  The possibility for proteins to aggregate in different superstructures, i.e.
large-scale polymorphism, has been widely observed, but an understanding of the
physico-chemical mechanisms behind it is still out of reach. Here we present a
theoretical model for the description of a generic aggregate formed from an
ensemble of charged proteins. The model predicts the formation of multi-fractal
structures with the geometry of the growth determined by the electrostatic
interactions between single proteins. The model predictions are successfully
verified in comparison with experimental curves for aggregate growth. The model
is general and is able to predict aggregate morphologies occurring both in vivo
and in vitro. Our findings provide for the first time a unifying and general
framework where the physical interactions between single proteins, the
aggregate morphology and the growth kinetics are connected into a single model
in excellent agreement with the experimental data.
