Single particle imaging by X-ray free electron lasers

コヒーレントX線による単粒子イメージング

河野 秀俊

Kono, Hidetoshi

The fourth generation light source, X-ray free electron lasers (XFELs) can potentially provide us a novel mean to determine the three-dimensional (3D) structure of bio-molecules from the diffraction data of single molecules. Conventionally, X-ray crystallography has been the principal tool to determine high resolution 3D structures of proteins, nucleic acids, and their complexes. However, a critical process is the crystallization. A sufficiently large crystal must be prepared. In addition, it is known that about 40% of bio-molecules, particularly membrane proteins, do not crystallize. The coherent X-ray diffraction imaging by XFELs does not require a crystal and will change such a situation. In order to realize the single molecule imaging, we have to overcome several difficulties. The diffraction from single molecule is very weak and suffered from so called quantum noises. A X-ray beam has to be strong enough to obtain diffraction to be used for reconstructing a 3D structure. However, such a strong X-ray will strip electrons bound to atoms, consequently leading to a coulomb explosion of a molecule. We have to measure diffraction before such molecular decay occurs. We have studied conditions required to realize a single molecule imaging. In my talk, a strategy to obtain a 3D image of molecule from diffraction data with minimum molecular decay is discussed.