Adsorption of IgG onto hydrophobic teflon. Differences between the F(ab) and F(c) domains.

The effect of differences in the degree of hydrophobicity of protein patches/fragments on the adsorption behaviour of the protein is investigated. The adsorption isotherm of a monoclonal mouse anti-human immunoglobulin G (isotype 2b) onto hydrophobic Teflon particles is measured using a depletion method. The adsorption-induced denaturation of the immunoglobulin as a function of the adsorbed amount is studied by differential scanning calorimetry, and the corresponding rearrangements in the secondary structure of the whole IgG molecule and its F(ab) and F(c) fragments are determined by circular dichroism spectroscopy. The effects of adsorption on the F(ab) and F(c) fragments in the intact IgG molecule occur independently. Adsorption of the whole IgG molecule leads to denaturation of the F(ab) fragments, whereas the F(c) fragment remains unperturbed; adsorption of the isolated fragments results in structural changes in both F(ab) and F(c). The surface hydrophobicity of the isolated fragments was studied by HPLC. These experiments support the hypothesis that differences in the degree of denaturation between F(ab) and F(c) are due to the higher degree of hydrophobicity of the F(ab) fragment. The adsorption-induced changes in the secondary structure are more prominent for the isolated fragments as compared to intact IgG. This is ascribed to the higher flexibility of the isolated fragment, as compared to the fragment in the whole molecule.