Dodecameric assembly. (A) A dimer building block of hDNPEP. (B) Surface representation of the arrangement of six dimers into a tetrahedron. The dimer building block, each coloured differently, is delineated by a red dotted line. The black-dotted line indicates the monomer-monomer interface within a dimer. Each dimer sits diagonally on six faces of a cubic box that encases the tetrahedron (red line, inset). Asterisks indicate positions of the narrow (yellow) and wide (blue) channels, which are located at 3-fold axes (arrow). (C) The openings of the narrow (top) and wide (bottom) channels. (D) Electron micrograph of negatively stained hDNPEP. (E) Examples of 2D classification images with a view down the wide channel, the 3-fold symmetry imposed in the right panel. (F) Fitting of hDNPEP crystal structure onto the 2D projection.