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蛋白，作为一种光感受器参与多种形态发生反应。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（114kDa，存在于二聚体中）光敏色素的结晶条件。以硫酸铵为沉淀剂可获得部分结晶块（0.5mm），但尚未成功制备大单晶。相反，开始了小的（59kDa，显色结构域）光敏色素的结晶，从目前获得的结果来看，这似乎是有希望的，并将继续进行。在上述研究的同时，利用共振拉曼散射研究了发色团的分子结构（Tokutomi et al., 1990, FEBS Lett.）。， Mizutani等人，Bioahem。， 1991)，在红色和远红色吸收形式之间显示出不同的原型结构。利用这些新信息构建了发色团的分子结构模型（Toktutomi et al., 1992, Photochem.）。光生物)，显示出拉长的分子结构。它在二聚光敏色素分子中的取向，基于小角度x射线散射提出（Nakasako et al., 1990, Photochem.）。（Toktutomiet al., 1992; Photoahem.），是根据定向分子的线性二色性来确定的。)，这表明在二聚体分子的一个平坦的发色团区域中很好地包含了发色团。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.