Interactions of β-Lactoglobulin Variants A and B with Vitamin A. Competitive Binding of Retinoids and Carotenoids

Abstract

β-Lactoglobulin (β-Lg) is the major whey protein of bovine milk present at a concentration of 2-3 g L(-1). Its biological role is still not well-known. However, many studies have suggested that β-Lg may play either nutritional or specific transporter role. The high affinity of β-Lg for retinol and other retinoids was reported. The results of interaction studies of β-Lg with carotenoids, that is, β-carotene, β-cryptoxanthin, and α-carotene, which display similar structures are reported in this study. The affinities of β-Lg for binding of retinoids and carotenoids were compared, providing more information about the binding site(s) of these molecules by β-Lg. Interactions were followed by the measurements of quenching of β-Lg tryptophan fluorescence and retinol fluorescence. The obtained results indicate that carotenoids are bound by β-Lg with high affinity of the order of 10(-8) M. Measurement of retinol competition with carotenoids for binding by β-Lg suggests that the binding of these two ligands occurs at two different sites of β-Lg.

Milk Fat Globule in Ruminant: Major and Minor Compounds, Nutritional Regulation and Differences Among Species

“…In milk, members of the retinol family and ß‐carotene are located in the cream fraction, meaning with the fat droplets . Retinoid compounds in the milk have been linked to several binding proteins, either specific, such as cellular retinol‐binding protein type III, or unspecific, such as ß‐lactoglobulin, or α and β‐caseins . Conversely, ß‐carotene is highly lipophilic and is always reported to be integrated inside fat droplets whatever the biological matrix, whereas a study demonstrated that it could also bind to ß‐lactoglobulin.…”

“…Retinoid compounds in the milk have been linked to several binding proteins, either specific, such as cellular retinol‐binding protein type III, or unspecific, such as ß‐lactoglobulin, or α and β‐caseins . Conversely, ß‐carotene is highly lipophilic and is always reported to be integrated inside fat droplets whatever the biological matrix, whereas a study demonstrated that it could also bind to ß‐lactoglobulin. However, xanthophylls (lutein and zeaxanthin in milk), the non‐provitamin‐A carotenoids, are less lipophilic than carotenes and are components of the MFGM, and are more likely integrated inside the lipidic membrane.…”

The effect of calcium and magnesium on the interaction between β‐lactoglobulin and carotenoids from sea buckthorn berries

“…Conversely, Trp 61 (emission at 350 nm) is partly exposed to solvents, is located near the disulfide bridge Cys 66 –Cys 160 , and produces only a minor contribution to the total Trp fluorescence . β‐Lactoglobulin has three potential lipophilic binding sites: the internal cavity of the β‐barrel (calyx), the surface hydrophobic pocket in a groove between the α‐helix and the β‐barrel, and the outer surface near Trp 19– Arg 124 residues . The surface hydrophobic pocket, also known as the superficial pocket, is located close to the dimer contact region, between the α‐helix (sited laterally to the calyx) and the calyx surface .…”

A comprehensive overview on the micro- and nano-technological encapsulation advances for enhancing the chemical stability and bioavailability of carotenoids

“…The central cavity of β-LG provides a ligand-binding site for hydrophobic molecules, including carotenoids (Mensi et al, 2013a), and opening its hydrophobic pocket (by increasing pH and ionic strength) could enhance binding affinity (Zhang et al, 2013b). Investigating the binding affinity of several carotenoids to variants A, B of milk derived β-LGs, β-carotene exhibited a better binding affinity to β-LG compared to α-carotene and β-cryptoxanthin, while no significant differences in their binding affinities as a function of β-LG variants were observed (Mensi et al, 2013a). The potential of β-LG as an encapsulating agent is associated with its ability to form aggregates under controlled temperature, pH and ionic strength or by high pressure via hydrophobic attraction and disulphide/sulfhydryl (S-S/SH) bridges (Mensi et al, 2013b;Nicolai et al, 2011).…”