Journal
FREE RADICAL BIOLOGY AND MEDICINE
Volume 143, Issue -, Pages 375-386Publisher
ELSEVIER SCIENCE INC
DOI: 10.1016/j.freeradbiomed.2019.08.023
Keywords
Rose bengal; Type 1 mechanism; Type 2 mechanism; Lysozyme; Protein cross-linking; Photo-oxidation; Tryptophan; Tyrosine
Funding
- Fondecyt [1180642]
- Novo Nordisk Foundation [NNF13OC0004294]
- Fondequip [EQM170120]
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This work examined the hypothesis that interactions of Rose Bengal (RB2-) with lysozyme (Lyso) might mediate type 1 photoreactions resulting in protein cross-linking even under conditions favoring O-1(2) formation. UV-visible spectrophotometry, isothermal titration calorimetry (ITC), and docking analysis were employed to characterize RB2--Lyso interactions, while oxidation of Lyso was studied by SDS-PAGE gels, extent of amino acid consumption, and liquid chromatography (LC) with mass detection (employing tryptic peptides digested in H-2 O-18 and H2O). Docking studies showed five interaction sites including the active site. Hydrophobic interactions induced a red shift of the visible spectrum of RB2- giving a K-d of 4.8 mu M, while data from ITC studies, yielded a K-d of 0.68 mu M as an average of the interactions with stoichiometry of 3.3 RB2- per Lyso. LC analysis showed a high consumption of readily-oxidized amino acids (His, Trp, Met and Tyr) located at different and diverse locations within the protein. This appears to reflect extensive damage on the protein probably mediated by a type 2 (O-1(2)) mechanism. In contrast, docking and mass spectrometry analysis provided evidence for the generation of specific intra- (Tyr23-Tyr20) and inter-molecular (Tyr23-Trp62) Lyso cross-links, and Lyso dimer formation via radical-radical, type 1 mechanisms.
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