what is a heterodimer
Homodimer and heterodimer formations of ERBB receptors. Receptors are shown as two lobes connected by a transmembrane stretch. Binding of a ligand, neuregulin (NRG, blue square) or something EGF-like to the extracellular lobe activates the receptors. On ErbB1, ErbB3, (note inactive kinase, marked by a cross) or ErbB4 induces homodimer formation.