Electron crystallography of membrane proteins.

Electron crystallography studies the structure of two-dimensional crystals of membrane proteins or other crystalline arrays. This method has been used to determine the atomic structures of six membrane proteins and tubulin, as well as several other structures at a slightly lower resolution, where secondary structure motifs could be identified. To preserve the high-resolution structure of 2D crystals, the meticulous sample preparation for electron crystallography is of outmost importance. Charge-induced specimen drift and lack of specimen flatness can severely affect the resolution of images for tilted samples. However, sample preparations that sandwich the two-dimensional crystals between symmetrical carbon films reduce the charge-induced specimen drift, and the flatness of the preparations can be optimized by the choice of the grid material and the preparation protocol. Data collection in the cryoelectron microscope using either the imaging or the electron diffraction mode has to be performed after low-dose procedures. Spot scanning further reduces the charge-induced specimen drift.