Molecular basis of thermal aggregation of bovine β-lactoglobulin A

Abstract

On heating, bovine 8-lactoglobulin A (8-lg A) dimers dissociate and then aggregate. The extent of aggregation of 8-19 A after a heat-quench treatment was studied quantitatively using photon correlation spectroscopy (PCS) ; circular dichroism (CD) spectroscopy was also carried out on heated solutions of 8-1s A to examine changes in the secondary and tertiary structure of t h e protein. In pH 7.0 solution the protein underwent a change in tertiary structure at 67 "C; by contrast, the secondary structure, containing ca. 50% 8-sheet, showed very little change up to 90°C. PCS showed that t h e extent of aggregation of 8-lg A depended on pH and buffer concentration; under some conditions it was observed that there was a temperature above which t h e rate of aggregation decreased. The pH-dependence of t h e temperature of onset of aggregation correlated with the conformational stability of 8-19 A. Detailed examination of the light scattering data suggested initial aggregation of the protein molecules to form linear, rod-like particles. It is proposed that, at later stages in the aggregation process, the rods themselves aggregate and start to form a network.

Structural modifications of β-lactoglobulin subjected to gamma radiation

“…The protein contains five cysteine residues per monomer, one free and four involved in two disulfide bridges. Native b-LG has 40-50% b-sheet, 10-15% a-helix and 40% random coil structure (Griffin, Griffin, Martin, & Price, 1993;Qi et al, 1997), data supported by Xray crystal structure . It can be obtained in large quantities and high purity by membrane filtration processes (Maubois, Pierre, Fauquant, & Piot, 1987).…”

Expression and Circular Dichroism Studies of the Extracellular Domain of the α Subunit of the Nicotinic Acetylcholine Receptor

“…For example, when bovine ␤-lactoglobulin A, a ␤-sheet-rich protein, is thermally denatured, the effect on the secondary structure (as measured by CD) is very small (36). It has been proposed that the aggregation/misfolding of many proteins is associated with the formation of intermolecular ␤-sheet structures (36,37).…”

“…For example, when bovine ␤-lactoglobulin A, a ␤-sheet-rich protein, is thermally denatured, the effect on the secondary structure (as measured by CD) is very small (36). It has been proposed that the aggregation/misfolding of many proteins is associated with the formation of intermolecular ␤-sheet structures (36,37). The relatively low temperature required to cause loss of binding activity of ␣210GPI and the inefficient folding of the ␣ subunit in vivo (with most of the newly synthesized ␣ subunit appearing as non-␣-Btx-binding aggregates) suggests that the ␣ subunit is susceptible to this form of misfolding.…”

Aggregated whey proteins and trace of caseins synergistically improve the heat stability of whey protein-rich emulsions

“…However, when heated above 70 C whey proteins unfold, exposing reactive groups that are responsible for protein aggregation (Griffin, Griffin, Martin, & Price, 1993;Roefs & De Kruif, 1994;Sawyer, 1968;Verheul, Roefs, & de Kruifs, 1998) and emulsion instability (Çakir-Fuller, 2015;Dybowska, 2011;Euston et al, 2000;Hunt & Dalgleish, 1995;McClements, 2004;Surel et al, 2014). It has been shown that the heat stability of whey protein-stabilized emulsions is dependent on the concentration of native whey protein in the dispersing phase (Çakir-Fuller, 2015;Dybowska, 2011;Euston et al, 2000).…”