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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 .
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 ...
Binding sites for a signalling phosphoprotein may be diverse in their chemical structure. [9] Phosphorylation of the hydroxyl group can change the activity of the target protein, or may form part of a signaling cascade via SH2 domain binding. [10] A tyrosine residue also plays an important role in photosynthesis.
Tyrosine kinases belong to a larger class of enzymes known as protein kinases which also attach phosphates to other amino acids such as serine and threonine. Phosphorylation of proteins by kinases is an important mechanism for communicating signals within a cell (signal transduction) and regulating cellular activity, such as cell division.
Tyrosin-protein kinase Lck (or lymphocyte-specific protein tyrosine kinase) is a 56 kDa protein that is found inside lymphocytes and encoded in the human by the LCK gene. [5] The Lck is a member of Src kinase family (SFK) and is important for the activation of T-cell receptor (TCR) signaling in both naive T cells and effector T cells.
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.
The structures of some autophosphorylation complexes are known from crystals of protein kinases in which the phosphorylation site (Ser, Thr, or Tyr) of one monomer in the crystal is sitting in the active site of another monomer of the crystal in a manner similar to known peptide-substrate/kinase structures. [6]
A second regulatory phosphorylation site in Src is Tyr-416. This is an autophosphorylation site in the activation loop. It was found that a phosphorylation of Tyr-416 and Tyr-416 can suppressing the transforming ability of the activating Tyr-527→Phe mutation by Tyr-416→Phe mutation leads to maximal stimulation of kinase activity. [11]