Macromolecular Complexation between Bovine Serum Albumin and the Self-Assembled Hydrogel Nanoparticle of Hydrophobized Polysaccharides

Macromolecular complexation between bovine serum albumin (BSA) and self-assembled hydrogel nanoparticle formed by the self-aggregation of cholesterol-bearing pullulan (CHP) was studied by high performance size exclusion column chromatography (HPSEC) and circular dichroism (CD). The CHP self-aggregates complexed with one BSA molecule to give colloidally stable nanoparticles (R G = 17 nm) at pH 7.0 and 25 °C. This was almost irrespective of the substitution degree of the cholesterol group of CHP. The helical content of BSA decreased upon complexation. Unfolding of BSA by either heating or a denaturant such as urea was largely suppressed upon complexation. BSA would be incorporated inside into the hydrogel matrix of the CHP nanoparticle. Kinetic analysis of the complexation suggested a two-step process: namely, the fast pre-equilibrium of looser binding of BSA to the CHP self-aggregate followed by the slower process of tighter inclusion into the hydrogel network. The substitution degree of the cholesterol group in CHP significantly affected the complexation kinetics.