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PubMed1981

Interaction of phospholipid vesicles with rat hepatocytes: further characterization of vesicle-cell surface interaction; use of serum as a physiological modulator.

We investigated the interaction of small unilamellar phospholipid vesicle, containing the water-soluble fluorescent dye carboxyfluorescein (CF), with rat hepatocytes in vitro. Fetal calf serum (FCS) was previously shown to interfere with hepatocyte-vesicle interaction using egg-lecithin as a liposomal marker [Hoekstra, D., Scherphof, G (1979): Biochim, biophys, Acta 551, pp. 109-121.] We now demonstrate that FCS affects the binding of intact vesicles to the cell surface, as well as the transfer of individual lipid molecules between vesicles and cells. By contrast, transfer of the entrapped fluorophore from the vesicles to the interior of the cell is unaffected. These observations lead us to suggest that the sites on the surface of the hepatocyte at which stable adsorption, the transfer of vesicle contents, and the transfer of individual phospholipid molecules take place are, at least kinetically, not identical. The potential importance of the inhibitory effect of serum on defined steps in the process of vesicle-cell interaction is emphasized.

Adsorption↗
PubMed1988

Ligand/receptor interactions--the influence of the microenvironment on macroscopic properties. Electrostatic interactions with the membrane phase.

The heterogeneous environment in which ligand/receptor interactions occur often leads to complex binding behaviour. We consider here the ligand/membrane interaction, emphasizing the possibilities of electrostatic modulation of the overall binding characteristics. The binding of Substance P to neutral or negatively charged planar lipid bilayers was monitored using the capacitance minimization technique. The electrostatic attraction to the charged bilayer potentiates the interaction by more than two orders of magnitude and leads to a nonlinearity in the Scatchard plot of bound vs. bulk concentrations. The Boltzmann accumulation factor, along with the direct measurement of the surface potential, provides an easy explanation of the effect. The general importance of electrostatic accumulation (or repulsion) at surfaces is discussed and the concept applied to examples from the literature.

Chemical Phenomena↗
PubMed2005

Apoptosis induced by the toll-like receptor adaptor TRIF is dependent on its receptor interacting protein homotypic interaction motif.

TLRs detect specific molecular features of microorganisms and subsequently engage distinct signaling networks through the differential use of Toll/IL-1R (TIR)-domain-containing adapter proteins. In this study, we investigated the control of apoptosis by the TIR domain-containing adapter proteins MyD88, TIR-domain containing adapter protein (TIRAP), TIR-domain-containing adapter-inducing IFN-beta (TRIF), TRIF-related adapter molecule (TRAM), and sterile alpha motifs and beta-catenin/armadillo repeats (SARM). Upon overexpression, TRIF was the sole TIR-adapter to potently engage mammalian cell death signaling pathways. TRIF-induced cell death required caspase activity initiated by the Fas/Apo-1-associated DD protein-caspase-8 axis and was unaffected by inhibitors of the intrinsic apoptotic machinery. The proapoptotic potential of TRIF mapped to the C-terminal region that was found to harbor a receptor interacting protein (RIP) homotypic interaction motif (RHIM). TRIF physically interacted with the RHIM-containing proteins RIP1 and RIP3, and deletion and mutational analyses revealed that the RHIM in TRIF was essential for TRIF-induced apoptosis and contributed to TRIF-induced NF-kappa B activation. The domain that was required for induction of apoptosis could activate NF-kappa B but not IFN regulatory factor-3, yet the activation of NF-kappa B could be blocked by superrepressor I kappa B alpha without blocking apoptosis. Thus, the ability of TRIF to induce apoptosis was not dependent on its ability to activate either IFN regulatory factor-3 or NF-kappa B but was dependent on the presence of an intact RHIM. TRIF serves as an adaptor for both TLR3 and TLR4, receptors that are activated by dsRNA and LPS, respectively. These molecular motifs are encountered during viral and bacterial infection, and the apoptosis that occurs when TRIF is engaged represents an important host defense to limit the spread of infection.

Adaptor Proteins, Signal Transducing↗
PubMed2000

Reassessment of interactions between hematopoietic receptors using common beta-chain and interleukin-3-specific receptor beta-chain-null cells: no evidence of functional interactions with receptors for erythropoietin, granulocyte colony-stimulating factor, or stem cell factor.

Mice lacking both the gene encoding the shared receptor for granulocyte macrophage-colony-stimulating factor (GM-CSF), interleukin-3 (IL-3), and IL-5 common beta-chain (B(c)) and the gene for the IL-3 specific receptor (BIL3) were generated. This was achieved by targeting the B(c) locus in embryonic stem cells that were heterozygous for a null mutation of BIL3. Cells from mice generated with the doubly targeted embryonic stem cells were unresponsive to all 3 cytokines. Considerable previous data suggested a role for common beta-chain (beta(c)) in modulating signaling of cytokines including erythropoietin (EPO), G-CSF, and stem cell factor (SCF). However, bone marrow cells from mice lacking beta(c) and beta(IL3) showed normal responsiveness to these cytokines. Thus, there was no evidence for a biologically significant interaction between signaling via beta(c) or beta(IL3) and signaling by EPO, G-CSF, or SCF. Previously documented biochemical phenomena, including receptor transmodulation, receptor transphosphorylation, and even direct physical interaction, involving the beta(c)/beta IL-3 receptor systems do not reflect genuine interactions of physiological significance in primary hematopoietic cells. This study provided results that challenge conclusions previously established using a variety of biochemical assays. (Blood. 2000;96:1588-1590)

Animals↗
PubMed1992

Mapping the site(s) of MgATP and MgADP interaction with the nitrogenase of Azotobacter vinelandii. Lysine 15 of the iron protein plays a major role in MgATP interaction.

Nitrogenase binds and hydrolyzes 2MgATP yielding 2MgADP and 2Pi for each electron that is transferred from the iron protein to the MoFe protein. The iron protein alone binds but does not hydrolyze 2MgATP or 2MgADP and the binding of these nucleotides is competitive. Iron protein amino acid sequences all contain a putatitive mononucleotide-binding region similar to a region found in other mononucleotide-binding proteins. To examine the role of this region in MgATP interaction, we have substituted glutamine and proline for conserved lysine 15. The amino acid substitutions, K15Q and K15P, both yielded a non-N2-fixing phenotype when the genes coding for them were substituted into the Azotobacter vinelandii chromosome in place of the wild-type gene. The iron protein from the K15Q mutant was purified to homogeneity, whereas the protein from the K15P mutant could not be purified in its native form. Unlike wild-type iron protein, the purified K15Q iron protein showed no acetylene reduction, H2 evolution, or ATP hydrolysis activities when complemented with wild-type MoFe protein. The K15Q iron protein and the normal iron protein had a similar total iron content and both proteins showed the characteristic rhombic EPR signal resulting from the reduced state of the single 4Fe-4S cluster bridging the two subunits. Unlike the wild-type iron protein, addition of MgATP to the K15Q iron protein did not result in the perturbation necessary to change the EPR signal of its 4Fe-4S center from a rhombic to an axial line shape. Also unlike the wild-type iron protein, addition of MgATP to K15Q iron protein in the presence of the iron chelator, alpha,alpha'-dipyridyl, did not result in a time-dependent transfer of iron to the chelator. Thus, even though the K15Q iron protein contains a normal 4Fe-4S center, it does not respond to MgATP like the wild-type protein. Examination of the ability of the K15Q iron protein to bind MgADP showed no change from the wild-type iron protein, but its ability to bind MgATP decreased to 35% of the wild-type protein. Thus, in A. vinelandii iron protein, lysine 15 is not needed for interaction with MgADP but is involved in the binding of ATP, presumably through charge-charge interaction with the gamma-phosphate. Based on the above data, this lysine appears to be essential for the MgATP induced conformational change of wild-type iron protein that is required for activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine Diphosphate↗
PubMed1992

pH dependence of the interaction between immunogenic peptides and MHC class II molecules. Evidence for an acidic intracellular compartment being the organelle of interaction.

The pH dependence of the interaction between immunogenic peptide and MHC class II was studied both in a direct biochemical binding assay and in a functional Ag presentation assay. The two approaches yielded similar results. All of the peptides tested bound optimally to their relevant MHC class II restriction element at around pH 4.5. Indeed, several of the peptides did not bind at neutral pH. These results demonstrate that Ag under physiologic conditions meet MHC class II in a quite acidic environment. The very acidic pH optimal for peptide-MHC class II interaction is only found intracellularly and most notably in the endosome-lysosome compartment in which Ag processing is thought to occur. Thus, Ag processing and interaction with MHC class II molecules can potentially happen in the very same compartment. This yet undefined acidic compartment would have to contain proteolytic enzymes and MHC class II molecules.

Amino Acid Sequence↗
PubMed2005

Advantage of a baculovirus expression system for protein-protein interaction studies. Involvement of posttranslational phosphorylation in the interaction between wt p53 protein and poly(ADP-ribose) polymerase-1.

We recently observed an interaction between poly(ADP-ribose) polymerase-1 (PARP-1) and the tumor suppressor p53 protein. However, more extensive studies on both proteins, especially those on characterization of their domains involved in the interaction were difficult due to very low expression levels of p53 in mammalian cells. Therefore, we generated recombinant proteins for such studies. To clarify which domains of human PARP-1 and of human wild-type (wt) p53 were involved in this protein-protein interaction, we generated baculoviral constructs encoding full length or distinct functional domains of both proteins. Full length PARP-1 was simultaneously coexpressed in insect cells with full length wt p53 protein or its distinct truncated fragments and vice versa. Reciprocal immunoprecipitation of Sf9 cell lysates revealed that the central and carboxy-terminal fragments of p53 each were sufficient to confer binding to PARP-1, whereas the amino-terminal part harbouring the transactivation functional domain was dispensable. On the other hand, the amino-terminal and central fragments of PARP-1 were both necessary for complex formation with p53 protein. Since the most important features of p53 protein are regulated by phosphorylation, we addressed the question whether its phosphorylation is essential for the binding between the two proteins. Baculovirally expressed wt p53 was post-translationally modified. At least six distinct p53 isomers were resolved by immunoblotting following two-dimensional separation of baculovirally expressed wt p53 protein. Using specific phospho-serine antibodies, we identified phosphorylation of baculovirally expressed p53 protein at five distinct sites. To define the role of p53 phosphorylation, pull-down assays using untreated and dephosphorylated p53 protein were performed. Dephosphorylated p53 failed to bind PARP-1, indicating that complex formation between the two proteins was regulated by phosphorylation of p53. The marked phosphorylation of p53 at Ser392 observed in unstressed cells suggests that the phosphorylated carboxy-terminal part of p53 undergoes complex formation with PARP-1 resulting in masking of the NES and thereby preventing its export.

Animals↗
PubMed1991

The interaction of plasminogen activator inhibitor 1 with plasminogen activators (tissue-type and urokinase-type) and fibrin: localization of interaction sites and physiologic relevance.

Plasminogen activator inhibitor 1 (PAI-1), an essential regulatory protein of the fibrinolytic system, harbors interaction sites for plasminogen activators (tissue-type [t-PA] and urokinase-type [u-PA]) and for fibrin. In this study, anti-PAI-1 monoclonal antibodies (MoAbs) were used to identify interaction sites of PAI-1 with these components. The binding sites of 18 different MoAbs were established and are located on five distinct "linear" areas of PAI-1. MoAbs, binding to two distinct areas of PAI-1, are able to prevent the inhibition of t-PA by PAI-1. In addition, two interaction sites for fibrin were identified on PAI-1. The area located between amino acids 110 and 145 of PAI-1 contains a binding site for both components and its significance is discussed in the context of the t-PA inhibition by fibrin-bound PAI-1. Subsequently, the MoAbs were used to assess the role of platelet-PAI-1 in clot-lysis. An in vitro clot-lysis system was used to demonstrate that clot-lysis resistance is dependent on the presence of activated platelets and that PAI-1 is a major determinant for lysis-resistance. We propose that, upon activation of platelets, PAI-1 is fixed within the clot by binding to fibrin and retains its full capacity to inhibit t-PA and u-PA.

Antibodies, Monoclonal↗
PubMedDate not supplied

[Theoretical studies of the electrostatic interactions in aspartic proteinases, intramolecular interactions in pepsin and penicillopepsin].

A semi-empirical approach has been used to estimate the intramolecular electrostatic interactions in pepsin and penicillopepsin. The pH-dependence of the free energy electrostatic term was calculated, and the pH-dependence of the domain interactions has been estimated. As it was shown, the contribution of electrostatic interactions is rather small for the stabilization of the native structure. At the same time the electrostatic repulsion between domains increases with the increase of pH. The later can be the cause of the alkaline denaturation of pepsin and domain mobility.

Aspartic Acid Endopeptidases↗
PubMed1985

Interaction of French-pressed liposomes with isolated bovine adrenal chromaffin cells. Characterization of the cell-liposome interactions.

Small unilamellar liposomes with an average external diameter of approximately 550 A were prepared by high pressure extrusion in a French press. Liposomes, composed of phosphatidylcholine, phosphatidylserine, and cholesterol at a molar ratio of 7:1:2, were incubated with suspensions of bovine adrenal chromaffin cells. The cell-liposome interactions were characterized using fluorescence and radiotracer techniques. Transfer of the liposomal contents into the cytoplasm was visualized by fluorescence microscopy, using fluorescence-labeled macromolecules, and further documented by flow cytometry with liposome-entrapped 5,6-carboxy-fluorescein. The dose dependence, time course, and temperature dependence of the cell-liposome association, as determined by radioactive labeling both the liposomal membranes and their contents, indicate saturable interaction of the cells with intact liposomes (KappM approximately 5 X 10(-7) M lipid/10(6) cells at 37 degrees C). Using nonexchangeable fluorescent phospholipid analogs, the cell-liposome interactions were characterized by fluorescence resonance energy transfer and by fluorescence recovery after photobleaching. From these latter experiments we conclude that after 1-h incubation of 10(6) cells with 1 microM lipid at 37 degrees C, 30% of the cell-associated liposomes will have fused with the plasma membranes, resulting in the delivery of the contents of approximately 1.25 X 10(5) liposomes into each cell. Thus, liposomal delivery is an effective means to gain access to the cytoplasm and can be exploited to modulate physiological responses from within intact chromaffin cells.

Adrenal Glands↗
PubMed1985

The interaction of human platelet thrombospondin with fibrinogen. Thrombospondin purification and specificity of interaction.

Human platelet thrombospondin (TSP) was purified to homogeneity by chromatography on fibrinogen coupled to cyanogen bromide-activated Sepharose. The yield of TSP was 1.3 mg or approximately 22% of that present in platelet-rich plasma as determined by radioimmunoassay. It analyzed on discontinuous sodium dodecyl sulfate gels as a single band having apparent molecular weights of 180,000 and greater than 400,000 under reducing and nonreducing conditions, respectively. Amino acid analysis gave results similar to previously published values. Antibodies raised in rabbits were monospecific as evaluated by radioimmunoassay. In double immunodiffusion tests, these antibodies gave one line of identity against TSP purified by this procedure and TSP purified by published procedures, confirming the identity of the material isolated. The protein possesses no lectin-like activity. The specificity of the TSP-fibrinogen interaction was investigated. TSP binding to fibrinogen-Sepharose occurred in the presence of EDTA, indicating that calcium and magnesium ions are not required for interaction of TSP with fibrinogen. The binding of TSP to fibrinogen-Sepharose was quantitatively blocked by pretreatment with an antibody to the cyanogen bromide cleavage fragment composed of residues 241-476 of the carboxyl-terminal end of the alpha chain of fibrinogen. Antibodies against the D and E domains of fibrinogen had no effect on the binding. Excess fibrinogen (30 mg/ml) added to platelet extract quantitatively inhibited binding of TSP to fibrinogen-Sepharose. TSP preferentially bound to uncross-linked fibrin, suggesting that the TSP-fibrinogen binding site is unavailable in cross-linked fibrin. These results indicate that TSP binds specifically to immobilized fibrinogen or uncross-linked fibrin through determinants present in the carboxyl-terminal portion of the alpha chain and that these interactions do not require calcium or magnesium ions.

Amino Acids↗
PubMed1985

Platelet interaction with subendothelial extracellular matrix: platelet-fibrinogen interactions are essential for platelet aggregation but not for the matrix-induced release reaction.

Cultured endothelial cells produce an extracellular matrix (ECM) to which platelets adhere and spread, ultimately resulting in platelet aggregation, thromboxane B2 production, and serotonin release. We have investigated the role of fibrinogen binding to the platelet GPIIb/IIIa complex in these reactions by comparing normal platelet-rich plasma (PRP), PRP from patients with Glanzman's thrombasthenia (whose platelets lack the GPIIb/IIIa complex), PRP in the presence of a monoclonal antibody that blocks the binding of fibrinogen to the GPIIb/IIIa complex, platelets washed free of fibrinogen, and washed platelets to which fibrinogen was added. Although platelet aggregation was virtually completely inhibited in the samples in which the normal interaction between fibrinogen and GPIIb/IIIa was impaired, adhesion of platelets to the matrix, spreading, and release of [14C]-serotonin were not affected. All of the platelet preparations released significant amounts of T X B2 with time, but there was a decrease in the amount produced by both the thrombasthenic and antibody-treated platelets. We conclude that the interaction of fibrinogen with platelet GPIIb/IIIa is not required for platelet adhesion to ECM or for adhesion-induced shape change or serotonin release. On the other hand, the platelet-fibrinogen interaction may play some role in augmenting adhesion-induced T X B2 production, and it is absolutely required for adhesion-induced platelet aggregation.

Animals↗
PubMed1979

Interaction of metal ions with nucleic acids. Interaction of copper(II) with pyrimidine nucleosides and their derivatives.

1. In aqueous and non-aqueous solutions, copper(II) interacts with the N-3 of cytidine but not with the carbonyl group oxygens of pyrimidine nucleosides. 2. In aqueous solution, copper(II) interacts with the phosphate group and ribose of pyrimidine nucleotides, and additionally with N-3 of 5'-CMP. 3. Broadening of resonance signals of the H-5 proton of 5'-UMP and C-5 of 5'-UMP and 5'-TMP results probably from the interaction between metal ion and the phosphate group situated in direct vicinity of the above atoms. 4. In the copper(II)-pyrimidine nucleotide complexes in solid state, copper is coordinated with the phosphate group, and in 5'-CMP additionally with the pyrimidine moiety of the nucleotide.

Binding Sites↗
PubMed1965

Clinically important examples of drug interaction. Psychotropic drugs (1). Interaction between centrally acting drugs in man: some general considerations.

As a biological phenomenon the interaction between drugs may be viewed in ;explanatory' or ;empirical' terms. In clinical psychopharmacology the former is rarely possible: two examples are cited, one concerning amphetamine and reserpine, the other desmethyl-imipramine and tetrabenazine. Among centrally acting substances, empirical studies of the interaction between alcohol and the barbiturates have been pursued intensively by several methods in clinic and laboratory. Both general considerations and recent work on the effects of amphetamine-barbiturate combinations suggest caution in the medical use of mixtures of psychotropic drugs. Adverse reactions caused by interaction between psychotropic drugs and other substances have still to be studied systematically as a potential hazard.

Amphetamine↗
PubMed1981

The interaction of metal ions with nucleic acids. NMR study of the copper(II) interaction with inosine derivatives.

The interaction of copper(II) with inosine derivatives substituted at the purine ring, modified at the ribose residue, and with the syn conformation at the glycosidic bond was examined using 1H and 13C nuclear magnetic resonance techniques. The results imply that, in non-aqueous medium, the main site of copper(II) binding is N7 of inosine derivatives. No interaction with ribose hydroxyl groups was observed. CNDO/2 calculations performed for a copper(II) complex with 9-methyl-hypoxanthine support direct bonding of copper(II) ion to the ring. In aqueous medium, coordination of copper(II) with N1 and N7 of inosine is p2H-dependent: 98.7% of Cu(II) is bound with N7 at p2H 3.6, 49.4% at p2H 6.9, and only 35% at p2H 8.2 The relative dipolar and scalar contributions to the proton and carbon-13 transverse relaxation of the inosine derivatives nuclei have been assessed. The distances between the metal ion and the carbon and proton nuclei can not be estimated from T1 measurements because dipolar interaction contributing to relaxation is not only between the paramagnetic ion and the affected nucleus; there is also an important contribution from unpaired spin density on the ligand.

Chemical Phenomena↗
PubMed1980

Interaction of thyroid hormone and hemoglobin. I. Nature of the interaction and effect of hemoglobin on thyroid hormone radioimmunoassay.

Gel filtration of human RBC lysate incubated with labeled T4 or T3 revealed co-elution of a major iodothyronine-binding fraction (R-2) and hemoglobin. Solutions of purified human hemoglobin and T3 also showed co-elution of hormone and hemoglobin. Because hematin and protoporphyrin were shown to bind labeled T3, the oxygen-binding site on hemoglobin was excluded as the site of iodothyronine-hemoglobin interaction. Analysis of hormone binding by heme and globin moieties showed T3 binding to be limited to the heme fraction. Addition of excess unlabeled T3 to hemoglobin or heme incubated with labeled T3 indicated 75% to 90% of hormone binding was poorly dissociable. These observations suggested that the presence of hemoglobin in RBC lysate or in serum could influence the measurement of T4 and T3 by specific RIA. Subsequent studies of the addition to serum of human hemoglobin revealed a significant reduction in T3 and T4 detectable by RIA in the presence of this protein. The effect was influenced by the concentration of hemoglobin and by duration and temperature of incubations of hemoglobin and serum prior to RIA. Incubated for 5 days at 4 degrees C, 14 sera containing 10 gm/dl hemoglobin showed a mean decrease in T3 concentration of 40% compared to sera incubated in the absence of hemoglobin (160.1 to 93.9 ng/dl, p less than 0.001); detectable serum T4 fell by 50% in 13 sera incubated under the same conditions (5.40 micrograms/dl without hemoglobin to 2.55 micrograms/dl in the presence of hemoglobin, p less than 0.001). Hemoglobin concentrations in serum as low as 0.1 and 0.5 gm/dl affected the RIAs significantly. Thus a major fraction of thyroid hormone binding in human RBC cytoplasm is accounted for by an interaction with hemoglobin. This interaction in serum or RBC lysates is a significant variable affecting iodothyronine determinations.

Anilino Naphthalenesulfonates↗
PubMed1997

[Biological effects of interacting shock waves. A modeling study of the effects of interacting shock waves using erythrocyte hemolysis].

AIM: The effects of high-energy shock wave on tissues were discussed in literature. The shock wave sources which were used for experiments were developed for stone fragmentation. The side effects of the applicators are generally low. Increase of shock wave pressure induce bigger negative pressure amplitude and this may cause significantly bigger side effects. We used tow shock waves, with time interval of 5 microseconds. In our opinion, the first shock wave causes acoustic inhomogenity in shock wave focus and therefore second shock wave acts in a region with different acoustic parameters. The second shock wave may loss energy in the focus area by dissipation or absorption. We termed the coupled shock waves as "interacting shock waves". METHODS AND RESULTS: Hemolysis of erythrocytes was used for examination of biological toxicity. Shock wave pressure was 80 MPa, the ratio of positive to negative pressure of single shock waves is 30. For correlation we applied 50 and 100 single shock waves and 50 or 100 couples of two shock waves. Hemolysis after 50 simple shock waves was 4.28 times lower compared with hemolysis after the same number of coupled shock waves (interacting shock waves). CONCLUSION: After 50 couples of shock waves hemolysis is 2.14 times higher compared with 100 single shock waves. This result suggests that the hypothesis of some interaction existing between two shocks applied in a very short time interval make future study rightful.

Hemolysis↗