TY - JOUR

T1 - Oxidation of lysozyme induced by peroxyl radicals involves amino acid modifications, loss of activity, and formation of specific crosslinks

AU - Fuentes-Lemus, Eduardo

AU - Mariotti, Michele

AU - Hagglund, Per

AU - Leinisch, Fabian

AU - Fierro, Angelica

AU - Silva, Eduardo

AU - Davies, Michael J.

AU - Lopez-Alarcon, Camilo

PY - 2021

Y1 - 2021

N2 - The present work examined the oxidation and crosslinking of the anti-bacterial enzyme lysozyme (Lyso), which is present in multiple biological fluids, and released from the cytoplasmic granules of macrophages and neutrophils at sites of infection and inflammation. It is therefore widely exposed to oxidants including peroxyl radicals (ROO?). We hypothesized that exposure to ROO? would generate specific modifications and inter- and intraprotein crosslinks via radical-radical reactions. Lyso was incubated with AAPH (2,2?-azobis(2-methylpropionamidine) dihydrochloride) as a ROO? source. Enzymatic activity was assessed, while oxidative modifications were detected and quantified using electrophoresis and liquid chromatography (UPLC) with fluorescence or mass detection (MS). Computational models of AAPH-Lyso interactions were developed. Exposure of Lyso to AAPH (10 and 100 mM for 3 h, and 20 mM for 1 h), at 37 ?C, decreased enzymatic activity. 20 mM AAPH showed the highest efficiency of Lyso inactivation (1.78 mol of Lyso inactivated per ROO?). Conversion of Met to its sulfoxide, and to a lesser extent, Tyr oxidation to 3,4-dihydroxyphenylalanine and diTyr, were detected by UPLCMS. Extensive transformation of Trp, involving short chain reactions, to kynurenine, oxindole, hydroxytryptophan, hydroperoxides or di-alcohols, and N-formyl-kynurenine was detected, with Trp62, Trp63 and Trp108 the most affected residues. Interactions of AAPH inside the negatively-charged catalytic pocket of Lyso, with Trp108, Asp52, and Glu35, suggest that Trp108 oxidation mediates, at least partly, Lyso inactivation. Crosslinks between Tyr20-Tyr23 (intra-molecular), and Trp62-Tyr23 (inter-molecular), were detected with both proximity (Tyr20-Tyr23), and chain flexibility (Trp62) appearing to favor the formation of covalent crosslinks.

AB - The present work examined the oxidation and crosslinking of the anti-bacterial enzyme lysozyme (Lyso), which is present in multiple biological fluids, and released from the cytoplasmic granules of macrophages and neutrophils at sites of infection and inflammation. It is therefore widely exposed to oxidants including peroxyl radicals (ROO?). We hypothesized that exposure to ROO? would generate specific modifications and inter- and intraprotein crosslinks via radical-radical reactions. Lyso was incubated with AAPH (2,2?-azobis(2-methylpropionamidine) dihydrochloride) as a ROO? source. Enzymatic activity was assessed, while oxidative modifications were detected and quantified using electrophoresis and liquid chromatography (UPLC) with fluorescence or mass detection (MS). Computational models of AAPH-Lyso interactions were developed. Exposure of Lyso to AAPH (10 and 100 mM for 3 h, and 20 mM for 1 h), at 37 ?C, decreased enzymatic activity. 20 mM AAPH showed the highest efficiency of Lyso inactivation (1.78 mol of Lyso inactivated per ROO?). Conversion of Met to its sulfoxide, and to a lesser extent, Tyr oxidation to 3,4-dihydroxyphenylalanine and diTyr, were detected by UPLCMS. Extensive transformation of Trp, involving short chain reactions, to kynurenine, oxindole, hydroxytryptophan, hydroperoxides or di-alcohols, and N-formyl-kynurenine was detected, with Trp62, Trp63 and Trp108 the most affected residues. Interactions of AAPH inside the negatively-charged catalytic pocket of Lyso, with Trp108, Asp52, and Glu35, suggest that Trp108 oxidation mediates, at least partly, Lyso inactivation. Crosslinks between Tyr20-Tyr23 (intra-molecular), and Trp62-Tyr23 (inter-molecular), were detected with both proximity (Tyr20-Tyr23), and chain flexibility (Trp62) appearing to favor the formation of covalent crosslinks.

KW - Lysozyme

KW - Peroxyl radicals

KW - Protein crosslinking

KW - Enzymatic activity

KW - Tryptophan oxidation

KW - Radical-radical reactions

KW - RANGE ELECTRON-TRANSFER

KW - EGG-WHITE LYSOZYME

KW - INDUCED INACTIVATION

KW - LIPID-PEROXIDATION

KW - PROTEIN OXIDATION

KW - TRYPTOPHAN

KW - TYROSINE

KW - GLUCOSE-6-PHOSPHATE-DEHYDROGENASE

KW - AGGREGATION

KW - MECHANISMS

U2 - 10.1016/j.freeradbiomed.2021.03.009

DO - 10.1016/j.freeradbiomed.2021.03.009

M3 - Journal article

C2 - 33731307

VL - 167

SP - 258

EP - 270

JO - Free Radical Biology & Medicine

JF - Free Radical Biology & Medicine

SN - 0891-5849

ER -