A 40-kDa epidermal growth factor/transforming growth factor α-binding domain produced by limited proteolysis of the extracellular domain of the epidermal growth factor receptor

Elucidation of the three-dimensional structure of the complex of the epidermal growth factor (EGF) and its receptor is essential for understanding the molecular mechanisms of the EGF-receptor interaction and EGF-induced receptor-receptor interaction. NMR is useful to investigate interactions in solution between macromolecules at atomic resolution, but has a limitation in molecular masses of target proteins: less than 300 residues. We have prepared a fragment with apparent molecular mass of 40 kDa in SDS gels from the soluble extracellular domain of the EGF receptor (sEGFR, 619 residues) by sequential limited proteolysis with proteinase K and bromelain. This fragment is a monomeric structural domain consisting of 202 amino acid residues (Cys³⁰²-Arg⁵⁰³) and 18-kDa sugar chains, and binds EGF and transforming growth factor-α (TGFα). This 40-kDa domain has a dissociation constant of about 1 μM for human TGFα, which is similar to that of the parental sEGFR. sEGFR oligomerizes in response to EGF and TGFα, while the 40-kDa domain does not, suggesting that the sequences other than this domain is required for receptor oligomerization. The 40-kDa ligand-binding domain described in this report is suitable for analysis by various physico-chemical approaches such as NMR.