Tyrosine kinase is a large group of proteins regulates the function of cell growth, differentiation, motility, cytoskeletal rearrangement and adhesion etc. They activate the target protein through transfer of phosphate from ATP to the hydroxyl group of a target protein tyrosine. Transmembrane receptor kinases and non-receptor cytoplasmic kinases are two main categories of the tyrosine kinases.
Receptor tyrosine kinases bind to extracellular ligands/growth factors, which promotes receptor dimerization and autophosphorylation of receptor tyrosine residues. This triggers a cascade of downstream events through phosphorylation of intracellular proteins that ultimately transduce the extracellular signal to the nucleus, causing changes in gene expression. Receptor tyrosine kinases include EGFR/ErbB, PDGFR, VEGFR, FGFR and MET subfamilies etc. Dysfunctions in tyrosine phosphorylation are linked to oncogenic transformation. In additions, various adaptor and effector proteins couple to carboxy-terminal of an active kinase. For instance, binding of the GRB2 adaptor protein activates EGFR and MAPK/ERK signaling.
Non-receptor tyrosine kinases involve many well-defined proteins (e.g. the Src family kinases, c-Abl, and Jak kinases) and other kinases which regulates cell growth and differentiation. For example, Src family kinases are curial for activating and inhibitory pathways in the innate immune response.