Dual specificity phosphatase, catalytic domain (Dual-sp_phosphatase_cat-dom)
Type: Domain

This entry represents dual specificity protein-tyrosine phosphatases. Ser/Thr and Tyr dual specificity phosphatases are a group of enzymes with both Ser/Thr (

) and tyrosine specific protein phosphatase (

) activity able to remove both the serine/threonine or tyrosine-bound phosphate group from a wide range of phosphoproteins, including a number of enzymes which have been phosphorylated under the action of a kinase. Dual specificity protein phosphatases (DSPs) regulate mitogenic signal transduction and control the cell cycle. The crystal structure of a human DSP, vaccinia H1-related phosphatase (or VHR), has been determined at 2.1 angstrom resolution . A shallow active site pocket in VHR allows for the hydrolysis of phosphorylated serine, threonine, or tyrosine protein residues, whereas the deeper active site of protein tyrosine phosphatases (PTPs) restricts substrate specificity to only phosphotyrosine. Positively charged crevices near the active site may explain the enzyme's preference for substrates with two phosphorylated residues. The VHR structure defines a conserved structural scaffold for both DSPs and PTPs. A "recognition region" connecting helix alpha1 to strand beta1, may determine differences in substrate specificity between VHR, the PTPs, and other DSPs.

These proteins may also have inactive phosphatase domains, and dependent on the domain composition this loss of catalytic activity has different effects on protein function. Inactive single domain phosphatases can still specifically bind substrates, and protect again dephosphorylation, while the inactive domains of tandem phosphatases can be further subdivided into two classes. Those which bind phosphorylated tyrosine residues may recruit multi-phosphorylated substrates for the adjacent active domains and are more conserved, while the other class have accumulated several variable amino acid substitutions and have a complete loss of tyrosine binding capability. The second class shows a release of evolutionary constraint for the sites around the catalytic centre, which emphasises a difference in function from the first group. There is a region of higher conservation common to both classes, suggesting a new regulatory centre .

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;

) 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 . The PTP superfamily can be divided into four subfamilies :

(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

Non-receptor (intracellular) PTPases

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 β-sheet with flanking α-helices containing a β-loop-α-loop that encompasses the PTP signature motif . Functional diversity between PTPases is endowed by regulatory domains and subunits.