Figure 1.

HER family receptors. Epidermal growth factor family (ErbB) receptors are characterized by an extracellular domain (ECD), consisting of two Leu-rich ligand-binding subdomains (LR) and two Cys-rich subdomains (CR), a α-helical transmembrane domain and a intracellular domain (ICD), comprising the catalytic protein tyrosine kinase subdomain (PTK) and multiple regulatory tyrosine residues which become phosphorylated on receptor activation. The crosses on the human epidermal growth factor receptor 2 (HER2) ligand-binding domains indicate their lack of functionality and on HER3 protein tyrosine kinase subdomain indicate that it is catalytically inactive.