Tracing nucleation pathways in protein aggregation by using small angle scattering methods

Abstract

Heat and alcohol-induced nucleation pathways of the whey protein β-lactoglobulin were investigated using small angle neutron and X-ray scattering for structural characterization. Protein solutions at various concentrations were either heated stepwise to 80 °C or mixed with ethanol to 50% (v/v). Heating induces dissociation of the β-lactoglobulin dimer in neutral pH aqueous medium, leading to nucleation at about 75 °C of tetrameric, cylindrical clusters, as indicated by three dimensional rigid body and bead modelling performed to fit scattering curves. In contrast to heating, ethanol addition induces the formation of fairly compact, internally disordered sphere-like clusters composed of rod-like submolecular structural units. At higher concentrations these clusters show typical colloidal behaviour, exhibiting long-range repulsive interactions, as also confirmed by dynamic light scattering measurements. The results contrast the effect of different unfolding scenarios on preferred nucleation pathways in subsequent protein assembly processes in various solution environments

Electrospinning of food-grade nanofibres from whey protein

“…Peak position Q ( Using the Guinier method an Rg value of (25 Å ± 9) Å was calculated ( Figure 5 Inset), similar to the size observed in previous measurements for the monomeric unit of β-lactoglobulin; 52,53 the slight increase in the scattering intensity at the lowest scattering vectors maybe indicative of an attractive potential between proteins. It is known that -lactoglobulin forms aggregates under certain conditions relating to the concentration, ionic strength and temperature 54 .…”

Thermally induced conformational changes and protein–protein interactions of bovine serum albumin in aqueous solution under different pH and ionic strengths as revealed by SAXS measurements

“…Interestingly, as reported by Vogtt et al, 71 where temperatureinduced aggregation of b-lactoglobulin was studied, the initial state of the protein was dimeric, and an increase in temperature led to dimer dissociation. For this system, thermodynamic studies also demonstrated non-linear van't Hoff plots for the dimerization constant, but, in contrast to BSA, with a positive slope.…”

β-Lactoglobulin Adsorption Layers at the Water/Air Surface: 5. Adsorption Isotherm and Equation of State Revisited, Impact of pH

“…On the other hand, the largest net charge at pH 3 (compared to pH 5 nd pH 7) generates the strongest intermolecular electrostatic repulsion that counteracts protein-protein cohesive interactions [65] and also favors the protein-solvent interactions (wetting) at the interface. Having in mind constancy of the Debye length at the fixed ionic strength used, those prerequisites can be regarded as determining the highest values for ω Π=0.1 and R ehc at pH 3, as the latter is merely twice the radius (≈1.75 ±0.04 nm [80,81]) of the spherical native BLG monomeric unit in bulk. With this in line, the decrease of |Z| entails the decreasing values for ω Π=0.1 and R ehc at pH 7 and pH 5.…”

“…It is possible that, under saturation conditions at c pH5 m2 ≈ 3 × 10 −7 M, the monolayer has gained some degree of heterogeneity near the onset of a secondary layer formation. The reasons for such disruption in the homogeneous 2-D monolayer's architecture could be either nonperfect alignment of the adsorbed BLG entities (monomers, dimers or mixtures of them) or effects by newly arriving dimers (prolate ellipsoids [81]), which might be not able to get incorporated into the compressed monolayer but may only partially penetrate it, leading this way to a "pseudo saturation." On the other hand, the monolayers at pH 3 and pH 7 exhibit similar adsorption behaviors, although the dimer fraction at c pH7 m2 (ca.…”