Localization of a major receptor-binding domain for epidermal growth factor by affinity labeling

Epidermal growth factor (EGF) receptor was affinity labeled with 125I-labeled EGF, using bifunctional covalent cross-linking agents. The affinity-labeled receptor was isolated and cleaved with CNBr to yield a single-labeled fragment, which was unequivocally identified by site-specific antibodies and other methods to encompass residues 294 to 543 of the EGF receptor. On the basis of amino acid sequence conservation, the extracellular portion of EGF receptor can be divided into four domains. The labeled CNBr fragment contains the entire sequence which is flanked by the two cysteine-rich domains of extracellular portion of the EGF receptor denoted as domain III. On the basis of these and other results, we propose that domain III contributes most of the interactions that define ligand-binding specificity of the EGF receptor.