Human epidermal growth factor receptor 2 domain II (HER2 domain II)

HER2 domain II is one of four extracellular domains on the HER2 (ErbB2) receptor tyrosine kinase, uniquely functioning as the "dimerization arm" of the HER family[1][2][7]. This domain is essential for mediating receptor-receptor interactions—it projects from the HER2 surface and is both necessary and sufficient for the formation of active HER2-containing dimers (notably with EGFR, HER3, and HER4), which are critical for downstream activation of proliferative and survival pathways in normal and malignant cells[2][7]. Structural studies indicate that the domain II of HER2 is the key interface for dimerization, the primary target of therapeutic antibodies such as pertuzumab, which sterically blocks dimer formation and HER2 activation[2][7]. Overexpression or hyperactivation involving HER2 domain II is tightly linked to the pathogenesis of several highly aggressive cancers, and blockade of domain II–mediated dimerization is a validated clinical strategy in HER2+ breast and gastric cancers[3][6][7]. HER2 domain II is distinct structurally and functionally from domains I (involved in ligand binding in other EGFR family members), III (another ligand-interacting domain), and IV (involved in other protein-protein interactions)[1][7]. Unlike other ErbB family members, HER2 does not have its own ligand but instead is an obligate dimerization partner, with domain II being central to this function[2][6]. Therapeutic antibodies (like pertuzumab) bind to a conformational epitope within domain II to block HER2 dimerization and subsequent signaling[2][7]. Aberrant domain II–mediated dimerization leads to constitutive kinase activation, supporting uncontrolled cell proliferation—a hallmark of HER2-driven malignancy[1][3][6].

Other names

ERBB2 domain IIHER2 dimerization armErbB-2 domain II

Blocking dimerization (antibodies like pertuzumab inhibit HER2 dimerization by binding domain II) and inhibiting HER2 signaling.