Elizabeth Escobar Álvarez

Título Tesis: “Role of tryptophan and tyrosine in the cross-linking and fragmentation of peptide and proteins mediated by peroxyl radicals”.

Resumen

Oxidation of peptides and proteins mediated by peroxyl radicals is a complex process following different reaction pathways. Oxidative modifications are mostly on Trp, Tyr, Met and Cys residues. In particular, mechanisms of Tyr and Trp oxidation, two aromatic residues, have been well described; alcohols, hydroperoxides, carbonyl groups, and dityrosine (di-Tyr), are usually determined as the main products.

The present thesis aimed to get more insights about the possible role that Tyr and Trp play in oxidation processes associated with cross-linking and fragmentation of peptides and proteins induced by peroxyl radicals. Oxidation of small peptides (with single Tyr and/or Trp), and proteins such as E. coli FtsZ (which has three Tyr and lack Trp), its mutant containing a single Trp at position 222 (Y222W), and superoxide dismutases from bovine (one Tyr) and human (one Trp), were studied. Working solutions of peptides and proteins were incubated with different concentrations of 2,2´-azo bis(2-amidino-propane) dihydrochloride (AAPH, which was used as peroxyl radical source), and analyzed by electrophoresis, chromatography, fluorescence, and mass spectrometry techniques.

The results emanated from the present thesis show that Tyr and Trp are involved in the oxidative modifications of proteins inducing changes in their molecular mass throughout different reaction pathways. The fate of Tyr or Trp reactions depend on the experimental conditions and also on the properties of the peptides or proteins under study. In particular, it is concluded that protein cross-linking and fragmentation, mediated by Trp oxidation should not be understood as a general mechanism; this is present in the oxidation of specific proteins and experimental conditions.