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Small-angle X-ray scattering (SAXS) is one of the techniques to investigate the molecular structures of proteins in solution. Here, we describe how SAXS of proteins are measured using synchrotron X-rays and what kind of structural information are obtainable on the low-resolution structures of phytochromes in solution in referring to our previous SAXS studies on phytochrome A and phytochrome B.

Coherent X-ray diffraction imaging (CXDI) is a lensless imaging technique for visualizing the structures of noncrystalline particles at a resolution of several tens of nanometers. The targets are particles with dimensions in the sub-micrometer to micrometer range. We carried out CXDI experiments at 66 K to investigate the internal structures of a whole frozen-hydrated cell and a chloroplast of Cyanidioschyzon merolae and a cyanobacteria cell by using coherent X-ray light sources, such as synchrotron and X-ray free-electron laser facilities. Owing to the short wavelength of the X-rays used (0.225 nm), the absorption and multiple scattering of X-rays inside the specimens were negligible. Diffraction patterns from each specimen particle adsorbed onto a thin membrane were collected at resolutions better than 50 μm -1 in reciprocal space. Therefore, structures of specimen particles can be illustrated at a resolution higher than 200 nm in real space. The most probable electron density map was retrieved from each diffraction pattern. Theinternal structures of the specimens are described here, particularly the structural correlation of the chloroplast of C. merolae and the cyanobacteria cell. Based on the experimental results, we discuss the feasibility of CXDI in the structural analyses of biological cells and cellular organelles.

カルシウム結合状態にある筋小胞体カルシウムポンプの結晶構造の予備的な解析結果について報告し、各機能ドメインの空間配置を明らかにした。

蛋白質合成系において重要な役割を担っているアミノアシルｔＲＮＡ合成酵素の中でクラスＩに属するものについて構造機能相関研究の現状を報告した。

蛋白質のＸ線結晶構造解析における回折強度測定について平易に説明し、最近開発された極低温Ｘ線回折実験手法についても報告を行った。