Tyrosine kinase

Receptor Tyrosine Kinases (RTK) are transmembrane proteins that directly phosphorylate tyrosines on themselves. RTKs have two receptors and they dimerize when a signal molecule binds onto those receptors. This causes cross-phosphorylation, activating the RTK. This activation occurs in two ways: tyrosines which are within the kinase domain are phosphorylated, and tyrosines on the outside of the domain are also activated. The phosphorylated tyrosines within the domain, increase the kinase activity, and the phosphorylated tyrosines outside result docking sites for the binding of certain intracellular signalling proteins. It is possible for these signalling proteins to be phosphorylated on the kinases, which leads to their activation.

Alberts, B. [et al], (2008), Molecular biology of the cell, 5th edition, New York: Garland Science, page 922-924