HER1 signaling is triggered by individual HER1 monomers each binding to its ligand followed by homodimerization and autophosphorylation. How do HER2/HER3 heterodimers initiate signaling? A. Neither HER2 nor HER3 bind ligands, but can form heterodimers that activate HER2 tyrosine kinase which creates a GRB2 binding site.
B. Neither HER2 nor HER3 bind ligands, but can form heterodimers that activate HER2 tyrosine kinase which creates a GRB2 binding site.
C. HER2 and HER3 monomers each bind to its ligand followed by heterodimerization and activation of both HER2 and HER3 tyrosine kinases which create a GRB2 binding site.
D. HER2, but not HER3 binds to its ligand, causing it heterodimerize with HER3. This activates HER3 tyrosine kinase which creates a GRB2 binding site.
E. HER3, but not HER2 binds to its ligand, causing it heterodimerize with HER2. This activates HER2 tyrosine kinase which creates a GRB2 binding site.

E. HER3, but not HER2 binds to its ligand, causing it heterodimerize with HER2. This activates HER2 tyrosine kinase which creates a GRB2 binding site.

Explanation:

The receptor tyrosine-protein kinase, also known as human epidermal growth factor receptor 3 (HER3), is a transmembrane tyrosine kinase receptor that doesn't have a kinase domain. HER3 binds to the HER2 protein (another receptor tyrosine kinase receptor) to form a heterodimeric complex. Conversely to the HER3 protein, HER2 lacks a ligand-binding domain. The HER2/HER3 complex triggers the activation of the HER2 kinase domain which then autophosphorylates and thus generates a binding site for the Growth factor receptor-bound protein 2 (Grb2).

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