Dual-specificity phosphatases

The classical PTPs can be subdivided into receptorlike PTPs and nonreceptor, cytosolic PTPs. The second category of PTPs are broadly defined as dual specificity phosphatases (DSPs), which dephosphorylate pSer/ pThr as well as pTyr. MAP kinase phosphatases (MKPs) ( MAP kinase cascades) and PTEN are examples of DSP family members. Remarkably, PTEN also has lipid phosphatase activity that is specific for phosphatidylinositol-3,4,5-trisphosphate generated in response to the actions of PI3K. Finally, the class of low molecular mass (LM-) PTPs and that of CDC25 PTPs accomplish the cells repertoire of PTPs (Fig. 3). 

DSPc Dual specificity phosphatase, catalytic domain E(MFP)B 5(5) 10(10) 1VHR... 

Denu, J.M. and J.E. Dixon. 1995. A catalytic mechanism for the dual-specific phosphatases. Biochemistry 92 5910-5914. 

Brault, L., Denance, M., Banaszak, E., Maadidi, S.E., Battaglia, E., Bagrel, D., and Samadi, M. (2007) Synthesis and biological evaluation of dialkylsubstituted maleic anhydrides as novel inhibitors of Cdc25 dual specificity phosphatases. European Journal of Medicinal Chemistry, 42, 243-247. 

On the other hand, a particular protein function can be realized with different protein folds, and an example of this are protein phosphatases. Protein phosphatases feature two distinctively different catalytic mechanisms for hydrolytically cleaving phosphorylated amino acid residues. The active sites of serine/threonine protein phosphatases (PPs) contain two metal centers that directly activate a water molecule for nucleophilic attack of the phosphate ester bond. In contrast, protein tyrosine phosphatases (PTPs) [105] possess a Cys residue present in the active site loop containing the conserved PTP signature motif HCXXXXXRS. The Cys sidechain acts as the attacking nucleophile in the formation of a phosphocysteine intermediate, which is eventually hydrolyzed by a water molecule [106], The same catalytic mechanism is also shared by dual-specificity phosphatases (see below). 

Laporte, J., Blondeau, F., Buj-Bello, A., Tender, D., Kretz, C., Dahl, N., and Mandel, J.L., 1998, Characterization of the myotubularin dual specificity phosphatase gene family from yeast to human. Hum. Mol. Genet. 7 1703-1712. 

For dephosphorylation reactions, many enzymes with different specificities are available There are phosphatases, specific for phosphotyrosyl residues, for Ser/Thr-bound phosphates, and dual-specificity phosphatases, recognizing both phosphotyrosyls and phosphoserines Tyrosine phosphatases and dual-specificity phosphatases have already been introduced (Chapter 3). Here, the properties of serine/threonine phosphatases will be described and their regulation by cellular relocation introduced. Much of what we know about the regulation of this class of phosphatases we owe to the work of P. Cohen and his colleagues. Table 7.1 lists common phosphoserine/phosphothreonine phosphatases of eukaryotes. 

Bembenek J, Yu H. Regulation of the anaphase-promoting com- 131. plex by the dual specificity phosphatase human Cdcl4a. J. Biol. 

Brisson M, Nguyen T, Vogt A, Yalowich J, Giorgianni A, Tobi D, Bahar I, Stephenson CR, Wipf P, Lazo JS. Discovery and characterization of novel small molecule inhibitors of human Cdc25B dual specificity phosphatase. Mol Pharmacol 200 66 824-33. 

The cell cycle control phosphatases Cdc25 are dual specificity phosphatases (DSPases) that dephosphorylate both phosphothreonine and phosphotyrosine... 

The PTPases share the signature motif (H/V)C(X)5R(S/T). This motif is also found in the low-molecular-weight PTPases, as well as in the VH 1-like dual-specific phosphatases, so-called because they dephosphorylate phosphotyrosine as well as phospho-Ser/Thr residues.129,149 These three groups of phosphatases have little sequence similarity other than the signature motif and the placement of the essential Cys and Arg residues in the active site. 

The X-ray structures of a number of PTPases have been reported, including the catalytic domains of PTP1B complexed with tungstate150 and of Yop51 from Yersinia (residues 163-468)151 with and without complexed tungstate. The structure of the human dual-specific phosphatase VHR (Vaccina HI-related) has also been determined,152 as well as those of several low-molecular-weight PTPases, including... 

KIEs and pH-rate dependencies for V/K were measured for the reactions of the dual-specificity phosphatase VHR177 and the Yersinia PTP178 with the alkyl phosphate mNBP, which, with a leaving group pK l of 14.9, is a better mimic for physiological alkyl phosphate substrates like phosphoserine or phosphothreonine. In... 

Lyon, M. A., Ducruet, A. R, Wipf, P., Lazo, J. Dual-specificity phosphatases as targets for antineoplastic agents. Nature Rev. Drug Discov. 2002,1, 961-976. 

Pulido B., Hooft van Huijsduijnen R (2008) Protein tyrosine phosphatases dual-specificity phosphatases in health and disease. FEBS J 275 848-866... 

Dual-specificity phosphatases critical regulators with diverse cellular targets. Biochem J 418 475 89... 

Hengge AC, Denu JM, Dixon JE (1996) Transition-state structures for the native dual-specific phosphatase VHR and D92N and S131A mutants. Contributions to the driving force for catalysis. Biochemistry 35 7084-7092... 

Johnston PA, Foster CA, Tierno MB et al (2009) Cdc25B dual-specificity phosphatase inhibitors identified in a high-throughput... 

Arrest in Gx phase can now be achieved in at least two ways, depending on the substrates of the Chkl and Chk2 enzymes. In one rapid way, the dual specificity phosphatase Cdc25C is phosphorylated on Ser 123 and is thereby targeted for ubiquitina-tion and degradation in the proteasome pathway. The lack of this enzyme locks the CDK2 kinase in the inactive form phosphorylated on threonine 14 and tyrosine 15.The cyclin E-CDK2 complex that is required for entry into S phase is inhibited, and the cell cycle arrests at Gj/S. It should be noted that the scheme in Fig. 13.19 is only a minimal scheme that does not address the participation of numerous other proteins that function as adaptors or structural proteins in these processes. 

The PTPs catalyze the hydrolysis of phosphorylated tyrosine residues in proteins, to yield the free tyrosine side chains and inorganic phosphate. They are classified according to substrate specificity (1) tyrosine-specific PTPs, such as the Yersinia PTP (YopH) and the mammalian PTPIB and PTPl, which in vivo hydrolyze only pTyr residues as well as (2) the dual-specificity phosphatases (DSPs), such as the human VHR and Cdc25, which hydrolyze pTyr and pSer and pThr residues of protein substrates. Based on their cellular localization, PTPs are classified as receptor-like or intracellular. ... 

The cytosolic PTPs are also classified according to their domain structures, which are understood to act as localization signals, directing the enzymes to the nucleus or cytoskeleton. Important subclasses, SHP-1 and SHP-2, possess SH2 domains. Others are characterized by the presence of PEST sequences (Pro-Glu/Asp-Sere/Thr) in the vicinity of the C-temtinus. Another subclass comprises dual specific phosphatases, which can dephosphorylate at both Tyr and Ser/Thr residues. The dual specific phosphatases also have homology with Cdc25, a regulator of mitosis in Schizoscccharomyces pombe. This activates cyclin dependent kinase-2 by dephosphorylation of adjacent threonine and tyrosine residues. 

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