Studies on oriented and reversible immobilization of glycoprotein using novel boronate affinity gel

Improvement of lipase activity by synergistic immobilization on polyurethane and its application for large-scale synthesizing vitamin A palmitate

We have developed an improved and effective method to immobilize lipase on hydrophobic polyurethane foam (PUF) with different modifications. PUF was treated with hydrochloric acid to increase the active sites and then the active carboxyl groups and amino groups were exposed. Enzyme activity of lipase immobilized on PUF-HCL (8000 U/g) was 50% higher than that of lipase immobilized on PUF (5300 U/g). There is an increase in the activity of the immobilized lipase on AA/PEI-modified support (115,000 U/g), a 2.17-fold increase compared to lipase immobilized on the native support was observed. The activity of immobilized lipases was dependent on the PEI molecular weight, with best results from enzyme immobilized on PUF-HCL-AA/PEI (MW 70,000 Da, 12,800 U/g)), which was 2.41 times higher compared to that of the same enzyme immobilized on PUF. These results suggest that the activity of immobilized lipase is influenced by the support surface properties, and a moderate support surface micro-environment is crucial for improving enzyme activity. Finally, the immobilized lipase was used for the production of vitamin A palmitate. The immobilized lipase can be reused for up to 18 times with a conversion rate above 90% for 12 h in a 3 L bioreactor. Research highlights An efficient immobilization protocol on polyurethane foam was developed Polyethyleneimine and acetic acid were used to regulate the micro-environment concurrently The activity of lipase immobilized on PUF-HCL-AA/PEI was improved by 2.41 times Immobilized lipase exhibited excellent operational stability for vitamin A palmitate synthesis.

Branched polyethyleneimine-assisted 3-carboxybenzoboroxole improved Wulff-type boronic acid functionalized magnetic nanoparticles for the specific capture of cis-diol-containing flavonoids under neutral conditions

Flavonoids have shown a variety of biological activities such as antimicrobial, antibacterial, antifungal, antiviral, antiinflammatory, antitumor, antiatherogenic, and antihyperglycemic activities. A lot of important flavonoids contain cis-diols such as rutin (Ru), quercetin (Qu), luteolin (Lu), myricetin (Myr) and baicalein (Ba) and so on. It is necessary to establish a simple, low-cost and efficient purification method for cis-diol-containing flavonoids from plant extracts. Boronate affinity materials are able to reversibly bind the cis-diols via boronic acids by forming a five- or six-membered boronic cyclic ester in aqueous media. However, conventional boronate affinity materials have to be used in alkaline media, which can lead to the oxidation of cis-diols in compounds. In this study, the polyethyleneimine (PEI)-assisted 3-carboxybenzoboroxole-functionalized magnetic nanoparticles (MNPs) were prepared to achieve efficient capture of cis-diol-containing flavonoids under neutral conditions. Branched PEI was applied as a scaffold to amplify the number of boronic acid moieties, while 3-carboxybenzoboroxole, exhibiting high affinity and excellent water solubility toward flavonoids, was used as an affinity ligand. The prepared boronate affinity MNPs exhibited high binding capacity and fast binding kinetics (equilibrium in 3 min) under neutral conditions. In addition, the obtained boronate affinity MNPs exhibited high binding affinity (K_d ≈ 10⁻⁴ M), low binding pH (pH ≥ 6.0) and tolerance of the interference to abundant sugars.

Flavonoids have shown a variety of biological activities such as antimicrobial, antibacterial, antifungal, antiviral, antiinflammatory, antitumor, antiatherogenic, and antihyperglycemic activities.

Pyridine boronic acid-polyoxometalate based porous hybrid for efficient depletion of high abundant glycoproteins in plasma

A porous hybrid, namely PW₁₂@TiO₂-Si(Et)Si/Pba, is fabricated by the modification of PW₁₂@TiO₂-Si(Et)Si with pyridine boronic acid via a solvothermal method. The covalent interactions between the boronic acid group of the hybrid and the glycosylated site of proteins provide the as-prepared hybrid with favorable adsorption performance towards glycoproteins. The adsorption behaviors of glycoproteins onto the hybrid fit well with the Langmuir model, and the adsorption capacities for glycoprotein IgG and Trf are high, up to 348.5 mg g^-1 and 262.6 mg g^-1, respectively. Thus, a protocol for the depletion of high abundant glycoproteins from human plasma is proposed. The percentage contents of Trf, IgG, haptoglobinis and IgM are reduced from 7.38%, 5.5%, 3.01% and 1.02% to 0.951%, 4.7%, 0.126% and 0.76%, respectively. 85 low abundant proteins are identified from the raw plasma after the depletion of the high abundance proteins, demonstrating the potential of PW₁₂@TiO₂-Si(Et)Si/Pba hybrid in proteomic studies.

Boronate affinity materials for separation and molecular recognition: structure, properties and applications

Boronate affinity materials, as unique sorbents, have emerged as important media for the selective separation and molecular recognition of cis-diol-containing compounds. With the introduction of boronic acid functionality, boronate affinity materials exhibit several significant advantages, including broad-spectrum selectivity, reversible covalent binding, pH-controlled capture/release, fast association/desorption kinetics, and good compatibility with mass spectrometry. Because cis-diol-containing biomolecules, including nucleosides, saccharides, glycans, glycoproteins and so on, are the important targets in current research frontiers such as metabolomics, glycomics and proteomics, boronate affinity materials have gained rapid development and found increasing applications in the last decade. In this review, we critically survey recent advances in boronate affinity materials. We focus on fundamental considerations as well as important progress and new boronate affinity materials reported in the last decade. We particularly discuss on the effects of the structure of boronate ligands and supporting materials on the properties of boronate affinity materials, such as binding pH, affinity, selectivity, binding capacity, tolerance for interference and so on. A variety of promising applications, including affinity separation, proteomics, metabolomics, disease diagnostics and aptamer selection, are introduced with main emphasis on how boronate affinity materials can solve the issues in the applications and what merits boronate affinity materials can provide.

Low physical activity and high screen time can increase the risks of mental health problems and poor sleep quality among Chinese college students

OBJECTIVE

To test the independent and interactive associations of physical activity (PA) and screen time (ST) with self-reported mental health and sleep quality among Chinese college students.

METHOD

Data were collected in October, 2013. The gender, age, residential background, body mass index (BMI), perceived family economy and perceived study burden were obtained from a total of 4747 college students (41.6% males and 58.4% females). The outcomes were self-reported PA status, ST, anxiety, depression, psychopathological symptoms and sleep quality. Analyses were conducted with logistic regression models.

RESULTS

Overall, 16.3%, 15.9% and 17.3% of the students had psychological problems, such as anxiety, depression and psychopathological symptoms, respectively. The prevalence of poor sleep quality was 9.8%. High ST was significantly positively associated with anxiety (OR=1.38, 95%CI: 1.15-1.65), depression (OR=1.76, 95%CI: 1.47-2.09), psychopathological symptoms (OR=1.69, 95%CI: 1.43-2.01) and poor sleep quality (OR=1.32, 95%CI: 1.06-1.65). High PA was insignificantly negatively associated with anxiety, depression, psychopathological symptoms and poor sleep. Low PA and high ST were independently and interactively associated with increased risks of mental health problems and poor sleep quality (p<0.05 for all).

CONCLUSION

Interventions are needed to reduce ST and increase PA in the lifestyles of young people. Future research should develop and measure the impacts of interventions and their potential consequences on sleep, health, and well being.

Fabrication of antibody microarrays by light-induced covalent and oriented immobilization

Antibody microarrays have important applications for the sensitive detection of biologically important target molecules and as biosensors for clinical applications. Microarrays produced by oriented immobilization of antibodies generally have higher antigen-binding capacities than those in which antibodies are immobilized with random orientations. Here, we present a UV photo-cross-linking approach that utilizes boronic acid to achieve oriented immobilization of an antibody on a surface while retaining the antigen-binding activity of the immobilized antibody. A photoactive boronic acid probe was designed and synthesized in which boronic acid provided good affinity and specificity for the recognition of glycan chains on the Fc region of the antibody, enabling covalent tethering to the antibody upon exposure to UV light. Once irradiated with optimal UV exposure (16 mW/cm(2)), significant antibody immobilization on a boronic acid-presenting surface with maximal antigen detection sensitivity in a single step was achieved, thus obviating the necessity of prior antibody modifications. The developed approach is highly modular, as demonstrated by its implementation in sensitive sandwich immunoassays for the protein analytes Ricinus communis agglutinin 120, human prostate-specific antigen, and interleukin-6 with limits of detection of 7.4, 29, and 16 pM, respectively. Furthermore, the present system enabled the detection of multiple analytes in samples without any noticeable cross-reactivities. Antibody coupling via the use of boronic acid and UV light represents a practical, oriented immobilization method with significant implications for the construction of a large array of immunosensors for diagnostic applications.

Pyridinylboronic acid-functionalized organic-silica hybrid monolithic capillary for the selective enrichment and separation of cis-diol-containing biomolecules at acidic pH

Boronate affinity chromatography (BAC) is a unique means for the selective separation and enrichment of 1,2 and 1,3 cis-diol-containing compounds. However, conventional boronate affinity materials require a basic binding pH (usually≥8.5), which gives rise to not only inconvenience in operation but also the risk of degradation of labile compounds. Although the applicable pH has been expanded to 5.0 in recent years, the current boronate affinity materials still fail to meet the acidic pH end of frequently used biosamples, particularly urine (pH 4.5). In this study, we report a 3-pyridylboronic acid-functionalized organic-silica hybrid monolithic capillary that exhibited a binding pH of 4.5, the lowest so far in BAC. Such a binding pH enabled direct extraction of cis-diol-containing biomolecules such as nucleosides from urine samples without pH adjustment. The boronate affinity monolithic capillary showed enhanced affinity toward negatively charged cis-diol-containing analytes such as ribonucleotides. Moreover, it could function as an anion exchanger at acidic pH (∼2). The column was found to retain multiple compounds from urine, which can be assumed to be at least mostly if not entirely cis-diol-containing compounds.

Fabrication of a detection platform with boronic-acid-containing zwitterionic polymer brush

Development of technologies for biomedical detection platform is critical to meet the global challenges of various disease diagnoses, especially for point-of-use applications. Because of its natural simplicity, effectiveness, and easy repeatability, random covalent-binding technique is widely adopted in antibody immobilization. However, its antigen-binding capacity is relatively low when compared to site-specific immobilization of antibody. Herein, we report that a detection platform modified with boronic acid (BA)-containing sulfobetaine-based polymer brush. Mainly because of the advantage of oriented immobilization of antibody endowed with BA-containing three-dimensional polymer brush architecture, the platform had a high antigen-binding capacity. Notably, nonspecific protein adsorption was also suppressed by the zwitterionic pendants, thus greatly enhanced signal-to-noise (S/N) values for antigen recognition. Furthermore, antibodies captured by BA pendants could be released in dissociation media. This new platform is promising for potential applications in immunoassays.

Improved activity of immobilized antibody by paratope orientation controller: probing paratope orientation by electrochemical strategy and surface plasmon resonance spectroscopy

Electrochemical method and surface plasmon resonance (SPR) spectroscopic analysis are utilized herein to investigate antibody immobilization without and with orientation control for site-positioning paratopes (antigen binding site) of the antibody molecules. Biotin and its antibody were selected in current study as model. Such an approach employed thiophene-3-boronic acid (T3BA) as paratope orientation controller, (i) enabled site orientation of the antibody molecules reducing the hiding of paratopes, and (ii) maintained the activity of the captured antibodies, as confirmed by electrochemical and SPR analysis. Anti-biotin antibody (a glycoprotein) was covalently bound to a self-assembled monolayer of T3BA modified on a nanogold-electrodeposited screen-printed electrode through boronic acid-saccharide interactions, with the boronic acid units specifically binding to the glycosylation sites of the antibody molecules. The immunosensor functioned based on competition between the analyte biotin and biotin-tagged, potassium hexacyanoferrate(II)-encapsulated liposomes. The current signal produced by the released liposomal Fe(CN)6(4-), measured using square wave voltammetry, yielded a sigmoidally shaped dose-response curve that was linear over eight orders of magnitude (from 10(-11) to 10(-3)M). Furthermore this biosensing system fabricated based on T3BA approach was found to possess significantly improved sensitivity, and the limit of detection toward biotin was calculated as 0.102 ng mL(-1) (equivalent to 6 μL of 4.19 × 10(-10)M biotin).

Boronic acid-functionalized core-shell-shell magnetic composite microspheres for the selective enrichment of glycoprotein

In this work, core-shell-shell-structured boronic acid-functionalized magnetic composite microspheres Fe3O4@SiO2@poly (methyl methacrylate-co-4-vinylphenylbornoic acid) (Fe3O4@SiO2@P(MMA-co-VPBA)) with a uniform size and fine morphology were synthesized. Here, Fe3O4 magnetic particles were prepared by a solvothermal reaction, whereas the Fe3O4@SiO2 microspheres with a core-shell structure were obtained by a sol-gel process. 3-(Trimethoxysilyl) propyl methacrylate (MPS)-modified Fe3O4@SiO2 was used as the seed in the emulsion polymerization of MMA and VPBA to form the core-shell-shell-structured magnetic composite microspheres. As the boronic acid groups on the surface of Fe3O4@SiO2@P(MMA-co-VPBA) could form tight yet reversible covalent bonds with the cis-1,2-diols groups of glycoproteins, the magnetic composite microspheres were applied to enrich a standard glycoprotein, horseradish peroxidase (HRP), and the results demonstrated that the composite microspheres have a higher affinity for the glycoproteins in the presence of the nonglycoprotein bovine serum albumin (BSA) over HRP. Additionally, different monomer mole ratios of MMA/VPBA were studied, and the results implied that using MMA as the major monomer could reduce the amount of VPBA with a similar glycoprotein enrichment efficiency but a lower cost.

Boronate derivatives of functionally diverse catechols: stability studies

Benzeneboronate of catecholic carboxyl methyl esters, N-acetyldopamine, coumarin and catechol estrogens were prepared as crystalline derivatives in high yield. Related catechol compounds with extra polar functional group(s) (OH, NH2) do not form or only partially form unstable cyclic boronate derivatives.

Sequential affinity purification of peroxidase tagged bispecific anti-SARS-CoV antibodies on phenylboronic acid agarose

Hybrid hybridomas (quadromas) are derived by fusing at least two hybridomas, each producing a different antibody of predefined specificity. The resulting cell secretes not only the immunoglobulins of both parents but also hybrid molecules manifesting the binding characteristics of the individual fusion partners. Purification of the desired bispecific immunoprobe with high specific activity from a mixture of bispecific and monospecific monoclonal antibodies requires special strategies. Using a dual, sequential affinity chromatography (Protein-G chromatography followed by m-aminophenyleboronic acid agarose column), we have purified bispecific monoclonal antibodies (BsMAb) as a preformed HRPO (Horseradish Peroxidase) complex (BsMAb-HRPO). The quadroma culture supernatant was initially processed on a Protein-G column to isolate all the species of immunoglobulins. This pre-enriched fraction was subsequently passed through the aminophenyleboronic acid column super saturated with HRPO. The column matrix has the ability to bind to proteins such as HRPO with vicinal diols. The enzyme loaded column captures the desired bispecific anti-SARS-CoVxanti-HRPO species with the elimination of the monospecific anti-SARS-CoV MAb to result in a high specific activity diagnostic probe. The presence of anti-HRPO MAb is an acceptable impurity as it will not bind to the target SARS-CoV NP antigen and will get washed out during the ELISA procedure.

Modification of aluminum chips for LDI mass spectrometry of proteins

Matrix-assisted laser desorption ionization time-of-flight mass spectroscopy (MALDI TOFMS) combined with affinity chromatography on immobilized phenylboronic acid agarose gels was used for selective enrichment and detection of specifically modified proteins such as glycated proteins in complex biological samples. Physicochemical grafting of hydrophilic polymers on aluminum surface was developed to reduce nonspecific protein sorption and to create a proper support layer for a three-dimensional affinity hydrogel. Grafted agarose allowed the fixation of three-dimensional agarose hydrogel on the chip surface. Both pinched polymers and hydrogels were effectively derivatized. 3-Aminophenylboronic acid (mPBA) was covalently immobilized as an affinity ligand to achieve specific binding of glycated plasma proteins. Alternatively, the affinity sorbent was immersed into the hydrogel to increase binding capacity. MALDI TOFMS was used to evaluate binding efficiency and molecular mass changes of human serum albumin due to glycation. Glycated proteins were captured directly on the chip with high selectivity and efficacy, and low nonspecific binding. Thus they could easily be characterized by MALDI TOFMS.

Application of phenylboronic acid modified hydrogel affinity chips for high-throughput mass spectrometric analysis of glycated proteins

The complexity of the human plasma proteome is greatly increased by post-translational modifications. Besides physiological modifications, pathological conditions such as diabetes are responsible for adding to this complexity by producing advanced glycation endproducts (AGEs). When searching for specific biomarkers it is a prerequisite to reduce this complexity prior to analysis. To do this, agarose hydrogel was used to create a high-capacity affinity layer on the modified aluminum surface of MALDI (matrix-assisted laser desorption/ionization) targets. 3-Aminophenylboronic acid was immobilized via cyanogen bromide activation as a ligand for affinity sorption of glycated proteins, followed by their direct detection by MALDI. High protein capacity of prepared MALDI chips, efficient separation and low non-specific protein binding were demonstrated. The results show that phenylboronic acid modified hydrogels are very suitable for creating affinity surfaces for the high-throughput analysis of AGEs.

Affinity interactions between phenylboronic acid-carrying self-assembled monolayers and flavin adenine dinucleotide or horseradish peroxidase

A method is provided for the recognition of glycated molecules based on their binding affinities to boronate-carrying monolayers. The affinity interaction of flavin adenine dinucleotide (FAD) and horseradish peroxidase (HRP) with phenylboronic acid monolayers on gold was investigated by using voltammetric and microgravimetric methods. Conjugates of 3-aminophenylboronic acid and 3,3'-dithiodipropionic acid di(N-hydroxysuccinimide ester) or 11-mercaptoundecanoic acid were prepared and self-assembled on gold surfaces to generate monolayers. FAD is bound to this modified surface and recognized by a pair of redox peaks with a formal potential of -0.433 V in a 0.1 M phosphate buffer solution, pH 6.5. Upon addition of a sugar to the buffer, the bound FAD could be replaced, indicating that the binding is reversible. Voltammetric, mass measurements, and photometric activity assays show that the HRP can also be bound to the interface. This binding is reversible, and HRP can be replaced by sorbitol or removed in acidic solution. The effects of pH, incubation time, and concentration of H(2)O(2) were studied by comparing the catalytic reduction of H(2)O(2) in the presence of the electron-donor thionine. The catalytic current of the HRP-loaded electrode was proportional to HRP concentrations in the incubation solution in the range between 5 microg mL(-1) and 0.1 mg mL(-1) with a linear slope of 3.34 microA mL mg(-1) and a correlation coefficient of 0.9945.

Polyvinylamine Boronate Adhesion to Cellulose Hydrogel

The adhesion of polyvinylamine to wet cellulose was significantly enhanced by the presence of pendant phenylboronic acid groups. It is proposed that adhesion results from boronate ester formation with cellulose at pH > 8. Experiments with phenol derivatized polyvinylamine gave low adhesion supporting the fact that the boronate moiety was responsible for strong adhesion to never-dried cellulose surfaces.

Interaction of sugars, polysaccharides and cells with boronate-containing copolymers: from solution to polymer brushes

Interaction of mono- and disaccharides, polysaccharide particles and yeast cells with boronate-containing copolymers (BCC) of N-acryloyl-m-aminophenylboronic acid (NAAPBA) with N,N-dimethylacrylamide (DMAA) or N-isopropylacrylamide (NIPAM) was studied. The binding of saccharides to BCC of NIPAM resulted in a shift of its phase transition temperature (DeltaTP), which provided a quantitative measure for the complex formation. Among the sugars typical of non-reducing ends of glycoproteins the DeltaTP decreased in the order: N-acetylneuraminic acid > xylose approximately galactose > mannose approximately fucose >> N-acetylglucosamine. Strong specific adsorption of the BCC on the cross-linked agarose gel Sepharose CL-6B (15-30 mg/ml gel at pH 9.2) was registered. The copolymers adsorption was due to boronate-sugar interactions and decreased with pH. Multivalent interaction of the BCC with the agarose gel has been proven by liquid column chromatography exhibiting a weak reversible adsorption of NAAPBA and almost irreversible adsorption of DMAA-NAAPBA copolymer from 0.1 M sodium phosphate buffer, pH 7.9. The two studied BCCs could be completely desorbed from the gel by 0.1 M fructose in aqueous buffered media with pH from 7.5 to 9.2. In turn, the agarose particles and yeast cells were found to adhere to siliceous supports end-grafted with boronate-BCC of N,N-dimethylacrylamide at pH > or = 7.5, due to the actions. Quantitative detachment of adhered particles or cells could be attained by addition of 20 mM or 100 mM fructose, respectively, in the pH range from 7.5 to 9.2. Affinity adhesion of micron-size carbohydrate particles to boronate-containing polymer brushes fixed on solid supports was considered as a model system suggesting a new approach to isolation and separation of living cells.

DNA-Directed immobilization: efficient, reversible, and site-selective surface binding of proteins by means of covalent DNA-streptavidin conjugates

Covalent DNA-streptavidin conjugates have been utilized for the reversible and site-selective immobilization of various biotinylated enzymes and antibodies by DNA-directed immobilization (DDI). Biotinylated alkaline phosphatase, beta-galactosidase, and horseradish peroxidase as well as biotinylated anti-mouse and anti-rabbit immunoglobulins have been coupled to the DNA-streptavidin adapters by simple, two-component incubation and the resulting preconjugates were allowed to hybridize to complementary, surface-bound capture oligonucleotides. Quantitative measurements on microplates indicate that DDI proceeds with a higher immobilization efficiency than conventional immobilization techniques, such as the binding of the biotinylated proteins to streptavidin-coated surfaces or direct physisorption. These findings can be attributed to the reversible formation of the rigid, double-stranded DNA spacer between the surface and the proteins. Moreover, BIAcore measurements demonstrate that DDI allows a reversible functionalization of sensor surfaces with reproducible amounts of proteins. Ultimately, the simultaneous immobilization of different compounds using microstructured oligonucleotide arrays as immobilization matrices demonstrate that DDI proceeds with site selectivity due to the unique specificity of Watson-Crick base pairing.

Oriented immobilization of biologically active proteins as a tool for revealing protein interactions and function

The advantages of oriented immobilization of biologically active proteins are good steric accessibilities of active binding sites and increased stability. This not only may help to increase the production of preparative procedures but is likely to promote current knowledge about how the living cells or tissues operate. Protein inactivation starts with the unfolding of the protein molecule by the contact of water with hydrophobic clusters located on the surface of protein molecules, which results in ice-like water structure. Reduction of the nonpolar surface area by the formation of a suitable biospecifc complex or by use of carbohydrate moieties thus may stabilize proteins. This review discusses oriented immobilization of antibodies by use of immobilized protein A or G. The section about oriented immobilization of proteins by use of their suitable antibodies covers immobilization of enzymes utilizing their adsorption on suitable immunosorbents prepared using monoclonal or polyclonal antibodies, preparation of bioaffinity adsorbent for the isolation of concanavalin A and immobilization of antibodies by use of antimouse immunoglobulin G, Fc-specific (i.e. specific towards the constant region of the molecule). In the further section immobilization of antibodies and enzymes through their carbohydrate moieties is described. Oriented immobilization of proteins can be also based on the use of boronate affinity gel or immobilized metal ion affinity chromatography technique. Biotin-avidin or streptavidin techniques are mostly used methods for oriented immobilization. Site-specific attachment of proteins to the surface of solid supports can be also achieved by enzyme, e.g., subtilisin, after introduction a single cysteine residue by site-directed mutagenesis.