Fractality of globular protein aggregates: From the molecular to the microscopic level

This paper presents a theoretical approach. of scattering by fractal aggregates based on a model with four parameters. It assumes that the aggregates are fractal and polydisperse with a number distribution which has a power law dependence on the molar mass. In addition the external cut-offs for the number distribution and the fractal structure are supposed to be stretched exponential functions. beta-lactoglobulin aggregates formed after heat-induced denaturation were studied by light and neutron scattering techniques over a range of wave vectors covering more than 4 decades. The results demonstrate clearly that the aggregates have a fractal structure at larger length scales and their number distribution is self similar. Their local structures depend on the pH and the ionic strength of the solutions and can be either globular at pH 7 or rigid rodlike at pH2 with a persistent length which increases with decreasing ionic strength. The explicit analysis of the dynamic light scattering data allows one to characterise precisely the mass distribution. The calculated structure factors are in good agreement with the experimental data.