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A subclass IgG4-specific antigen-binding radioimmunoassay (RIA): comparison between IgG and IgG4 antibodies to food and inhaled antigens in adult atopic dermatitis after desensitization treatment and during development of antibody responses in children.

A liquid-phase, antigen-binding radioimmunoassay measuring subclass IgG4 antibody (ab) to allergens has been developed. This assay, which uses monoclonal anti-IgG4 to bind IgG4, allows direct comparison of class (IgG)- and subclass (IgG4)-specific ab levels. These assays used radiolabeled purified allergens, Der p I (Ag P1) from the dust mite Dermatophagoides pteronyssinus, Lol p I (Rye 1), from ryegrass pollen, hen's egg ovalbumin, and beta-lactoglobulin from cow's milk. We have investigated IgG4 abs in several clinical situations. The results confirm that IgG ab responses to both inhalants and food proteins unequivocally include IgG4 ab. On average, the proportion of IgG4 ab to these antigens is far higher than the contribution of IgG4 to total IgG. In patients with adult atopic dermatitis, levels of both class and subclass ab were higher than in control subjects; however, the ratio of IgG4:IgG varied widely in patients and control subjects. During desensitization treatment of patients with perennial rhinitis, levels of IgG4 ab to Der p 1 increased sharply, but there were also increases in the total IgG ab responses so that the percentage contribution of IgG4 was only moderately increased (mean values: before, 29%; after, 36%). In a prospective study of children from atopic families, IgG4 abs to food proteins were detectable as early as 3 months. IgG abs to hen's egg ovalbumin and beta-lactoglobulin from cow's milk increased to a maximum at 3 years and declined by 5 years. However, specific IgG4 as a percentage of specific IgG increased progressively from a mean value of approximately 15% at 6 months to approximately 50% at 5 years of age.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Inhalation↗

Antibodies IgG, IgA, and IgM to food antigens during the first 18 months of life in relation to feeding and development of atopic disease.

Serum levels of IgG, IgA, and IgM antibodies against ovalbumin, beta-lactoglobulin, and gliadin were measured in a series of 210 "allergy-risk" infants and their mothers. The antibody levels were determined with ELISA in sera obtained from mothers at delivery, and from their babies at birth, 6 weeks, 6 months, and 18 months. High levels of maternal IgG, IgA, or IgM antibodies to food at delivery did not appear to protect the baby against development of atopic disease. Maternal avoidance of cow's milk and egg during pregnancy had no significant influence on the level of food antibodies in cord blood, but the mother's intake of these foods during lactation affected the immunologic response of the baby, not only to these antigens but also to gliadin as well. Babies with minimal cow's milk exposure before 6 months had significantly lower levels of IgG to beta-lactoglobulin than babies regularly exposed to cow's milk. We conclude that maternal elimination diet during lactation influences the immunologic response of the baby, but if this prevents the development of atopic disease or just delays the immunologic maturation remains to be evaluated.

Animals↗

Sex determination and milk protein genotyping of preimplantation stage bovine embryos using multiplex PCR.

A method for determining the sex and milk protein genotypes (RFLPs) of preimplantation stage bovine embryos using multiplex polymerase chain reaction (PCR) is described. Day 6 to 7 embryos were micromanipulated to isolate 5 to 6 cells. These cells were then dried in reaction tubes for transport to the laboratory. Subsequently, two sets of PCRs were performed using Y chromosome, k-casein and beta-lactoglobulin gene specific primers, followed by electrophoretic analysis of the PCR products. The presence or absence of the Y chromosome was ascertained in 90 of 92 embryos. Moreover, the k-casein specific fragment was amplified and detected in all these embryos. The PCR products were digested in order to genotype the k-casein gene. In 70% of the embryos, the beta-lactoglobulin specific fragment was amplified, although together with some unspecific fragments.

Journal Article↗

Thermal denaturation of whey proteins and its effect in dairy technology.

The irreversible denaturation of the most important whey protein fractions, namely beta-lactoglobulin A and B and alpha-lactalbumin were studied. The orders of the reactions, the rate constants and the activation energies were determined. The experiments were extended to include whey protein solutions of different concentrations and mixtures of whey proteins and caseins in different proportions. The kinetic data found by experiment make it possible to calculate in advance the precise degree of irreversible denaturation. It was found that the denaturation of beta-lactoglobulin was a good test parameter in technological studies and that there was a close correlation between the degree of denaturation and the results of important dairy processes.

Animals↗

Effect of trimming inhibitors on the secretion and biological activity of a murine IgE monoclonal antibody.

Since secretion of IgE antibodies is known to be blocked by tunicamycin, the first aim of the present study was to determine at which step of glycosylation or processing secretion was restored. For this purpose, murine hybridoma cells secreting an anti beta-lactoglobulin IgE were incubated either in the presence of inhibitors of glucosidase I (castanospermine or N-methyl-1-deoxynojirimycin), or of an inhibitor of Golgi mannosidase II (swainsonine). Terminal galactoses predominate on the native IgE N-linked carbohydrate chains. The action of the trimming inhibitors, which results in changes in these terminal galactose residues, was monitored through detecting binding modifications to Concanavalin A and to the lectin of Ricinus communis. The antibody activity was also evaluated by a radioimmunoassay. It was shown that neither secretion nor anti beta-lactoglobulin activity of the IgE antibody are modified in the presence of any of the trimming inhibitors, whereas secretion is blocked in the presence of tunicamycin. Other biological activities of this IgE were investigated: no difference was observed in the binding of the carbohydrate-modified IgE molecules to normal mouse mast cells, nor to RBL-1 cells, as demonstrated by passive cutaneous anaphylaxis and in vitro binding tests respectively. However, traces of unglycosylated epsilon chain (mol. wt 61,000) found in tunicamycin treated cell supernatant did not bind to RBL-1 cell Fc epsilon receptors. These findings globally suggest that secretion occurs only if the tetradecasaccharide precursor of N-linked carbohydrate chains is transferred from its lipid-carrier to the polypeptide. Further, the presence of such non-processed oligosaccharides (Glc3Man9GlcNAc2) on IgE, does not seem to modify any of the biological activities of this molecule.

1-Deoxynojirimycin↗

Application of polymorphic DNA sequences to differentiate the origin of decomposed bovine meat.

Two bovine meat samples were analysed although the samples were already in a state of advanced decomposition. The isolated DNA was extremely degraded and not suitable for conventional DNA fingerprinting (profiling), thus the polymerase chain reaction (PCR) was applied to screen for a Y-chromosome specific fragment and the loci of the two milk proteins kappa-casein and beta-lactoglobulin. Both samples contained Y-chromosome specific DNA and the kappa-casein genotype AA but they differed at the beta-lactoglobulin locus (BB versus AB). Thus a different origin (carcass) could be verified for the two samples and a subject was exonerated from a case of meat larceny.

Animals↗

Human tear viscosity: an interactive role for proteins and lipids.

Human tear viscosity is poorly understood. Tears need to remain on the ocular surface for lubrication without causing damage to the surface epithelia due to drag when blinking. Whole tears are shear-thinning (non-Newtonian), which cannot be explained by the amount of mucin present, nor by individual proteins. Whole tears minus lipids become Newtonian. Though no free lipids had previously been found in collected tears, tear lipocalin (TL), a major tear protein, is known to bind lipids. In this study, we aimed to confirm whether there are any free lipids in collected tears, and to clarify the combined contribution of tear proteins to viscosity, including experiments on recombinant TL, both without (apo-TL) and with (holo-TL) bound lipid. We also investigated possible oligomer formation by holo- and apo-TL as a mechanism for viscosity using SDS-PAGE and analytical ultracentrifugation (AU). For comparison, we have included results for beta-lactoglobulin, a well-characterised lipocalin protein. No free lipids were detected in whole tears. Rheology showed that any protein combination that included lysozyme or lactoferrin was shear-thinning, as was apo-TL, though holo-TL was Newtonian (linear). Results from SDS-PAGE and AU showed apo-TL to be entirely monomeric, but holo-TL showed some dimerization. Both apo- and holo-beta-lactoglobulin exhibited a monomer-dimer equilibrium. We conclude that hetero-protein interactions, possibly electrostatic, involving lipid-binding-induced structural changes to TL, significantly contribute to the viscosity of human tears.

Carrier Proteins↗

High pressure-low temperature processing of food proteins.

High pressure-low temperature (HP-LT) processing is of interest in the food field in view of: (i) obtaining a "cold" pasteurisation effect, the level of microbial inactivation being higher after pressurisation at low or sub-zero than at ambient temperature; (ii) limiting the negative impact of atmospheric pressure freezing on food structures. The specific effects of freezing by fast pressure release on the formation of ice I crystals have been investigated on oil in water emulsions stabilized by proteins, and protein gels, showing the formation of a high number of small ice nuclei compared to the long needle-shaped crystals obtained by conventional freezing at 0.1 MPa. It was therefore of interest to study the effects of HP-LT processing on unfolding or dissociation/aggregation phenomena in food proteins, in view of minimizing or controlling structural changes and aggregation reactions, and/or of improving protein functional properties. In the present studies, the effects of HP-LT have been investigated on protein models such as (i) beta-lactoglobulin, i.e., a whey protein with a well known 3-D structure, and (ii) casein micelles, i.e., the main milk protein components, the supramolecular structure of which is not fully elucidated. The effects of HP-LT processing was studied up to 300 MPa at low or sub-zero temperatures and after pressure release, or up to 200 MPa by UV spectroscopy under pressure, allowing to follow reversible structural changes. Pressurisation of approximately 2% beta-lactoglobulin solutions up to 300 MPa at low/subzero temperatures minimizes aggregation reactions, as measured after pressure release. In parallel, such low temperature treatments enhanced the size reduction of casein micelles.

Animals↗

Preferential hydration and solubility of proteins in aqueous solutions of polyethylene glycol.

This paper is focused on the local composition around a protein molecule in aqueous mixtures containing polyethylene glycol (PEG) and the solubility of proteins in water+PEG mixed solvents. Experimental data from literature regarding the preferential binding parameter were used to calculate the excesses (or deficits) of water and PEG in the vicinity of beta-lactoglobulin, bovine serum albumin, lysozyme, chymotrypsinogen and ribonuclease A. It was concluded that the protein molecule is preferentially hydrated in all cases (for all proteins and PEGs investigated). The excesses of water and deficits of PEG in the vicinity of a protein molecule could be explained by a steric exclusion mechanism, i.e. the large difference in the sizes of water and PEG molecules. The solubility of different proteins in water+PEG mixed solvent was expressed in terms of the preferential binding parameter. The slope of the logarithm of protein (lysozyme, beta-lactoglobulin and bovine serum albumin) solubility versus the PEG concentration could be predicted on the basis of experimental data regarding the preferential binding parameter. For all the cases considered (various proteins, various PEGs molecular weights and various pHs), our theory predicted that PEG acts as a salting-out agent, conclusion in full agreement with experimental observations. The predicted slopes were compared with experimental values and while in some cases good agreement was found, in other cases the agreement was less satisfactory. Because the established equation is a rigorous thermodynamic one, the disagreement might occur because the experimental results used for the solubility and/or the preferential binding parameter do not correspond to thermodynamic equilibrium.

Models, Theoretical↗

Mobility-based selective on-line preconcentration of proteins in capillary electrophoresis by controlling electroosmotic flow.

A simple method to perform selective on-line preconcentration of protein samples in capillary electrophoresis (CE) is described. The selectivity, based on protein electrophoretic mobility, was achieved by controlling electroosmotic flow (EOF). A short section of dialysis hollow fiber, serving as a porous joint, was connected between two lengths of fused silica capillary. High voltage was applied separately to each capillary, and the EOF in the system was controlled independently of the local electric field intensity by controlling the total voltage drop. An equation relating the EOF with the total voltage drop was derived and evaluated experimentally. On-line preconcentration of both positively charged and negatively charged model proteins was demonstrated without using discontinuous background electrolytes, and protein analytes were concentrated by approximately 60-200-fold under various conditions. For positively charged proteins, positive voltages of the same magnitude were applied at the free ends of the connected capillaries while the porous joint was grounded. This provided a zero EOF in the system and a non-zero local electric field in each capillary to drive the positively charged analytes to the porous joint. CE separation was then initiated by switching the polarity of the high voltage over the second capillary. For negatively charged proteins, the procedure was the same except negative voltages were applied at the free ends of the capillaries. Mobility-based selective on-line preconcentration was also demonstrated with two negatively charged proteins, i.e. beta-lactoglobulin B and myoglobin. In this case, negative voltages of different values were applied at the free ends of the capillaries with different values, which provided a non-zero EOF in the system. The direction of EOF was the same as that of the electrophoretic migration velocities of the protein analytes in the first capillary and opposite in the second capillary. By controlling the EOF, beta-lactoglobulin B, which has a higher mobility, could be concentrated over 150-fold with a 15 min injection while myoglobin, which has a lower mobility, was eliminated from the system.

Electrophoresis, Capillary↗

High-performance liquid chromatography of governing liquid to detect illegal bovine milk's addition in water buffalo Mozzarella: comparison with results from raw milk and cheese matrix.

A method to detect fraudulent addition of bovine milk in water buffalo Mozzarella cheese by gradient high-performance liquid chromatography (RP-HPLC), relying on the measurement of quantity ratios within beta-lactoglobulin protein family, is described. Analyses were performed on raw milk, cheese matrix and cheese governing liquid using a C4 column and UV detection. This work demonstrated that bovine milk addition during cheesemaking can be detected in governing liquid of Mozzarella down to the EU law limit of 1% as well as in raw milk and cheese matrix. A significant lowering of peaks' areas and heights was observed in cheese matrix and governing liquid samples in comparison with the corresponding milk ones, possibly due to proteins' degradation during the cheesemaking process. The results show that, unlike previous works reported, the use of a matrix-specific calibration curve is essential in order to achieve a proper quantitation of beta-lactoglobulin proteins, thus allowing a reliable estimation of bovine milk addition.

Animals↗

Features of the milk whey protein partitioning in polyethyleneglycol-sodium citrate aqueous two-phase systems with the goal of isolating human alpha-1 antitrypsin expressed in bovine milk.

Partitioning behaviour of the bovine whey proteins (bovine serum albumin, alpha-lactoalbumin and beta-lactoglobulin) and human alpha-1 antitrypsin in aqueous two-phase systems prepared with polyethyleneglycol (molecular masses: 1000, 1450 and 3350)-sodium citrate was analysed at pH 5.2, 6.2 and 8.2. Alpha lactoalbumin concentrated in the polyethyleneglycol rich-phase, while beta-lactoglobulin, bovine serum albumin and alpha-1 antitrypsin showed affinity for the citrate rich-phase. In aqueous two-phase systems of high medium pH and high polyethyleneglycol molecular mass the protein partitioning equilibrium is displaced to the citrate rich-phase. The polyethyleneglycol 1450-pH 5.2 system with a top/bottom phase-volume ratio of 3 showed to have the best capability of recovering the alpha-1 antitrypsin from a mixture prepared with natural milk whey and human alpha-1 antitrypsin. The recovery of this protein in the bottom phase was of 90% and the purity of the obtained product was of 98%. The method appears to be suitable as a starting point to isolate other human proteins expressed in transgenic bovine milk.

Animals↗

Model for Plateau border drainage of power-law fluid with mobile interface and its application to foam drainage.

A model for drainage of a power-law fluid through a Plateau border is proposed which accounts for the actual Plateau border geometry and interfacial mobility. The non-dimensionalized Navier-Stokes equations have been solved using finite element method to obtain the contours of velocity within the Plateau border cross section and average Plateau border velocity in terms of dimensionless inverse surface viscosity and power-law rheological parameters. The velocity coefficient, the correction for the average velocity through a Plateau border of actual geometry compared to that for a simplified circular geometry of the same area of cross section, was expressed as a function of dimensionless inverse surface viscosity and flow behavior index of the power-law fluid. The results of this improved model for Plateau border drainage were then incorporated in a previously developed foam drainage model [G. Narsimhan, J. Food Eng. 14 (1991) 139] to predict the evolution of liquid holdup profiles in a standing foam. Foam drainage was found to be slower for actual Plateau border cross section compared to circular geometry and faster for higher interfacial mobility and larger bubble size. Evolution of liquid holdup profiles in a standing foam formed by whipping and stabilized by 0.1% beta-lactoglobulin in the presence of xanthan gum when subjected to 16g and 45g centrifugal force fields was measured using magnetic resonance imaging for different xanthan gum concentrations. Drainage resulted in the formation of a separate liquid layer at the bottom at longer times. Measured bubble size, surface shear viscosity of beta-lactoglobulin solutions and literature values of power-law parameters of xanthan gum solution were employed in the current model to predict the evolution of liquid holdup profile which compared well with the experimental data. Newtonian model for foam drainage for zero shear viscosity underpredicted drainage rates and did not agree with the experimental data.

Journal Article↗

In silico approaches reveal the potential for DNA sequence-dependent histone octamer affinity to influence chromatin structure in vivo.

Nucleosome positioning signals embedded within the DNA sequence have the potential to influence the detailed structure of the higher-order chromatin fibre. In two previous studies of long stretches of DNA, encompassing the chicken beta-globin and ovine beta-lactoglobulin genes, respectively, we mapped the relative affinity of every site for the core histone octamer. In both cases a periodic arrangement of the in vitro positioning sites suggests that they might influence the folding of a nucleosome chain into higher-order structure; this hypothesis was borne out in the case of the beta-lactoglobulin gene, where the distribution of the in vitro positioning sites is related to the positions nucleosomes actually occupy in sheep liver cells. Here, we have exploited the in vitro nucleosome positioning datasets to simulate nucleosomal organisation using in silico approaches. We use the high-resolution, quantitative positioning maps to define a one-dimensional positioning energy lattice, which can be populated with a defined number of nucleosomes. Monte Carlo techniques are employed to simulate the behaviour of the model at equilibrium to produce a set of configurations, which provide a probability-based occupancy map. Employing a variety of techniques we show that the occupancy maps are a sensitive function of the histone octamer density (nucleosome repeat length) and find that a minimal change in this property can produce dramatic localised changes in structure. Although simulations generally give rise to regular periodic nucleosomal arrangements, they often show octamer density-dependent discontinuities, which tend to co-localise with sequences that adopt distinctive chromatin structure in vivo. Furthermore, the overall organisation of simulated chromatin structures are more closely related to the situation in vivo than is the original in vitro positioning data, particularly at a nucleosome density corresponding to the in vivo state. Although our model is simplified, we argue that it provides a unique insight into the influence that DNA sequence can have in determining chromatin structure and could serve as a useful basis for the incorporation of other parameters.

Base Sequence↗

Identification and quantification of major bovine milk proteins by liquid chromatography.

In the field of food quality, bovine milk products are of particular interest due to the social and economic importance of the dairy products market. However, the risk of fraudulent manipulation is high in this area, for instance, replacing milk powder by whey is very interesting from an economic point of view. Therefore, there is a need to have suitable analytical methods available for the determination of all milk components, which is currently not the case, especially for the main proteins. The detection of potential manipulations requires then a clear analytical characterisation of each type of bovine milk, what constitutes the goal of this work. The separation of the major milk proteinic components has been carried out by ion-pair reversed-phase HPLC with photodiode array detection, using a C4 column. The overall optimisation has been achieved using a statistical experimental design procedure. The identification of each protein was ascertained using retention times, peak area ratios and second derivative UV spectra. Quantification was based on calibration curves drawn using purified proteins. Major sources of uncertainty were identified and the full uncertainty budget was established. The procedure was initially developed using the skimmed milk powder certified reference material CRM 063R and then applied to various types of commercial milks as well as to raw milk. The method is able to separate and quantify the seven major proteins (K-casein, alphas2-casein, alphas1-casein, beta-casein, alpha-lactalbumin, beta-lactoglobulin B and beta-lactoglobulin A) in one run and also to provide precise determinations of the total protein concentration. These are important results towards the further development of a reference method for major proteins in milk. In addition, the use of a certified material reference is suggested in order to make comparisons of method performances possible.

Animals↗

Preparation and use of ion-exchange chromatographic supports based on perfluoropolymers.

A poly(vinyl alcohol) (PVA) coated particulate perfluoropolymer (FEP) support has been functionalised with ion-exchange groups for use in ion-exchange chromatography of proteins. Anion-exchange (DEAE and Q) and cation-exchange (SP) groups were introduced to PVA-FEP which had previously been activated using cyanuric chloride. The equilibrium adsorption capacities of SP-PVA-FEP were 31.8 and 25.2 mg ml-1 for lysozyme and IgG respectively while for DEAE-PVA-FEP, the equilibrium adsorption capacities were 14.9 and 9.7 mg ml-1 for beta-lactoglobulin and HSA respectively. The equilibrium adsorption capacities for Q-PVA-FEP were determined to be 17.2 and 13.5 mg ml-1 for beta-lactoglobulin and HSA respectively. Experiments carried out to investigate the resolving power of materials showed that both SP and Q-PVA-FEP were able to resolve proteins with only small differences in their isoelectric points and that this resolution could be maintained at a flow-rate of 1500 cm h-1. SP-PVA-FEP was used to purify lysozyme from egg whites where a 50-fold purification, to homogeneity, was achieved in 98% yield. The anion exchanger, Q-PVA-FEP could be used to purify G6PDH from a clarified homogenate of bakers' yeast 14.3-fold in 81% yield.

Adsorption↗

Ultrarapid detection of bovine whey proteins in powdered soybean milk by perfusion reversed-phase high-performance liquid chromatography.

A perfusion reversed-phase high-performance liquid chromatographic method has been developed to simultaneously separate soybean and bovine whey proteins (alpha-lactalbumin and beta-lactoglobulins (A + B)) in a very short analysis time (approximately 5 min). The method consisted of a linear binary gradient water-acetonitrile-0.10% trifluoroacetic acid at a flow-rate of 3 ml/min, with the column thermostated at 60 degrees C, and ultraviolet detection at 254 nm. This method enables the rapid detection of adulterations of powdered soybean milks by addition of bovine whey proteins. When bovine whey proteins were too low to be detected by direct injection of the sample, a previous acidic precipitation step was required in order to concentrate these proteins. Quantitatve analysis of bovine whey proteins was also successfully performed. In fact, it was possible to detect about 1% and 1.3% of alpha-lactalbumin and beta-lactoglobulins, respectively, in a commercial powdered soybean milk in which these proteins were included in its formulation. Results were compared with those obtained by conventional reversed-phase high-performance liquid chromatography.

Animals↗

Evaluation of volatile eluents and electrolytes for high-performance liquid chromatography-electrospray ionization mass spectrometry and capillary electrophoresis-electrospray ionization mass spectrometry of proteins. II. Capillary electrophoresis.

Peptides and proteins were separated by capillary electrophoresis (CE) in fused-silica capillaries coated with an irreversibly adsorbed monolayer of derivatized polystyrene nanoparticles. Whereas phosphate buffer, pH 3.10, enabled the highly efficient separation of basic proteins with plate counts up to 1,400,000 m-1, volatile buffer components such as formic acid or acetic acid titrated with ammonia to the desired pH had to be used for the direct coupling of CE with electrospray ionization mass spectrometry (ESI-MS). Compared to 40 mM phosphoric acid-sodium hydroxide, pH 3.10, a background electrolyte containing 125 mM formic acid-ammonia, pH 4.00, was shown to yield equivalent separation efficiency. Investigation of the influence of buffered electrolytes on the ESI-MS signal of lysozyme at pH 2.70-4.00 showed that the charge state distribution shifted to lower charge states at higher pH with a concomitant five-fold decrease in signal intensity of the most abundant signal. The presence of trifluoroacetic acid in the background electrolyte greatly increased the level of baseline noise and completely inhibited the observation of any mass signals related to proteins. Full scan spectra could be acquired from 50-500 fmol amounts of proteins during coupled CE-ESI-MS utilizing 100-125 mM formic acid-ammonia, pH 3.10. However, compared to UV detection, considerable band broadening is observed with ESI-MS detection which is mainly attributed to column overloading, band spreading in the interface, and scanning data acquisition. Finally, the major whey proteins beta-lactoglobulin A, beta-lactoglobulin B, and alpha-lactalbumin were identified in a whey drink by comparison of molecular masses determined by CE-ESI-MS to molecular masses calculated from the amino acid sequence.

Chromatography, High Pressure Liquid↗