title: Improved specimen preparation for cryo-electron microscopy using a symmetric carbon sandwich technique.
abstract: Image shift due to beam-induced specimen charging has become the most severe problem in electron microscopy for imaging two-dimensional (2D) crystals of biological macromolecules, especially in the case of highly tilted specimens. Image shift causes diffraction spots perpendicular to the tilt axis to disappear even at medium or low resolution. The yield of good images from tilted specimens prepared on a single layer of continuous carbon support film is therefore very low. In this paper, we have used 2D crystals of aquaporin-4 to investigate the effect of a carbon sandwich preparation method on specimen charging. We find that a larger number of images show sharp diffraction spots perpendicular to the tilt axis if crystals are placed in between two sheets of carbon film as compared to images taken from specimens prepared by the conventional single carbon support film technique. Our results demonstrate that the reproducible carbon sandwich preparation technique overcomes the severe specimen charging problem and thus has the potential to significantly speed up structure analysis by electron crystallography.
authors.affiliation: Department of Biophysics, Faculty of Science, Kyoto University, Kyoto-fu, Japan.
authors.forename: Nobuhiko
authors.initials: N
authors.lastname: Gyobu
authors.forename: Kazutoshi
authors.initials: K
authors.lastname: Tani
authors.forename: Yoko
authors.initials: Y
authors.lastname: Hiroaki
authors.forename: Akiko
authors.initials: A
authors.lastname: Kamegawa
authors.forename: Kaoru
authors.initials: K
authors.lastname: Mitsuoka
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Fujiyoshi
mesh_terms: D051401:Aquaporin 4; D020346:Aquaporins / Q000737:chemistry; D002244:Carbon; D020285:Cryoelectron Microscopy / Q000379:methods*; D003460:Crystallization; D013048:Specimen Handling / Q000379:methods* / Q000592:standards
chemical_list: D051401:Aquaporin 4; D020346:Aquaporins; D002244:Carbon