α→β transition of β-lactoglobulin as evidenced by heteronuclear NMR

Abstract

Whereas bovine β-lactoglobulin is a predominantly β-sheet protein, it has a marked α-helical preference and can be considered to be a useful model of the α→β transition, a key issue for understanding the folding and biological function of a number of proteins. In order to understand the mechanism of the α→β transition, the backbone structures of the recombinant bovine β-lactoglobulin A in the native state and in the highly helical state induced by 2,2,2-trifluoroethanol were characterized by 1H, 13C and 15N multidimensional NMR spectroscopy. Overall, the secondary structures in the native state were similar to those of the crystal structure. On the other hand, β-lactoglobulin in the 2,2,2-trifluoroethanol state was composed of many α-helical segments. The presence of the persistent α-helices in the helical state and the core β-sheet in the native state suggested that during folding native-like core β-sheet and several non-native helices are formed first and the remaining β-sheet is subsequently 'induced' through interaction with the pre-existing β-sheet.