Figure 1. ErbB receptors and their ligands.

All four members of the ErbB receptor family share high homology in the extracellular domain and the kinase domain. However, ErbB3 is not kinase active. So far no ligand has been found for p185^her2/neu, which has been found to be the preferred dimerization partner for other receptors. Only a few examples of receptor dimers are shown here. Ectodomain-truncated receptors also exist in some cancer cells. NRG1, neuregulin 1.