Topographic analysis of human epidermal growth factor by monospecific antibodies and synthetic peptides

The mode of interaction between human epidermal growth factor (hEGF) and its receptor has been investigated by immunochemical studies and a synthetic peptide approach. Two types of monoclonal and five different monospecific polyclonal antibodies against hEGF have been prepared, whose epitopes are regions 1-13, 13-32, 33-53, 33-43, 22-32, and discontinuous sequences of hEGF. Antibody against 22-32 (Type I) and antibody against 33-53 (PRE 4) inhibited the binding of 125I-hEGF to membrane receptor on A 431 cells more markedly than the other antibodies. When hEGF was bound to the receptor, only antibody against 13-32 (PRE 2) could bind to hEGF-receptor complex whereas antibody against 22-32 (Type I) could not. These data suggest that region 13-20 is exposed outside during receptor-binding and both region 22-32 and region 33-53 contact the hEGF receptor. The activity of synthetic peptides corresponding to the amino acid residues 1-13, 13-32, 33-53, 13-20, 22-32, and 33-43 of hEGF was also examined. Out of the six peptides, only 13-32 stimulated DNA synthesis of BALB 3T3 cells. The activity was approximately 1/10(6) of that of intact hEGF. All of these data suggest that region 22-32 is responsible for binding to the receptor for signal transduction and region 33-53 binds to the receptor to stabilize the ligand-receptor interaction. This dual binding model fits in well with the three-dimensional hEGF structure deduced from NMR spectra.