Protein Tyrosine Phosphatase Catalytic Domain Research Articles

Expression, purification, and characterization of human osteoclastic protein-tyrosine phosphatase catalytic domain in Escherichia coli

Osteoclastic protein tyrosine phosphatase (PTP-oc) is a structurally unique transmembrane protein tyrosine phosphatase (PTP) that contains only a relatively small intracellular PTP catalytic domain, does not have an extracellular domain, and lacks a signal peptide proximal to the NH2 terminus. The present study reports the expression, purification, and characterization of the intracellular catalytic domain of PTP-oc (ΔPTP-oc). ΔPTP-oc was expressed in Escherichia coli cells as a fusion with a six-histidine tag and was purified via nickel affinity chromatography. When with para-nitrophenylphosphate (p-NPP) as a substrate, ΔPTP-oc exhibited classical Michaelis–Menten kinetics. Its responses to temperature and ionic strength were similar to those of other PTPs. The optimal pH value of ΔPTP-oc is approximately 7.0, unlike other PTPs, whose optimal pH values are approximately 5.0.

Structure, function, and pathogenesis of SHP2 in developmental disorders and tumorigenesis.

Src homology 2 (SH2)-containing protein tyrosine phosphatase 2 (SHP2), encoded by the human PTPN11 gene, is a ubiquitously expressed protein tyrosine phosphatase (PTP) that consists of two tandem Src homology (SH2) domains (N-SH2 and C-SH2), a PTP catalytic domain, and a C-terminal tail with tyrosyl phosphorylation sites. It plays critical roles in numerous cellular processes through the regulation of various signaling pathways in PTP catalytic activity-dependent and -independent manners. Dysfunction of SHP2 resulting from pathogenic mutations and aberrant expression leads to the dysregulation of multiple signaling pathways, thus contributing to different human disorders. Germline and somatic mutations in PTPN11 are involved in Noonan syndrome (NS), LEOPARD syndrome (LS), and hematological malignancies, as well as several solid tumors. In this report, we provide an overview of the current knowledge of the structure and function of SHP2, and further discuss the molecular and pathogenic mechanism of SHP2 in human diseases, with a special focus on tumorigenesis. Furthermore, we summarize that SHP2 might itself represent a potential drug target for cancer prevention and treatment. Ongoing research and development of SHP2-specific inhibitors would enhance this potential.

Regulation of the Src Kinase-associated Phosphoprotein 55 Homologue by the Protein Tyrosine Phosphatase PTP-PEST in the Control of Cell Motility

PTP-PEST is a cytosolic ubiquitous protein tyrosine phosphatase (PTP) that contains, in addition to its catalytic domain, several protein-protein interaction domains that allow it to interface with several signaling pathways. Among others, PTP-PEST is a key regulator of cellular motility and cytoskeleton dynamics. The complexity of the PTP-PEST interactome underscores the necessity to identify its interacting partners and physiological substrates in order to further understand its role in focal adhesion complex turnover and actin organization. Using a modified yeast substrate trapping two-hybrid system, we identified a cytosolic adaptor protein named Src kinase-associated phosphoprotein 55 homologue (SKAP-Hom) as a novel substrate of PTP-PEST. To confirm PTP-PEST interaction with SKAP-Hom, in vitro pull down assays were performed demonstrating that the PTP catalytic domain and Proline-rich 1 (P1) domain are respectively binding to the SKAP-Hom Y260 and Y297 residues and its SH3 domain. Subsequently, we generated and rescued SKAP-Hom-deficient mouse embryonic fibroblasts (MEFs) with WT SKAP-Hom, SKAP-Hom tyrosine mutants (Y260F, Y260F/Y297F), or SKAP-Hom SH3 domain mutant (W335K). Given the role of PTP-PEST, wound-healing and trans-well migration assays were performed using the generated lines. Indeed, SKAP-Hom-deficient MEFs showed a defect in migration compared with WT-rescued MEFs. Interestingly, the SH3 domain mutant-rescued MEFs showed an enhanced cell migration corresponding potentially with higher tyrosine phosphorylation levels of SKAP-Hom. These findings suggest a novel role of SKAP-Hom and its phosphorylation in the regulation of cellular motility. Moreover, these results open new avenues by which PTP-PEST regulates cellular migration, a hallmark of metastasis.

Regulation of lymphoid tyrosine phosphatase activity: inhibition of the catalytic domain by the proximal interdomain.

The lymphoid tyrosine phosphatase LYP, encoded by the PTPN22 gene, recently emerged as a major player and candidate drug target for human autoimmunity. The enzyme includes a classical N-terminal protein tyrosine phosphatase catalytic domain and a C-terminal PEST-enriched domain, separated by an approximately 300-amino acid interdomain. Little is known about the regulation of LYP. Herein, by analysis of serial truncation mutants of LYP, we show that the phosphatase activity is strongly inhibited by protein regions C-terminal to the catalytic domain. We mapped the minimal inhibitory region to the proximal portion of the interdomain. We show that the activity of LYP is inhibited by an intramolecular mechanism, whereby the proximal portion of the interdomain directly interacts with the catalytic domain and reduces its activity.

PTPN11 (Shp2) Mutations in LEOPARD Syndrome Have Dominant Negative, Not Activating, Effects

Multiple lentigines/LEOPARD syndrome (LS) is a rare, autosomal dominant disorder characterized by Lentigines, Electrocardiogram abnormalities, Ocular hypertelorism, Pulmonic valvular stenosis, Abnormalities of genitalia, Retardation of growth, and Deafness. Like the more common Noonan syndrome (NS), LS is caused by germ line missense mutations in PTPN11, encoding the protein-tyrosine phosphatase Shp2. Enzymologic, structural, cell biological, and mouse genetic studies indicate that NS is caused by gain-of-function PTPN11 mutations. Because NS and LS share several features, LS has been viewed as an NS variant. We examined a panel of LS mutants, including the two most common alleles. Surprisingly, we found that in marked contrast to NS, LS mutants are catalytically defective and act as dominant negative mutations that interfere with growth factor/Erk-mitogen-activated protein kinase-mediated signaling. Molecular modeling and biochemical studies suggest that LS mutations contort the Shp2 catalytic domain and result in open, inactive forms of Shp2. Our results establish that the pathogenesis of LS and NS is distinct and suggest that these disorders should be distinguished by mutational analysis rather than clinical presentation.

Structure of the Hematopoietic Tyrosine Phosphatase (HePTP) Catalytic Domain: Structure of a KIM Phosphatase with Phosphate Bound at the Active Site

Hematopoietic tyrosine phosphatase (HePTP) is a 38kDa class I non-receptor protein tyrosine phosphatase (PTP) that is strongly expressed in T cells. It is composed of a C-terminal classical PTP domain (residues 44-339) and a short N-terminal extension (residues 1-43) that functions to direct HePTP to its physiological substrates. Moreover, HePTP is a member of a recently identified family of PTPs that has a major role in regulating the activity and translocation of the MAP kinases Erk and p38. HePTP binds Erk and p38 via a short, highly conserved motif in its N terminus, termed the kinase interaction motif (KIM). Association of HePTP with Erk via the KIM results in an unusual, reciprocal interaction between the two proteins. First, Erk phosphorylates HePTP at residues Thr45 and Ser72. Second, HePTP dephosphorylates Erk at PTyr185. In order to gain further insight into the interaction of HePTP with Erk, we determined the structure of the PTP catalytic domain of HePTP, residues 44-339. The HePTP catalytic phosphatase domain displays the classical PTP1B fold and superimposes well with PTP-SL, the first KIM-containing phosphatase solved to high resolution. In contrast to the PTP-SL structure, however, HePTP crystallized with a well-ordered phosphate ion bound at the active site. This resulted in the closure of the catalytically important WPD loop, and thus, HePTP represents the first KIM-containing phosphatase solved in the closed conformation. Finally, using this structure of the HePTP catalytic domain, we show that both the phosphorylation of HePTP at Thr45 and Ser72 by Erk2 and the dephosphorylation of Erk2 at Tyr185 by HePTP require significant conformational changes in both proteins.

The Yersinia tyrosine phosphatase YopH targets a novel adhesion-regulated signalling complex in macrophages.

The Yersinia protein tyrosine phosphatase (PTP) YopH is translocated into eukaryotic cells by a type III secretion system that requires bacterial-host cell contact. YopH is composed of two modular effector domains: a substrate-binding domain located in the N-terminal region (residues 1-130) and a PTP catalytic domain located in the C-terminal region (residues 206-468). Previous studies have shown that YopH selectively targets tyrosine-phosphorylated proteins of approximate molecular weight 120 kDa (p120) and 55 kDa (p55) in murine macrophages. It has been demonstrated that p120 actually represents two tyrosine-phosphorylated target proteins, Cas and Fyb. We used the substrate-binding domain of YopH to affinity purify tyrosine-phosphorylated target proteins from lysates of J774A.1 macrophages. Protein microsequencing identified p55 as murine SKAP-HOM. Direct interaction between SKAP-HOM and a catalytically inactive form of YopH was demonstrated in vitro and in macrophages. In addition, we obtained evidence that SKAP-HOM is tyrosine phosphorylated in response to macrophage cell adhesion and that it forms a signalling complex with Fyb. We suggest that dephosphorylation of SKAP-HOM and Fyb by YopH allows yersiniae to interfere with a novel adhesion-regulated signal transduction pathway in macrophages.

The Caenorhabditis elegans SH2 domain-containing protein tyrosine phosphatase PTP-2 participates in signal transduction during oogenesis and vulval development.

Src homology-2 (SH2) domain-containing protein tyrosine phosphatases (SHPs) have been identified as either positive or negative regulators of signaling events downstream of receptor protein tyrosine kinases (R-PTKs). We describe here our characterization of ptp-2, a Caenorhabditis elegans gene that encodes a 668-amino-acid SHP. We isolated a recessive ptp-2 loss-of-function allele, op194, that lacks the conserved protein tyrosine phosphatase catalytic domain by screening for transposon-mediated deletion mutations. Homozygous ptp-2(op194) hermaphrodites exhibit a completely penetrant zygotic semisterile/maternal effect lethal phenotype, characterized by the presence of abnormally large oocytes in the zygotic semisterile animals. These phenotypes indicate that PTP-2 activity is essential for proper oogenesis. Gain-of-function let-60 ras alleles rescued the defects associated with ptp-2(op194), suggesting that LET-60 Ras acts downstream of, or in parallel to, PTP-2 during oogenesis. Although ptp-2 function is not required for normal vulval development, ptp-2(op194) altered significantly the vulval phenotypes caused by mutations in several genes of the inductive signaling pathway. The penetrance of the multivulva phenotype caused by loss-of-function mutations in lin-15, and gain-of-function mutations in let-23 or let-60 ras, was reduced by ptp-2(op194). Moreover, ptp-2(op194) increased the penetrance of the vulvaless phenotype conferred by a weak loss-of-function sem-5 allele. Taken together, our genetic data positions PTP-2 activity downstream of LET-23 in the vulval induction signaling pathway. Although PTP-2 functions to transmit a requisite signal during oogenesis, PTP-2 function during C. elegans vulval cell differentiation appears to be directed at regulating the overall strength of the inductive signal, which may contribute to the quantitative differences in signaling required for the proper specification of the 1 degrees , 2 degrees , and 3 degrees vulval cell fates.

PTP NE-6: a brain-enriched receptor-type protein tyrosine phosphatase with a divergent catalytic domain.

A receptor-type protein tyrosine phosphatase, PTP NE-6, was identified from rat olfactory epithelial cDNA and cloned from a rat brain cDNA library. PTP NE-6 mRNA is abundant in brain and expressed at lower levels in olfactory tissue and adrenal gland. In situ hybridization demonstrates that PTP NE-6 mRNA is expressed throughout the brain, with highest levels in the medial habenula and at intermediate levels in layer IV of cortex, medial geniculate nucleus, inferior colliculus, hypothalamus, and thalamus. The predicted amino acid sequence demonstrates that PTP NE-6 contains a single catalytic domain that diverges from the consensus protein tyrosine phosphatase catalytic domain by expressing an aspartate instead of the conserved alanine residue in the catalytic site. Recombinantly expressed PTP NE-6 does not exhibit detectable phosphatase activity. Upon mutation of the aspartate to the consensus alanine, phosphatase activity toward p-nitrophenyl phosphate is observable with a k(cat) value of 3.7 s(-1) and a Km of 980 microM. These data demonstrate that the inactivity of native PTP NE-6 toward p-nitrophenyl phosphate is due to the divergent aspartate in the catalytic site and not to variant amino acids within the phosphatase domain.

Cloning and Characterization of Islet Cell Antigen-related Protein-tyrosine Phosphatase (PTP), a Novel Receptor-like PTP and Autoantigen in Insulin-dependent Diabetes

Cloning of the cDNA encoding a novel human protein- tyrosine phosphatase (PTP) called islet cell antigen-related PTP (IAR) predicts a receptor-like molecule with an extracellular domain of 614 amino acids containing a hydrophobic signal peptide, one potential N-glycosylation site, and an RGDS peptide which is a possible adhesive recognition sequence. The 376-amino acid intracellular region contains a single catalytic domain. Recombinant IAR polypeptide has phosphatase activity. Northern blot analysis shows tissue-specific expression of two IAR transcripts of 5.5 and 3. 7 kilobases, which are most abundant in brain and pancreas. The IAR PTP is homologous in its intracellular region to IA-2, a putative PTP that is an insulin-dependent diabetes mellitus (IDDM) autoantigen. IAR is also reactive with IDDM patient sera. IAR and IA-2 may distinguish different populations of IDDM autoantibodies since they identify overlapping but nonidentical sets of IDDM patients. Thus IAR is likely to be an islet cell antigen useful in the preclinical screening of individuals for risk of IDDM.

Cloning and expression of PCPTP1 encoding protein tyrosine phosphatase

A novel cDNA encoding PTP (protein tyrosine phosphatase) was cloned from PC12h cells and designated as PCPTP1 (gene encoding PC12 protein Tyr phosphatase). The longest open reading frame (ORF) of this clone encodes a 656-amino-acid (aa) protein with a single PTP catalytic domain. Western blot analysis using a polyclonal Ab (antibody) raised against the cytoplasmic region of PCPTP1 detected two products, a major 65-kDa and minor 42-kDa protein, designated PCPTP1-MFI and PCPTP1-MVQ, respectively, in PC12h cells. These two proteins correspond to the products translated from the second and fifth methionine of PCPTPI, respectively. The bacterially expressed GST::PCPTP1-MVQ fusion protein had phosphatase activity with pNPP (p-nitrophenyl phosphate) as a substrate. Alignment of the aa sequence of PCPTP1-MVQ with those of other PTP showed the highest similarity to STEP and LC-PTP/HePTP, with 54 and 51 % identity, respectively. Northern blot analysis showed only one 3.9-kb transcript in PC12h cells, indicating that PCPTP1 corresponds to this 3.9-kb transcript. The 3.9-kb PCPTPI mRNA was detected in the brain and adrenal gland, but not in other non-neuronal tissues in adult rats. Two other transcripts of 3.3 and 1.7 kb were also detected in brain. NGF (nerve growth factor) and glucocorticoid are known to bimodally regulate the cell fate decision of sympathoadrenal precursors like PC12 cells, with NGF promoting the neuronal phenotype and glucocorticoid promoting the chromaffin phenotype. Still, both agents decreased the level of PCPTPI mRNA in PC12h cells. Therefore, it is likely that the decrease in the level of PCPTP1 mRNA might be associated or correlated with cell differentiation in PC12h cells.

Molecular cloning and tissue-specific RNA processing of a murine receptor-type protein tyrosine phosphatase.

The molecular cloning of a murine receptor-type protein tyrosine phosphatase, termed PTP NU-3, with an extracellular cell-adhesion-molecule-like domain is reported. NU-3 was isolated from 11.5-day total mouse embryonic RNA by reverse-transcriptase PCR using degenerate oligonucleotides flanking the conserved protein tyrosine phosphatase catalytic domain. This produced a 280-bp DNA probe which was subsequently employed to screen a mouse embryonic kidney library. Several overlapping cDNA clones were isolated, collectively forming a cDNA of 6.0 kb that encodes a putative 211-kDa protein. Northern-blot analysis of total RNA from adult and embryonic mouse tissues indicates the existence of two major PTP NU-3 transcripts of approximately 6 kb and 7 kb. Both messages are expressed predominantly in brain tissues and neuronal-derived cell lines, although detectable levels of the 7-kb message were found in other non-neuronal tissues. We have identified a unique 132-bp exon segment that is present in the 7-kb message but is completely absent in the 6-kb transcript, suggesting tissue-specific levels of expression and RNA processing. Analysis of the amino acid sequence encoded by the 132-bp segment reveals that it completes a partial fibronectin type-III element resulting in a protein with a total of nine such elements. Bacterial expression of the two catalytic domains demonstrated that only the first domain possesses enzymic activity towards a tyrosine phosphorylated substrate.

Molecular cloning of a novel protein-tyrosine phosphatase containing a membrane-binding domain and GLGF repeats

A full-length cDNA encoding a novel cytosolic protein-tyrosine phosphatase (PTP), PTP-BAS, was cloned from human basophils. Due to in-frame deletions in the coding region, PTP-BAS exists in three isoforms: 7,455 bp (2,485 aa) for type 1, 7,398 bp (2,466 aa) for type 2 and 6,882 bp (2,294 aa) for type 3. All three isoforms contain a single PTP catalytic domain at the carboxyl termini as well as two distinct structural sequences. Amino terminal sequences of 300 amino acids are homologous to membrane-binding domains of eytoskeleton-associated proteins. Three 90 amino acid internal repetitive sequences are homologous to the GLGF repeats found in guanylate kinase proteins. PTP-BAS was expressed in various human tissues, especially highly in the kidney and lung. Interestingly, the BAS mRNA level in the fetal brain was remarkably high.

Cloning, Expression and Mutational Analysis of SH-PTP2, Human Protein-Tyrosine Phosphatase

A human cDNA clone encoding a nonreceptor protein-tyrosine-phosphatase (PTP) has been isolated and sequenced. The 2.1 kilobase pair cDNA encodes for a 593 amino acid protein that contains a single tyrosine phosphatase catalytic domain at the C-terminus. At the N-terminus the protein has two adjacent copies of Src homology region (SH2 domain) which show 61% and 73% identity at the amino acid level to the SH2 domains of the human PTP1C and Drosophila corkscrew protein, respectively. The overall homology between SH-PTP2 and PTP1C or to corkscrew protein is 58%. When this protein (or its catalytic domain) was expressed in E. coli as a glutathione-S-transferase fusion protein tyrosine-phosphatase activity was detected in bacterial cell extracts. Site-directed mutation made at the conserved cysteine (459) residue to serine within the highly conserved VHCXAGXXR sequence in the PTP catalytic domain resulted in complete loss of enzymatic activity demonstrating the importance of this cysteine residue in catalysis. Northern blot analysis showed that SH-PTP2 is expressed as a 6.5 kilobase mRNA in a number of fetal and adult human tissues and cell lines. The highest levels of its mRNA were detected in fetal brain and in adult heart tissue. The identification of SH-PTP2 along with PTP1C and corkscrew protein suggest that there exist a family of nonreceptor PTP containing SH2-domain which will participate in specific signal transduction pathways involving tyrosine phosphorylation-dephosphorylation.

Cloning and characterization of a human cDNA encoding a novel putative cytoplasmic protein-tyrosine-phosphatase

We have cloned and characterized a human cDNA encoding a new member of the family of cytosolic type protein-tyrosine-phosphatase (PTP), designated as PTPG1, from an adult colon tissue cDNA library by using the PCR product as probe. We obtained 5 cDNA clones, which cover the predicted open reading frame encoding a 88-kDa protein composed of 780 amino acids, and it had no apparent signal or transmembrane sequences, suggesting that it is a cytosolic protein. The N-terminal region had a PTP catalytic domain that is 30–40% identical to previously reported human PTPs. This revealed that the enzyme composes an additional family of human PTPs. PTPG1 was characterized by a long non-enzymatic domain located at the C-terminus, including PEST sequences which are characteristic for short half-life proteins in eukaryotes. Northern blot analysis of PTPG1 mRNA showed a 4.6-kb transcript that was detected in a wide variety of cell lines to suggest its extensive expression.