Molecular architecture of light-harvesting complexes of chromophytes

褐藻和硅藻的主要捕光蛋白岩藻黄素- chl a/c蛋白（FCP）是一种非常不稳定的蛋白质，当暴露在常规的分离绿色植物中各种光活性蛋白的洗涤剂中时，其在色素之间的激发能传递非常容易受到破坏。我们研究了从褐藻菌体中分离FCP的条件，发现FCP的组装体与光化学反应中心结合形成配合物，并嵌入到类囊体中，如绿藻中的LHCP。FCP的单体形式由分子量为20,226的蛋白质（以Ectocarpus为例），4 Chl a， 1 Chl c和4岩藻黄素组成，其天然形式在岩藻黄素*Chl a， Chl c*Chl a之间表现出高效的能量转移（高于95%）。FCP中结合的岩藻黄素比释放的岩藻黄素表现出更大的红移吸光度，其吸光度光谱与溶解在含亚胺的极溶剂中相似。当温度升高到40ºC时，红移的FCP变为绿色，反映了岩藻黄素的蓝移，同时CD信号丢失，表明色素分子发生了紊乱。然而，蓝移FCP的共振拉曼光谱与天然FCP没有变化，表明FCP中活跃于激发能转移的岩藻黄素与Chl a高度相互作用，这种相互作用导致了岩藻黄素的红移。

Fucoxanthin-Chl a/c protein (FCP), the major light harvesting protein of brown algae and diatoms, is very unstable and its excitation energy transfer between pigments was very readily injured when exposed to detergents conventionally used for isolating various photoactive protens from green plants. We studied on the conditions of FCP isolation from the thalli of brown algae, and revealed that the assemblies of FCP are bound with photochemical reaction center to form complexes which are embedded in thylakoids, like LHCP in green algae. Monomeric form of FCP consisted of a protein with MW 20,226 (in the case of Ectocarpus), 4 Chl a, 1 Chl c and 4 fucoxanthin, and its native form showed an highly efficient energy transfer (higher than 95%) between fucoxanthin*Chl a, Chl c*Chl a. Fucoxanthin bound in FCP showed more red-shifted absorbance than liberated one, showing an absorbance spectrum similar to that dissoved in imidoN-containing, polarsolvets. Exposed to warm temperature (40ﾟC), the red-shifted FCP turned to green reflecting the blue-shift of fucoxanthin with concomitant loss of CD signals, indicating the disarrangement pigment molecules. However, the resonance Raman spectrum of blue-shifted FCP stayd unaltered from the native FCP,suggesting that fucoxanthin active in excitation energy transfer is highly interacted with Chl a in FCP,and this interaction is responsible to the red shift of fucoxanthin.