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PubMed1975

[The interrelationship between the inhibitory activity of milk with different types of beta-lactoglobulins and the resistance of cattle to mastitis].

In the course of the investigation of piebald (black-white) cattle it is found that 17,62% animals produce the AA type beta-lactoglobulin, 49,52%--the AB type and 32,86%--the BB type. The higher inhibitory activity of milk with the BB type beta-lactoglobulin was found which retained in dilution 1 : 32. The total flora of teat, cyst and parenchyma milk of animals with the BB type beta-lactoglobulin as well as Enterococcus bacteria were much lower than in milk of cows with the AA type homogenous form. The animals with the first type of milk protein had mastitis more rarely as compared to those with the second type. The animals with heterogenous form of beta-lactoglobulin had intermediate values in most of their characteristics.

Animals↗

PubMedDate not supplied

[Beta-lactoglobulin AB fluorescence under different physico-chemical conditions. Denaturation by urea and organic solvents].

Dependences of different fluorescence parameters of bovine beta-lactoglobulin AB on the concentrations of urea (pH 2.8-8.8), ethanol (pH 2.1-10.2), and dioxane (pH 5.3) have been investigated. The denaturation properties (the free energy and the stoichiometry of denaturative interaction) are highly dependent on pH values. The data obtained indicate that the hydrophobic interactions are the determining forces in the stabilization process of the beta-lactoglobulin molecule. The relative contribution of these interactions lowers with pH rise. The denaturation of beta-lactoglobulin AB proceeds through two stages under conditions when the protein octamer exists. Up to 30 vol.% of ethanol and dioxane, the penetration of the organic molecules into the external parts of the protein globule takes place. At the concentration of the solvent exceeding 50 vol.% structural transitions are observed. The comparison of fluorescence and perturbation spectral data enables one to localise tryptophan residues in the protein more precisely. The results of this and former reports lead to hypothesis that beta-lactoglobulin may serve as a transporter of some substances which are unstable to acidic media.

Animals↗

PubMed1993

Selective removal of beta-lactoglobulin directly from cow's milk and preparation of hypoallergenic formulas: a bioaffinity method.

beta-Lactoglobulin, a major allergen of cow's milk, can pass into the breast milk of mothers consuming dairy products and thus sensitize a predisposed infant with a family history of atopic allergy. beta-Lactoglobulin coupled to Sepharose 4B can be used as a specific affinity matrix to remove beta-lactoglobulin from milk without the use of buffer systems. The tendency of beta-lactoglobulin to polymerize reversibly in milk promotes binding of the soluble protein to the coupled protein and a significant retardation in its elution with respect to the other milk proteins. The matrix can be regenerated with water and used repeatedly. These unique characteristics can be exploited in bioreactors designed to treat milk for the preparation of new hypoallergenic hyposensitizing milk formulas to be used by lactating mothers.

Allergens↗

PubMed1998

Kinetics of beta-lactoglobulin adsorption onto stainless steel surfaces

Adsorption kinetics of beta-lactoglobulin onto stainless steel at low concentrations were studied to determine adsorption rate constants for monolayer coverage. Experimental data obtained from a batch reactor were described quantitatively using a reversible adsorption model which becomes the Langmuir-type adsorption isotherm at equilibrium. The forward rate constant, k1, and backward rate constant, k2, were 10(5) mL g-1 min-1 and 5 x 10(-)3 min-1, respectively. A high-performance liquid chromatographic system using a stainless steel column packed with stainless steel particles (column adsorption reactor) was also used to measure adsorption with a step change of beta-lactoglobulin solution. The difference in behavior of an adsorption and a desorption isotherm in this column adsorption reactor suggested surface denaturation of beta-lactoglobulin after adsorption which was consistent with other research work. beta-lactoglobulin adsorption in the column adsorption reactor was affected by volumetric flow rate and concentration up to 4 mL min-1 and 100 &mgr;g mL-1, respectively.

Journal Article↗

PubMed1991

The binding ability of alpha-lactalbumin and beta-lactoglobulin to mutagenic heterocyclic amines.

The binding ability of bovine milk proteins with mutagenic heterocyclic amines was investigated. Binding was determined with 2 mg of beta-lactoglobulin and 20 micrograms of heterocyclic amine in .4 ml of pH 7.4, 50 mM phosphate buffer, at 37 degrees C, in a shaker for 10 min. The unbound heterocyclic amine in protein-free ultrafiltrate was analyzed by HPLC method. The binding of alpha-lactalbumin, beta-lactoglobulin A and beta-lactoglobulin B were 90.44, 81.38, and 89.18%, respectively, with 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole; 37.85, 34.04, and 43.90%, respectively, with 3-amino-1-methyl-5H-pyrido[4,3-b]indole; and 49.11, 43.25, and 57.44%, respectively, with 2-amino-6-methyldipyrido[1,2-a:3',2'-d] imidazole. Binding of beta-lactoglobulin and alpha-lactalbumin to 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole and 3-amino-1-methyl-5H-pyrido [4,3-b]-indole was higher at pH conditions above 7.4, and binding was lost at pH less than 5.5. Maximum binding of both proteins to 2-amino-6-methyl-dipyrido[1,2-a:3',2'-d]imidazole was at pH 7.4, and binding was inhibited at pH conditions above 8.5 and less than 6.5.

Amines↗

PubMed1997

Molten globule state of equine beta-lactoglobulin.

The acid-unfolded state of equine beta-lactoglobulin was characterized by means of circular dichroism, nuclear magnetic resonance, analytical gel-filtration chromatography, and analytical centrifugation. The acid-unfolded state of equine beta-lactoglobulin has a substantial secondary structure as shown by the far-ultraviolet circular dichroism spectrum but lacks persistent tertiary packing of the side chains as indicated by the near-ultraviolet circular dichroism and nuclear magnetic resonance spectra. It is nearly as compact as the native conformation as shown by the gel filtration and sedimentation experiments, and it has the exposed hydrophobic surface as indicated by its tendency to aggregate. All of these characteristics indicate that the acid-unfolded state of equine beta-lactoglobulin is a molten globule state. The alpha helix content in the acid-unfolded state, which has been estimated from the circular dichroism spectrum, is larger than that in the native state, suggesting the presence of nonnative alpha helices in the molten globule state. This result suggests the generality of the intermediate with nonnative alpha helices during the folding of proteins having the beta-clam fold.

Acids↗

PubMed1996

Secondary structure changes and peptic hydrolysis of beta-lactoglobulin induced by diols.

The addition of ethylene glycol, and 1,2- and 1,3-propanediol, decreases the bulk dielectric constant of the medium, and according to CD measurements, increases significantly the proportion of helical structure in beta-lactoglobulin. The medium-induced folding changes followed by limited peptic hydrolysis show that the cleavage of beta-lactoglobulin by pepsin is triggered by structural transformations induced by ethylene glycol only and not by 1, 2- and 1, 3-propanediol. Density measurements, at constant chemical potential and constant molality, demonstrate that all diols are present in the immediate domain of the protein. They are engaged in hydrophobic interactions with the amino acids of beta-lactoglobulin core inducing the formation of additional alpha-helices.

Alcohols↗

PubMed2001

High pressure effect on foaming properties of beta-lactoglobulin and dextran sulfate mixture.

The foaming behaviour of the beta-lactoglobulin + dextran sulfate (DS) mixture was investigated by recording the small pressure changes in the head space above the collapsing foam in a closed container. The foaming ability was based on the highest pressure obtained from the complete decay of foam. The foam stability was based on the foam decay rate constant of the first-order kinetic law calculated from the pressure change as a function of time. The foamability and foam stability were also assessed in terms of visual measurements of foam half-life and initial foam volume. A good correlation was found between foam stability results based on visual measurements and those based on the differential pressure monitoring technique. Foaming was studied at a beta-lactoglobulin/DS weight ratio of 3 with the protein concentration of 0.15 wt.-% at pH 7.0. The surface tension measurements showed no change in the activity of protein upon addition of DS. Pressure treatment (0-800 MPa) of pure protein solution indicated no change in the foamability and foam stability. Pressure-treated solutions of beta-lactoglobulin + DS showed an improvement in the foaming ability and a reduction in foam stability suggesting that polysaccharide molecules prevent protein molecules against aggregation.

Anticoagulants↗

PubMed1989

The stabilization of beta-lactoglobulin by glycine and NaCl.

Effect of glycine and NaCl on the thermal denaturation of beta-lactoglobulin was examined. The results showed that the transition temperature of beta-lactoglobulin is increased by the addition of glycine and NaCl at 0.5 and 1M. This observed stabilization by glycine and NaCl was interpreted in terms of their favorable interactions with the native state of beta-lactoglobulin and unfavorable interactions with the denatured state.

Glycine↗

PubMed2005

Porcine beta-lactoglobulin chemical unfolding: identification of a non-native alpha-helical intermediate.

The chemical unfolding behavior of porcine beta-lactoglobulin (PLG) has been followed at pH 2 and 6 in the presence of guanidinium hydrochloride. The PLG unfolding transition, monitored by tryptophan fluorescence, far and near UV circular dichroism and 1D-NMR, can be described by a three-state transition suggesting the presence of at least one intermediate state that appears to display an excess of non-native alpha-helical structures. The thermodynamic parameters, as determined through a global analysis fitting procedure, give estimates of the free energy differences of the transitions connecting the native, the intermediate and the unfolded state: DeltaG(NI) (0) = 2.8 +/- 0.7 kcal mol(-1) (pH 2) and 4.2 +/- 0.5 kcal mol(-1) (pH 6) and DeltaG(NU) (0) = 7.2 +/- 0.6 kcal mol(-1) (pH 2) and 6.9 +/- 0.6 kcal mol(-1) (pH 6). CD unfolding data of the bovine species (BLG) have been collected here under the same experimental conditions of PLG to allow a careful comparison of the two beta-lactoglobulins. Intermediates with different characteristics have been identified for BLG and PLG, and their nature has been discussed on a structural analysis basis. The thermodynamic data reported here for PLG and BLG and the comparative analysis with data reported for equine beta lactoglobulin, show that homologous beta-barrel proteins, belonging to the same family and displaying high sequence identity (52-64%) populate unfolding intermediates to different extents, even though a common tendency to the formation of non-native alpha-helical intermediates, can be envisaged. The present results provide a prerequisite foundation of knowledge for the design and interpretation of future folding kinetic studies.

Animals↗

PubMed1996

Beta-lactoglobulin B: a proposed standard for the study of reversible self-association reactions in the analytical ultracentrifuge?

Bovine beta-lactoglobulin B is proposed for use as a standard in the measurement of reversible self-association reactions in the analytical ultracentrifuge. The protein is well understood on a molecular level, is readily obtainable, and is stable under harsh conditions. Bovine beta-lactoglobulin B undergoes a simple monomer-dimer equilibrium which can be predictably controlled and consistently reproduced. In this investigation bovine beta-lactoglobulin B has been studied via sedimentation equilibrium experiments in the XL-A analytical ultracentrifuge at 5-30 degrees C in buffers of ionic strength 0.1-0.2 M and pH 2.0-3.0. Samples subjected to a number of different treatments and storage methods all yielded similar results. Molar equilibrium constants for the association reaction were determined by nonlinear regression fitting of a monomer-dimer model of association either to concentration versus radius data, using the programs NONLIN and ORIGIN, or to Omega versus concentration data using the program DUGOM. At 20 degrees C and pH 2.6, over the ionic strength range 0. 1-0.2 M, the equilibrium constant for the association reaction ranges between 1 x 10(4) and 5 x 10(4) M-1. The parameters of nonideal self-association behavior were found to be independent of the particular analysis strategy. Fitting to the concentration distribution, the apparent weight-average molecular weight, or the Omega function all returned identical parameters.

Animals↗

PubMed1995

Regulation of ovine beta-lactoglobulin gene expression during the first stage of lactogenesis.

In the lactating mammary gland, expression of the ovine beta-lactoglobulin gene correlates with the presence of a strong DNaseI hypersensitive site encompassing the promoter region. At this stage of lactogenesis, prolactin is required for optimal expression. Using DNaseI as a probe for formation of a transcription complex on the beta-lactoglobulin promoter, the temporal pattern of ovine beta-lactoglobulin expression during pregnancy has been addressed. The appearance of nuclease hypersensitivity during pregnancy correlates with rising levels of placental lactogen which suggests that this hormone may be the stimulus for expression during the first stage of lactogenesis. This raises the possibility that a different signalling pathway to that present in the lactation functions during pregnancy.

Animals↗

PubMed1997

The equilibrium intermediate of beta-lactoglobulin with non-native alpha-helical structure.

It is generally considered that intermediates of protein folding contain partially formed native-like secondary structures. In contrast, we recently reported that the kinetic folding intermediate of bovine beta-lactoglobulin contains non-native alpha-helical structures. To understand the mechanism that stabilizes the non-native intermediate, we characterized by circular dichroism (CD) the equilibrium unfolding transition of beta-lactoglobulin induced by guanidine hydrochloride (Gdn-HCl) at pH 2 and 4 degrees C. The unfolding transition measured by near-UV CD preceded the transition measured by far-UV CD, indicating the accumulation of the intermediate state. The far-UV CD spectrum of the intermediate, obtained by global fitting analysis of the CD spectra in the presence of various concentrations of Gdn-HCl, was similar to the burst-phase intermediate observed in the refolding kinetics, and contained non-native alpha-helical structures. Addition of 10% (v/v) 2,2,2-trifluoroethanol (TFE) increased the helical content of the equilibrium intermediate, although the protein still assumed the native structure in the absence of Gdn-HCl. A phase diagram of the conformational states, i.e. the alpha-helical intermediate, unfolded and native states, against the concentration of TFE and Gdn-HCl was constructed. This indicated that, because of the high helical preference of the amino acid sequence of beta-lactoglobulin, the helical region protrudes into the boundary between the native and unfolded states, resulting in non-monotonic accumulation of the helical intermediate upon equilibrium unfolding of the native beta-sheet structure. This is the first observation to indicate that a non-native alpha-helical intermediate accumulates during equilibrium unfolding of a predominantly beta-sheet protein.

Animals↗

PubMed1998

alpha-->beta transition of beta-lactoglobulin as evidenced by heteronuclear NMR.

Whereas bovine beta-lactoglobulin is a predominantly beta-sheet protein, it has a marked alpha-helical preference and can be considered to be a useful model of the alpha-->beta transition, a key issue for understanding the folding and biological function of a number of proteins. In order to understand the mechanism of the alpha-->beta transition, the backbone structures of the recombinant bovine beta-lactoglobulin A in the native state and in the highly helical state induced by 2,2,2-trifluoroethanol were characterized by 1H, 13C and 15N multidimensional NMR spectroscopy. Overall, the secondary structures in the native state were similar to those of the crystal structure. On the other hand, beta-lactoglobulin in the 2,2,2-trifluoroethanol state was composed of many alpha-helical segments. The presence of the persistent alpha-helices in the helical state and the core beta-sheet in the native state suggested that during folding native-like core beta-sheet and several non-native helices are formed first and the remaining beta-sheet is subsequently "induced" through interaction with the pre-existing beta-sheet.

Animals↗

PubMed2000

Is folding of beta-lactoglobulin non-hierarchic? Intermediate with native-like beta-sheet and non-native alpha-helix.

The refolding of beta-lactoglobulin, a beta-barrel protein consisting of beta strands betaA-betaI and one major helix, is unusual because non-native alpha-helices are formed at the beginning of the process. We studied the refolding kinetics of bovine beta-lactoglobulin A at pH 3 using the stopped-flow circular dichroism and manual H/(2)H exchange pulse labeling coupled with heteronuclear NMR. The protection pattern from the H/(2)H exchange of the native state indicated the presence of a stable hydrophobic core consisting of betaF, betaG and betaH strands. The protection pattern of the kinetic intermediate obtained about one second after initiating the reaction was compared with that of the native state. In this relatively late kinetic intermediate, which still contains some non-native helical structure, the disulfide-bonded beta-hairpin made up of betaG and betaH strands was formed, but the rest of the molecule was fluctuating, where the non-native alpha-helices may reside. Subsequently, the core beta-sheet extends, accompanied by a further alpha-helix to beta-sheet transition. Thus, the refolding of beta-lactoglobulin exhibits two elements: the critical role of the core beta-sheet is consistent with the hierarchic mechanism, whereas the alpha-helix to beta-sheet transition suggests the non-hierarchic mechanism.

Animals↗

PubMed2000

Molten globule structure of equine beta-lactoglobulin probed by hydrogen exchange.

The molten globule structure of equine beta-lactoglobulin has been inferred from the hydrogen exchange protection of the backbone amide protons. In order to make it possible to measure the hydrogen exchange kinetics of the individual backbone amide protons, the uniformly (15)N-labeled recombinant protein was expressed in Escherichia coli and the NMR peak assignment was obtained for most of the backbone protons. The chemical shift and NOE results obtained under the condition where the protein assumes the native structure are fully consistent with the known secondary structure of bovine beta-lactoglobulin, indicating that the equine protein has a similar native conformation to that of the bovine protein. The hydrogen exchange rate of the individual backbone amide protons was measured under the conditions where the protein assumes the native and molten globule states. In the native state, strong protection was observed for the residues located in the eight (A to H) strands, which form a barrel structure, and residues of a major helix. In the molten globule state at acidic pH conditions, significant protection from the exchange has been observed for residues located in the A, F, G and H strands in the native structure. The pattern of protection is consistent with a native-like beta-sheet formation by these strands. The residues located in a major helix of the native structure are also protected, suggesting that this helix is formed in the molten globule and is packed against the sheet as in the native structure. These results indicate that a native-like subdomain is formed in the molten globule state of equine beta-lactoglobulin.

Amides↗

PubMed2001

Native-like beta-hairpin retained in the cold-denatured state of bovine beta-lactoglobulin.

Bovine beta-lactoglobulin is denatured by increased temperature (heat denaturation) and by decreased temperature (cold-denaturation) in the presence of 4 M urea at pH 2.5. We characterized the structure of the cold-denatured state of beta-lactoglobulin using circular dichroism (CD), small-angle X-ray scattering (SAXS) and heteronuclear nuclear magnetic resonance (NMR). CD and SAXS indicated that the cold-denatured state, in comparison with the highly denatured state induced by urea, is rather compact, retaining some secondary structure, but no tertiary structure. The location of the residual structures in the cold-denatured state and their stability were characterized by 1H/2H exchange combined with heteronuclear NMR. The results indicated that the residues adjacent to the disulfide bond (C106-C119) connecting beta-strands G and H had markedly high protection factors, suggesting the presence of a native-like beta-hairpin stabilized by the disulfide bond. Since this beta-hairpin is conserved between different conformational states, including the kinetic refolding intermediate, it should be of paramount importance for the folding and stability of beta-lactoglobulin. On the other hand, the non-native alpha-helix suggested for the folding intermediate was not detected in the cold-denatured state. The 1H/2H exchange experiments showed that the protection factors of a mixture of the native and cold-denatured states is strongly biased by that of the labile cold-denatured state, consistent with a two-process model of the exchange.

Amino Acid Sequence↗

PubMed1995

Exon organization and sequence of the genes encoding alpha-lactalbumin and beta-lactoglobulin from the tammar wallaby (Macropodidae, Marsupialia).

Clones encompassing the genes encoding alpha-lactalbumin and beta-lactoglobulin were isolated from a tammar wallaby genomic library, the exons localized using end-labeled oligonucleotides and the DNA sequences determined. The tammar beta-lactoglobulin gene has the same 7 exon-6 intron structure as the sheep homologue. Potential binding sites for mammary gland-specific transcription factors were identified, on the basis of similarity to sites in the sheep gene, in the promoter region of the tammar beta-lactoglobulin gene. The tammar gene encoding alpha-lactalbumin appears to contain four introns rather than three as are present in the eutherian homologues, or the evolutionarily related lysozyme gene. The additional intron appears to occur within the 5' noncoding region of the tammar gene.

Amino Acid Sequence↗