Receptor tyrosine-protein kinase erbB-2 extracellular domain II (HER2 ECD II)

The **extracellular domain II of receptor tyrosine-protein kinase erbB-2 (HER2/ERBB2)** is a key structural region critical for **dimerization with other members of the epidermal growth factor receptor (EGFR/ErbB) family**. This domain is known as the "dimerization arm" and mediates the process by which HER2 forms homodimers (with itself) or heterodimers (most commonly with EGFR or HER3), triggering potent proliferative and anti-apoptotic signaling via its intracellular kinase activity[1][2][5]. Unlike other EGFR family receptors, HER2 is ligand-independent: it does not bind a soluble activating ligand but is instead kept in a conformation ready for dimerization, with domain II playing a central role in this readiness[2][5]. Drugs such as **Pertuzumab** specifically target domain II to block dimerization, a mechanism leveraged in the clinical management of HER2-positive cancers[6]. HER2 overexpression and the prevalence of its active extracellular domain (including domain II) are hallmarks of aggressive breast, gastric, and other cancers, making it a **clinically validated therapeutic target and biomarker**[3][4]. The domain's structure is characterized by disulfide-rich loops and a predominantly β-strand conformation, supporting strong protein-protein interactions necessary for receptor activation[1][3][5]. Domain II thus represents a focal point for both oncogenic activity and targeted intervention in HER2-driven malignancies.

Other names

HER2 domain IIERBB2 extracellular domain IIHER2 dimerization armDomain II of HER2ErbB-2 extracellular domain II

Inhibition of HER2 dimerization with other EGFR family receptors (e.g., Pertuzumab blocks domain II-mediated dimerization); Blockade of downstream signal transduction; Induction of antibody-dependent cellular cytotoxicity (for some drugs such as Trastuzumab)