Trifluoroethanol-induced beta -> alpha transition in beta-lactoglobulin: hydration and cosolvent binding studied by 2H, 17O, and 19F magnetic relaxation dispersion.

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Abstract

Alcohols, such as 2,2,2-trifluoroethanol (TFE), have been shown to induce a cooperative transition to an open helical structure in many proteins, but the underlying molecular mechanism has not been identified. Here, we employ the technique of magnetic relaxation dispersion (MRD) to study the TFE-induced transition of -lactoglobulin at pH 2.4. Unlike traditional techniques that focus on protein secondary structure, the MRD method directly monitors the solvent, providing quantitative information about preferential solvation and solvent penetration and about the overall size and structural integrity of the protein. In this multinuclear MRD study, we use the 2H and 17O resonances to examine hydration and the 19F resonance to study TFE. The transformation from the native to the helical state via an intermediate state at 300 K is found to be accompanied by a progressive expansion of the protein and loss of specific long-lived hydration sites. The observation of 17O and 19F dispersions from the helical state shows that water and TFE penetrate the protein. The MRD data indicate a strong accumulation of TFE at the surface as well as in the interior of the protein. At 277 K, BLG is much less affected by TFE, remaining in the native state at 16% TFE, but adopting a nonnative structure at 30% TFE. This nonnative structure is not penetrated by long-lived water molecules. The implications of these findings for the mechanism of TFE-induced structural transformations are discussed.

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  • Biochemistry and Molecular Biology
Original languageEnglish
Pages (from-to)13708-13716
JournalBiochemistry
Volume42
Issue number46
Publication statusPublished - 2003
Publication categoryResearch
Peer-reviewedYes