Phase transformations of bovine serum albumin: Evidences from Rayleigh-Brillouin light scattering

Rayleigh-Brillouin light-scattering studies of a high-concentration solution of bovine serum albumin (BSA, pH = 7.45, C = 100 mg/ml) in a sodium phosphate buffer in the temperature range 300-370 K are presented. It is shown that the temperature dependences of relative changes in the Brillouin shift and half width at half maximum and intensity of the Brillouin doublet and intensity of Rayleigh components exhibit anomalies in the vicinity of 335, 345, and 363 K. Analysis of the literature data allowed us to construct a phase diagram showing a sequence of BSA phase transformations in the temperature range from 300 to 375 K and to correlate the anomalies in the scattering spectra to the regions of phase transformations. The anomalies in the behavior of the light-scattering spectra in the vicinity of T-m = 335 K are attributable to the melting temperature and the formation of BSA self-assembled aggregates. The formation of a phase with oriented beta-sheet rich mature fibrils at T-m T < 347 K is confirmed by elastic light scattering experiments. This phase passes into a gel-like phase in which the aggregates are rearranged and a polymer network, which is finally converted to a gel in the vicinity of 363 K is formed. Thus, the Rayleigh-Brillouin scattering experiments demonstrated the evolution of the structure, which manifested itself in the anomalous temperature behavior of the intensities of the Rayleigh and Brillouin components in the light-scattering spectra. The anomalous low-frequency dynamics of the BSA solution at denaturing and transition into a gel phase was clearly observed in the anomalous Brillouin shift behavior in the vicinity of 335 and 363 K. The sequence of phase transformations in BSA at heating from 300 to 375 K in the phase diagram correlates well with the anomalies observed in the evolution of Rayleigh-Brillouin light scattering.