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I Clark-Lewis

Publications and source records attributed to I Clark-Lewis.

At least 91 records · Page 5Linked to original sources
PubMed1995

Non-radioactive method to measure CD45 protein tyrosine phosphatase activity isolated directly from cells.

Preparation of radioactive phosphorylated substrates is laborious, yields a limited amount of substrate with a short half-life and generates a low percentage of phosphorylated product which then has to be separated from non-phosphorylated material. These factors limit the usefulness of radioactive phosphorylated substrates in phosphatase assays and prohibit their use for kinetic analysis, which often requires large amounts of substrate. An alternative method for the kinetic analysis of purified or recombinant soluble phosphatases uses the malachite green reagent which can detect nanomoles of phosphate released from chemically synthesized phosphorylated peptides. In this report we describe a rapid and sensitive non-radioactive method that can be used to measure protein tyrosine phosphatase (PTP) activities of both transmembrane and soluble phosphatases immunoprecipitated directly from cells. This colorimetric microassay is performed in 96 well microtitre plates and can reliably detect 100 pmol of free phosphate released, using a standard microplate reader. The phosphatase activity of CD45, a transmembrane PTP, was determined from as few as 1 x 10(4) lymphoid cells. The development of this colorimetric assay to measure immunoprecipitated CD45 PTP activity isolated from very small numbers of cells has general applicability for other PTPs and will help identify the cellular situations and conditions that result in changes in PTP activity.

Amino Acid Sequence↗
PubMed1995

Isolation of a gene encoding a developmentally regulated T cell-specific protein with a guanine nucleotide triphosphate-binding motif.

In this study, we describe a novel full length cDNA clone designated Tgtp that encodes a predicted 415-amino acid a T cell-specific guanine nucleotide triphosphate-binding protein (TGTP) bearing the characteristic motifs of a guanine nucleotide triphosphate (GTP) binding protein. Tgtp is expressed preferentially, if not exclusively, in T cells, and is up-regulated in both unfractionated and in purified CD4+8+ thymocytes upon TCR cross-linking. In contrast, expression of Tgtp is peripheral T cells is maintained at relatively high levels and is not grossly affected by TCR cross-linking. Antiserum generated against synthetic peptides from the predicted TGTP amino acid sequence recognized a single protein with a molecular mass of approximately 50 kDa, corresponding well with the computed molecular mass of 47 kDa. The only known relative of Tgtp is MUSGTP, which is reportedly expressed in B cells and bears a GTP binding motif. Thus, the discovery of Tgtp resolves a subfamily of molecules with GTP binding motifs and apparent lymphoid lineage-restricted expression. Given the restricted expression pattern in T cells, the up-regulated expression observed in response to TCR signaling in immature thymocytes, and the presence of the motifs characteristic of GTP binding proteins, we suggest that TGTP may have an important function in T cell development and/or T cell activation.

Amino Acid Sequence↗
PubMed1995

Antagonists of monocyte chemoattractant protein 1 identified by modification of functionally critical NH2-terminal residues.

Monocyte chemoattractant protein (MCP)-1 analogues were designed to determine the role of the NH2-terminal region in structure and function. The NH2-terminal residue was important for function and receptor binding, as it could not be deleted or extended. However the NH2-terminal pyroglutamate residue of the wild type was not essential as it could be replaced by several other noncyclic amino acids without loss of activity. Residues 7-10 were essential for receptor desensitization, but were not sufficient for function, and the integrity of residues 1-6 were required for functional activity. A peptide corresponding to MCP-1, 1-10 lacked detectable receptor-binding activities, indicating that residues 1-10 are essential for MCP-1 function, but that other residues are also involved. Several truncated analogues, including 8-76, 9-76, and 10-76, desensitized MCP-1-induced Ca2+ induction, but were not significantly active. These analogues were antagonists of MCP-1 activity with the most potent being the 9-76 analogue (IC50 = 20 nM) The 9-76 specifically bound to MCP-1 receptors with a Kd of 8.3 nM, which was three-fold higher than MCP-1 (Kd 2.8 nM). The 9-76 analogue desensitized the Ca2+ response to MCP-1 and MCP-3, but not to other CC chemokines, suggesting that it is MCP receptor specific. The availability of these compounds will be helpful in evaluating MCP receptor antagonists as anti-inflammatory therapeutics.

Amides↗
PubMed1995

Structure-activity relationships of chemokines.

Structural analysis of chemokines has revealed that the alpha/beta structural-fold is highly conserved among both the CXC and CC chemokine classes. Although dimerization and aggregation is often observed, the chemokines function as monomers. The critical receptor binding regions are in the NH2-terminal 20 residues of the protein and are the least ordered in solution. The flexible NH2-terminal region is the most critical receptor binding site and a second site also exists in the loop that follows the two disulfides. The well-ordered regions are not directly involved in receptor binding but, along with the disulfides, they provide a scaffold that determines the conformation of the sites that are critical for receptor binding. These general requirements for function are common to all the chemokines. For the CC chemokines, receptor activation and receptor binding regions are separate within the 10 residue NH2-terminal region. This has allowed identification of high affinity analogs that do not activate the receptor and are potent antagonists.

Amino Acid Sequence↗
PubMed1994

Solution structure of GRO/melanoma growth stimulatory activity determined by 1H NMR spectroscopy.

The three-dimensional solution structure of the growth-related protein-alpha/melanoma growth stimulatory activity (GRO/MGSA) has been solved by two-dimensional 1H nuclear magnetic resonance spectroscopy. The GRO/MGSA monomer consists of an NH2-terminal loop, a three-stranded antiparallel beta-sheet, and a COOH-terminal alpha-helix. Dimerization, which is apparent under the experimental conditions used (2 mM, pH 5.10, 30 degrees C), results in a six-stranded antiparallel beta-sheet and a pair of helices with 2-fold symmetry. While the basic fold is similar to that seen for interleukin-8 (IL-8) (Clore, G. M., Appella, E., Yamada, M., Matsushima, K., and Gronenborn, A. M. (1990) Biochemistry, 29, 1689-1696), there are differences in the ELR motif (residues 6-8), the turn involving residues 31-36, which is linked to the NH2-terminal region through the 9-35 disulfide bond. The most significant differences are in the NH2-terminal loop (residues 12-23). In IL-8, all the corresponding regions have been shown to be required for receptor binding (Clark-Lewis, I., Dewald, B., Loetscher, M., Moser, B., and Baggiolini, M. (1994) J. Biol. Chem. 269, 16075-16081). The structural differences thus have been identified between GRO/MGSA and IL-8 could contribute to their different receptor binding specificities.

Amino Acid Sequence↗
PubMed1994

Synthesis of proteins by native chemical ligation.

A simple technique has been devised that allows the direct synthesis of native backbone proteins of moderate size. Chemoselective reaction of two unprotected peptide segments gives an initial thioester-linked species. Spontaneous rearrangement of this transient intermediate yields a full-length product with a native peptide bond at the ligation site. The utility of native chemical ligation was demonstrated by the one-step preparation of a cytokine containing multiple disulfides. The polypeptide ligation product was folded and oxidized to form the native disulfide-containing protein molecule. Native chemical ligation is an important step toward the general application of chemistry to proteins.

Amino Acid Sequence↗
PubMed1994

Influence of charge, charge distribution, and hydrophobicity on the transport of short model peptides into liposomes in response to transmembrane pH gradients.

Previous work [Chakrabarti et al. (1992) Biophys. J. 61, 228-234] has shown that basic amino acids and peptides, in which the C-terminal carboxyl groups have been modified to form amides or methyl esters, can be rapidly and efficiently accumulated into large unilamellar vesicle (LUV) systems in response to transmembrane pH gradients (delta pH, inside acidic). In this work, the ability of small (di and tri) peptides, composed exclusively of basic (lysine) and hydrophobic (tryptophan) amino acids, to accumulate into LUV systems in response to delta pH has been investigated. In the case of the dipeptides Trp-Lys-amide and Lys-Trp-amide, remarkable differences in the rate constants associated with net transport were observed. In EPC:cholesterol LUV systems exhibiting a delta pH of 3 units (pHi = 4.0; pHo = 7.0), for example, the rate constant for the uptake of Lys-Trp-amide is some 5 x 10(3) faster than for Trp-Lys-amide. Activation energies associated with the uptake also varied from 24 (Lys-Trp) to 29 kcal/mol (Trp-Lys). Related effects were observed for the tripeptides composed of one lysine and two tryptophan residues; however, the differences in rate constants were less sensitive to amino acid sequence. It is concluded that different charge distributions in short peptides of identical amino acid composition can strongly influence the ability of these groups to associate with and permeate across lipid bilayers. These observations may have relevance to the ability of basic peptides, such as signal sequences and peptide hormones, to translocate across biological membranes.

Amino Acid Sequence↗
PubMed1994

Structural requirements for interleukin-8 function identified by design of analogs and CXC chemokine hybrids.

Structure-activity relationships of human interleukin-8 (IL-8) were probed using chemically synthesized analogs with single or double amino acid substitutions, as well as hybrids derived by substituting IL-8 regions into IP10, a related protein that lacks IL-8 activity. The analogs were tested for functional activity by measuring induction of elastase release from human neutrophils and competition for binding of radiolabeled IL-8. The hybrid studies indicated that Gly31 and Pro32, as well as the NH2-terminal region from IL-8 are required to convert IP10 into a fully functional protein, suggesting that these elements are critical for IL-8 activity. Both disulfide bridges, linking residue 7 to 34 and residue 9 to 50, were critical for function, as shown by substituting the cysteine pairs with alpha-aminobutyric acid. Single conservative substitutions were generally accepted into the 10-22 region of IL-8, which contrasts with the ELR motif (residues 4-6), previously shown to be essential for activity. The importance of residues within the 10-15 region and the 17-22 region was demonstrated with hybrids. In addition, some of the 4-22 residues have structural roles that may be important; for example, Tyr13, Phe17, and Phe21 are involved in aromatic interactions in the IL-8 structure, and are also moderately sensitive to modification. Except for Cys50, the results argue against a role for the 36-72 region, including the COOH-terminal alpha-helix, in receptor binding. We conclude that the disulfide bridges and 30-35 turn provide a structural scaffold for the NH2-terminal region which includes the primary receptor-binding site (the ELR motif) and secondary binding and conformational determinants between residues 10 and 22.

Amino Acid Sequence↗
PubMed1994

1H NMR studies of interleukin 8 analogs: characterization of the domains essential for function.

1H NMR studies were carried out on interleukin 8 (IL-8) analogs in order to probe the structural features that are essential for receptor binding and function. The analogs studied were the chemically synthesized IL-8 (1-72), a series of N-terminally truncated derivatives (4-72, 5-72, and 6-72), and derivatives with single amino acid substitutions (I10A, R6K, and H33A). Previous functional studies have shown that the N-terminal residues, especially the residues at positions 4-6, and the beta turn containing Cys-34, which is disulfide linked to Cys-7, are important for receptor affinity and functional activity [Clark-Lewis, I., Schumacher, C., Baggiolini, M., & Moser, B. (1991) J. Biol. Chem. 266, 23128-23134; Clark-Lewis, I., Dewald, B., Loetscher, M., Moser, B., & Baggiolini, M. (1994) J. Biol. Chem. (in press)]. The 6-72 and R6K analogs also showed properties of an antagonist. Analysis of the 1H NMR parameters such as chemical shifts, amide proton chemical shift temperature coefficients, and NOESY data indicates that the core structure is the same for all these proteins. Small differences were observed in some of the NMR properties for some of the residues in the N-terminal region and the turn containing Cys-34. Detailed analysis suggests that there is no correlation between these differences and observed function. Thus functional differences between the N-terminal analogs are a direct consequence of changes in receptor binding due to substitutions/deletions in the N-terminal sequence and not due to structural changes elsewhere.(ABSTRACT TRUNCATED AT 250 WORDS)

Amides↗
PubMed1994

Neutrophil activation by monomeric interleukin-8.

Interleukin-8 (IL-8), a pro-inflammatory protein, has been shown by nuclear magnetic resonance (NMR) and x-ray techniques to exist as a homodimer. An IL-8 analog was chemically synthesized, with the amide nitrogen of leucine-25 methylated to selectivity block formation of hydrogen bonds between monomers and thereby prevent dimerization. This analog was shown to be a monomer, as assessed by analytical ultracentrifugation and NMR. Nevertheless, it was equivalent to IL-8 in assays of neutrophil activation, which indicates that the monomer is a functional form of IL-8.

Calcium↗
PubMed1994

Both interleukin-8 receptors independently mediate chemotaxis. Jurkat cells transfected with IL-8R1 or IL-8R2 migrate in response to IL-8, GRO alpha and NAP-2.

Neutrophil leukocytes, the target cells for interleukin-8 and related CXC chemokines, bear high numbers of two types of IL-8 receptors (IL-8R1 and IL-8R2). By cDNA transfection Jurkat cell lines were generated that stably express either IL-8R1 or IL-8R2 (J-IL8R1 and J-IL8R2). J-IL8R1 expressed 4,000 +/- 1,000 copies of IL-8R1, and bound IL-8 with high affinity (Kd 1-4 nM) and GRO alpha and NAP-2 with low affinity (Kd 200-500 nM). J-IL8R2 expressed 17,000 +/- 3,000 copies of IL-8R2, and bound all three chemokines with high affinity. Both transfectants showed a similar degree of chemotactic migration after stimulation with IL-8, GRO alpha and NAP-2. All three chemokines were equally potent as attractants of J-IL8R2, whereas IL-8 was 300 to 1,000-fold more potent than GRO alpha or NAP-2 as attractant of J-IL8R1. The potencies, therefore, agree with the affinities of the ligands to IL-8R1 and IL-8R2. Our results demonstrate that both IL-8 receptors function independently, and mediate chemotaxis in response to IL-8 and other CXC chemokines.

Animals↗
PubMed1994

Structure characterization of membrane bound and surface adsorbed protein.

X-ray standing waves (XSW) have been used to study the topology of the protein cytochrome c, bound to a negatively charged model membrane and adsorbed at a metal surface. At the metal surface, cytochrome c forms an hexagonally close-packed monolayer. A similar packing arrangement is observed at the surface of a self-assembled lipid film on silver. The data suggest that cytochrome c maintains its native globular structure upon surface binding and subsequent storage for an extended period. Further, the data are consistent with a protein docking mechanism wherein the heme plane is oriented perpendicular to and with its exposed edge facing the surface. This study demonstrates the utility of XSW as a new and powerful structural tool for investigating membrane- and surface-protein interactions.

Adsorption↗
PubMed1994

Characterization and kinetic analysis of the intracellular domain of human protein tyrosine phosphatase beta (HPTP beta) using synthetic phosphopeptides.

The intracellular domain of human protein tyrosine phosphatase beta (HPTP beta) (44 kDa) was expressed in bacteria, purified using epitope 'tagging' immunoaffinity chromatography, and characterized with respect to kinetic profile, substrate specificity and potential modulators of enzyme activity. A chromogenic assay based on the Malachite Green method was employed for the detection of inorganic phosphate (Pi) released from phosphopeptides by HPTP beta. This assay, modified so as to improve its sensitivity, was adapted to a 96-well microtitre plate format, and provided linear detection between 50 and 1000 pmol of Pi. The cytoplasmic domain of HPTP beta was strongly inhibited by vanadate, molybdate, heparin, poly(Glu, Tyr) (4:1) and zinc ions. In order to explore the substrate preferences of this PTPase, we generated 13-residue synthetic phosphotyrosine-containing peptides that corresponded to sites of physiological tyrosine phosphorylation. HPTP beta demonstrated kcat. values between 76 and 258 s-1 using four different phosphopeptides. The substrate preference of HPTP beta was in the order srcTyr-527 > PDGF-RTyr-740 > ERK1Tyr-204 >> CSF-1RTyr-708 with Km values ranging from 140 microM to greater than 10 mM. The variations in affinity were probably due to differences among the four phosphopeptides compared, particularly with respect to the character of the charged amino acids flanking the phosphotyrosine residue.

Amino Acid Sequence↗
PubMed1994

Characterization of protein tyrosine phosphatase SH-PTP2. Study of phosphopeptide substrates and possible regulatory role of SH2 domains.

The src homology 2 (SH2) domain containing protein-tyrosine-phosphatase SH-PTP2, was over-expressed in Escherichia coli for a kinetic study employing a set of synthetic 13- to 14-mer phosphopeptide substrates. The full-length SH-PTP2 protein, as well as a truncated form, lacking the two amino terminus SH2 domains (SH-PTP2(delta SH2)), exhibited Michaelis-Menten kinetics, and demonstrated striking substrate preferences on phosphopeptides having sequences based on sites of intracellular protein tyrosine phosphorylation. For example, while a KM of 59 microM and kcat/KM of 1.1 x 10(5) were obtained using SH-PTP2(delta SH2) and PDGFRY1021, a phosphorylation site within the platelet-derived growth factor receptor, other peptides revealed no detectable phosphate release. PDGFRY1009, modeled after a sequence identified as an in vivo binding site for SH-PTP2, was also a good substrate for this enzyme. The truncated form, lacking the SH2 domains demonstrated higher catalytic efficiency than the full-length enzyme. Interestingly, soluble SH2 domains were found to inhibit the catalytic activity of SH-PTP2 in a concentration-dependent manner. There was also evidence of a non-phosphotyrosine-mediated association between the two domains. These observations suggested that the SH2 domains have a direct role in regulating the catalytic activity of SH-PTP2.

Amino Acid Sequence↗
PubMed1994

HIV-1 transactivator protein Tat induces proliferation and TGF beta expression in human articular chondrocytes.

The human immunodeficiency virus-1 (HIV-1) protein Tat binds to cell surface antigens and can regulate cellular responses. Tat has similar immunosuppressive effects as transforming growth factor-beta (TGF beta) and both inhibit lymphocyte proliferation. TGF beta is expressed by primary human articular chondrocytes and is their most potent growth factor. The present study analyzed the interactions of TGF beta and HIV Tat in the regulation of human articular chondrocytes. Synthetic or recombinant full-length Tat (1-86) induced chondrocyte proliferation and this was of similar magnitude as the response to TGF beta. Tat peptides that did not contain the RGD motif had similar chondrocyte stimulatory activity as full-length Tat. Among a series of Tat peptides, peptide 38-62 which contains the basic domain was the only one active, suggesting that this region is responsible for the effects on chondrocyte proliferation. Full-length Tat and peptide 38-62 synergized with TGF beta and induced proliferative responses that were greater than those obtained with any combination of the known chondrocyte growth factors. Further characterization of the interactions between Tat and TGF beta showed that Tat increased synthesis and TGF beta activity and TGF beta 1 mRNA levels. The stimulatory effects of Tat and peptide 38-62 on chondrocyte proliferation were reduced by neutralizing antibodies to TGF beta and by TGF beta antisense oligonucleotides. These results identify a virally encoded protein and a synthetic peptide derived from it as novel and potent chondrocyte growth stimuli which act at least in part through the induction of TGF beta.

Base Sequence↗
PubMed1994

Monocyte chemotactic proteins MCP-1, MCP-2, and MCP-3 are major attractants for human CD4+ and CD8+ T lymphocytes.

The responses of lymphocytes to six CC chemokines--MCP-1, MCP-2, MCP-3, MIP-1 alpha, MIP-1 beta, and RANTES--were studied using cloned human CD4+ and CD8+ T cells. All CC chemokines tested induced migration of both types of lymphocytes, whereas two CXC chemokines used as controls, IL-8 and IP-10, were inactive. The monocyte chemotactic proteins (MCP-1, MCP-2, and MCP-3) showed a typically bimodal concentration dependence, and were considerably more effective than MIP-1 alpha, MIP-1 beta, or RANTES. All CC chemokines also induced a rapid and transient rise in cytosolic free Ca2+ in either type of T cell. The rise was prevented by Bordetella pertussis toxin treatment, indicating that G-protein-coupled receptors are involved in signaling. It was most pronounced with MCP-1 and MCP-3, which is in agreement with the efficacy of these chemokines as chemoattractants. The responses to MCP-2, MIP-1 alpha, MIP-1 beta, and RANTES were weaker, and no changes were obtained on stimulation with IL-8 or IP-10. Freshly isolated human blood lymphocytes were also tested, but neither migration nor Ca2+ changes were observed. Low numbers of high-affinity receptors for MCP-1 were found on CD4+ and CD8+ cells ( < 900 per cell, Kd < 1 nM), and desensitization experiments showed that MCP-1, MCP-2, and MCP-3 share receptors. Owing to their superior effectiveness on CD4+ and CD8+ T cells, the monocyte chemotactic proteins could play a major role in the recruitment of activated T lymphocytes.

CD4-Positive T-Lymphocytes↗