Tyrosine kinase receptor

Tyrosine kinase receptors have intrinsic enzyme activity, unlike cytokine receptors. They are the most common type of enzyme linked receptors and are involved in the regulation of protein activity and gene expression. Receptor tyrosine kinases (RTKs) are transmembrane proteins; the intracellular region contains the tyrosine kinase enzyme; the enzyme is not very active when a ligand is not bound to the ligand binding site on the extracellular region. When ligands bind to growth factor tyrosine kinase receptors, they cause a conformational change that creates a cross-linking of the extracellular regions of two RTKs (dimerization). This allows two tyrosine kinases in the intracellular domain to phosphorylate each other and become active, which results in further autophosphorylation of other tyrosine kinases. The phosphorylated tyrosine kinases act as docking stations for other signalling proteins such as those involved in the Ras pathway[5].