Structural lesion to ribonuclease A caused by reductive stress: Assessment by Raman spectroscopy

The damages induced by reductive radical stress on bovine pancreatic ribonuclease A (RNAse A) were investigated by Raman spectroscopy. Gamma-irradiation was used to simulate the endogenous formation of reductive species, in particular H-center dot atom that is a simple one-electron equivalent reducing agent. Specific damages occur at sensitive amino acid sites, selectively, rather than indiscriminately, leading to the structure modification of the protein. Sulfur-containing residues (Met and Cys) and aromatic residues are appreciably attacked. In particular, extensive changes in the disulfide bridge conformations are induced as well as conformational changes of the protein secondary structure; a gradual conversion of alpha-helical to pleated-sheet geometry was evidenced, indicating a higher ability of reducing radicals in denaturing the protein structure compared with that of oxidizing radical species.