Three-dimensional electron diffraction of PhoE porin to 2.8 A resolution

A three-dimensional set of electron diffraction intensities of PhoE porin embedded in trehalose extending to 2.8 A resolution has been collected and analyzed. The strongest high-resolution intensities are distributed as a figure of revolution about the z*-axis and are located primarily in a resolution range of 4.5 A to 5.0 A. Within this region, centered near 4.8 A resolution the brightest intensities are clustered about inclination angles of 35 degrees and 0 degrees from the a*, b* plane. This distribution of intensities indicates that the beta-sheet in PhoE porin is arranged to form a cylinder-like structure that contains major populations of beta-sheet strands tilted an average of 35 degrees and 0 degrees with respect to the membrane plane normal. This cylindrical structure has been seen previously in the high-resolution projection map of PhoE as an elliptical ring of high density.