Tyrosine phosphorylation

Tyrosine phosphorylation is the addition of a phosphate (PO43−) group to the amino acid tyrosine on a protein. It is one of the main types of protein phosphorylation. This transfer is made possible through enzymes called tyrosine kinases. Tyrosine phosphorylation is a key step in signal transduction and the regulation of enzymatic activity. Tyrosine phosphorylation is the addition of a phosphate (PO43−) group to the amino acid tyrosine on a protein. It is one of the main types of protein phosphorylation. This transfer is made possible through enzymes called tyrosine kinases. Tyrosine phosphorylation is a key step in signal transduction and the regulation of enzymatic activity. In the summer of 1979, studies of polyomavirus middle T and v-Src associated kinase activities led to the discovery of tyrosine phosphorylation as a new type of protein modification. Following the 1979 discovery that Src is a tyrosine kinase, the number of known distinct tyrosine kinases grew rapidly, accelerated by the advent of rapid DNA sequencing technology and PCR. About one year later, researchers discovered an important role for tyrosine phosphorylation in growth factor signaling and proliferation, and by extension in oncogenesis through hijacking of growth factor tyrosine phosphorylation signaling pathways. In 1990 receptor tyrosine kinase (RTK) initiation of intracellular signaling was detected. Phosphotyrosine (P.Tyr) residues on activated RTKs are recognized by a phosphodependent-binding domain, the SH2 domain. The recruitment of SH2 domain proteins to autophosphorylated RTKs at the plasma membrane is essential for initiating and propagating downstream signaling. SH2 domain proteins may have a variety of functions, including adaptor proteins to recruit other signaling proteins, enzymes that act on membrane molecules, such as phospholipases, cytoplasmic tyrosine kinases that relay signals, E3 ubiquitin ligases, and transcription factors. In 1995 proteins were found containing a second type of P.Tyr-binding domain, PTB, in RTK signaling. Gradually the number of identified tyrosine kinases and receptor tyrosine kinases grew. As of 2002, of the 90 known human tyrosine kinases, 58 were RTKs, and opposing the action of the tyrosine kinases were 108 protein phosphatases that can remove phosphate from P.Tyr in proteins. Ushiro and Cohen (1980) discovered the important role of the phosphorylation of tyrosine as a regulator of intracellular processes and revealed changes in the tyrosine kinase activity of proteins in mammalian cells. Subsequently, the change in protein tyrosine kinase activity was shown to underlie the Ras-MAPK signaling pathway regulated by mitogen-activated protein (MAP) kinases.