Diffusive dynamics of ordered solutions of apoferritin near the structure factor peak

Abstract

Aqueous solutions of apoferritin, which consists of 24 proteins assembled into a spherical shell (outer diameter 12 nm), represent highly monodisperse systems. In low-salt solutions, a pronounced peak in the static structure factor S(q) indicates intermolecular interactions due to the net negative charge (pH ≈ 5) of apoferritin. We have investigated both the structure and dynamics of ordered solutions for the first time in the vicinity of the S(q) peak at q*. Coherent small-angle neutron scattering experiments were performed at the Institute Laue-Langevin (Grenoble) and the dynamics was studied using the high-resolution neutron spin echo spectrometer IN15. The dynamics at q > q* coincides with extrapolated results of previous experiments. For low-salt solutions, the normalized intermediate-scattering function has a shape that qualitatively resembles that of S(q) in the vicinity of q*. However, the inverse effective diffusion constant differs quantitatively from S(q) below q*.