Heat-Induced Secondary Structure and Conformation Change of Bovine Serum Albumin Investigated by Fourier Transform Infrared Spectroscopy

Fourier transform infrared (FT-IR) spectra were measured for an aqueous solution (pD = 5.40) of defatted monomer bovine serum albumin (BSA) over a temperature range of 25−90 °C to investigate temperature-induced secondary structure and conformation changes. The curve fitting method combined with the Fourier self-deconvolution technique allowed us to explore details of the secondary structure and conformation changes in defatted BSA. Particularly striking in the FT-IR spectra was an observation of the formation of an irreversible intermolecular β-sheet of BSA on heating above 70 °C. A band at 1630 cm-1 in the spectra was assigned to short-segment chains connecting α-helical segments. The transition temperature for the short-segment chains connecting α-helical segments is lower by 17−18 °C, when compared to those of the α-helix, turn, and intermolecular β-sheet structures of BSA, suggesting that the α-helix and turn structures of BSA are cooperatively denatured on heating. Moreover, the results give an important feature in heat-induced denaturation of BSA that the conformation changes occur twice around both 57 and 75 °C. The appearance of two peaks is interpreted by the collapse of the N-terminal BSA domain due to the crevice in the vicinity between domains I and II at low-temperature transition and by the change in cooperative unit composed of the other two BSA domains at high-temperature transition.