PROTEIN DENATURATION INDUCED BY CYCLIC SILICONE

While it has been demonstrated that such low-molecular-weight cyclic s ilicones as octamethylcyclotetrasiloxane (D-4) exhibit adjuvant activi ty, the mechanism of immunological response to silicone is still not c lear. This study therefore used fluorescence and circular dichroism (C D) spectroscopy to investigate the denaturation and conformational cha nge of two proteins, fibronectin (Fn) and fibrinogen (Fbg), induced by D-4 in vitro. Incubating D-4 with Fbg or Fn at D-4-to-protein ratios of >100 or for >10 h yielded white and mould-like precipitates of the proteins, indicating massive denaturation and aggregation. The fact th at the decrease in fluorescence intensity of D-4-treated Fn and Fbg wa s accompanied by a red shift in the maximum wavelength also indicated that denaturation of the proteins had taken place. These changes in fl uorescence might result from exposure of tryptophan residuals in the p roteins to polar water molecules inasmuch as the denaturation would le ad to changes in the tertiary structures of the proteins and rearrange ment of the tryptophan residues. The loss of the tertiary structure le ads to protein denaturation and, consequently, precipitation. The diff erence in CD spectra between control Fbg (or Fn) and D-4-treated Fbg ( or Fn) indicated conformational changes of the proteins when incubated with D-4. Thus it has been demonstrated that D-4 can induce denaturat ion and conformational changes in Fbg and Fn and it can be expected th at protein molecules that have undergone denaturation or conformationa l change induced by D-4 may act as antigens and stimulate the immune s ystem to generate antibodies, ultimately resulting in autoimmune disea se. (C) 1998 Elsevier Science Limited. All rights reserved.