The Interaction between Human Serum Albumin and Cholesterol-modified Pullulan Nanoparticle

The interaction between human serum albumin and cholesterol-modified pullulan (CHP) nanoparticles with different degrees of substitution (DS) of cholesterol moiety was investigated using spectroscopic and thermodynamic methods. Albumin fluorescence intensity was quenched by nanoparticles with maximum emission intensity decreasing at the initial reaction and increasing at the last reacted period. Binding constants (Kb) were 1.12 x 105 M-1, 4.12 x 105 M-1 and 7.44 x 105 M-1 to CHP-3.11, CHP-6.03 and CHP-6.91, respectively, as determined by Stern-Volmer analysis. Adsorption of albumin to nanoparticles was an exothermic reaction process and revealed a higher DS of cholesterol moiety with higher enthalpy and entropy changes. Upon interaction with nanoparticles, albumin conformation changed with a reduction of α-helix, suggesting a partial protein unfolding. Furthermore, albumin could gradually change its helical structure due to the structural change of the complexed nanoparticle. Particle hydrophobicity and shell-core structure play a main role in the alteration of albumin conformation in the nanoparticle-protein interaction process.