InterPro domain: IPR036196

Protein tyrosine (pTyr) phosphorylation is a common post-translational modification which can create novel recognition motifs for protein interactions and cellular localisation, affect protein stability, and regulate enzyme activity. Consequently, maintaining an appropriate level of protein tyrosine phosphorylation is essential for many cellular functions. Tyrosine-specific protein phosphatases (PTPase; 3.1.3.48 ) catalyse the removal of a phosphate group attached to a tyrosine residue, using a cysteinyl-phosphate enzyme intermediate. These enzymes are key regulatory components in signal transduction pathways (such as the MAP kinase pathway) and cell cycle control, and are important in the control of cell growth, proliferation, differentiation and transformation [ 1 , 2 ]. The PTP superfamily can be divided into four subfamilies [ 3 ]:

• (1) pTyr-specific phosphatases
• (2) dual specificity phosphatases (dTyr and dSer/dThr)
• (3) Cdc25 phosphatases (dTyr and/or dThr)
• (4) LMW (low molecular weight) phosphatases

Based on their cellular localisation, PTPases are also classified as:

• Receptor-like, which are transmembrane receptors that contain PTPase domains [ 4 ]
• Non-receptor (intracellular) PTPases [ 5 ]

All PTPases carry the highly conserved active site motif C(X)5R (PTP signature motif), employ a common catalytic mechanism, and share a similar core structure made of a central parallel beta-sheet with flanking alpha-helices containing a beta-loop-alpha-loop that encompasses the PTP signature motif [ 6 ]. Functional diversity between PTPases is endowed by regulatory domains and subunits.

This entry represents the low molecular weight (LMW) protein-tyrosine phosphatases (or acid phosphatase), which act on tyrosine phosphorylated proteins, low-MW aryl phosphates and natural and synthetic acyl phosphates [ 7 , 8 ]. The structure of a LMW PTPase has been solved by X-ray crystallography [ 9 ] and is found to form a single structural domain. It belongs to the alpha/beta class, with 6 alpha-helices and 4 beta-strands forming a 3-layer alpha-beta-alpha sandwich architecture.

1. Protein tyrosine phosphatases: mechanisms of catalysis and regulation. Cell. Mol. Life Sci. 2, 633-41
2. Receptor and nonreceptor protein tyrosine phosphatases in the nervous system. Protein Sci. 60, 2465-82
3. An overview of the protein tyrosine phosphatase superfamily. Dev. Biol. 3, 739-48
4. The crystal structure of human receptor protein tyrosine phosphatase kappa phosphatase domain 1. null 15, 1500-5
5. The nonreceptor protein tyrosine phosphatase corkscrew functions in multiple receptor tyrosine kinase pathways in Drosophila. null 180, 63-81
6. The structure and mechanism of protein phosphatases: insights into catalysis and regulation. null 27, 133-64
7. Sequencing, cloning, and expression of human red cell-type acid phosphatase, a cytoplasmic phosphotyrosyl protein phosphatase. J. Biol. Chem. 267, 10856-65
8. Identification of the adipocyte acid phosphatase as a PAO-sensitive tyrosyl phosphatase. Protein Sci. 1, 710-21
9. The crystal structure of a low-molecular-weight phosphotyrosine protein phosphatase. Nature 370, 575-8