The E2 domain is the largest of the conserved domains of the amyloid precursor protein. The structure of E2 consists of two coiled-coil sub-structures connected through a continuous helix, and bears an unexpected resemblance to the spectrin family of protein structures.E 2 can reversibly dimerise in solution, and the dimerisation occurs along the longest dimension of the molecule in an antiparallel orientation, which enables the N-terminal substructure of one monomer to pack against the C-terminal substructure of a second monomer. The high degree of conservation of residues at the putative dimer interface suggests that the E2 dimer observed in the crystal could be physiologically relevant. Heparin sulfate proteoglycans, the putative ligands for the precursor present in extracellular matrix, bind to E2 at a conserved and positively charged site near the dimer interface [1].

1: The X-ray structure of an antiparallel dimer of the human amyloid precursor protein E2 domain. Wang Y, Ha Y; Mol Cell. 2004;15:343-353. PMID:15304215