A tyrosine kinase is an enzyme that can transfer a phosphate group to a tyrosine residue in a protein, an example of a protein kinase. This is an important function in signal transduction to regulate enzyme activity.
There are over 100 3D structures of tyrosine kinases available at the Protein Data Bank. An example is PDB 1IRK, the crystal structure of the tyrosine kinase domain of the human insulin receptor. The first non-receptor tyrosine kinase identified was the v-Src oncogenic protein. Most animal cells contain one or more members of the Src family of tyrosine kinases. A chicken sarcoma virus was found to carry mutated version of the normal cellular Src gene. The mutated v-src gene has lost the normal built-in inhibion of enzyme activity that is characteristic of cellular SRC (c-src) genes. SRC family members have been found to regulate many cellular processes. For example, the T-cell antigen receptor leads to intracellular signalling by activation of Lck and Fyn, two proteins that are structurally similar to Src.
