Low glutathione levels are associated with crystallin oxidation in age-related nuclear cataract. To understand the role of cysteine residue oxidation, we used the novel approach of comparing human cataracts with glutathionedepleted LEGSKO mouse lenses for intra-versus intermolecular disulfide crosslinks using 2D-PAGE and proteomics, and then systematically identified in vivo and in vitro all disulfide forming sites using ICAT labeling method coupled with proteomics. Crystallins rich in intramolecular disulfides were abundant at young age in human and WT mouse lens but shifted to multimeric intermolecular disulfides at older age. The shift was 4x accelerated in LEGSKO lens. Most cysteine disulfides in β-crystallins (except βA4 in human) were highly conserved in mouse and human and could be generated by oxidation with H 2 O 2 , whereas γ-crystallin oxidation selectively affected γC23/42/79/80/154, γD42/33, and γS83/115/130 in human cataracts, and γB79/80/110, γD19/109, γF19/79, γE19, γS83/130, and γN26/128 in mouse. Analysis based on available crystal structure suggests that conformational changes are needed to expose Cys42, Cys79/80, Cys154 in γC; Cys42, Cys33 in γD, and Cys83, Cys115, and Cys130 in γS. In conclusion, the β-crystallin disulfidome is highly conserved in age-related nuclear cataract and LEGSKO mouse, and reproducible by in vitro oxidation, whereas some of the disulfide formation sites in γ-crystallins necessitate prior conformational changes. Overall, the LEGSKO mouse model is closely reminiscent of age- Aging lens crystallins accumulate post-synthetic modifications that can be broadly classified into three categories, namely (1) protein backbone changes, such as racemization and truncation (1-3), (2) conversion of one amino acid into another, such as deamidation of asparagine into aspartate or deguanidination of arginine into ornithine, deamination of lysine into allysine and 2-aminoadipic acid (4 -6), and (3) amino acid residue damage from reactive carbonyls and reactive oxygen species (7,8). Carbonyl damage results from the Maillard Reaction by glucose, methylglyoxal, or oxidation products of ascorbate, tryptophan or lipids which form adducts and crosslinks with nucleophilic group of lysine, arginine and cysteine. Examples include carboxymethyl-lysine, pentosidine, methylglyoxal hydroimidazolones, HNE-cysteine adducts and kynurenine (7,9 -12). Oxidative damage results from reactive oxygen species that directly damage amino acid residues, e.g. oxidizing tryptophan into N-formyl kynurenine and kynurenine, methionine into its sulfoxide, and cysteine into cysteine disulfides or cysteic acid (13)(14)(15).Because of their relevance to age-related cataract, the impact of each of these modifications on crystallin structure and stability is the subject of intense investigation. Importantly, Benedek proposed that high molecular weight (HMW) 1 crystallin aggregates the size of 50 million daltons are needed in order for lens opacification to be visible (16,17). Crystallin aggregation conceivably occurs by o...

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SummaryAge‐related cataractogenesis is associated with disulfide‐linked high molecular weight (HMW) crystallin aggregates. We recently found that the lens crystallin disulfidome was evolutionarily conserved in human and glutathione‐depleted mouse (LEGSKO) cataracts and that it could be mimicked by oxidation in vitro (Mol. Cell Proteomics, 14, 3211‐23 (2015)). To obtain a comprehensive blueprint of the oxidized key regulatory and cytoskeletal proteins underlying cataractogenesis, we have now used the same approach to determine, in the same specimens, all the disulfide‐forming noncrystallin proteins identified by ICAT proteomics. Seventy‐four, 50, and 54 disulfide‐forming proteins were identified in the human and mouse cataracts and the in vitro oxidation model, respectively, of which 17 were common to all three groups. Enzymes with oxidized cysteine at critical sites include GAPDH (hGAPDH, Cys247), glutathione synthase (hGSS, Cys294), aldehyde dehydrogenase (hALDH1A1, Cys126 and Cys186), sorbitol dehydrogenase (hSORD, Cys140, Cys165, and Cys179), and PARK7 (hPARK7, Cys46 and Cys53). Extensive oxidation was also present in lens‐specific intermediate filament proteins, such as BFSP1 and BFSP12 (hBFSP1 and hBFSP12, Cys167, Cys65, and Cys326), vimentin (mVim, Cys328), and cytokeratins, as well as microfilament and microtubule filament proteins, such as tubulin and actins. While the biological impact of these modifications for lens physiology remains to be determined, many of these oxidation sites have already been associated with either impaired metabolism or cytoskeletal architecture, strongly suggesting that they have a pathogenic role in cataractogenesis. By extrapolation, these findings may be of broader significance for age‐ and disease‐related dysfunctions associated with oxidant stress.

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