Epidermal growth factor
Epidermal growth factor receptor (EGFR) is a transmembrane protein that is activated by binding of its specific ligands, including epidermal growth factor and transforming growth factor α (TGFα) ErbB2 has no known direct activating ligand, and may be in an activated state constitutively or become active upon heterodimerization with other family members such as EGFR.