Structural analysis of the transmembrane domain of the epidermal growth factor receptor

The ligand-binding domain of the epidermal growth factor (EGF) receptor is separated from the cytoplasmic protein tyrosine kinase domain by a predicted single transmembrane segment. Antipeptide antibodies prepared against the outer portion of the predicted transmembrane segment confirmed this area was exposed only when cells were treated with permeabilizing agents. To investigate structural requirements for signal transduction by the transmembrane domain, three types of mutant EGF receptor were prepared. The first type was designed to shorten the transmembrane domain, the second to place proline substitutions within this domain, and the third to make amino acid substitutions analogous to those present in the transforming c-erbB2/neu oncoprotein. Mutant human receptors were expressed in null recipient mouse B82L and Chinese hamster ovary cells. All receptors bound EGF and exhibited EGF-stimulated protein tyrosine kinase activity in vivo as assayed using a 125I-labeled monoclonal anti-phosphotyrosine antibody. EGF stimulated growth of cells expressing each mutant receptor with similar dose-response characteristics. In contrast to other growth factor receptors, the transmembrane domain of the EGF receptor is tolerant to a variety of changes which neither mimic EGF action by constitutive activation nor interfere with ligand-induced signal transduction.