Preparation of single crystal of phytochrome and its preliminary structural analysis by X-ray crystallography

光敏色素是绿色植物中的一种色素蛋白，它作为一种光感受器参与各种形态发生反应。以阐明其三维结构。晶体学研究已经开始。首先，系统地研究了大分子光敏色素（分子量为114kDa，以二聚体形式存在）的结晶条件。用硫酸铵作沉淀剂，得到了0.5mm的部分结晶块体，但大单晶的制备还没有成功。相反，开始结晶小的（59kDa，发色域）光敏色素，从迄今为止获得的结果来看，这似乎是有希望的，并且将继续进行。与上述研究平行，使用共振拉曼散射研究发色团的分子结构（Tokutomi等人，1990年，《联邦通讯社快报》，Mizutani等人，你好，1991年），它显示了红色和远红色吸收形式之间的不同原型结构。使用这些新的信息构建发色团的分子结构的模型（Toktutomi等人，1992年，光化学。Photobiol.），表明了拉长的分子结构其在二聚光敏色素分子中的取向，基于小角X射线散射提出（Nakasako等人，1990年，光化学。光生物学），基于取向分子的线性二向色性（Toktutomietal.，1992年，摄影师。Photobiol.），这表明发色团很好地包含在二聚体分子的平坦发色结构域中。这些结果可为光敏色素的晶体学分析提供有用的信息。

Phytochrome is a chromoprotein in green plants, which serves as a photoreceptor for a variety of morphogenetic responses. In order to elucidate its three-dimensional structure. crystallographic study has been started. First, conditions for crystallization of large (114kDa, exist in a dimer) phytochrome was investigated systematically. Partly crystallized blocks (0.5mm) were obtained using ammonium sulfate as precipitant, however, preparation of large single crystals has not been successful yet. In stead, crystallization of small (59kDa, chromophoric domain) phytochrome was started, which seems promissing judging from the results obtained so far, and is to be continued.In parallel to the above research, molecular structure of the chromophore was studied using resonance Raman scattering (Tokutomi et al., 1990, FEBS Lett., Mizutani et al., Bioahem., 1991), which showed a different protoated structure between the red- and far redabsorbing forms. A model for molecular struture of the chromophore was constructed using these new informations (Toktutomi et al., 1992, Photochem. Photobiol.), indicated elongated molecular structure. Its orientation in the dimeric phytochrome molecule, proposed based on small-angle X-ray scattering (Nakasako et al., 1990, Photochem. photobiol.), was determined based on linear dichroism of oriented molecules (Toktutomiet al., i992, Photoahem. Photobiol.), which shows that the chromophore is well contained in a flat chromophoric domain of the dimeric molecule. These results can supply useful informations to the crystallographic anlysis of phytochrome.