Invited Review: β-Lactoglobulin: Binding Properties, Structure, and Function (original) (raw)
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International journal of biological macromolecules, 2018
The milk protein β-lactoglobulin has been widely studied since its discovery, both as a purified protein and in mixtures with other milk proteins, where its effect on the processing properties is of importance to the dairy industry. The protein can bind a variety of small hydrophobic molecules, which may allow its use as an oral delivery vehicle. In the present study we have examined the binding of odd-numbered fatty acids by isothermal calorimetry (ITC), X-ray crystallography and computer modelling to provide a clearer picture of the extent and variability of the central binding pocket. The Kd values for the fatty acids C13, C15, C16, C17 and C19 as determined by ITC are 1.93, 2.91, 3.05, 4.11 and 8.67 × 10 M, respectively. The molecular structures revealed the ligands bound in the central cavity with generally well ordered lipophilic tails but significant positional variation at the carboxyl group end. In silico docking analyses identified the lipophilic interactions within the ce...
Journal of Dairy Science, 1995
β-lactoglubulin is the major whey protein in-the milk of ruminants and some nonruminants, such as pigs and horses. Although β-lactoglobulin was first isolated 60 yr ago, no function has been definitely ascribed to β-lactoglobulin. Recent x-ray crystallographic studies have advanced knowledge of the structure of β-lactoglobulin, which is homologous with that of retinol-binding protein and lipocalycins; the function of these proteins seems to be participation in the transport of small hydrophobic substances. By analogy, this protein has been suggested as having a role as a transporter of fatty acids and retinol. This review reassesses the function of β-lactoglobulin in light of the large amount of information that has accrued in the last few years. In particular, this review concentrates upon studies of the binding of retinol and fatty acids to β-lactoglobulin, including the binding constants and number of binding sites, the location of the binding sites, and the influence of chemical modifications in the interaction of the protein with both ligands. This study also describes studies of the influence of β-lactoglobulin on several biological processes that may be relevant to the possible biological role of this protein.
FEBS Letters, 1999
Human glycodelin, a lipocalin with a high amino acid similarity to L L-lactoglobulins, appears as various glycoforms with different biological activities in endometrium (glycodelin-A) and seminal plasma (glycodelin-S). We found that the structures of these glycodelins and L L-lactoglobulin are similar. Despite this structural similarity, unlike L L-lactoglobulin, glycodelin-A binds neither retinoic acid nor retinol. It was impossible to detect any endogenous retinoids or steroids in any of the two purified glycodelins. Both their glycoforms share similar thermodynamic parameters of reversible denaturation suggesting that native folding of glycodelin-A and glycodelin-S is not influenced by the differences in glycosylation or by ligand binding.
Bovine β-lactoglobulin/fatty acid complexes: binding, structural, and biological properties
Dairy Science & Technology, 2014
Ligand-binding properties of β-lactoglobulin (β-lg) are well documented, but the subsequent biological functions are still unclear. Focusing on fatty acids/β-lg complexes, the structure-function relationships are reviewed in the light of the structural state of the protein (native versus non-native aggregated proteins). After a brief description of β-lg native structure, the review takes an interest in the binding properties of native β-lg (localization of binding sites, stoichiometry, and affinity) and the way the interaction affects the biological properties of the protein and the ligand. The binding properties of non-native aggregated forms of β-lg that are classically generated during industrial processing are also related. Structural changes modify the stoichiometry and the affinity of β-lg for fatty acids and consequently the biological functions of the complex. Finally, the fatty acid-binding properties of other whey proteins (αlactalbumin, bovine serum albumin) and some biological properties of the complexes are also addressed. These proteins affect β-lg/fatty acids complex in whey given their competition with β-lg for fatty acids.
Biochemical Pharmacology, 2002
Interaction between the Vitamin A derivative all-trans retinoic acid and the lipocalin member bovine b-lactoglobulin (BLG) was studied by circular dichroism (CD) and electronic absorption spectroscopy at different pH values. In neutral and alkaline solutions achiral retinoic acid forms a non-covalent complex with the protein as indicated by the appearance of a negative Cotton effect around 347 nm associated to the narrowed and red shifted p±p à absorption band of the ligand. The induced optical activity is attributed to the helical distortion of the conjugated chain caused by the chiral protein binding environment. As the disappearing CD activity showed in the course of CD±pH titration experiment, retinoic acid molecules dissociate from BLG upon acidi®cation but this release is completely reversible as proved by the reconstitution of the CD and absorption spectra after setting the pH back to neutral. This unique behavior of the complex is explained by the conformational change of BLG (Tanford transition) which involves a movement of the EF loop at the entrance of the central cavity from open to closed conformation in the course of pH lowering. From these results it was inferred that retinoic acid binds within the hydrophobic calyx of the b-barrel. # (F. Zsila).
Colloids and Surfaces B: Biointerfaces, 2010
Bovine -lactoglobulin (-LG) present in milks has been found "in vivo" in complexes with lipids such as butyric and oleic acids. To elucidate the still unknown structure-function relationship in this protein, the structural changes of -lactoglobulin variant A (-LG A) in the presence of cationic surfactant such as dodecyltrimethyl ammonium bromide (DTAB) have been investigated using various experimental techniques such as UV-vis spectrophotometry, fluorimetry, isothermal titration calorimetry (ITC) and circular dichroism (CD). Subsequently, the retinol binding by -LG has been investigated in the presence of various amounts of this surfactant as its extrinsic functional binding fluorophore. Comparison of the results allowed to determine the binding of retinol by -LG in the presence of DTAB. The results of UV-vis and fluorescence studies showed a red shift in wavelength and an increase in absorbance and enhancement in the intensity of the quantum yield of protein during its interaction with DTAB. The results of UV-vis also showed two distinct conformational changes corresponding first to precipitation and second to solubilization of the precipitated -LG at pH 6.7 and 8.0. The results indicate the cooperative character of binding at pH 2.0. The results of fluorescence studies showed that the binding strength of -LG/DTAB complex increases with the increase of the pH. CD results showed the shifts in positions of the major minima and change in magnitude of ellipticity and subsequently signified two significant changes in structure of -LG between 10-30 and 50-100 molar ratio of [DTAB]/[-LG]. ITC measurements indicated the endothermic nature of -LG/DTAB interactions at pH 6.7 and the exothermic nature of -LG/DTAB interactions at pH 8.0. The analysis of the binding data demonstrates the absence of significant changes in retinol-binding properties of -LG in the presence of various amounts of this surfactant. This implies that surfactant binding does not change the conformation of -LG in the regions defining retinol-binding site nor interferes with retinol binding by a competition for the same binding site(s).
Covalent Structure of the Minor Monomeric β-Lactoglobulin II Component from Donkey Milk
Biological Chemistry Hoppe-Seyler, 1990
The complete primary structure of the minor /3-lactoglobulin II component from donkey milk is presented. It has been established by aminoacid sequencing and mass-spectrometry analysis of intact protein and peptides obtained after enzymatic and chemical cleavages. The molecular mass and the pi of the protein are calculated to be 18 261 Da and 4.5 respectively. Despite the close structural similarity of the donkey and horse major/3-lactoglobulin I components , their minor /3-lactoglobulin II components show substantial differences in sequence. Most observed exchanges are clustered at residues 78-106 where only 6 amino-acid residues are conserved.The primary structure of donkey /3-lactoglobulin II reveals some unusual features of minor /3-lactoglobulins II and gives new light to the evolution of /3-lactoglobulins and other lipocalins involved in retinol binding or reproductive functions. Primarstruktur der monomer en ß-Lactoglobulin-II-Nebenkomponente aus Eselsmilch Zusammenfassung: Die vollständige Primärstruktur der /3-Lactoglobulin-II-Nebenkomponente aus Eselsmilch wird präsentiert. Sie wurde mit Hilfe von Aminosäuresequenzierung und Massenspektrometrie des intakten Proteins sowie enzymatischer und chemischer Spaltpeptide gefunden. Die molekulare Masse beträgt 18261 Da und der p/-Wert 4.5. Im Gegensatz zur großen Ähnlichkeit zwischen den Hauptkomponenten (/3-Lactoglobulin I) von Esel und Pferd zeigen ihre Nebenkomponenten (/3-Lactoglobulin II) sub-stantielle Unterschiede. Die meisten der Aminosäure-Austausche treten gehäuft im Bereich von Position 78-106 auf. Diese Bereiche stimmen nur in 6 Aminosäureresten überein. Die Primärstruktur des /3-Lactoglobulins II vom Esel zeigt einige ungewöhnliche Eigenschaften dieser Lactoglobulin-Nebenkomponenten und wirft neues Licht auf die Frage der Evolution von /3-Lactoglobulinen und anderen Lipocalinen, die an der Retinolbindung beteiligt sind oder Funktionen bei der Reproduktion haben.
Ligand binding and self-association cooperativity of β-lactoglobulin
Journal of Molecular Recognition, 2013
Unlike most small globular proteins, lipocalins lack a compact hydrophobic core. Instead, they present a large central cavity that functions as the primary binding site for hydrophobic molecules. Not surprisingly, these proteins typically exhibit complex structural dynamics in solution, which is intricately modified by intermolecular recognition events. Although many lipocalins are monomeric, an increasing number of them have been proven to form oligomers. The coupling effects between self-association and ligand binding in these proteins are largely unknown. To address this issue, we have calorimetrically characterized the recognition of dodecyl sulfate by bovine b-lactoglobulin, which forms weak homodimers at neutral pH. A thermodynamic analysis based on coupled-equilibria revealed that dimerization exerts disparate effects on the ligand-binding capacity of b-lactoglobulin. Protein dimerization decreases ligand affinity (or, reciprocally, ligand binding promotes dimer dissociation). The two subunits in the dimer exhibit a positive, entropically driven cooperativity. To investigate the structural determinants of the interaction, the crystal structure of b-lactoglobulin bound to dodecyl sulfate was solved at 1.64 Å resolution.