alpha-to-beta structural transformation of ovalbumin: Heat and pH effects

Ovalbumin is an important member of the serpin superfamily without inhibito ry activity. The heat- and pH-induced alpha-to-beta structural transformati ons of ovalbumin were investigated by means of circular dichroism and bindi ng of ANS and Congo red dyes. The native ovalbumin shows a mixture of alpha -helix and beta-sheet, while both the heat and alkali treatments are able t o transform the native protein into a predominance of beta-sheet secondary structure. The free energy changes during transitions to the unfolded state are 5.19 kcal/mol from the native state and 4.00 kcal/mol from the heat-tr eated one. The binding abilities of the heat-treated and the alkali-treated forms to ANS and Congo red suggest that the altered forms exhibit hydropho bic exposure and intermolecular interaction. The results substantiate that the altered protein forms bearing increased beta-sheet structures are prone to aggregation, which is implicated in the pathogenesis of some conformati onal diseases.