Structural models and immunogenic regions of EED isoform 3. (A), Seven-bladed β-propeller model of the EED core domain, based on sequence homology with the beta subunit of the bovine G protein (Gβ ; [27, 28]). Shown is a ribbon representation of the polypeptide backbone atoms of EED3 isoform (amino acid residues 84–441), with secondary and tertiary structures of the different β-blades. (B), 3D-model of the EED3 seven-bladed β-propeller, deduced from crystallographic data (modified, from ). The black arrow indicates the major difference between our putative model (A) and the crystal model (B), consisting of the α1 helical region facing the β-strand β17 in β-blade IV. (C), Position of immunogenic epitopes (depicted in green) on the 3D-model of EED polypeptide backbone (represented in blue). (D), Primary and secondary structures of EED3, deduced from crystallographic data . The amino acid sequence was numbered according to the accepted nomenclature  : Met95 in EED1 isoform represented Met1 in EED3 ; thus, the C-terminal residue L440 in EED3 corresponded to L535 in EED1. Regions in β-strand structure are represented by horizontal arrows, with reference to the blade number and β-strand letter a, b, c or d ; α-helices are represented by spirals, and turns by TT. Helical regions marked α1 and η1, and the β-strand region marked β17, were structurized domains of EED which were unique among representatives of WD-40 proteins. The relative accessibility of each residue (acc) in the 3D structure was extracted from the dictionary of protein structure , and indicated as coloured bars under the sequence with the following colour code : dark blue, highly accessible ; light blue, accessible ; white, buried. Discrete regions recognized by anti-EED IgG are indicated by green boxes. The binding sites of HIV-1 matrix protein (MA) and integrase (IN) are underlined by solid black lines.