Receptor tyrosine kinases initiate a signal transduction cascade

Overview of Receptor Tyrosine Kinase (RTK) Activation

• RTKs are membrane-bound receptors possessing intrinsic tyrosine-kinase enzymatic activity.

• Activation begins when an extracellular ligand (growth factor, hormone, etc.) binds the RTK’s ligand-binding domain.

• Ligand binding drives receptor dimerization/oligomerization ("aggregation" or "clustering")—crucial for subsequent catalytic events.

• Once clustered, each RTK monomer phosphorylates tyrosine residues on its dimer partner (trans-phosphorylation), a process called auto-phosphorylation.

• Auto-phosphorylated tyrosines serve as high-affinity docking sites for cytosolic signaling proteins that carry Src-Homology-2 (SH2) domains.

Auto-Phosphorylation Mechanism

• "Auto" here does not mean a single receptor phosphorylates itself; rather, one monomer