Three-dimensional structure of gap junctions in fragmented plasma membranes from rat liver

Gap junctions forming extensive hexagonal crystalline sheets (unit cell dimension, a = 89 A) were obtained by mild mechanical disruption of plasma membranes from rat liver. The sheets were analysed in three dimensions by negative stain electron microscopy and Fourier image processing. The crystallographic symmetry was shown to approximate to the two-sided plane group p622, indicating that the sheets are composed of two equivalent, oppositely-facing membrane assemblies. The structure of the connexon in these near-to-native junctions is essentially the same as that found in detergent-extracted junctions, the subunits appearing slightly tilted tangential to the central six-fold axis and aligned almost perpendicular to the membrane plane.