3-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 2·8resolution has been collected and analyzed. The strongest highresolution intensities are distributed as a figure of revolution about the z*-axis and are located primarily in a resolution range of 4·5to 5·0Within this region, centered near 4·8resolution the brightest intensities are clustered about inclination angles of 35° and 0° from the a*, b* plane. This distribution of intensities indicates that the β-sheet in PhoE porin is arranged to form a cylinder-like structure that contains major populations of β-sheet strands tilted an average of 35° and 0° 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. © 1990, Academic Press Limited. All rights reserved.