Structural changes of IgG induced by heat treatment and by adsorption onto a hydrophobic Teflon surface studied by circular dichroism spectroscopy

Thermal denaturation of mouse monoclonal immunoglobulin G (isotype 1), as well as structural rearrangements resulting from adsorption on a hydrophobic Teflon surface, are studied by circular dichroism spectroscopy. Both heat-induced and adsorption-induced denaturation do not lead to complete unfolding into an extended polypeptide chain, but leave a significant part of the IgG molecule in a globular or corpuscular form. Heating dissolved IgG causes a decrease of the fractions of β-sheet and β-turn conformations, whereas those of random coil and, to a lesser extent, α-helix increase. Adsorption enhances the formation of α-helices and random coils, but the β-sheet content is strongly reduced. Heating adsorbed IgG results in a gradual break-down of the α-helix and β-turn contents, and a concomitant formation of β-sheet structures. Thus, the structural changes in IgG caused by heating and by adsorption, respectively, are very different. However, after heating, the structure of adsorbed IgG approaches the structure of thermally denatured IgG in solution.