Heat-induced formation of ordered structures of ovalbumin at low ionic strength studied by small angle X-ray scattering

Small angle X-ray scattering (SAXS) has been performed on native ovalbumin solutions and heated ovalbumin systems at neutral pH and low ionic strength. In native ovalbumin solutions there is a partial ordering, where the interparticle distance (dmax) scales with the protein concentration (C) as d max ~ C-0.28. This exponent indicates that the ovalbumin monomers behave as a uniform distribution of charged spheres in solution. The q-dependent scattering intensity of ovalbumin aggregates can be well described by a form factor of rods. The dependence of dmax for aggregates on the protein concentration was found to be dmax ~ C-0.51, this scaling behavior is in good agreement with that theoretically derived for the distribution of spaces in a random network of straight fibers. The existence of a well-defined interparticle distance between aggregates is confirmed by cryo-TEM. The scattering profiles of native and aggregated ovalbumin were successfully fitted including both form factor and structure factor, using the preferred distance (L), a measure of disorder (¿/L), and the radius (R or a) as fitting parameters.