Claim: The E1 domain contains two independent folding units, GFLD has a highly charged basic surface and is tightly packed on a triple-stranded beta-sheet which is a secondary structure in proteins.
Evidence: The E1 domain contains two independent folding units, the growth factor-like domain (GFLD) and the copper-binding domain (CuBD). GFLD has a highly charged basic surface and a highly flexible region consisting of an N-terminal loop formed by a disulphide bridge. CuBD consists of an alpha-helix that is tightly packed on a triple-stranded beta-sheet. The β-sheet (also β-pleated sheet) is a common motif of regular secondary structure in proteins.