Showing papers on "Protein A published in 1996"

Fluid Flow Rapidly Activates G Proteins in Human Endothelial Cells: Involvement of G Proteins in Mechanochemical Signal Transduction

Abstract: Fluid shear stimulates endothelial cells, with the external hemodynamic forces transduced across the plasma membrane to modulate intracellular events. We report the first direct evidence that identifies specific GTP binding proteins (G proteins) activated within 1 second of flow onset, representing one of the earliest mechanochemical signal transduction events reported to date in shear-stimulated endothelium. A nonhydrolyzable GTP photoreactive analogue, azidoanilido [α-32P]GTP (AAGTP), allowed irreversible labeling of flow-stimulated G proteins, with two protein bands (42 kD and 31 kD) identified in human umbilical vein endothelial cells (HUVECs) subjected to laminar flow (10 dyne/cm2) in a parallel-plate flow chamber. Immunoprecipitation of labeled whole-cell lysates identified the specific G-protein subunits Gαq/α11 and Gαi3/αo as being activated by flow. Endothelial cell membrane vesicles were sheared in a cone-and-plate viscometer, with the 42-kD protein band labeled by AAGTP, but the 31-kD protein a...

Protein a mimetic peptide ligand for affinity purification of antibodies

Abstract: A peptide mimicking protein A for its ability to recognize the Fc immunoglobulin portion has been identified through screening of a synthetic multimeric peptide library. Screening of the multimeric library, composed of randomized synthetic tripeptide tetramers, has been carried out using a very simple assay, measuring the library ability to interfere with the interaction between protein A and biotinylated immunoglobulins, monitored on solid phase using an enzyme-linked immunosorbent assay format. The tetrameric tripeptide identified after three screening cycles was produced in larger amounts and then immobilized in high yield on preactivated solid support for the preparation of affinity columns, which proved useful for a very convenient one-step purification of antibodies directly from crude sera. Antibody purity after affinity purification was close to 95 per cent, as determined by densitometric scanning of sodium dodecyl sulphate-polyacrylamide gel electrophoresis gels of purified fractions, and up to 2 mg of antibody could be purified from 1 ml of peptide-derivatized affinity support. The ligand was stable to treatment with a vast array of sanitation agents, such as ethanol and 0.1 M sodium hydroxide, and to repeated use, thus making the ligand applicability extremely attractive for the purification of monoclonal antibodies for therapeutic use. Column binding selectivity was similar to that of protein A-affinity columns, since immunoglobulin G from several sources (rabbit, goat, sheep, mouse) was conveniently purified, with no detection of leaked ligand fragments in the purified preparations.

High resolution analysis of the readthrough domain of beet necrotic yellow vein virus readthrough protein: a KTER motif is important for efficient transmission of the virus by Polymyxa betae.

Abstract: The 5′-terminal cistron of beet necrotic yellow vein furovirus RNA 2 encodes the 21 kDa major viral coat protein and terminates with an amber stop codon which can undergo suppression to give rise to a 75 kDa readthrough (RT) protein referred to as P75. P75 is a minor component of virions and the 54 kDa RT domain following the coat protein sequence is important both for virus assembly and transmission by the fungal vector Polymyxa betae. To better define the regions of the RT domain involved in these two steps, RNA 2 transcripts encoding different in-frame RT domain deletion mutants were tested for their ability to form virions when inoculated to plants with the other viral RNAs and to be fungus-transmitted. All deletions in the N-terminal half of the RT domain interfered with virus assembly and partially or completely inhibited fungus transmission. A 411 nucleotide deletion within the C-terminal half of the RT domain did not inhibit assembly but blocked fungus transmission of the virus. Alanine scanning mutagenesis within the aforesaid 411 nucleotide subdomain identified a peptide motif (KTER) which is important for the fungus transmission process.

A hemoglobin-binding outer membrane protein is involved in virulence expression by Haemophilus ducreyi in an animal model.

Abstract: Haemophilus ducreyi exhibits a requirement for exogenously supplied heme for aerobic growth in vitro. Nine of ten wild-type isolates of H. ducreyi were shown to contain a readily detectable hemoglobin-binding activity. Spontaneous hemoglobin-binding-negative mutants of two of these wild-type isolates lost the ability to express an outer membrane protein with an apparent molecular mass of approximately 100 kDa. Similarly, the single wild-type isolate that lacked the ability to bind hemoglobin also appeared to lack expression of this same 100-kDa protein. A monoclonal antibody (5A9) to this 100-kDa protein was used to identify a recombinant clone which possessed an H. ducreyi chromosomal fragment containing the gene encoding the 100-kDa protein; this protein was designated hemoglobin utilization protein A (HupA). Nucleotide sequence analysis of the hupA gene revealed that the predicted protein, with a calculated molecular mass of 108 kDa, was similar to TonB-dependent outer membrane proteins of other bacteria. Increasing the concentration of heme in the growth medium resulted in decreased expression of the HupA protein. Mutant analysis was used to prove that the HupA protein was essential for the utilization by H. ducreyi of both hemoglobin and hemoglobin-haptoglobin as sources of heme in vitro. In addition, it was found that an isogenic hupA mutant was less virulent than the wild-type parent strain in the temperature-dependent rabbit model for dermal lesion production by H. ducreyi.

Cell wall sorting of lipoproteins in Staphylococcus aureus.

Abstract: Many surface proteins are thought to be anchored to the cell wall of gram-positive organisms via their C termini, while the N-terminal domains of these molecules are displayed on the bacterial surface. Cell wall anchoring of surface proteins in Staphylococcus aureus requires both an N-terminal leader peptide and a C-terminal cell wall sorting signal. By fusing the cell wall sorting of protein A to the C terminus of staphylococcal beta-lactamase, we demonstrate here that lipoproteins can also be anchored to the cell wall of S. aureus. The topology of cell wall-anchored beta-lactamase is reminiscent of that described for Braun's murein lipoprotein in that the N terminus of the polypeptide chain is membrane anchored whereas the C-terminal end is tethered to the bacterial cell wall.

Stimulation of natural interferon-alpha/beta-producing cells by Staphylococcus aureus.

Abstract: Human peripheral blood mononuclear cells (PBMCs) produced high levels of antiviral activity, as determined by bioassay, when stimulated by Staphylococcus aureus Cowan I (SAC) and E. coli. Specific immunoassays demonstrated the presence of both IFN-alpha and gamma and, for SAC, also low levels of IFN-beta. The frequencies of SAC-induced IF N-alpha-producing cells (IPCs) were up to 1-2 per 10(3) PBMCs. These IPCs expressed the HLA-DR and CD4 antigens but not CD3, CD14, or CD19, thus resembling the natural IFN-alpha-producing cells (NIPC). The SAC was more efficient as IFN inducer when heat killed than when streptomycin inhibited. The SAC was inhibitory to virally induced IFN-alpha responses, in particular when streptomycin inhibited. Both pronase treatment and mechanical disruption of SAC cells abolished their capacity to induce IFN-alpha production. Staphylococcal strains lacking or expressing low levels of protein A (SpA) showed a decreased ability to induce IFN-alpha production. However, purified SpA did not itself induce IFN-alpha. Possibly, SpA together with other bacterial surface proteins is important for the capacity of SAC to induce IFN-alpha production in NIPC.

Methods and means for targeted gene delivery

Abstract: A method for producing viral gene delivery vehicles which can be transferred to pre-selected cell types by using targeting conjugates. The gene delivery vehicles comprise: 1) the gene of interest; and 2) a viral capsid or envelope carrying a member of a specific binding pair, the counterpart of which is not directly associated with the surface of the target cell. These vehicles can be rendered unable to bind to their natural cell receptor. The targeting conjugates include the counterpart member of the specific binding pair, linked to a targeting moiety which is a cell-type specific ligand (or fragments thereof). The number of the specific binding pair present on the viral vehicles can be, for example, an immunoglobulin binding moiety (e.g., capable of binding to a Fc fragment, protein A, protein G, FcR or an anti-Ig antibody), or biotin, avidin or streptavidin. The virus' outer membrane or capsid may contain a substance which mediates entrance of the gene delivery vehicle into the target cell. Due to the specificity of the ligand, the binding pair's high affinity, and the gene delivery vehicle's inability to be targeted when used alone, the universality of the method for gene delivery, together with its high cell type selectively can be achieved by using various targeting conjugates.

Detection of Protein A Produced by Staphylococcus aureus with a Fiber-optic-based Biosensor

Abstract: Staphylococcus aureus is a pathogen important in causing human infections and intoxication. A sensitive fiber-optic that produces evanescent waves was developed for the detection of protein A, a product secreted only by S. aureus. In the immunosensor, a 40-mV argon-ion laser that generated laser light at 488 nm was used together with plastic optical fiber and antibodies to protein A were physically adsorbed onto the fiber. The principle of the detection involved a sandwich immunoassay with fluorescein isothiocyanate conjugated with anti-(protein A) immunoglobulin G to produce signals of the antigen-antibody reaction. The detection limit was 1 ng of protein A per milliliter. The fiber-optic immunosensor could be used for rapid and specific detection of S. aureus in clinical specimens and foods.

Peptide variants of protein A

Abstract: Z domain variants of staphylococcal protein A have significantly reduced size but possess IgG-binding affinity equivalent to the wild type Z domain. These Z domain variants are suitable for use in affinity chromatography purification of proteins and in the treatment of staphylococcic diseases.

Isotype and antibody specificity of spontaneously formed immunoglobulins in pig fetuses and germ-free piglets: production by CD5− B cells

Abstract: Pig fetuses, colostrum-deprived newborns and germ-free (GF) piglets, animals in which B-cell development is not influenced by maternal regulatory factors, were employed to study the occurrence and specificity of natural antibodies (NAb). Serum immunoglobulins of all isotypes were found in 44-day-old fetuses (the gestation period in pigs lasts 114 days) and their level, with predominating IgM, was increased during fetal ontogeny. In sera of fetuses at the end of embryonic life as well as of newborns and older GF piglets, antibody activity against autoantigens (thyroglobulin, hormones, ssDNA), phylogenetically conserved proteins (myosin), haptens (trinitrophenyl; TNP) and bacterial components (Escherichia coli O86, tetanic anatoxin) was detected by enzyme-linked immunosorbent assay. The antigen-biding activity of IgM NAb increased after isolation of the serum immunoglobulins on a Staphylococcus Protein A (SPA)-Sepharose column. IgM reactivity similar to that detected in serum was found in supernatants from polyclonally stimulated cultures of spleen of 8- and 12-day-old GF piglets. Pig fetal liver IgM+ B cells, which were able to produce IgM after polyclonal stimulation, did not express the CD5 molecule. Our results indicate that pig preimmune repertoire is comparable to that described in humans and mice, although in contrast to these species pig B-1 cells do not express CD5.

Purification and characterisation of a plasmin-sensitive surface protein of Staphylococcus aureus

Abstract: Certain methicillin-resistant Staphylococcus aureus strains contain a 230-kDa cell-wall protein which is not present on the surface of other staphylococci. The presence of this 230-kDa protein is associated with a negative test result in commercial assays designed to detect fibrinogen-binding proteins and/or protein A on the staphylococcal surface. We have purified and partially characterised the 230-kDa protein from a lysostaphin digest of a non-agglutinating methicillin-resistant S. aureus strain. Partial amino acid sequence data obtained from the purified protein did not reveal any significant similarities to known proteins which indicates that the protein is novel. The 230-kDa protein was very sensitive to proteolysis; soluble plasmin, or plasmin formed on the bacterial-cell surface, rapidly degraded the 230-kDa protein to a 175-kDa form. The finding that the 230-kDa protein bound to lectins allowed its purification by affinity chromatography on immobilised wheat germ agglutinin. Furthermore, the degradation of the 230-kDa protein was associated with an increased adherence of non-agglutinating methicillin-resistant S. aureus cells to solid-phase fibronectin, fibrinogen or IgG.

Inhibition of Immunoglobulin Production In Vitro by IgG and F(ab′)2 Fragments, but not by the Fc Portion

Abstract: Antibody-secreting B cells were measured as plaque-forming cells (PFC) in a modified haemolysis-in-gel assay, using protein A coupled sheep erythrocytes as targets. Human lymphocytes from blood (PBL), bone marrow or spleen were stimulated in vitro by various polyclonal B-cell activators and incubated with intravenous immunoglobulin (IVIG) or peptide fragments of IVIG. IgG and IgM production from PBL and bone marrow cells, measured as PFC, was inhibited more than 50% by IVIG 2.5 mg/ml, compared to controls without IVIG. Inhibition of the IgG and IgM response of spleen cells by IVIG varied depending on the stimuli. Using Staphylococcus aureus protein A (SPA), inhibition was almost 90% (P < 0.001). The inhibition of the IgG and IgM responses to lipopolysaccharide from Escherichia coli (LPS) were 70% (P < 0.01) and 28% (P < 0.05), respectively. IgG stimulation by pokeweed mitogen (PWM) was inhibited by 57% (P < 0.01), but the IgM response was inhibited only by the higher IVIG concentration of 5.0 mg/ml. In mixed lymphocyte cultures of spleen cells, IgG and IgM production were inhibited by more than 60% (P < 0.05). The effect of IgG, IgG-F(ab')2 and IgG-Fc on LPS or PWM-stimulated spleen cells were compared, using equimolar concentrations of the various preparations. IgG- and IgM-producing PFC were significantly (P < 0.05) inhibited in a dose-dependent fashion by IgG and F(ab')2, but not by Fc. LPS-induced IgG and IgM production was inhibited also when IgG and F(ab')2 were added up to 48 h after the stimulator. A comparison of IgG, F(ab')2 and Fc products from different companies showed that all IgG and F(ab')2 preparations significantly inhibited IgG and IgM production of LPS-stimulated spleen cells. No significant inhibition was obtained with any of the purified Fc products.

Expression of a bifunctional chimeric protein A-Vargula hilgendorfii luciferase in mammalian cells.

Abstract: We have designed and constructed a novel chimeric protein that consisted of a single domain of protein A and luciferase derived from sea-firefly Vargula hilgendorfii with the goal of obtaining a heterofunctional immunological tool. The structural gene of luciferase was fused to the 3' terminus of the D domain gene of protein A with/without a short linker of five amino acids. The resulting constructs under the transcriptional regulation of the Rous sarcoma virus (RSV) promoter, were expressed transiently in simian COS-1 and stably in Chinese hamster ovary (CHO) cells. The properties of the resultant chimeric protein were characterized. The results indicated that the dual properties of the chimeric protein could be retained only after the introduction of a linker of (Gly)4 Ser between the two conjugated moieties. Moreover, the chimeric protein was found to retain at least 50% of the specific activity as compared with the non-fused luciferase. The future prospect of the usage of this chimeric protein in the field of diagnostics was further evaluated by performing bioluminescent immunoassays.

High efficiency tissue specific compound delivery system using streptavidin-protein a fusion protein

Abstract: The invention relates to a method of delivering toxins or nucleic acids into specific cell types and to the complexes for the practice of the method. According to the invention, an antibody that recognizes a cell surface antigen is non-covalently bound to the antibody binding site of a ST-PA fusion protein; a biotinylated toxin or nucleic acid is bound to the biotin-binding site. In an alternative embodiment, the toxin or nucleic acid can be bound to a third biotinylated molecule, an adapter, which is bound to the biotin-binding site.

A cellular protein activates the sequence-specific DNA-binding of p53 by interacting with the central conserved region.

Abstract: Mutational inactivation of the p53 gene product is one of the most common genetic aberations so far identified in human cancers. The p53 protein suppresses the transformed phenotype by transactivation or repression of genes involved in cell growth control. Missense mutations in the p53 protein coding sequence observed in human cancers are clustered within a central conserved (conformational) domain spanning amino acid residues 100-300 of a total of 393. Using the conformational domain of p53 fused with protein A, we have shown that the p53 conformational domain possesses Zn+2-dependent, sequence-specific DNA-binding activity. In addition to binding DNA, this domain interacts with at least five cellular proteins ranging in sizes from 30K to 90K M(r) and with the SV40 large T antigen viral oncoprotein. We investigated these cellular proteins for their modulatory effects on the sequence-specific DNA binding activity of full-length wild-type p53. A mixture of p53 conformational domain-binding proteins in bulk enhanced the DNA-binding activity of p53 greater than two-fold. Selective elution of the p53-binding proteins from the p53 hybrid protein by using a sequential step-wise NaCl gradient implicated one protein of 35K M(r) as contributing to a greater than four-fold activation of p53 DNA-binding activity. A p53 conformational domain protein containing a tumor-derived mutation at amino acid 175 failed to associate with the 35K M(r) protein. We propose that proteins interacting with the conformational domain of wild type p53 regulate the DNA-binding activity of p53, thus providing a biochemical basis for the alterations in its function induced by point mutations.

Transient expression of a mitochondrial precursor protein - A new approach to study mitochondrial protein import in cells of higher eukaryotes

Abstract: In order to study mitochondrial protein import in the context of whole cell metabolism, we have used the transfection technique based on Semliki Forest virus (SFV) to express a mitochondrial precursor protein within BHK21 cells and human fibroblasts. Recombinant SFV particles mediate a highly efficient, transient transfection of higher eukaryotic cells. The mitochondrial precursor protein used is a fusion protein consisting of the mitochondrial targeting sequence of Neurospora crassa ATPase subunit 9 and mouse dihydrofolate (H2folate) reductase. Transfected BHK21 cells synthesized substantial amounts of subunit-9-H2folate-reductase. Immunofluorescence staining revealed that the protein colocalized with the mitochondria. The precursor protein was processed to the intermediate and mature form, implying that is was successfully imported into the mitochondrial matrix. Import was dependent on a proton gradient across the mitochondrial membranes since uncoupling of oxidative phosphorylation inhibited the process. The mature-sized protein was folded into a protease-resistant conformation. These results indicate that, in mammalian cells, transport of the precursor subunit-9-H2folate-reductase into mitochondria and its subsequent maturation occurs in a similar way as in lower eukaryotes. Import and processing of the fusion protein proceeded very rapidly in BHK21 cells but were substantially slower in human fibroblasts. SFV-mediated transfection proved to be excellently suited to study protein import into mitochondria of living cells and is probably applicable to transport studies with other organelles as well. The approach could also be helpful in the diagnosis of hereditary disorders or organelle protein import.