Thermal induced conformational changes involved in the aggregation pathways of beta-lactoglobulin.

Aggregation of proteins appears to be associated most often with conformational and structural changes that lead to exposure of some apolar residues. Depending on the native structure of the protein in exam, aggregation is a process that involves different mechanisms, whose time of occurrence and interplay can depend upon temperature. To single out information about the multistages of the aggregation pathway, here we investigate the thermally induced conformational and structural changes of the beta-lactoglobulin (BLG). The experimental approach consists in studying steady-state fluorescence spectra of intrinsic chromophores, two tryptophans, and Anylino-Naphthalene-Sulfonate dye (ANS) molecular probe. This technique revealed to be particularly suitable in investigating samples in the low concentration range and at the initial steps of the aggregation process. The Rayleigh scattering of the exciting light follows the growth of the intermolecular interactions at the same time. Complementary information is also obtained by circular dichroism (CD) measurements on samples in the same experimental conditions. The obtained data indicate a well-defined interconversion between quaternary, ternary and secondary structures, together with conformational rearrangements driven by hydrophobic interactions and intermolecular bonds. The results are also discussed in comparison with similar studies on BSA aggregation.