GM1-induced structural changes of bovine serum albumin after chemical and thermal disruption of the secondary structure: A spectroscopic comparison

GM1-induced structural transitions of native and unfolded conformers of bovine serum albumin (BSA) have been studied where in the unfolded conformers, the secondary structures were disrupted either chemically by 8 M urea or thermally by heating at 65 degrees C. With decreasing protein:ganglioside ratio at pH 7.0, the native BSA partially unfolds and expands, while the urea-denatured BSA forms an a.-helical structural pattern with shrinking in the conformational space. However, a continuous loss of alpha-helicity with minor increase in size was observed for the thermally altered protein in the presence of the GM1 micelle. The changes in the secondary structural content were followed by far-UV circular dichroism (CD) analysis. The dynamic light scattering (DLS) experiments were used to study the variation of the size of the protein-GM1 complexes with increasing concentration of the GM1. Fluorescence experiments show that tryptophan residues of BSA experience a more hydrophobic environment in the presence of the GM1 micelle with a decreasing protein:ganglioside ratio at pH 7.0. The present study shows that GM1 has a strong effect on the conformation of BSA depending on the conformational states of the protein that would relate to a physiological function of GM1 such as acting as the receptor of proteins in the cell membrane.