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Tyrosine phosphorylation is the addition of a phosphate (PO 4 3−) 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 .
Kinase is a large family of enzymes that are responsible for catalyzing the transfer of a phosphoryl group from a nucleoside triphosphate donor, such as ATP, to an acceptor molecule. [2] Tyrosine kinases catalyze the phosphorylation of tyrosine residues in proteins. [2]
Tyrosine phosphorylation is a fast, reversible reaction, and one of the major regulatory mechanisms in signal transduction. Cell growth, differentiation, migration, and metabolic homeostasis are cellular processes maintained by tyrosine phosphorylation. The function of protein tyrosine kinases and protein-tyrosine phosphatase counterbalances ...
Phosphorylation can occur on serine, threonine and tyrosine side chains (in other words, on their residues) through phosphoester bond formation, on histidine, lysine and arginine through phosphoramidate bonds, and on aspartic acid and glutamic acid through mixed anhydride linkages.
Src family kinases contain six distinct domains including a myristoylated N-terminal segment, an SH2 domain, an SH3 domain, a linker region, a tyrosine kinase domain, and a C-terminal tail. Src kinases are known for having a characteristically short C-terminal tail that contains an autoinhibitory phosphorylation site.
The protein furthermore contains a SH3 domain, a SH2 domain and in the C-terminal part the tyrosine kinase domain. The two main phosphorylation sites on Lck are tyrosines 394 and 505. The former is an autophosphorylation site and is linked to activation of the protein.
Tyrosine kinases of Src family contain the same typical structure: myristoylated terminus, a region of positively charged residues, a short region with low sequence homology, SH3 and SH2 domains, a tyrosine kinase domain, and a short carboxy-terminal tail. There are two important regulatory tyrosine phosphorylation sites.
Dimerization brings the two receptors into close proximity. This stimulates the kinase activity of EGFR, which leads to transautophosphorylation on multiple tyrosine residues in C-terminal end of the molecule. The phosphorylated tyrosine residue can then serve as a docking site for downstream signaling proteins. [21] (Fig. 1).