Danneggiamento per via radicalica di proteine contenenti residui solforati e formazione di lipidi trans in sistemi modello

Abstract

The present thesis deals with structural changes of sulfur-containing proteins exposed to radiation and the damage induced by thiyl radicals (RS•) generated from these proteins to unsaturated lipids in large unilamellar vesicles (LUVET). In particular, the production of H• atoms under reductive stress conditions was correlated to the specific damage of sulphur moieties of analyzed proteins with release of low-molecular-weight thiols. In parallel, it was demonstrated that structural changes of -amyloid (A) induced by NO2• and CO3•– radicals, involved mainly the oxidation of the Met35. -Radiolysis was the source of oxidative damage in lipid vesicle suspensions (DOPC, POPC), in the presence of sulphur-containing either proteins (RNase A, lysozyme) or an amino acid (Met) that were used as source of thiyl radical damage occurring in vivo. Biomimetic models of thiyl radical–catalyzed isomerization of cis phospholipids, were used to demonstrate that when thiyl radicals are generated in the aqueous compartment and are able to diffuse in the lipid bilayer, then their interaction with unsaturated fatty acyl chains efficiently produces trans double bonds. Methionine could be the main source of thiyl radicals. Control experiments in the absence of sulphur-containing proteins (RNase T1) or by replacing sulphur-containing proteins with a protein lacking sulphur-containing amino acids, (histone H1), did not show any isomerization. The formation of thyil radicals by degradation of sulphur-containing amino acids could produces a tandem radical damage involving both protein and lipid domains.