Immobilization Of Ligands Research Articles

Effect of Jagged-1 and Dll-1 on osteogenic differentiation by stem cells from human exfoliated deciduous teeth

ObjectiveThe aim of the present study was to determine the influence of Notch ligands, Jagged-1 and Dll-1, on osteogenic differentiation by stem cells from human exfoliated deciduous teeth. DesignNotch ligands were immobilized on tissue culture surface using an indirect affinity immobilization technique. Cells from the remaining of dental pulp tissues from human deciduous teeth were isolated and characterized using flow cytometry and differentiation assay. Alkaline phosphatase (ALP) enzymatic activity, osteogenic marker gene expression, and mineralization were determined using ALP assay, real-time polymerase chain reaction, and alizarin red staining, respectively. ResultsThe isolated cells exhibited CD44, CD90, and CD105 expression but lack of CD45 expression. Further, these cells were able to differentiate toward osteogenic lineage. The upregulation of HES-1 and HEY-1 was observed in those cells on Dll-1 and Jagged-1 coated surface. The significant increase of ALP activity and mineralization was noted in those cells seeded on Jagged-1 surface and these results were attenuated when cells were pretreated with gamma secretase inhibitor. The significant upregulation of ALP and collagen type I gene expression was also observed in those cells seeded on Jagged-1 surface. The inconsistent Dll-1 induced osteogenic differentiation was found and high Dll-1 immobilized dose (50nM) slightly enhanced alkaline phosphatase enzymatic activity. However, the statistical significant difference was not obtained as compared to the hFc control. ConclusionThe surface immobilization of Notch ligands, Jagged-1 and Dll-1, likely to enhance osteogenic differentiation of SHEDs. However, Jagged-1 had more ability in enhancing osteogenic differentiation than Dll-1 in our model.

Selective recovery of heavy rare earth elements from apatite with an adsorbent bearing immobilized tridentate amido ligands

Abstract Apatite, which is used in the production of phosphorus fertilizers, contains small amounts of rare earth elements (REEs; 0.1–1%). Apatite deposits occur all over the world and thus have the potential to be a secure source of REEs. We investigated a method for recovery of REEs from an apatite sample; specifically, REEs were leached from the sample with an H2SO4 solution, the acid that is most commonly used for fertilizer production. At high H2SO4 concentrations, most of the REEs in the solution were lost to precipitation as insoluble gypsum (CaSO4·2H2O). However, at H2SO4 concentrations of

Surface Plasmon Resonance Analysis of Heparin-Binding Angiogenic Growth Factors.

Surface plasmon resonance (SPR) is an optical technique to evaluate biomolecular interactions. Briefly, SPR measures the capacity of two molecules to bind each other by detecting reflected light from a prism-gold film interface. One of the two putative interactants (called ligand) is chemically immobilized onto the gold film. When the sensor is exposed to a sample containing the second interactant (called analyte), its binding to the immobilized ligand causes a change of the refractive index of the material above the gold surface that is monitored as a real-time graph of the response units against time, producing a real-time graph called sensorgram. SPR has become a golden standard technology for label-free, real-time interaction analysis in basic research and drug discovery in a wide array of biomedical areas, including oncology and virology [1, 2]. Here we describe the exploitation of SPR for the study of the capacity of the pro-oncogenic, pro-angiogenic HIV-1 p17 matrix protein [3, 4] to bind to heparin, a structural analog of heparan sulfate proteoglycans (HSPGs) receptors, and for the identification of novel HSPGs-antagonists to be used as anti-p17 drugs.

Assessing of lead(III) capturing from contaminated wastewater using ligand doped conjugate adsorbent

A ligand doped conjugate adsorbent was prepared by indirect ligand immobilization onto the mesoporous silica for lead (Pb(II)) ions detection and adsorption from aqueous media. The solution acidity played a key factor for sensitive Pb(II) ions detection. The data clarified that the adsorbent was able to detect low level Pb(II) ions with one-step detection procedure without using any sophisticated instruments. The detection platform exhibited the high sensitivity and selectivity toward Pb(II) ions and determined limit of detection was 1.2μg/L. The effects of different parameters such as solution acidity, interaction time, initial concentration, ion selectivity and regeneration were investigated on the Pb(II) adsorption by the conjugate adsorbent. The data clarified that the Pb(II) ions adsorption process was found to be relatively fast. The adsorption isotherms of Pb(II) ions from aqueous solutions onto the adsorbent were measured, and the results showed that the Langmuir isotherm was found to be the best represent the measured adsorption data. The maximum adsorption capacity was determined to be 188.67mg/g. The Pb(II) adsorption efficiency was not affected in the presence of co-existing ions. Moreover, this technique achieved residual Pb(II) concentration less than 10μg/L, which is acceptable by water quality regulations. In addition, the conjugate adsorbent was regenerated by 0.10M HCl treatment the Pb(II) ion adsorption efficiency was retained after nine adsorption-elution-regeneration cycles. The results suggested that conjugate adsorbent had the potential to become a promising technique for in situ Pb(II) contaminated groundwater remediation with naked-eye monitoring. Therefore, the ligand doped conjugate adsorbent is efficient and cost-effective potential materials for sensitive and selective Pb(II) detection and adsorption from aqueous solution.

Identification of a peptide ligand for antibody immobilization on biosensor surfaces

The construction of biosensors with antibodies as the biological sensing element requires the integration of antibodies into the biosensor such that their activity is reproducibly retained. In this work, a peptide ligand was identified from phage-displayed heptameric peptide libraries for the purpose of antibody immobilization on biosensor surfaces. For biopanning of peptides specific to the Fc region of the antibody, rabbit anti-goat immunoglobulin G (IgG) antibody was immobilized on a culture dish coated with goat IgG, which enabled exposure of the Fc region of rabbit antibody on the surface with the Fab region bound to the surface-adsorbed goat IgG. The library phages were added to the dish and phages displaying antibody-binding peptides were competitively eluted using the rabbit antibody. After four rounds of biopanning, 22 phage plaques were randomly selected and their nucleotide sequences corresponding to the random peptide were determined. Three enriched sequences were selected and analyzed for their rabbit antibody-binding activity. One of these sequences (KHRFNKD), which was rich in positive charge and homologous to the IgG-binding domains of Staphylococcal protein A, exhibited a high and specific affinity to rabbit antibody. This peptide was immobilized on a quartz crystal microbalance (QCM) biosensor, and the resulting QCM was found to be capable of capturing antibody and detecting antigen, with potential applications in antibody purification and enzyme immunoassay.

Direct site-specific immobilization of protein A via aldehyde-hydrazide conjugation.

Immobilization of affinity ligands on supporting matrices is a key step for the preparation of affinity chromatography resins, and an efficient coupling strategy can significantly improve the validity and cost of the affinity system, especially for systems that employ expensive recombinant proteins or antibodies as affinity ligands. This study described a simple method for obtaining site-specific immobilization of protein A (the ligand) via aldehyde-hydrazide conjugation and its application in antibody purification via protein A chromatography. An aldehyde group was generated at the N-terminus of protein A in vivo by co-expressing a formylglycine-generating enzyme (FGE) and recombinant protein A containing a FGE recognizing sequence (aldehyde tag) in Escherichia coli. The resulting aldehyde allowed direct immobilization of protein A onto the hydrazide-modified agarose matrices under mild condition. We found that 100mM aniline was most effective for catalyzing the coupling reaction, and the recombinant protein A could be coupled with high selectivity, directly from a crude cell extract. The site-specific immobilized protein A showed good capacity for antibody purification. The specificity of the aldehyde-hydrazide reaction not only allowed site-specific immobilization of affinity ligands, but also improved the cost of the process by employing unpurified ligands, a method that might be of great use to industrial applications.

Chemokine Detection Using Receptors Immobilized on an SPR Sensor Surface.

Chemokines and their receptors take part in many physiological and pathological processes, and their dysregulated expression is linked to chronic inflammatory and autoimmune diseases, immunodeficiencies, and cancer. The chemokine receptors, members of the G protein-coupled receptor family, are integral membrane proteins, with seven-transmembrane domains that bind the chemokines and transmit signals through GTP-binding proteins. Many assays used to study the structure, conformation, or activation mechanism of these receptors are based on ligand-binding measurement, as are techniques to detect new agonists and antagonists that modulate chemokine function. Such methods require labeling of the chemokine and/or its receptor, which can alter their binding characteristics. Surface plasmon resonance (SPR) is a powerful technique for analysis of the interaction between immobilized receptors and ligands in solution, in real time, and without labeling. SPR measurements nonetheless require expression and purification steps that can alter the conformation, stability, and function of the chemokine and/or the chemokine receptor. In this review, we focus on distinct methods to immobilize chemokine receptors on the surface of an optical biosensor. We expose the advantages and disadvantages of different protocols used and describe in detail the method to retain viral particles as receptor carriers that can be used for SPR determinations.

Calibration free concentration analysis by surface plasmon resonance in a capture mode

Surface plasmon resonance (SPR) is the gold standard for determining rate and equilibrium constants of bimolecular complexes. Accuracy of these parameters depends on the correct determination of the concentration of the injected analyte. Calibration free concentration analysis (CFCA) has been developed to overcome the limitation of measuring protein concentrations spectroscopically, which may overestimate the fraction of the protein that really binds to the immobilized ligand, i.e. the active concentration. In this work, we demonstrate that CFCA can also be implemented in a capture format for measuring active concentrations. Capture CFCA (CCFCA) was first validated by measuring the concentration of a HLA-B*44:02 antigen solution. The active concentration of this molecule determined by CCFCA was similar to that obtained by covalent CFCA. CCFCA was then used to determine the concentration of the W6/32 pan class I HLA monoclonal antibody over three different HLA molecules captured by another specific antibody. This could not have been performed by covalent CFCA because immobilized HLA molecules cannot withstand regeneration. By exploring different capture levels we also show that CCFCA gives consistent results even at low capture levels. Knowing the active concentration of W6/32, we then determined the rate and equilibrium constants of W6/32-HLA complexes on the same flow cell. CCFCA is of general use for measuring active concentrations and of great interest for analytes recognizing ligands that cannot be covalently immobilized on sensor chips. The capture mode also allows determining the kinetic constants of multiple analyte-ligand complexes on the same flow cell. This increases experiments throughput and reduces sensor chip consumption.

Molecular insight in the purification of immunoglobulin by pseudobiospecific ligand l-histidine and histidyl moieties in histidine ligand affinity chromatography (HLAC) by molecular docking.

Pseudobiospecific ligand l-histidine is an inexpensive, highly stable, non-toxic ligand explored successfully over the last twenty years for the purification of immunoglobulins in immobilised histidine ligand affinity chromatography. It is of great interest to know the molecular recognition sites of IgG to immobilized l-histidine. Here, we have used an in silico approach to explore the molecular recognition of l-histidine by IgG. We have assessed the feasible binding modes of histidine and its moieties at different sites of IgG and considered only those binding conformations which are exhibited via the imidazole ring NH group or any other OH donating group apart from the ones which are terminally conjugated with the support matrix. We categorised binding site into two categories; category I: inner binding groove and category II: surface binding groove and observed that the hinge region of IgG has most favourable binding pocket for l-histidine and histidyl moieties. Ser and Tyr residues on the hinge region make several significant interactions with l-histidine and histidyl moieties. In case of Fc region of IgG, l-histidine and histidyl moieties closely resemble the binding modes of Protein A, biomimetic ligand 22/8 and B domain of SpA to IgG. In addition to these we have also observed a significant binding site for l-histidine and histidyl moieties at Fab region of IgG.

Quantification of Amino Groups on Solid Surfaces Using Cleavable Fluorescent Compounds.

We quantified amino groups displayed on inorganic and organic surfaces in aqueous solution using different types of cleavable fluorescent compounds and an aldehyde dye. The cleavable fluorescent compounds were designed to bind covalently to amino groups and then liberated under specific conditions. Among the investigated materials, cleavable coumarin was most appropriate for the quantification of amino groups on silica and resin surfaces. The developed method can measure small amounts (∼pmol/cm(2)) of amino groups on a flat polymeric surface, detecting only amino groups that are exposed to aqueous solution and available for surface immobilization of ligands and biomolecules.

Cell, isoform, and environment factors shape gradients and modulate chemotaxis.

Chemokine gradient formation requires multiple processes that include ligand secretion and diffusion, receptor binding and internalization, and immobilization of ligand to surfaces. To understand how these events dynamically shape gradients and influence ensuing cell chemotaxis, we built a multi-scale hybrid agent-based model linking gradient formation, cell responses, and receptor-level information. The CXCL12/CXCR4/CXCR7 signaling axis is highly implicated in metastasis of many cancers. We model CXCL12 gradient formation as it is impacted by CXCR4 and CXCR7, with particular focus on the three most highly expressed isoforms of CXCL12. We trained and validated our model using data from an in vitro microfluidic source-sink device. Our simulations demonstrate how isoform differences on the molecular level affect gradient formation and cell responses. We determine that ligand properties specific to CXCL12 isoforms (binding to the migration surface and to CXCR4) significantly impact migration and explain differences in in vitro chemotaxis data. We extend our model to analyze CXCL12 gradient formation in a tumor environment and find that short distance, steep gradients characteristic of the CXCL12-γ isoform are effective at driving chemotaxis. We highlight the importance of CXCL12-γ in cancer cell migration: its high effective affinity for both extracellular surface sites and CXCR4 strongly promote CXCR4+ cell migration. CXCL12-γ is also more difficult to inhibit, and we predict that co-inhibition of CXCR4 and CXCR7 is necessary to effectively hinder CXCL12-γ-induced migration. These findings support the growing importance of understanding differences in protein isoforms, and in particular their implications for cancer treatment.

(S)‐BINOL Immobilized onto Multiwalled Carbon Nanotubes through Covalent Linkage: A New Approach for Hybrid Nanomaterials Characterization

Abstract(S)‐6‐(4‐(Methoxycarbonyl)phenyl)‐1,1′‐bis‐2‐naphthol, a chiral 1,1′‐bis‐2‐naphthol (BINOL) derivative, was prepared via Suzuki C−C coupling and immobilized onto diamine‐functionalized multiwalled carbon nanotubes. The BINOL was first derivatized with a carboxylic acid, capable of forming an amide linkage with the amine–carbon nanotube modified surface. The 4‐methoxyphenylboronic acid was replaced by 3‐fluoro‐4‐(methoxycarbonyl)phenylboronic acid and (S)‐6‐(3‐fluoro‐4‐(methoxycarbonyl)phenyl)‐1,1′‐bis‐2‐naphthol was obtained and used as a probe to better quantify the organic material. It was found that in the hybrid material, 1/3 of amine groups have been transformed into the corresponding amide (S)‐BINOL derivative. The chemical and electronic integrity of the chiral BINOL ligand is maintained after the ligand immobilization. Evaluation in diethyl zinc and Ti(OiPr)4‐catalyzed alkylation of benzaldehyde showed that both methoxycarbonylphenyl and fluoromethoxycarbonylphenyl BINOL moieties do not significantly influence the catalytic activity or selectivity of the process. However, when hybrid materials were used, similar activities were obtained, but with lower enantioselectivities. This result could be due to a competitive alkylation reaction occurring on the carbon surface or by the constraint caused by the ligand proximity on the support surface.

Preparation of nano-magnetite impregnated mesocellular foam composite with a Cu ligand for His-tagged enzyme immobilization

A nano-sized magnetite (NSM) impregnated mesocellular foam (MCF) composite was synthesized to improve enzymatic activity and reusability in the immobilized state. 3-Chloropropyltriethoxy silane-di-(2-picolyl)amine was linked to the particle for cooperative complex formation with an enzyme through coordinated bonding with Cu (NSM/MCF-Cu). The NSM/MCF-Cu immobilized by histidine-tagged enzymes exhibited the high protein content and specific activity, showing an approximately 5 times higher protein content and 3 times higher specific activity compared to physically immobilized MCF particles. The NSM/MCF-Cu particles were recovered by magnetic separation and approximately 80% of the initial activity was retained even after 10 uses.

A generic magnetic microsphere platform with "clickable" ligands for purification and immobilization of targeted proteins.

While much effort has been made to prepare magnetic microspheres (MMs) with surface moieties that bind to affinity tags or fusion partners of interest in the recombinant proteins, it remains a challenge to develop a generic platform that is capable of incorporating a variety of capture ligands by a simple chemistry. Herein, we developed core-shell structured magnetic microspheres with a high magnetic susceptibility and a low nonspecific protein adsorption. Surface functionalization of these MMs with azide groups facilitates covalent attachment of alkynylated ligands on their surfaces by "click" chemistry and creates a versatile platform for selective purification and immobilization of recombinant proteins carrying corresponding affinity tags. The general applicability of the approach was demonstrated in incorporating four widely used affinity ligands with different reactive groups (-CHO, -SH, -COOH, and -NH2) onto the MMs platform for purification and immobilization of targeted proteins. The azide-functionalized MMs would be applicable for a variety of ligands and substrates that are amenable to alkynylation modification.

Peptide-nanoparticle ligation mediated by cutinase fusion for the development of cancer cell-targeted nanoconjugates.

The relationship between the positioning of ligands on the surface of nanoparticles and the structural features of nanoconjugates has been underestimated for a long time, albeit of primary importance to promote specific biological recognition at the nanoscale. In particular, it has been formerly observed that a proper molecular orientation can play a crucial role, first optimizing ligand immobilization onto the nanoparticles and, second, improving the targeting efficiency of the nanoconjugates. In this work, we present a novel strategy to afford peptide-oriented ligation using genetically modified cutinase fusion proteins, which combines the presence of a site-directed "capture" module based on an enzymatic unit and a "targeting" moiety consisting of the ligand terminal end of a genetically encoded polypeptide chain. As an example, the oriented presentation of U11 peptide, a sequence specific for the recognition of urokinase plasminogen activator receptor (uPAR), was achieved by enzyme-mediated conjugation with an irreversible inhibitor of cutinase, an alkylphosphonate p-nitrophenol ester linker, covalently bound to the surface of iron oxide nanoparticles. The targeting efficiency of the resulting protein-nanoparticle conjugates was assessed using uPAR-positive breast cancer cells exploiting confocal laser scanning microscopy and quantitative fluorescence analysis of confocal images. Ultrastructural analysis of transmission electron micrographs provided evidence of a receptor-mediated pathway of endocytosis. Our results showed that, despite the small average number of targeting peptides presented on the nanoparticles, our ligand-oriented nanoconjugates proved to be very effective in selectively binding to uPAR and in promoting the uptake in uPAR-positive cancer cells.

Reactivity and kinetics of vinyl sulfone-functionalized self-assembled monolayers for bioactive ligand immobilization.

A new vinyl sulfone (VS) disulfide, 1,2-bis(11-(vinyl sulfonyl)undecyl)disulfane, was synthesized to enable the preparation of VS-presenting self-assembled monolayers (VS SAMs) on Au substrates. The VS SAMs were used as a model system to assess the reaction kinetics of bioactive ligands, i.e., glutathione (GSH), N-(5-amino-1-carboxypentyl)iminodiacetic acid (ab-NTA), and mannose, toward the VS groups on the SAM surface. The VS SAMs and the ligand immobilization were characterized by X-ray photoelectron spectroscopy (XPS), contact angle goniometry, and protein-binding experiments using a quartz crystal microbalance (QCM). Kinetic studies showed that the surface VS groups undergo pseudo-first-order reactions with various ligands, with the observed rate constant being 0.057 min(-1) for GSH at pH 7.5, 0.011 min(-1) for ab-NTA at pH 8.5, and 0.009 min(-1) for mannose at pH 10.5. This work advanced our understanding of the reactivity of VS-bearing functional surfaces and further demonstrated the versatile potential of VS chemistry to prepare ligand-immobilized bioactive surfaces.

A surface plasmon resonance assay for measurement of neuraminidase inhibition, sensitivity of wild-type influenza neuraminidase and its H274Y mutant to the antiviral drugs zanamivir and oseltamivir

Antiviral resistance is currently monitored by a labelled enzymatic assay, which can give inconsistent results because of the short half-life of the labelled product, and variations in assay conditions. In this paper, we describe a competitive surface plasmon resonance (SPR) inhibition assay for measuring the sensitivities of wild-type neuraminidase (WT NA) and the H274Y (histidine 274 tyrosine) NA mutant to antiviral drugs. The two NA isoforms were expressed in High-five™ (Trichoplusia ni) insect cells. A spacer molecule (1,6-hexanediamine (HDA)) was conjugated to the 7-hydroxyl group of zanamivir, and the construct (HDA-zanamivir) was immobilized onto a SPR sensor chip to obtain a final immobilization response of 431 response units. The immobilized HDA-zanamivir comprised a bio-specific ligand for the WT and mutant proteins. The effects of the natural substrate (sialic acid) and two inhibitors (zanamivir and oseltamivir) on NA binding to the immobilized ligand were studied. The processed SPR data was analysed to determine 50% inhibitory concentrations (IC50-spr ), using a log dose-response curve fit. Although both NA isoforms had almost identical IC50-spr values for sialic acid (WT = 5.5 nM; H274Y mutant = 3.25 nM) and zanamivir (WT = 2.16 nM; H274Y mutant = 2.42 nM), there were significant differences between the IC50-spr values obtained for the WT (7.7 nM) and H274Y mutant (256 nM) NA in the presence of oseltamivir, indicating that oseltamivir has a reduced affinity for the H274Y mutant. The SPR inhibition assay strategy presented in this work could be applied for the rapid screening of newly emerging variants of NA for their sensitivity to antiviral drugs.

N-terminal processing of affinity-tagged recombinant proteins purified by IMAC procedures.

The ability of a new class of metal binding tags to facilitate the purification of recombinant proteins, exemplified by the tagged glutathione S-transferase and human growth hormone, from Escherichia coli fermentation broths and lysates has been further investigated. These histidine-containing tags exhibit high affinity for borderline metal ions chelated to the immobilised ligand, 1,4,7-triazacyclononane (tacn). The use of this tag-tacn immobilised metal ion affinity chromatography (IMAC) system engenders high selectivity with regard to host cell protein removal and permits facile tag removal from the E. coli-expressed recombinant protein. In particular, these tags were specifically designed to enable their efficient removal by the dipeptidyl aminopeptidase 1 (DAP-1), thus capturing the advantages of high substrate specificity and rates of cleavage. MALDI-TOF MS analysis of the cleaved products from the DAP-1 digestion of the recombinant N-terminally tagged proteins confirmed the complete removal of the tag within 4-12 h under mild experimental conditions. Overall, this study demonstrates that the use of tags specifically designed to target tacn-based IMAC resins offers a comprehensive and flexible approach for the purification of E. coli-expressed recombinant proteins, where complete removal of the tag is an essential prerequisite for subsequent application of the purified native proteins in studies aimed at delineating the molecular and cellular basis of specific biological processes.

In Vitro and Ex Vivo Evaluation of Biomaterials' Distinctive Properties as a Result of Thiolation

Polysaccharide hyaluronic acid (HA) was chemically modified with cysteine ethyl ester (CYS). By immobilization of the thiol-bearing ligand on the polymeric backbone the thiolated bioconjugate HA-CYS was obtained. METHODOLOGY & RESULTS: Mucoadhesion, permeation enhancement effect and stability was tested. Furthermore mechanical, physicochemical properties as well as mucoadhesive strength, swelling index and residence time on the mucosa were investigated. The developed thiolated bioconjugate displayed 1.5-fold improved mucoadhesiveness on buccal mucosa as well as an enhanced permeation behavior and 2.5-fold higher polymer stability. The near neutral pH and 2.49±0.49% cytotoxicity over 12-h studies indicated their non-irritability and biocompatible nature with biological tissues. Further, the model drug sulforhodamine 101 was incorporated to determine its drug release profiles, which revealed a 2.8-fold controlled release of HA-CYS in comparison to unmodified HA. Thus, the promising results encourage further investigations and exploitation of this versatile polysaccharide.

Hybrid materials comprising trimethylglycinamide groups: immobilization consequences for anion binding affinities

A thorough binding study of three trimethylglycinamide functionalized mesoporous silica gels is reported. Anion-exchange properties of these hybrid materials were established alongside the properties of their organic analogues, to provide insight into the effects of ligand immobilization on the selectivity and effectiveness of anion binding. Chloride, benzoate, nitrate, oxalate, dichromate and phosphate salts were examined. Materials and compounds after the ion exchange were studied by potentiometric titration, FTIR and 1H NMR spectroscopy. The data acquired indicate that immobilization is a viable alternative to high preorganization of a successful host molecule.