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PubMed1991

Human IgE-binding synthetic peptides of bovine beta-lactoglobulin and alpha-lactalbumin. In vitro cross-reactivity of the allergens.

The allergenicity of cow's milk whey proteins, purified by high performance liquid chromatography (HPLC), was examined by the radio-allergosorbent test (RAST) against the sera of children immediately hypersensitive to milk. beta-lactoglobulin and alpha-lactalbumin bound specific IgE in the sera of 63% and 75% of these patients respectively. These allergens were tested for cross reactivity with each other by RAST inhibition. Both inhibited the binding of IgE, in the sera of allergic patients, to the other protein. Two possible determinant peptides, one from beta-lactoglobulin and one from alpha-lactalbumin, were selected by computer prediction of antigenic sites and synthesized by the fluorenylmethoxycarbonyl (FMOC)-polyamide method. The peptides were adsorbed to nitrocellulose discs and used in further RAST studies with sera from the allergic children. Both peptides bound specific IgE in the RAST assay.

Allergens↗
PubMed1976

The interaction between Beta-lactoglobulin and sodium N-dodecyl sulphate.

1. The binding of sodium n-dodecyl sulphate to beta-lactoglobulin was studied in the pH range 3.5-7.0 by equilibrium dialysis, ultracentrifugation and microcalorimetry. 2. At low binding concentrations (less than 30 bound surfactants anions per protein molecule) the complexes formed aggregates in solution. 3. At higher binding concentrations aggregation does not occur at low ionic strength (0.01 mol/litre), but continues at high ionic strength (0.1 mol/litre). 4. At 25 degrees C the enthalpy of interaction of sodium n-dodecyl sulphate with beta-lactoglobulin can be interpreted as the sum of the enthalpies of formation of a complex with 2 bound surfactant anions, with an enthalpy change of -9.5 kJ-mol-1 of bound surfactant, and complexes containing at least 22 bound surfactant anions, with limiting enthalpies per bound surfactant anion of -12.4 kJ-mol-1 at pH 3.5 and -3.25 kJ-mol-1 at pH 5.5. 5. The binding of surfactant and the enthalpy of interaction at pH 3.5 ARE NOT SIGNIFICANTLY AFFECTED BY THE ADDITION Of 8 M-urea. 6. The data indicate that at low binding concentrations the interaction is of an ionic nature, and is accompanied by a conformational change in the protein.

Calorimetry↗
PubMed1977

The state of aggregation of red deer (Cervus elaphus L.) beta-lactoglobulin preparations near neutral pH.

1. The state of aggregation of four red-deer (Cervus elaphus L.) beta-lactoglobulin preparations and a control ox beta-lactoglobulin A preparation was studied by sedimentation-equilibrium experiments at pH 6.5 and 20 degrees C. 2. Three of the deer preparations and the ox control each behaved as a monomer-dimer system, with a value of log K (where K is the association constant in litres/mol) in the range 5.4-5.5. 3. When one of these deer preparations was examined in the presence of dithiothreitol, log K appeared to decrease to 4.5.4. One deer preparation, comprising recovered material, appeared to have undergone irreversible changes and to behave like a non-equilibrating system containing monomer, dimer and trimer. 5. The sedimentation-equilibrium properties of the deer monomer was studied in 6M-guanidine hydrochloride at pH 7.0; the mol.wt. was 17600, the second virial coefficient was 3.4 x 10(-3) ml - mol - g-2, and the apparent partial specific volume 0.724 ml/g, a value indicating an appreciable decrease in volume on dissociation and denaturation.

Animals↗
PubMed1992

Mammary development and milk secretion in transgenic mice expressing the sheep beta-lactoglobulin gene.

Mammary development and milk secretion were studied in transgenic mice which exhibited mammary tissue-specific expression of the sheep beta-lactoglobulin gene, and secreted significant quantities of the foreign protein in milk. Mammary development was unaffected by transgenesis. Tissue DNA content and the activities of several key enzyme markers of cell differentiation were similar in transgenic mice and non-transgenic controls. Milk yield, whether estimated by pup weight gain or measured by a 3H2O-dilution method, was unchanged by foreign gene expression. Gross milk composition, including milk protein concentration, was also similar in transgenic and non-transgenic animals, even though beta-lactoglobulin accounted for 29% of total milk protein. Therefore the foreign gene product was synthesized at the expense of endogenous milk proteins. However, transgenic mammary tissue in vitro exhibited a significantly higher rate of total protein synthesis than did control tissue. This suggested that a factor limiting milk protein synthesis or secretion in transgenic mice in vivo may have been removed by short-term explant culture of mammary tissue. The results emphasize that the use of transgenesis for manipulating milk composition may depend not only on high-level mammary-specific expression of the foreign gene, but also on the biosynthetic capacity of the mammary gland itself.

Aging↗
PubMed1995

Effect of magnetic field strength on the linewidth and spin-lattice relaxation time of the thiocyanate carbon of cyanylated beta-lactoglobulin B: optimization of the experimental parameters for observing thiocyanate carbons in proteins.

The linewidths and spin-lattice relaxation times of the 13C-n.m.r. signal at 109.7 p.p.m. due to the thiocyanate carbon of intact [cyanato-13C]cyanylated-beta-lactoglobulin-B have been determined at magnetic field strengths of 1.88, 6.34 and 11.74 T as well as the spin-lattice relaxation times of its backbone alpha-carbon atoms. The linewidths were directly proportional to the square of the magnetic field strength and we conclude that, at magnetic field strengths of 6.34 T or above, more than 70% of the linewidth will be determined by chemical-shift anisotropy. We estimate that the spin-lattice relaxation time resulting from the chemical-shift anisotropy of the thiocyanate carbon is 1.52 +/- 0.1 s and we conclude that for magnetic field strengths of 6.34 T and above the observed spin-lattice relaxation time of the thiocyanate carbon will be essentially independent of magnetic field strength. Using the rigid-rotor model we obtain estimates of the rotational correlation time of [cyanato-13C]cyanylated-beta-lactoglobulin-B and of the chemical-shift anisotropy shielding tensor of its thiocyanate carbon. We have calculated the linewidths and spin-lattice relaxation times of thiocyanate carbons at magnetic field strengths of 1.88-14.1 T in proteins with M(r) values in the range 10,000-400,000. The effects of magnetic field strength on the resolution and signal-to-noise ratios of the signals due to thiocyanate carbons attached to proteins of M(r) greater than 10,000 are discussed.

Carbon↗
PubMed2001

Thermal unfolding of monomeric and dimeric beta-lactoglobulins.

The thermal stabilities of dimeric bovine beta-lactoglobulin and monomeric equine beta-lactoglobulin were investigated at neutral pH by means of differential scanning calorimetry, circular dichroism, tryptophan fluorescence, and by binding of an hydrophobic probe. Differential scanning calorimetry showed the presence of two structural domains with different thermal stabilities in both proteins. Thermodynamic analysis of the calorimetric signal revealed that the two domains unfold independently according to a mechanism where an equilibrium step is followed by an irreversible transition. The spectroscopic data supported this model and allowed recognition of the structural regions corresponding to the more thermally stable domain. The differences in thermal stability between the two proteins can be primarily ascribed to the properties of the less stable domain.

Animals↗
PubMed1999

Immunoglobulin E suppression and cytokine modulation in mice orally tolerized to beta-lactoglobulin.

This study was designed to confirm the tolerogenic properties of beta-lactoglobulin in a mouse model and to assess specific oral tolerance induction in humoral and cellular compartments. BALB/c mice were fed beta-lactoglobulin (BLG) or whey proteins at different ages and subsequently intraperitoneally challenged 5 days later with both BLG and a non-specific antigen, ovalbumin (OVA). Three weeks later, oral tolerance induction was analysed in CMP-fed, versus saline-fed mice, by measuring specific seric and intestinal antibody responses, delayed-type hypersensitivity (DTH), specific splenocyte proliferation, and cytokine secretion patterns. Three-week-old mice fed high doses of either whey proteins or BLG (respectively 3 mg/g or 5 mg/g of body weight) were found to achieve oral tolerization. At humoral and mucosal levels, anti-BLG immunoglobulin E (IgE) were suppressed in these groups when compared with saline fed mice. With respect to cellular responses, systemic DTH and lymphocyte proliferation to BLG were also inhibited in CMP-fed mice. Weaning time was determined to be the best period for oral tolerance induction. Kinetic analyses showed however, that a minimum of 2 weeks was required for oral tolerance detection. Finally, cytokine profiles indicated a reciprocal decrease of interleukin-2 (IL-2) and interferon-gamma (IFN-gamma) versus an increase of IL-10 and transforming growth factor-beta (TGF-beta) secretions in tolerized mice. Taken together, these results clearly showed that oral administration of high doses of cows' milk proteins can induce significant hyposensitization in mice, in a specific inhibition of T helper 1 (Th1) lymphocytes with the participation of suppressor cytokines.

Age Factors↗
PubMed2002

Thermodynamic stability of porcine beta-lactoglobulin. A structural relevance.

The proposed biological function of beta-lactoglobulins as transporting proteins assumes a binding ability for ligands and high stability under the acidic conditions of the stomach. This work shows that the conformational stability of nonruminant porcine beta-lactoglobulin (BLG) is not consistent with this hypothesis. Thermal denaturation of porcine BLG was studied by high-sensitivity differential scanning calorimetry within the pH range 2.0-10.0. Dependences of the denaturation temperature and enthalpy on pH were obtained, which reveal a substantial decrease in both parameters in acidic and basic media. The denaturation enthalpy follows a linear dependence on the denaturation temperature. The slope of this line is 9.4 +/- 0.6 kJ.mol-1. K-1,which is close to the denaturation heat capacity increment DeltadCp = 9.6 +/- 0.5 kJ.mol-1.K-1, determined directly from the thermograms. At pH 6.25 the denaturation temperatures of porcine and bovine BLG coincide, at 83.2 degrees C. At this pH the denaturation enthalpy of porcine BLG is 300 kJ.mol-1. The denaturation transition of porcine BLG was shown to be reversible at pH 3.0 and pH 9.0. The transition profile at both pH values follows the two-state model of denaturation. Based on the pH-dependence of the transition temperature and the linear temperature dependence of the transition enthalpy, the excess free energy of denaturation, DeltadGE, of porcine BLG was calculated as a function of pH and compared with that of bovine BLG derived from previously reported data. The pH-dependence of DeltadGE is analysed in terms of the contributions of side-chain H-bonds to the protein stability. Interactions stabilizing native folds of porcine and bovine BLG are discussed.

Animals↗
PubMed1995

Transport of beta-lactoglobulin and alpha-lactalbumin in enterocyte-like Caco-2 cells.

The transport of [14C]-radiolabelled beta-lactoglobulin and alpha-lactalbumin through Caco-2 cell monolayers grown on permeable filters was studied in order to evaluate the different protein pathways through the intestinal epithelium. beta-Lactoglobulin or alpha-lactalbumin (0.25-3 mg/ml) was introduced on the apical side of the monolayer and both the transport and the release of labelled material from the cells were measured following different incubation times. The labelled material was analysed by either trichloroacetic acid precipitation or by high pressure liquid chromatography. Despite some differences between the 2 proteins, the overall mechanism followed approximately the same pattern. Part of the intact internalized protein was either recycled (10-15%) or transported via transcytosis (about 5%). Another pathway corresponded to the intracellular degradation of the protein. The calculation of the different routes followed by the proteins indicated that the main part of the degraded fraction (about 70%) was recycled whereas approximately 30% was transported to the other side. Moreover, 5-10% of the endocytosed material was retained intracellularly.

Biological Transport↗
PubMed2006

Time-resolved small-angle neutron scattering during heat-induced fibril formation from bovine beta-lactoglobulin.

We study in situ the kinetics of heat-induced fibrilar aggregation of bovine beta-lactoglobulin at pH 2.0 and 80 degrees C for the first time by time-resolved small-angle neutron scattering. A simple model for the scattering from a mixture of monodisperse charged spheres (monomeric beta-lactoglobulin) interacting via a screened electrostatic repulsion and noninteracting long cylinders (protein fibrils) is used to describe the data. The experimental data are fitted to the model and the concentration of the monomeric protein and the protein incorporated in fibrils are obtained as adjustable parameters. Thus, a simple physical model allows the determination of realistic kinetic parameters during fibrilar protein aggregation. This result constitutes an important step in understanding the process of irreversible fibrilar aggregation of proteins.

Animals↗
PubMed2001

Lifetimes of intermediates in the beta -sheet to alpha -helix transition of beta -lactoglobulin by using a diffusional IR mixer.

The extremely slow alpha-helix/beta-sheet transition of proteins is a crucial step in amylogenic diseases and represents an internal rearrangement of local contacts in an already folded protein. These internal structural rearrangements within an already folded protein are a critical aspect of biological action and are a product of conformational flow along unknown metastable local minima of the energy landscape of the compact protein. We use a diffusional IR mixer with time-resolved Fourier transform IR spectroscopy capable of 400-micros time resolution to show that the trifluoroethanol driven beta-sheet to alpha-helix transition of beta-lactoglobulin proceeds via a compact beta-sheet intermediate with a lifetime of 7 ms, small compared with the overall folding time of beta-lactoglobulin.

Diffusion↗
PubMed2000

What is the role of non-native intermediates of beta-lactoglobulin in protein folding?

The mechanism of alpha-->beta transition in folding of beta-lactoglobulin is discussed based on free energy landscape analysis of a long lattice model. It is found that helical propensity of beta-lactoglobulin is driven by conformational entropy and is intrinsically coded in its native structure. We propose a view on a role of folding intermediate, which is "on-pathway" but rich in non-native structures. The present results suggest that the native structure topology plays an important role in alpha-->beta transition.

Computer Simulation↗
PubMed2002

Manipulating monomer-dimer equilibrium of bovine Beta -lactoglobulin by amino acid substitution.

Bovine beta-lactoglobulin, a major protein in cow's milk composed of nine beta-strands (betaA-betaI) and one alpha-helix, exists as a dimer at neutral pH while it dissociates to a native monomer below pH 3.0. It is assumed that the intermolecular beta-sheet formed between I-strands and salt bridges at AB-loops play important roles in dimer formation. Several site-directed mutants in which intermolecular interactions stabilizing the dimer would be removed were expressed in the methylotrophic yeast Pichia pastoris, and their monomer-dimer equilibria were studied by analytical ultracentrifugation. Various I-strand mutants showed decreases in K(a), suggesting that the intermolecular beta-sheet is essential for dimer formation. By substituting either Asp(33) or Arg(40) on the AB-loop to oppositely charged residues (i.e. R40D, R40E, and D33R), a large decrease in K(a) was observed probably because of the charge repulsion, which is consistent with the role of electrostatic attraction between Arg(40) on one monomer and Asp(33) on the other monomer in the wild-type dimer. However, when two of these mutants, R40D and D33R, were mixed, a heterodimer was formed by the electrostatic attraction between Arg(33) and Asp(40) of different molecules. These results suggested that protein-protein interactions of bovine beta-lactoglobulin can be manipulated by redesigning the residues on the interface without affecting global folding.

Amino Acid Substitution↗
PubMed2000

The effect of hormone replacement therapy on the immunoreactive concentrations in the endometrium of oestrogen and progesterone receptor, heat shock protein 27, and human beta-lactoglobulin.

We determined the expression of oestrogen receptor (ER), progesterone receptor (PR), heat shock protein 27 (HSP27) and human beta-lactoglobulin in the endometrium under hormone replacement therapy (HRT). The immunohistochemical expression during the late progestogenic phase of sequential HRT was compared semi-quantitatively and using image analysis, to the early, mid-, and late luteal phase of the physiological cycle. Under sequential HRT, smaller glands were positive for the ER but larger glands with more advanced secretory features were negative. ER expression was lower in the stroma under HRT, and the difference was statistically significant compared with the early luteal phase (P < 0.05). Expression of HSP27 under HRT was lower in the epithelium but higher in the stroma compared with the physiological luteal phase. Epithelial PR expression was lower under HRT compared with the early, but not the mid- or the late luteal phase. The number of PR-positive stromal cells under HRT was lower compared with the physiological cycle, and the difference was statistically significant in comparison with the early luteal phase (P < 0.05). The glandular area expressing human beta-lactoglobulin during the late progestogenic phase was statistically significantly higher compared with the early, but lower in comparison with the mid- or the late luteal phase (P < 0.05). The study demonstrates a sub-physiological progestogenic response superimposed on evidence of a hypo-oestrogenism, and a differential response in the epithelium and stroma.

Endometrium↗
PubMed1989

Interaction of fatty acids with beta-lactoglobulin and albumin from ruminant milk.

beta-Lactoglobulin isolated from milk of cow, sheep, and goat had about 0.5 mol of fatty acids bound per mol of monomer protein. Fatty acids, mainly palmitic and oleic acids, were the major components (about 75% of total lipids). Albumin isolated from the same samples had about 4.5 mol of fatty acids bound per mol of protein. These two proteins were the only whey proteins able to bind labeled fatty acids in vitro. Interaction of beta-lactoglobulin and albumin with insolubilized fatty acids showed some differences, suggesting different structures of the respective fatty acid binding sites.

Albumins↗
PubMed1992

Molecular dynamics simulations of the whey protein beta-lactoglobulin.

Molecular dynamics simulations have been used to model the motions and conformational behavior of the whey protein bovine beta-lactoglobulin. Simulations were performed for the protein by itself and complexed to a single retinol ligand located in a putative interior binding pocket. In the absence of the retinol ligand, the backbone loops around the opening of this interior pocket shifted inward to partially close off this cavity, similar to the shifts observed in previously reported molecular dynamics simulations of the uncomplexed form of the homologous retinol binding protein. The protein complexed with retinol does not exhibit the same conformational shifts. Conformational changes of this type could serve as a recognition signal allowing in vivo discrimination between the free and retinol complexed forms of the beta-lactoglobulin molecule. The unusual bending of the single alpha-helix observed in the simulations of retinol binding protein were not observed in the present calculations.

Animals↗
PubMed1982

Nonspecific suppressor cell activity and lymphocyte response to beta-lactoglobulin in cow's milk protein hypersensitivity.

beta-Lactoglobulin (BLG) is clinically the most frequent allergen in cow's milk protein hypersensitivity (CMPH). We therefore assessed its in vitro blastogenic effect on lymphocytes of patients suffering from CMPH. Twenty-two patients aged from 1 to 20 months were investigated. beta-Lactoglobulin produced a significantly (p less than 0.00003) higher blastogenic response in lymphocytes of patients with CMPH (mean stimulation index 7.7 +/- 0.7 SEM) than in 26 age-matched controls (2.7 +/- 0.4). This response was age related, being most marked in infants up to 5 months of age. Lymphocyte proliferation following stimulation with BLG can be a useful in vitro test in the diagnosis of CMPH. Because of this augmented lymphocyte response, we considered the possibility of a related defect in immune suppression. Nonspecific concanavalin A-induced suppressor cell activity was assessed in the above patient and control populations. Concanavalin A-induced suppressor cell activity was significantly (p less than 0.05) reduced in patients with CMPH. This too was most marked in the first few months of life. We suggest that the development of CMPH may be due to delayed maturation of a suppressor cell population.

Concanavalin A↗
PubMed1996

Gut permeability to human alpha-lactalbumin, beta-lactoglobulin, mannitol, and lactulose in celiac disease.

Our objective was to examine the permeability of the gut to protein macromolecules and sugar probes and their possible association in celiac disease patients. We studied the permeability to human alpha-lactalbumin, beta-lactoglobulin, mannitol, and lactulose on 46 occasions in 33 celiac disease patients in various phases of the disease; in addition, mannitol and lactulose permeability was studied in 18 healthy controls. Lactalbumin absorption was detected in 19 of 42 patients tested, more often in celiac disease patients with villous atrophy than in those with normal jejunal biopsy (p = 0.01). Higher absorption of lactalbumin was found in patients with subtotal villous atrophy than in those with normal biopsy (p = 0.02). beta-lactoglobulin was found in four of 42 patients tested. Less mannitol was absorbed by patients with either subtotal or partial villous atrophy than by those with normal histology (p = 0.001 and 0.006, respectively). Lactulose recovery was higher in newly diagnosed patients and patients with subtotal villous atrophy than in controls (p = 0.007 and 0.03, respectively). The lactulose/mannitol ratio was higher in newly diagnosed patients and patients with villous atrophy than in controls (p = 0.002 and 0.002, respectively). The correlation between permeability to lactalbumin and mannitol and lactulose was poor. We conclude that permeability to proteins and sugar molecules is abnormal in celiac disease patients with mucosal damage and that they probably reflect different mechanisms of penetration.

Adolescent↗