Rigid structure of fractal aggregates of lysozyme

The aggregation of hen egg-white lysozyme upon salt addition was studied by quasi-elastic light scattering. Our results agree with the fractal structure of the aggregates already reported in the literature. However, we also demonstrate that these aggregates are rigid, since they do not display any fluctuation of internal concentration. Such a rigid internal structure is a key point to reconcile the fractal structure of the aggregates and their colloid-like ordering. Furthermore, this result has to be considered for understanding crystal nucleation.