三角褐指藻岩藻黄素-叶绿素蛋白复合体的分离纯化和功能研究

ISOLATION AND FUNCTIONAL STUDIES ON FUCOXANTHIN-CHLOROPHYLL PROTEIN FROM PHAEODACTYLUM TRICORNUTUM

通过改进硅藻主要捕光天线(FCP)的分离和提取方法,得到高纯度、高均一性的三角褐指藻FCP蛋白,并通过电泳、液相色谱、质谱和吸收荧光光谱学等手段研究三角褐指藻FCP的氨基酸序列、色素组成和捕光特点等,初步预测三角褐指藻的结构和功能特点。结果表明三角褐指藻FCP含有198个氨基酸,与高等植物LHCII的序列Identity约为24%。三维结构预测显示FCP具有与LHCII相似的三次跨膜螺旋框架结构,但跨膜螺旋较短,且无膜表面螺旋结构。FCP中主要结合了叶绿素a、叶绿素c、岩藻黄素,不含叶绿素b,Chl.a/c为3.0。光谱学分析表明岩藻黄素可以在水下弱光环境中有效地捕获绿光,并高效地传递至叶绿素。而岩藻黄素在400—500 nm区域吸收的光能,向叶绿素传递效率较低,预示着岩藻黄素在强光下也有一定的光保护功能。FCP中有4个叶绿素结合的保守氨基酸位点,可能是其叶绿素结合位置,但岩藻黄素的结合位置因其结构和结合位点的变化而无法预测。研究为进一步探索FCP的结构和功能特性奠定了基础。

In this study, we optimized the isolation method of fucoxanthin-chlorophyll protein （FCP） from Phaeodactylum tricornutum. The sequence, pigments and spectra of FCP were analyzed after the purification and homogenization of the protein. The sequence analysis showed that FCP consisted of 198 amino acids and the sequence shared 24% similarity with LHCII of higher plants. The mimic model predicted that similar to LHCII, FCP had three short transmembrane helixes but there was no helix on the membrane surface. We also found that FCP was associated with chlorophyll a, chlorophyll c and fucoxanthin, and the chl a/c ratio was 3.0. The absorption and fluorescence spectra demonstrated that fucoxanthin could absorb and transfer the green light energy to chlorophyll with high efficiency and thus provide sufficient energy in the low-light environment under the water. Moreover, the light energy at 400-500 nm was transferred by fucoxanthin with low efficiency, implying that fucoxanthin played a photo-protective role in response to strong lights. There are 4 conserved chlorophyll-binding sites in FCP; however, it was difficult to deter mine the fucoxanthin-binding sites due to the conformational change. This study laid a foundation for the further exploration of the structure and function of FCP.