STRUCTURAL-CHANGES OF IGG INDUCED BY HEAT-TREATMENT AND BY ADSORPTIONONTO 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 h ydrophobic Teflon surface, are studied by circular dichroism spectrosc opy. 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 for m. Heating dissolved IgG causes a decrease of the fractions of beta-sh eet and beta-turn conformations, whereas those of random coil and, to a lesser extent, alpha-helix increase. Adsorption enhances the formati on of alpha-helices and random coils, but the beta-sheet content is st rongly reduced. Heating adsorbed IgG results in a gradual break-down o f the alpha-helix and beta-turn contents, and a concomitant formation of beta-sheet structures. Thus, the structural changes in IgG caused b y heating and by adsorption, respectively, are very different. However , after heating, the structure of adsorbed IgG approaches the structur e of thermally denatured IgG in solution. (C) 1998 Elsevier Science B. V. All rights reserved.