Protein adsorption and conformational change on small polymer particles

Adsorption of proteins and their conformational changes upon adsorption on artificial surfaces may play an important role in determining the subsequent biological process when a polymeric particle is brought in contact with biological fluids. Previously, we have shown that protein adsorptionon polystyrene particles (0.08 to 0.305 μm in diameter) can be reduced to a negligible amount if the particles were precoated with polymeric surfactants—Pluronic F108 or Tetronic 908. In the present study, we have extended our measurements from 25 to 37°C and also included the three major serum proteins—albumin, fibrinogen, and immunologlobulin—as well as whole plasma. Protein resistance was demonstrated by the unchanged particle size of the surfactant-coated polystyrene particles upon addition of proteins. This finding was further substantiated by the constancy of the rotational correlation times, φ, of the proteins in the presence of excess F108-coated polystyrene particles. The unchanged rotational correlation time of the protein observed is indicative of the unperturbed protein molecular rotation and is consistent with the absence of interaction between the protein molecule and the polymer particles. These φ parameters were determined by the technique of fluorescence anisotropy dcay using 1-pyrenesulfonyl chloride as the extrinsic probe for the three serum proteins. Previously, W. Norde et al. (J. Colloid Interface Sci. 66, 257, 295 (1978)) showed by circular dichroism that denaturation occurred for proteins which were desorbed from polymer particles. In the present work, we have demonstrated by fluorescence anisotropy decay that denaturation occurred not only for proteins desorbed from particles but also for those which remain adsorbed on the particle surface, in situ. In the case of protein adsorption on the uncoated polystyrene, the rotational correlation time of the protein, φ, increases with the increasing number of particles resulting from restricted molecular rotation of the protein upon adsorption. This φ parameter was reduced to zero, however, upon further addition of polymer, particularly those with large particle sizes. This is attributed to the unfolding of the adsorbed protein molecule, resulting in the exposure of the probe site to an aqueous environment. The zero φ value was also observed for proteins desorbed from plystyrene using Pluronic F108 as the desorbing agent. These results suggest that proteins become unfolded upon adsorption on polystyrene particles and also retain their denaturated state even after desorption.