The reductive desulfurization of Met and Cys residues in bovine RNAse A associated with the trans lipid formation in a mimetic model of biological membranes

Damage to bovine pancreatic RNase A, due to the Ho atom and/or solvated electron attack at protein sulfur-containing residues, was investigated by Raman spectroscopy and mass spectrometry techniques. To the already known desulfurization process affecting Met residues, novel reactivity was observed involving disulfide moieties, leading to the chemical transformation of Cys into Ala residues. Mapping experiments demonstrated that desulfurization selectively affected Met79, Cys110, Cys58 and Cys72 during first stages of reaction. While this reaction was performed on protein species added to large unilamellar vescicles, desulfurization yielded sulfur radicals able to induce a cis-trans isomerization of lipids at the onset of irradiation. These findings reveal new scenarios on reactions generated by radical stressing conditions, suggesting the need for specific assays and for future investigations to detect these modifications in proteins and lipids within challenged cells.