A graphical representation of image quality for three-dimensional structure analysis of two-dimensional crystals.

Electron crystallography of two-dimensional (2D) crystals is a powerful approach for the analysis of membrane protein structure. Three-dimensional (3D) structures are derived by merging data from 2D crystals at varying tilt axes and tilt angles. A graphical representation was developed that incorporates the tilt geometry to display the quality of each image. Information that can be extracted from the plot includes a symbol for each image that reflects the completeness of the data for that crystal. The polar plot also includes a novel parameter that reflects the minimal variation in tilt axis to ensure overlap of data points in reciprocal space between images at the same tilt angle. The tilt geometry and image quality plot is especially useful for tracking the progress of data collection and for assessing the completeness of two data sets prior to determination of difference maps.