Receptor Tyrosine Kinase (RTK)

Receptor tyrosine kinases (RTKs) are enzyme-linked cell-surface receptors (Figure 1). A kinase is an enzyme that transfers phosphate groups from ATP to another protein. RTKs transfers phosphate groups to tyrosine molecules (tyrosine residues). First, signaling molecules bind to the extracellular domain of two nearby RTK (Figure 1). The two neighboring receptors then bond together, or dimerize. Phosphates are then added to tyrosine residues on the intracellular domain of the receptors (phosphorylation). The phosphorylated residues can then transmit the signal to the next messenger within the cytoplasm. Vascular endothelial growth factor receptor(VEGFR) is a widely studied example of RTKs.

First image at the top of the figure presents two blue, thin, rectangularly shaped structures, aligned vertically and called receptor tyrosine kinase, which are embedded inside the plasma membrane. The upper part of the receptors is sticking out towards the environment and the bottom part is sticking out towards the cytoplasm. Inside the bottom part, the tyrosine residues are marked as Y letters. The arrow, describing the event when the signaling molecule binds to the receptors and they dimerize, points down to the middle image that presents the same receptors, but now brought together closer. To each upper part of the two blue receptors, a red sphere is attached, called signalling molecule. Finally, the last arrow, describing phosphorylation of the intracellular domains and trigger of downstream cellular response, points down to the bottom image that presents the same blue, dimerized structures with red spheres at the upper part of them, but now to the lower part where the letter Y where, green small spheres are attached with letter P inside. From this phosphorylated tyrosine residues, purple arrow points towards cellular response.

Figure 1: A receptor tyrosine kinase (RTK) is an enzyme-linked receptor with a single transmembrane region, and extracellular and intracellular domains. Binding of a signaling molecule to the extracellular domain causes the receptor to dimerize. Tyrosine residues on the intracellular domain are then autophosphorylated, triggering a downstream cellular response. The signal is terminated by a phosphatase that removes the phosphates from the phosphotyrosine residues.

Acknowledgement The content of these theory pages has been developed based on the resources provided by: OpenStax College, Biology. (OpenStax CNX. Mar 13, 2015)