is one promising strategy to regulate spectral coverage for photon capture and to improve the photosynthetic efficiency of these proteins. Conversion from the bacteriochlorophyll (BChl) skeleton (7,8,17,18-tetrahydroporphyrin) to the Chl skeleton (17,18-dihydroporphyrin) produces the most drastic change of the spectral range of absorption by light-harvesting proteins. We demonstrated in situ selective oxidation of B800 BChl a in light-harvesting protein LH2 from a purple bacterium Rhodoblastus acidophilus by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone. The newly formed pigment, 3-acetyl Chl a, interacted with the LH2 polypeptides in the same manner as native B800. B850 BChl a was not oxidized in this reaction. CD spectroscopy indicated that the B850 orientation and the content of the α-helices were unchanged by the B800 oxidation. The nonameric circular arrangement of the oxidized LH2 protein was visualized by AFM; its diameter was almost the same as that of native LH2. The in situ oxidation of B800 BChl a in LH2 protein with no structural change will be useful not only for manipulation of the photofunctional properties of photosynthetic pigment-protein complexes but also for understanding the substitution of BChl to Chl pigments in the evolution from bacterial to oxygenic photosynthesis.
将叶绿素（Chl）色素与光合作用的光捕获光捕获蛋白结合是一种很有前途的策略，可以调节光子捕获的光谱覆盖范围，并提高这些蛋白质的光合作用效率。从细菌叶绿素（BChl）骨架（7,8,17,18-四氢卟啉）到叶绿素骨架（17,18-二氢卟啉）的转化会导致光捕获蛋白的吸收光谱范围发生最剧烈的变化。我们通过 2,3-二氯-5,6-二氰基-1,4-苯醌在来自紫色细菌 Rhodoblastus acidophilus 的 LH2 捕光蛋白中证明了 B800 BChl a 的原位选择性氧化。新形成的色素 3-乙酰 Chl a 与 LH2 多肽以与天然 B800 相同的方式相互作用。B850 BChl a 未在该反应中氧化。CD 光谱表明，B850 取向和α-螺旋含量未通过 B800 氧化而改变。通过 AFM 可视化了氧化 LH2 蛋白的非十九元环状排列；其直径几乎与天然 LH2 相同。LH2 蛋白中 B800 BChl a 的原位氧化而不发生结构变化不仅将有助于操纵光合作用色素蛋白复合物的光功能特性，而且有助于理解从细菌到产氧光合作用中 BChl 取代 Chl 色素的进化。
