X-ray and light scattering study of the structure of large protein aggregates at neutral pH

The structure of large ovalbumin and β-lactoglobulin aggregates formed after heat-denaturation at neutral pH was studied using a combination of light and small-angle X-ray scattering. The effect of the electrostatic interactions was investigated by varying the ionic strength. The results were compared with images obtained using cryo-TEM. The structure of ovalbumin aggregates is compatible with that of semi-flexible strings of monomers that are more flexible and increasingly branched with increasing ionic strength. The persistence length increases with decreasing ionic strength. β-lactoglobulin aggregates consist of clusters of primary aggregates that are formed in the first step of the aggregation process. At low ionic strength the association of primary aggregates is mostly head to tail, while with increasing ionic strength denser clustering of the primary aggregates is observed.