Receptor tyrosine-protein kinase erbB-3 is an enzyme that in humans is encoded by the ERBB3 gene. This gene encodes a member of the epidermal growth factor receptor (EGFR) family of receptor tyrosine kinases. ERBB3 belongs to the protein kinase superfamily,tyr protein kinase family and EGF receptor subfamily.It contains 1 protein kinase domain and it is expressed in Epithelial tissues and brain. This membrane-bound protein has a neuregulin binding domain but not an active kinase domain. It therefore can bind this ligand but not convey the signal into the cell through protein phosphorylation. However, it does form heterodimers with other EGF receptor family members which do have kinase activity.