Receptor Tyrosine Kinase

There are approximately 60 receptor tyrosine kinases.

Critical roles in cell growth, cell differentiation, cellular metabolism, cell adhesion, cell motility and cell death.

Receptor tyrosine kinases have an extracellular domain that binds specific proteins. When the protein or substrate binds to the extracellular portion of the enzyme, the tyrosine kinase undergoes a conformational change, alterations in its structure, which are propagated to the intracellular domain to allow for enzyme activation. A transmembrane domain that crosses through the cell membrane and stabilizes the kinase within the phospholipid bilayer while exposing it to the extracellular matrix and outer aspects of the cell. And an intracellular catalytic domain which binds substrates and transfer the phosphate group to them.
Phosphorylation of proteins eventually leads to changes in gene expression as many of the proteins can now enter the nucleus.

Tyrosine kinases are well-known to be involved in cancer promotion, oncogenesis. Tyrosine kinases can become cancer promoting proteins, oncogenes, either through gene mutations, changes in their regulation leading to over-expression or chromosomal changes, such as with translocations.

Such changes confer to the tyrosine kinase unrestricted activity which leads to unrestricted growth of a cell without the need for ligand binding to the kinase to activate it. The tyrosine kinase has become constitutively activated.