Artificial Chaperone Polysaccharide Nanogels for Protein Delivery: A Thermodynamic Study of Protein-Nanogel Interactions Using Fluorescence Correlation Spectroscopy

Molecular chaperones selectively trap heat-denatured proteins or their intermediates, primarily by hydrophobic interactions, to prevent irreversible aggregation resulting from macromolecular host (molecular chaperone)-guest (protein) interactions. The molecular chaperone function is an important concept that is expected to lead to breakthroughs in drug delivery systems, especially for protein or peptide delivery in regenerative medicine, such as bone regeneration. We have reported that polysaccharide nanogels act as artificial molecular chaperones. To further clarify the molecular chaperone function of nanogels as protein carriers, the elucidation of nanogel-protein interactions are especially important. Here, we investigated the interaction of a protein with a polysaccharide nanogel using fluorescence correlation spectroscopy at variable temperatures, using fluorescence-labeled bovine serum albumin (BSA) as a model protein. In particular, thermodynamic parameters of the heat-induced complexation of protein with CHP nanogels were evaluated using the van't Hoff plot. The plot shows that the CHP nanogels strongly complexed with heat-denatured BSA. The increased hydrophobicity of the denatured, unfolded protein may prefer complexation with amphiphilic hydrogel nanoparticles over complexation with the completely folded native protein. Thermodynamic parameters suggest that the complexation is entropically driven, rather than enthalpically, under the conditions studied.