基于結構的光合作用狀態轉換機理研究立項報告

柳振峰 劉秀穎

摘 要：自然界的光照條件隨著季節和一天中的不同時段會不斷地發生變化，光的強度和光線的光譜特征都會發生劇烈變化。對于像植物和藻類這些放氧光合生物來說，它們進化出了一系列的有效機制，用以應對光照環境的變化，一方面保護自身不受過強光線照射所造成的光損傷；另一方面又能夠在弱光條件下達到最為優化的光合作用效率。狀態轉換是這一些巧妙調節機制中的一種，通過這一機制，放氧光合生物得以響應光質條件的變化而調節光能在兩個光系統之間的平衡分配。狀態轉換過程中涉及一對關鍵的激酶和磷酸酶，即Stt7/STN7激酶和PPH1/TAP38磷酸酶。它們是狀態轉換所必需的一對蛋白，并且與捕光蛋白LHCII的磷酸化和去磷酸化密切相關。該課題以植物狀態轉換機制為主題，開展Stt7/STN7激酶和PPH1/TAP38磷酸酶的結構與功能研究，目標是在高分辨率三維結構分析基礎上結合生物化學研究方法深入探討光合作用狀態轉換的分子機理。對于光合作用狀態轉換中所形成的捕光蛋白LHCII與兩個光系統（PSII或PSI）所形成的超級復合物樣品進行分離純化制備，通過嘗試三維結晶或應用電子顯微鏡分析其三維結構，以獲得較為精確的關于捕光蛋白LHCII與PSII或pLHCII與PSI相互作用的結構信息。

關鍵詞：光合作用 狀態轉換 膜蛋白 捕光復合物

Abstract： The lighting conditions in nature are constantly changing on daily or seasonal bases. The intensity and spectroscopic features of the light are subject to drastic changes. For oxygenic photosynthetic organisms， like plants and algae， they have evolved a series of effective mechanisms in order to adapt to the fluctuation of lighting conditions. On one hand， these mechanisms will protect them from photodamage caused by excess energy intensity， while one the other hand， they can achieve optimal photosynthesis efficiency under dim light conditions. State transition is one of these sophisticated regulatory mechanisms through which the oxygenic photosynthesis organisms are able to respond to the change of light quality and regulate energy distribution balance between the two photosystems. A pair of vital kinase and phosphatase， namely Stt7/STN7 kinases and PPH1/TAP38 phosphatases， are involved in the state transition. They are essential for the operation of state transition， and closely related to the phosphorylation and dephosphorylation of light-harvesting complex II （LHCII）. This project centers on the mechanistic studies of plant state transition process. Structural and functional studies of Stt7/STN7 kinases and PPH1/TAP38 phosphatases are being carried out. The aim is to investigate the molecular mechanism of photosynthetic state transition by combining the analysis of high-resolution structures and biochemical studies. The supercomplexes between LHCII and the two photosystems （PSII or PSI） formed during state transition will be isolated and purified. Three-dimensional crystallization and electron microscopic analysis will be attempted in order to characterize the three-dimensional structures of these supercomplexes and obtain the precise information about the interactions between LHCII and PSII or pLHCII and PSI.

Key Words： Photosynthesis； State transition； Membrane protein； Light-harvesting complexes

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