PaPTP1, a Gene Encoding Protein Tyrosine Phosphatase from Orchid, Phalaenopsis amabilis, is Regulated During Floral Development and Induced by Wounding
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Lotus japonicus
The transient inactivation of protein phosphatases contributes to the efficiency and temporal control of kinase-dependent signal transduction. In particular, members of the protein tyrosine phosphatase family are known to undergo reversible oxidation of their active site cysteine. The thiol oxidation step requires activation of colocalized NADPH oxidases and is mediated by locally produced reactive oxygen species, in particular H2 O2 . How oxidized phosphatases are returned to the reduced active state is less well studied. Both major thiol reductive systems, the thioredoxin and the glutathione systems, have been implicated in the reactivation of phosphatases. Here, we show that the protein tyrosine phosphatase PTP1B and the dual-specificity phosphatase PTEN are preferentially reactivated by the thioredoxin system. We show that inducible depletion of thioredoxin 1(TRX1) slows PTEN reactivation in intact living cells. Finally, using a mechanism-based trapping approach, we demonstrate direct thiol disulphide exchange between the active sites of thioredoxin and either phosphatase. The application of thioredoxin trapping mutants represents a complementary approach to direct assays of PTP oxidation in elucidating the significance of redox regulation of PTP function in the control of cell signaling.TRX1 physically interacts with PTP1B by anti tag coimmunoprecipitation (1, 2).
Immunoprecipitation
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Phosphatases are remarkably diverse, having evolved up to 10 distinct protein folds to mediate the removal of phosphate from substrates. Their functions are correspondingly wide ranging and a number are important clinical targets. As for kinases, several phosphatase classes comprise catalytically dead members. The classical protein tyrosine phosphatases (PTPs) are a subclass that utilise a cysteine nucleophile for catalysis and are critical for the control of cellular phosphotyrosine levels. Of the 49 human PTP domains, 19 possess sequence variants in key catalytic motifs defining them as pseudophosphatase domains. Strikingly, in all but two cases the catalytic cysteine remains intact. This is in contrast to other pseudophosphatases such as the pseudo-dual specificity phosphatase (DUSP) MK-Styx, which is inactivated by loss of its catalytic cysteine. We find that, like many pseudokinases, pseudoPTPs can mediate protein-protein interactions, providing scaffolding functions, but also substrate recruitment to active PTP domains. Finally, given the striking conservation of cysteine residues in the pseudoPTPs, we have also explored a potential role for redox regulation in their signalling mechanisms.
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Dual-specificity phosphatase
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Druggability
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Dual-specificity phosphatases (DUSPs) constitute a subfamily of protein tyrosine phosphatases, and are intimately involved in the regulation of diverse parameters of cellular signaling and essential biological processes. DUSP28 is one of the DUSP subfamily members that is known to be implicated in the progression of hepatocellular and pancreatic cancers, and its biological functions and enzymatic characteristics are mostly unknown. Herein, we present the crystal structure of human DUSP28 determined to 2.1 Å resolution. DUSP28 adopts a typical DUSP fold, which is composed of a central β-sheet covered by α-helices on both sides and contains a well-ordered activation loop, as do other enzymatically active DUSP proteins. The catalytic pocket of DUSP28, however, appears hardly accessible to a substrate because of the presence of nonconserved bulky residues in the protein tyrosine phosphatase signature motif. Accordingly, DUSP28 showed an atypically low phosphatase activity in the biochemical assay, which was remarkably improved by mutations of two nonconserved residues in the activation loop. Overall, this work reports the structural and biochemical basis for understanding a putative oncological therapeutic target, DUSP28, and also provides a unique mechanism for the regulation of enzymatic activity in the DUSP subfamily proteins.
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Dual-specificity phosphatase
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A detailed microscopical analysis of the morphological features that distinguish different developmental stages of nodule organogenesis in wild-type Lotus japonicus ecotype Gifu B-129-S9 plants was performed, to provide the necessary framework for the evaluation of altered phenotypes of L. japonicus symbiotic mutants. Subsequently, chemical ethyl methanesulfonate (EMS) mutagenesis of L. japonicus was carried out. The analysis of approximately 3,000 M 1 plants and their progeny yielded 20 stable L. japonicus symbiotic variants, consisting of at least 14 different symbiosis-associated loci or complementation groups. Moreover, a mutation affecting L. japonicus root development was identified that also conferred a hypernodulation response when a line carrying the corresponding allele (LjEMS102) was inoculated with rhizobia. The phenotype of the LjEMS102 line was characterized by the presence of nodule structures covering almost the entire root length (Nod ++ ), and by a concomitant inhibition of both root and stem growth. A mutation in a single nuclear gene was shown to be responsible for both root and symbiotic phenotypes observed in the L. japonicus LjEMS102 line, suggesting that (a) common mechanism(s) regulating root development and nodule formation exists in legumes.
Lotus japonicus
Organogenesis
Nodule (geology)
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Although reactive oxygen species play important roles in cellular physiology as signalling molecules, their molecular targets are largely unknown. A probable group of targets for mediating many of the effects of reactive oxygen species on cell signalling is the large diverse family of cysteine-dependent phosphatases, which includes the protein tyrosine phosphatases. Our work and that of others suggest that the oxidative inactivation of protein and lipid phosphatases plays an important part in signalling, downstream of many cellular stimuli. Future studies should give us a clearer picture of the role of phosphatase inactivation in cellular behaviour and explain how specificity is achieved in redox signalling.
Signalling
Cell Signaling
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Extracellular signal-regulated kinases 1 and 2 (ERKs) are central regulators of many physiological and pathological processes. Their activity is regulated by phosphorylation on both tyrosine and threonine residues within their activation loops by MAPK / ERK kinases 1 and 2 (MEKs). Removal of phosphate from either the tyrosine, the threonine, or from both residues together can inactivate ERKs. Indeed members of the three groups of protein phosphatases, protein Ser / Thr phosphatase, protein Tyr phosphatase, and dual specificity phosphatases have been implicated in the inactivation of ERKs. In this review, we describe the various mechanisms involved in the inactivation of ERKs during different stages of mitogenic stimulation of quiescent cells. Keywords: erk, mapk, mkp, protein tyr phosphatase, protein ser thr phosphatase
Dual-specificity phosphatase
DUSP6
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Read the full review for this Faculty Opinions recommended article: Preferential oxidation of the second phosphatase domain of receptor-like PTP-alpha revealed by an antibody against oxidized protein tyrosine phosphatases.
Alpha (finance)
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