Evidence for a rigid structure in lysozyme fractal aggregates

We have studied by quasi-elastic light scattering the aggregation of hen egg-white lysozyme upon salt addition. Our results show that these aggregates are fractal, in agreement with the results reported in the literature, and that they do not display any fluctuation of internal concentration. Lysozyme aggregates are rigid at the time scale considered. Such a rigidity of the internal structure is a key point to reconcile the fractal structure of the aggregates and their colloid-like ordering. Furthermore, we think that this result plays an important role in the understanding of crystal nucleation.