Free Radicals and Proteins - Research Progress on Sulfur-containing Proteins under Radical Stress: a helpful Contribute from Raman Spectroscopy

The continuous increase in interest in free radicals associated with life sciences is motivated by the discovery of numerous processes in biology that make use of these species as key intermediates in their mechanism. Free radicals are constantly formed in human body, but they can become toxic when generated in excess or in the presence of a deficiency in the naturally occurring antioxidant defences. Thus, they can affect the structural and functional integrity of bio-molecules as lipids, proteins and nucleic acids, leading to modifications. These modifications are nowadays recognized to be involved in diseases such as cancer, as well as in the ageing process. In particular, exposure of proteins to free radicals may cause structural modifications of primary, secondary and tertiary assembly. Consequently, the activity of enzymes, receptors and membrane transporters can be greatly affected. The most studied intermediates known to cause protein damage are reactive oxygen species, in particular oOH radicals, whereas reductive stress has been much less considered. Recently, reducing species like Ho and eaq - have been found to produce a specific damage to proteins that consists of a desulfurization reaction involving sulfurcontaining amino acid residues. This reaction corresponds to a mutation of the natural sequence. Another relevant characteristic of this damage is that the amino acid desulfurization is accompanied by the formation of low-molecular-weight sulfur-centred radicals able to reach lipid bilayer causing further damage. These results suggest that reductive stress could be of relevance and should be more considered.