Low dose techniques and cryo-electron microscopy.

Our understanding of subcellular structures has been greatly increased owing to electron microscopy, even though radiation damage of biological samples by the electron beam demanded staining techniques. Technological and instrumental advances of electron microscopy have, however, established various highly sophisticated techniques to study biological systems in their native states without staining and thus facilitated comprehension of rather intact structures of biological components. Among these techniques, electron crystallography is a well-established one to analyze membrane protein structures within lipid bilayers, without staining at close-to-physiological conditions. Structures of membrane proteins could be analyzed at resolutions better than 3Å by electron crystallography due to techniques of low dose and cryo-electron microscopy (cryo-EM). Here, recent cryo-EM technological and instrumental advances crucial to optimal data collection in electron crystallography are summarized as well as examples of structures of membrane proteins analyzed with the help of this method.