CONFORMATIONAL-CHANGES INVOLVED IN THE SWITCH FROM OVALBUMIN TO S-OVALBUMIN

For the first time a comparative study on conformational differences b etween 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 meas urements have been performed on ovalbumin and S-ovalbumin denatured wi th different concentrations of guanidine hydrochloride, and by heating the proteins at acid pH. The intensity scattering curves provide evid ence that the intermediate states in the unfolding process are globula r for both proteins while their compactness changes. The reported expe rimental results suggest that the ovalbumin to S-ovalbumin transformat ion can be considered a protein-switch triggered by changes in the che mical conditions of the protein environment. Because the conformationa l changes are likely to be of functional importance, we infer that the occurrence in vivo of S-ovalbumin is thus determined by the transform ation of ovalbumin, with a functional role for embryonic development, into a new protein with a different function.