Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198 Gif-sur-Yvette, France.
Osaka City University, Graduate School of Science, Sumiyoshi Ku, 3-3-138 Sugimoto, Osaka 5588585, Japan.
Biochim Biophys Acta Bioenerg. 2021 May 1;1862(5):148384. doi: 10.1016/j.bbabio.2021.148384. Epub 2021 Feb 3.
The siphonaxanthin-siphonein-chlorophyll-a/b-binding protein (SCP), a trimeric light-harvesting complex isolated from photosystem II of the siphonous green alga Codium fragile, binds the carotenoid siphonaxanthin (Sx) and/or its ester siphonein in place of lutein, in addition to chlorophylls a/b and neoxanthin. SCP exhibits a higher content of chlorophyll b (Chl-b) than its counterpart in green plants, light-harvesting complex II (LHCII), increasing the relative absorption of blue-green light for photosynthesis. Using low temperature absorption and resonance Raman spectroscopies, we reveal the presence of two non-equivalent Sx molecules in SCP, and assign their absorption peaks at 501 and 535 nm. The red-absorbing Sx population exhibits a significant distortion that is reminiscent of lutein 2 in trimeric LHCII. Unexpected enhancement of the Raman modes of Chls-b in SCP allows an unequivocal description of seven to nine non-equivalent Chls-b, and six distinct Chl-a populations in this protein.
从脆性马尾藻（ Codium fragile ）的光系统 II 中分离出来的三聚体捕光复合物——硅甲藻黄素-硅甲藻素-叶绿素 a/b 结合蛋白（SCP），除叶绿素 a/b 和新黄质外，还结合类胡萝卜素硅甲藻黄素（Sx）及其酯硅甲藻素，代替叶黄素。SCP 比其在绿色植物中的对应物——光系统 II 捕光复合物 II（LHCII）含有更高的叶绿素 b（Chl-b）含量，从而增加了光合作用对蓝绿光的相对吸收。通过低温吸收和共振拉曼光谱，我们发现 SCP 中存在两个不等效的 Sx 分子，并将其吸收峰分配到 501nm 和 535nm。红吸收 Sx 群体表现出明显的变形，类似于三聚体 LHCII 中的叶黄素 2。SCP 中 Chls-b 的拉曼模式的意外增强允许对该蛋白中七个到九个不等效的 Chls-b 和六个不同的 Chl-a 群体进行明确描述。
