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PubMed1999

Solution structure and dynamics of bovine beta-lactoglobulin A.

Using heteronuclear NMR spectroscopy, we studied the solution structure and dynamics of bovine beta-lactoglobulin A at pH 2.0 and 45 degrees C, where the protein exists as a monomeric native state. The monomeric NMR structure, comprising an eight-stranded continuous antiparallel beta-barrel and one major alpha-helix, is similar to the X-ray dimeric structure obtained at pH 6.2, including betaI-strand that forms the dimer interface and loop EF that serves as a lid of the interior hydrophobic hole. [1H]-15N NOE revealed that betaF, betaG, and betaH strands buried under the major alpha-helix are rigid on a pico- to nanosecond time scale and also emphasized rapid fluctuations of loops and the N- and C-terminal regions.

Amino Acid Sequence↗
PubMed1999

New insight into the pH-dependent conformational changes in bovine beta-lactoglobulin from Raman optical activity.

We have studied the conformation of beta-lactoglobulin in aqueous solution at room temperature over the pH range approximately 2.0-9.0 using vibrational Raman optical activity (ROA). The ROA spectra clearly show that the basic up and down beta-barrel core is preserved over the entire pH range, in agreement with other studies. However, from the shift of a sharp positive ROA band at approximately 1268 to approximately 1294 cm(-1) on going from pH values below that of the Tanford transition, which is centered at pH approximately 7.5, to values above, the Tanford transition appears to be associated with changes in the local conformations of residues in loop sequences possibly corresponding to a migration into the alpha-helical region of the Ramachandran surface from a nearby region. These changes may be related to those detected in X-ray crystal structures which revealed that the Tanford transition is associated with conformational changes in loops which form a doorway to the interior of the protein. The results illustrate how the ability of ROA to detect loop and turn structure separately from secondary structure is useful for studying conformational plasticity in proteins.

Animals↗
PubMed2000

New insight on beta-lactoglobulin binding sites by 1-anilinonaphthalene-8-sulfonate fluorescence decay.

The fluorescence time decay parameters of the beta-lactoglobulin-1-anilinonaphthalene-8-sulfonate complex have been investigated under physical and chemical perturbations (2 < pH < 8 and added electrolyte 0 < NaCl < 0.5 M) to obtain new insight on the nature of the protein binding interactions. A double exponential decay of the bound probe lifetime has been confirmed by the presence of a longer component, 11 to 14.5 ns, and a shorter component, 2.5 to 3.5 ns. The two lifetimes are ascribed to different binding modes associated also with different exposure to the solvent; in particular, the longer component is attributed to binding inside the hydrophobic beta barrel, while a "surface" site is suggested for the shorter component. A detailed analysis of the lifetime fractional intensities correlates the binding constants with ionic strength and supports the presence of electrostatic effects at both sites. A Debye-Hückel approach, applied to extrapolate the electrostatic free energy contribution vs. pH at vanishing ionic strength, gives interesting clues on the effective charge felt by the ANS ligands in the proximity of each site. In particular, binding is found to parallel the aspartate and glutamate titrations between pH 3 and pH 4.5; the "surface" site mainly responds to the presence of these local titrating charges while the "internal" site more closely follows the overall protein net charge.

Anilino Naphthalenesulfonates↗
PubMed2000

Bovine beta-lactoglobulin: interaction studies with palmitic acid.

Bovine beta-lactoglobulin (BLG) in vivo has been found complexed with fatty acids, especially palmitic and oleic acid. To elucidate the still unknown structure-function relationship in this protein, the interactions between 13C enriched palmitic acid (PA) and BLG were investigated by means of one-, two-, and three-dimensional NMR spectroscopy in the pH range 8.4-2.1. The NMR spectra revealed that at neutral pH the ligand is bound within the central cavity of BLG, with the methyl end deeply buried within the protein. The analysis of 13C spectra of the holo protein revealed the presence of conformational variability of bound PA carboxyl end in the pH range 8.4-5.9, related to the Tanford transition. The release of PA starts at pH lower than 6.0, and it is nearly complete at acidic pH. This finding is relevant in relation to the widely reported hypothesis that this protein can act as a transporter through the acidic gastric tract. Ligand binding and release is shown to be completely reversible over the entire pH range examined, differently from other fatty acid binding proteins whose behavior is analyzed throughout the paper. The mode of interaction of BLG is compatible with the proposed function of facilitating the digestion of milk fat during the neonatal period of calves.

Animals↗
PubMed1989

Evidence for a third allele at the beta-lactoglobulin (beta-Lg) locus of sheep milk and its occurrence in different breeds.

Milk samples from 189 Merinoland Sheep, 145 Black Faced Mutton Sheep, 89 East Friesian Milk Sheep, 36 Rhön, 36 Pleven, 23 Tsigaja, 25 Black Razka and 86 Hungarian Merino X Pleven (F1) sheep were analysed by polyacrylamide gel electrophoresis under acid conditions and isoelectric focusing in ultrathin layer polyacrylamide gels with carrier ampholytes. Six different beta-lactoglobulin (beta-Lg) phenotypes (A, AB, B, AC, BC and C) were observed by both methods. The occurrence of three codominant alleles (beta-LgA, beta-LgB, beta-LgC) at an autosomal locus (beta-Lg) was supported by family and population data on genetic equilibrium. Differences in gene frequencies between the breeds were observed.

Alleles↗
PubMed1992

Temperature gradient gel electrophoresis: detection of a single base substitution in the cattle beta-lactoglobulin gene.

An A in equilibrium with G transition in exon III is known to differentiate alleles A and B of the cattle beta-lactoglobulin (BLG) gene. A BLG exon III fragment containing the transition site was amplified by the polymerase chain reaction. Temperature gradient gel electrophoresis (TGGE) was then used to detect this transition and hence to genotype cattle: the AT base-pair in allele A was readily distinguished from the GC base-pair of allele B. TGGE can be used to detect any single base-pair substitution, and thus is a powerful method of detecting genetic variability.

Alleles↗
PubMed1990

Bovine beta-lactoglobulin in human milk from atopic and non-atopic mothers. Relationship to maternal intake of homogenized and unhomogenized milk.

Human milk samples (n = 300) were collected during a 3-week period from 10 healthy mothers and from 10 atopic mothers, all with healthy, solely breast-fed infants. The milk samples were analysed by an enzyme-linked immunosorbent assay (ELISA) for the content of bovine beta-lactoglobulin (BLG). In a cross-over design the atopic and non-atopic mothers alternated their intake of milk between homogenized and unhomogenized milk each week. On day 7, in each week, consecutive milk samples were taken before and 4, 8, 12 and 24 hr after a single ingestion of 500 ml of homogenized or unhomogenized milk. Detectable amounts of BLG (0.9-150 micrograms/l, median value 4.2 micrograms/l) were measured in 19/20 of the mothers (95%), in 9 of 10 atopic mothers and in all 10 of 10 non-atopic mothers. No correlation was found between the type of milk preparation (homogenized or unhomogenized) and the presence of BLG or the level of BLG in human milk. A great intra-individual and inter-individual variation of BLG level was found, and no relationship was observed between BLG levels and atopic status of the mothers. The interval between ingestion of 500 ml of milk and the maximal concentration of BLG on milk-free diet varied between 4 and 24 hr, median value 8 hr. The presence of BLG in human milk is a common finding in both atopic and non-atopic mothers.

Adult↗
PubMed1993

Bovine beta-lactoglobulin levels in hydrolysed protein formulas for infant feeding.

A bovine milk protein, beta-lactoglobulin (beta LG), was measured by an enzyme-linked immunosorbent assay (ELISA) in seven different infant formulas based on protein hydrolysates from cows' milk whey or casein, and from bovine collagen and soy. beta LG levels in the formulas were 1/100 to 1/4,800,000 lower than in cows' milk (CM). There was a great difference in the beta LG level between the partly and the extensively hydrolysed formulas; the amount of beta LG was 40,000-fold higher in the partial hydrolysates vs the extensively hydrolysed formulas. Residual beta LG may have been responsible for the allergic reactions described in some children with cows' milk allergy (CMA) receiving these formulas.

Animals↗
PubMed1994

A major continuous allergenic epitope of bovine beta-lactoglobulin recognized by human IgE binding.

Hexapeptides of sequential overlapping sequences of beta-lactoglobulin (BLG) were used to probe serum from children with immediate-type cow milk allergy for IgE binding to continuous epitopes of BLG in an enhanced enzyme-linked immunosorbent assay (ELISA). Six regions of IgE binding were identified on the BLG molecule and these were synthesized as dodecapeptides. Inhibition of IgE binding to whole BLG was used to confirm the BLG-specific binding of IgE to each of the synthesized peptides. One of the peptides, peptide 4, showed inhibition in an IgE anti-BLG radioimmunoassay to all 16 sera tested. The patterns of inhibition with the native BLG molecule and peptide 4 were significantly correlated (P = 0.005), suggesting that this peptide contains a major continuous IgE binding epitope of BLG.

Allergens↗
PubMed2005

Oral administration of recombinant Lactococcus lactis expressing bovine beta-lactoglobulin partially prevents mice from sensitization.

BACKGROUND: The use of probiotics such as Lactococcus lactis and other lactic acid bacteria (LAB) has been proposed for the management of food allergy. However, no experimental study has clearly demonstrated any preventive or therapeutic inhibition of an allergen-specific IgE response. OBJECTIVE: We aimed to study the immunomodulatory effect of recombinant L. lactis expressing bovine beta-lactoglobulin (BLG), a major cow's milk allergen, in a validated mouse model of allergy. METHODS: Six-week-old female Balb/c mice received five repeated doses of BLG, of L. lactis plus BLG, or of recombinant L. lactis by gavage. Different recombinant strains were inoculated, which corresponded to BLG doses ranging from 4 to 70 microg/mice. Mice were then sensitized by intra-peritoneal injection of BLG emulsified in incomplete Freund's adjuvant to induce high IgE concentrations. RESULTS: Pre-treatment with natural L. lactis plus BLG allowed induction of BLG-specific T-helper type 1 (Th1) response, and abrogated the oral tolerance induced by BLG alone, demonstrating the adjuvant effect of this non-colonizing LAB. Moreover, pre-treatment with some of the recombinant strains favoured the development of a Th1 response inhibiting the Th2 one: it induced a significant decrease of specific IgE response, and an intense increase of specific IgG2a and IFN-gamma productions. The most efficient strains that inhibited the IgE response were those producing the highest amounts of the BLG protein. CONCLUSION: Oral administration of some recombinant L. lactis was demonstrated to induce a specific Th1 response down-regulating a further Th2 one. Prophylaxis protocols will thus be evaluated using the most efficient strains.

Administration, Oral↗
PubMed2006

Specific effects of denaturation, hydrolysis and exposure to Lactococcus lactis on bovine beta-lactoglobulin transepithelial transport, antigenicity and allergenicity.

BACKGROUND: Food allergy in developed countries represents a growing concern as reflected by epidemiological studies, indicating that up to 4% of the overall population is affected. Reduction of symptoms takes place following eviction or processing of some allergens. However, it cannot be predicted which structural changes will be associated with significant effects on the allergenicity. OBJECTIVE: To determine how various treatments of bovine beta-lactoglobulin (BLG) used as a model antigen alters its immunoreactivity and transepithelial transport, and whether this correlates with reduced allergenicity using an in vitro basophil activation assay. METHODS: BLG was subjected to reduction/alkylation, trypsin digestion or exposed to Lactococcus lactis. The remaining immunoreactivity toward IgG raised against native BLG was assessed by ELISA. Transepithelial transport of BLG and derivatives was examined using polarized Caco-2 cell monolayers mimicking the intestinal epithelium. Selective passage of tryptic peptides was determined using colchicine and cytochalasin D. Basophil activation was measured following stimulation with BLG and derivatives. RESULTS: Reduction/alkylation, trypsin digestion or incubation with L. lactis was associated with decreased BLG recognition by IgG antibodies raised against the native protein. All treatments also resulted in a more efficient transepithelial transport of BLG. BLG crossed the Caco-2 monolayer through passage across the cell, whereas tryptic peptides followed both the para- and transcellular routes. With the exception of denaturation by reduction/alkylation, cross-linking of IgE antibodies by BLG derivatives led to lower basophil degranulation. CONCLUSION: In vitro dissection of antigenicity and allergenicity may be a valid and convenient alternative to evaluate the effects of biotechnological processing on dietary proteins. In addition, it can help to define the molecular and cellular mechanisms that will provide improved means of diagnosis and possibly therapy of food-allergic disorders.

Allergens↗
PubMed1994

Human alpha-lactalbumin and bovine beta-lactoglobulin absorption in infants.

We investigated gut permeability to human alpha-lactalbumin (ALA) and bovine beta-lactoglobulin (BLG) in 20 infants from birth to 8 months or until weaning, before which they were on a strictly cow's-milk-free diet. We measured the proteins with a sensitive, solid-phase, double-sandwich immunofluorometric assay. Median (range) levels of serum ALA on days 3-4 after birth, and at 1 and 2 months of age were 31 (12-225), 6 (0-55), and 2 (0-16) micrograms/l serum per g ALA given per kg body weight, respectively. At 3, 5, and 8 months of age, only trace amounts of ALA were found. One week after weaning, serum BLG was found in 5/13 infants (38%) and at 2 weeks in 3/14 infants (21%), with median concentrations of 7 and 4 micrograms/l serum per g BLG given per kg body weight, respectively. No ALA could be detected in any of these samples. In absorption of ALA, the four infants who had allergic symptoms did not differ from those without symptoms. Thus, systemic absorption of ALA and BLG does occur in infants. Absorption of ALA is greatest after birth, when 3 x 10(-4) (median) of the given antigens are absorbed, but absorption decreases rapidly. The gut may often be transiently permeable to BLG when cow's-milk-based formula is started.

Age Factors↗
PubMed1984

Physicochemical properties of maltosyl and glucosaminyl derivatives of beta-lactoglobulin.

Maltosyl and glucosaminyl derivatives of beta-lactoglobulin (b-LG) were analyzed for their physicochemical properties: reduced viscosity, ultraviolet difference spectra, intrinsic fluorescence, hydrophobicity and circular dichroism. The viscosity of these derivatives increased as the mass of the carbohydrates covalently linked to b-LG increased. The ultraviolet difference spectra and the intrinsic fluorescence of these proteins revealed that the microenvironments of aromatic amino acid residues of b-LG were increasingly exposed to the surface of the protein as the extent of modification increased; and the polarity of these residues also increased as modification increased. The hydrophobicities of M-b-LG derivatives decreased as the extent of modification increased while the hydrophobicities of G-b-LG derivatives were relatively unchanged. The circular dichroic analysis of these proteins indicated that the order secondary structures of the extensively modified derivatives of b-LG were partially unfolded. Thus, the carbohydrates covalently linked to b-LG altered many physiochemical properties. These physicochemical changes of b-LG apparently resulted from an alteration of forces stabilizing the structure of the protein.

Animals↗
PubMed2004

BCG vaccine modulates intestinal and systemic response to beta-lactoglobulin.

Beta-Lactoglobulin (BLG) is a clinically important antigen in cow's milk and one of the major allergens causing cow's milk allergy. Bacillus Calmette-Guerin (BCG) vaccination has been suggested to modify immune response possibly decreasing the risk of allergy to some antigens in both human and experimental animals. In the present study, we have analyzed whether the early BCG vaccination has any effect on the markers of systemic and gastrointestinal (GI) sensitization to BLG. We immunized two groups of Hooded-Lister rat puppets with intraperitoneal injections of native BLG at 43 and 62 days with pertussis vaccine as adjuvant, one group receiving additionally BCG. The animals were then fed native and denatured milk products twice weekly from 73 to 131 days of age, when they were killed. Control group was not vaccinated and received normal rat forage. Total immunoglobulin E (IgE) levels and BLG-specific IgG(1) and IgG(2a) concentrations were determined in serum samples. Spontaneous interleukin (IL)-4 and interferon (IFN)-gamma production from duodenal specimens were measured, and the inflammatory cells were quantitated in specimens from different sections of the GI tract. Administration of BCG simultaneously with BLG resulted in reduced IgE concentration in serum, while the specific IgG(1) and IgG(2a) antibody responses and the spontaneous secretion of IL-4 and IFN-gamma were not affected. Furthermore, BCG-induced eosinophilic infiltration and increase of intraepithelial lymphocytes (IEL) in the GI mucosa, and a trend toward increased number of lamina propria mononuclear inflammatory cells in the colon (BCG compared with BLG, p = 0.09; BCG compared with controls, p = 0.02). Controls showed increment of IgG(1) response in comparison with the BLG group (p = 0.04) and increase of mucosal eosinophilic infiltration. The BCG modified the response to BLG both at the systemic level as shown by decrease of total IgE and at GI mucosa where increase of eosinophilic infiltration and increased number of IEL were seen. Increment of IgG(1) level and eosinophils in the controls might be related with the lack of modulatory effect of pertussis vaccination. A shift of response toward the lower GI tract after BCG immunization as shown by a trend for increase of mononuclear inflammatory cells in colon lamina propria mimics disease development in some cases of clinical food allergy, and emphasizes the need for evaluation of the changes in the whole GI tract in food allergy models.

Animals↗
PubMed2006

Changes in humoral responses to beta-lactoglobulin in tolerant patients suggest a particular role for IgG4 in delayed, non-IgE-mediated cow's milk allergy.

The major cow's milk allergen beta-lactoglobulin (beta-LG) is relatively resistant to enzymatic degradation and may therefore be involved in non-immunoglobulin (Ig)E-mediated cow's milk allergy (CMA) with delayed gastrointestinal symptoms. Serum levels of beta-LG-specific IgG(1), IgG(4), IgE, and IgA were compared in clinically reactive and tolerized IgE-mediated and non-IgE-mediated CMA with delayed gastrointestinal symptoms (n = 29) and controls (n = 10). Tolerance was associated with decreased beta-LG-specific IgE, IgG(1), and IgG(4) levels in both patient groups. However, the significantly increased beta-LG-specific IgG(4) levels in clinically reactive non-IgE-mediated CMA patients, and its median 36-fold reduction in tolerant patients, suggested a possible immunopathological role for IgG(4) in delayed CMA. Similarly, the significantly increased beta-LG-specific IgE levels in IgE-mediated CMA patients were decreased 44-fold in tolerant patients. The tolerant patients had apparently shifted the humoral immune response from a beta-LG-specific IgE- and/or IgG(4)-dominated immune response to an IgA-dominated immune response as the IgA/IgE or IgA/IgG(4) ratios increased 90- and 15-fold in tolerant IgE-mediated-, and non-IgE-mediated CMA patients, respectively. Thus, the marked difference in beta-LG-specific Ig ratios suggested a tolerance-induced inhibition of a Th(2)-type of immune response with significantly increased IgA dominance in both CMA patient groups.

Adolescent↗
PubMed1997

Beta-lactoglobulin suppresses melanogenesis in cultured human melanocytes.

The effects of whey proteins from bovine milk on melanogenesis in cultured human melanocytes were examined. Among the major protein components of milk whey including beta-lactoglobulin (BLG), alpha-lactalbumin, serum albumin, and IgG, only BLG exhibited the depigmenting effect at a concentration of 1 mg/ml. Also, BLG suppressed the activity of tyrosinase in these cells. Retinol, to which BLG is known to bind, slightly increased the pigmentation of the cells at concentrations in the range of 1-100 nM, and retinoic acid, a metabolite of retinol, exhibited a strong pigmentation-promoting effect within the same concentration range. Treatment of the cells with 1 mg/ml BLG completely abrogated the pigmentation induced by these A vitamins. These results demonstrate a novel biological activity of BLG and suggest that this activity is dependent on its ability to bind retinol.

Animals↗
PubMed1996

Human milk proteins may interfere in ELISA measurements of bovine beta-lactoglobulin in human milk.

It is widely believed that cow's milk proteins ingested by the mother, in particular beta-lactoglobulin (beta-LG), can pass into breast milk and thus sensitize predisposed infants. However, studies to evaluate bovine beta-LG in human milk have given conflicting results. The aim of this study was to analyse the correlation between the amount of cow's milk in the mother's diet and the presence of bovine beta-LG in breast milk. Human milk samples from 14 healthy non-atopic women on diets with different cow's milk contents were examined. The total concentration of bovine beta-LG or beta-LG immuno-like proteins (beta-LGIP) was determined by enzyme-linked immunosorbent assay (ELISA). Two separation procedures utilizing ELISA plates and an affinity chromatography column were set up to identify the human whey components recognized by the anti-beta-LG antibodies. beta-LGIP reactivities of milk from three groups on different diets were not significantly different. After splitting the antigen-antibody complexes, three main protein components, human lactoferrin, human beta-casein and human alpha-lactalbumin, were identified. This study would suggest that, at least in healthy subjects, false-positive results in ELISA determinations of bovine beta-LG in human milk might be due to cross-reactions between polyclonal antibodies and different protein antigens.

Adult↗