Radical approach to protein damage

Italian researchers have shown that Raman spectroscopy could be a useful tool in investigating radical-based damage to proteins. Armida Torreggiani, Maurizio Tamba, Immacolata Manco, M.R. Faraone-Mennella, Carla Ferreri, and C. Chatgilialoglu of the ISOF Institute of the National Research Council in Bologna and Naples University have investigated the gamma-irradiation of bovine pancreatic ribonuclease A (RNase A) in aqueous solution using vibrational spectroscopy as well as enzymatic assay, electrophoresis, and HPLC analysis. They found that Raman spectroscopy in particular could reveal conformational changes in the protein and locate the amino acid residues most susceptible to radical attack. Free radicals are an essential component of many biochemical processes, but they are also the underlying cause of molecular damage in radical-mediated tissue damage to the heart or brain for instance when blood flow is restored after stroke or cardiac arrest, or under conditions of inflammatory stress. As such, free radical damage to proteins can cause harmful protein-protein cross links to form. Irradiating bovine RNase A provides a useful model of the conformational and residue changes that might occur, particularly because it has numerous sulfur-containing residues. Such residues are thought to be easy targets for free radicals. The team found that following the partial structural changes that occurred after the initial radical attack, the internal sulfur-containing amino acid residues, tyrosine and methionine, were rendered susceptible to transformation, the team found on the basis of Raman data. Further, by carrying out the experiment in a biomimetic model using dioleoyl phosphatidyl choline vesicles to emulate fatty cell membrane molecules containing RNase A, the team could correlate the damage to methione residues with parallel alteration of membrane unsaturated lipids. They explain that sulfur-containing thiyl radicals formed by degradation of the protein can diffuse into the lipid bilayer and isomerize carbon-carbon double bonds from the cis to the trans form. In other words, normal fatty acids are converted into trans-unsaturated fatty acids in the vesicles. "The presence of trans-unsaturated acid have been correlated with higher serum lipoprotein cholesterol and triglyceride levels and an increasing risk of heart disease," Torreggiani told SpectroscopyNOW, "In addition, endogenous trans fatty acids are starting to be correlated with several diseases which include radical stress, such as atopic eczema and dermatitis." If this model proves valid in actual cell membranes, then it suggests that free radical damage following stroke, heart attack, and in inflammation, not only causes damage to protein, but can damage the cell membrane itself. Additionally, lipophilic compounds containing a polyconjugated double bond group inhibit the cis-trans isomerization process. "In this respect," adds Torreggiani, "retinoids and carotenoids that are well known to participate in diverse processes, such as vision, growth, development and anti-autoxidation, could be protective agents for the double bond geometry." "Source":[ http://www.spectroscopynow.com/coi/cda/detail.cda?id=11562&type=Feature&chId=6&page=1].

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