Conformational changes involved in the switch from ovalbumin to S-ovalbumin

For the first time a comparative study on conformational differences between native ovalbumin and its heat-stable form, called S-ovalbumin, using small angle x-ray scattering, is reported. To detect a different pathway in the folding mechanism of the two proteins, scattering measurements have been performed on ovalbumin and S-ovalbumin denatured with different concentrations of guanidine hydrochloride, and by heating the proteins at acid pH. The intensity scattering curves provide evidence that the intermediate states in the unfolding process are globular for both proteins while their compactness changes. The reported experimental results suggest that the ovalbumin to S-ovalbumin transformation can be considered a protein-switch triggered by changes in the chemical conditions of the protein environment. Because the conformational changes are likely to be of functional importance, we infer that the occurrence in vivo of S-ovalbumin is thus determined by the transformation of ovalbumin, with a functional role for embryonic development, into a new protein with a different function.