Figure 2. Ligand-receptor cross-reactivity in the ErbB receptor family.

Ligands and receptors in this family show a complex pattern of cross-reactivities. Complicating matters yet further, the receptor protein ErbB2 does not bind directly to any known ligand, but when present on cells is the preferred heterodimerization partner for other ErbB family members. In contrast, ErbB3 can bind ligands, but lacks an active kinase domain and so can signal only as part of a heterodimer with a kinase-active ErbB partner. See text for further details. (A color version of this figure is available in the inline version of this article.)