Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0086543 (cataract)
 29,165 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Buthionine sulfoximine (BSO), a specific inhibitor of glutathione biosynthesis, induces oxidative cataracts following multiple injections into mice at 1 week of age. Cultures of lenses with (35)S-methionine have previously demonstrated altered patterns of protein biosynthesis that precede and accompany these cataracts. To obtain parallel information about changes in protein phosphorylation during cataract development, lenses from BSO-treated or control mouse pups were cultured for 3 hr at 37 degrees C with (32)P(i), homogenized in phosphate buffer, and resolved by centrifugation into water-soluble (WS) and water-insoluble (WI) fractions. These were characterized by 2D-gel electrophoresis, Coomassie blue staining, phosphorimaging, immunoblotting, and tandem mass spectrometry. Heaviest labelling was in the WI fraction. The labelled 2D-gel spots included: (1) a series of phosphorylated filensins at 95 kDa; (2) a major radioactive spot at 45-50 kDa, slightly anodic to actin and the beaded filament protein, phakinin (CP 49); (3) a phosphorylated betaB1-crystallin, considerably anodic to parent betaB1; (4) an acidic cluster of labelled alphaA-crystallins, phosphorylated in part at serine-148, and (5) a labelled trace alpha crystallin, slightly anodic to alphaB-crystallin. The results confirm previously reported phosphorylations of actin, phakinin, alphaA- and alphaB-crystallin, demonstrate previously unrecognized phosphorylations of filensin and betaB1-crystallin, and provide unequivocal evidence for phosphorylation of alphaA-crystallin at serine-148. The earliest changes in phosphorylation detected after BSO treatment were increased labelling of alphaA- and alphaB-crystallin during cataract stages 1-3, coupled with a general decrease in protein labelling. In stage 5 cataracts, phosphorylated alpha crystallins persisted as the dominant labelled species. However, the major modifications of alphaA-crystallin in advanced BSO cataracts were unlabelled and partially degraded, in contrast to phosphorylated alphaA. It is therefore proposed that phosphorylation of alphaA-crystallin may confer resistance to proteolytic degradation.
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PMID:Altered patterns of phosphorylation in cultured mouse lenses during development of buthionine sulfoximine cataracts. 1238 96

Galactokinase (GALK1) deficiency is an autosomal recessive disorder, which causes cataract formation in children not maintained on a lactose-free diet. Galactokinase deficiency results from mutation in the GALK1 gene mapped on 17q24. Since GK1 cDNA was cloned about 20 mutations (prevalently deletions and missense) have been reported to date. Most of these reported mutations are confined to single families, and only one of them, P28T, has been referred as the founder Romani mutation. In this paper we report two novel missense mutations in GALK1 gene, identified in two unrelated patients with galactokinase deficiency. One mutation, g.575G>A, substitutes a valine for a methionine at amino acid 32 (p.V32M), while the other mutation, g.2839G>A, results in the arginine to glutamine substitution p.R239Q (GenBank sequence L76927). Biochemical studies demonstrate that these mutations led to a drastic modification in GALK activity when individual mutant cDNAs were expressed in an E. coli system. These findings indicate the pathogeneticity of these mutations causing GALK deficiency.
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PMID:Biochemical characterization of two GALK1 mutations in patients with galactokinase deficiency. 1502 38

In order to investigate the relationship between lens opacities and the various modifications of lens proteins, we analyzed and compared the properties of lens proteins of 85-day old normal Wistar rats and the hereditary cataract model, ICR/f rats. The present study identified many differences between normal and mutant lens proteins. In the ICR/f mutant rats, the relative amounts of gamma-crystallin decreased and high molecular weight (HMW) protein increased. Racemization and isomerization of Asp-151 of alpha A-crystallin was observed in the mutant ICR/f rats, and Met-1 of alpha A-crystallin was oxidized to methionine sulfoxide. These modifications were not found in the age-matched normal rats. These tendencies are consistent with aged and cataractous human lenses.
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PMID:Comparison of post-translational modifications of alpha A-crystallin from normal and hereditary cataract rats. 1504 43

Age-related cataract, an opacity of the eye lens, is the leading cause of visual impairment in the elderly, the etiology of which is related to oxidative stress damage. Oxidation of methionine to methionine sulfoxide is a major oxidative stress product that reaches levels as high as 60% in cataract while being essentially absent from clear lenses. Methionine oxidation results in loss of protein function that can be reversed through the action of methionine sulfoxide reductase A (MsrA), which is implicated in oxidative stress protection and is an essential regulator of longevity in species ranging from Escherichia coli to mice. To establish a role for MsrA in lens protection against oxidative stress, we have examined the levels and spatial expression patterns of MsrA in the human lens and have tested the ability of MsrA to protect lens cells directly against oxidative stress. In the present report, we establish that MsrA is present throughout the human lens, where it is likely to defend lens cells and their components against methionine oxidation. We demonstrate that overexpression of MsrA protects lens cells against oxidative stress damage, whereas silencing of the MsrA gene renders lens cells more sensitive to oxidative stress damage. We also provide evidence that MsrA is important for lens cell function in the absence of exogenous stress. Collectively, these data implicate MsrA as a key player in lens cell viability and resistance to oxidative stress, a major factor in the etiology of age-related cataract.
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PMID:Methionine sulfoxide reductase A is important for lens cell viability and resistance to oxidative stress. 1519 88

The sulphonium compound [Formula: see text] (AdoMet) plays a central role in many metabolic reactions of cellular metabolism, acting both as a propylamine donor in the biosynthesis of polyamines as well as a methyl donor in the transmethylation reactions. Moreover, AdoMet is a key intermediate of the transsulphuration pathway by which methionine is converted into cysteine, a precursor of glutathione. The aim of this study was to investigate the methionine and AdoMet metabolism in bovine lenses cultured in the presence of labelled methionine, upon treatment with H(2)O(2), as the experimental model for studying the molecular mechanisms responsible for the onset of senile cataract. The results reveal that one of the earliest changes following an oxidative stress is a severe impairment of protein synthesis. As far as the synthesis of AdoMet is concerned, a small but significant decrease in the conversion of labelled methionine into AdoMet occurs in treated lenses compared to the controls. In order to verify if the decreased AdoMet synthesis would lead in turn to alterations of methyl transfer reactions, we examined changes in the levels of various macromolecular methylations, such as protein methyl esterification and phospholipid methylation. The data clearly indicate that both the synthesis of AdoMet and the methyl transfer reactions could be significantly affected in eye lens upon an oxidative stress, suggesting that these alterations could be one of the biochemical events related to the ethiology of senile cataract. Finally, the question of whether or not H(2)O(2)-induced alterations of methionine and AdoMet metabolism could, in turn, affect some closely related metabolism, such as glutathione-associated reactions, is also discussed.
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PMID:Effect of an oxidative stress on methionine and S-adenosylmethionine metabolism in cultured bovine eye lens. 1537 84

Molecular models of human gamma-crystallins and the 'alpha-crystallin domain' of human alphaA-crystallin have been built based on available related X-ray crystal structures. The accessibilities of the component cysteine, methionine and tryptophan side chains in the crystallin models have been calculated. The reactivities of these cysteines, which are oxidised in cataract, are assessed based on their known modifications and within the context of their location within the 3D models.
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PMID:Sulfur in human crystallins. 1564 19

Age is by far the biggest risk factor for cataract, and it is sometimes assumed that cataract is simply an amplification of this aging process. This appears not to be the case, since the lens changes associated with aging and cataract are distinct. Oxidation is the hallmark of age-related nuclear (ARN) cataract. Loss of protein sulfhydryl groups, and the oxidation of methionine residues, are progressive and increase as the cataract worsens until >90% of cysteine and half the methionine residues are oxidised in the most advanced form. By contrast, there may be no significant oxidation of proteins in the centre of the lens with advancing age, even past age 80. The key factor in preventing oxidation seems to be the concentration of nuclear glutathione (GSH). Provided that nuclear GSH levels can be maintained above 2 mm, it appears that significant protein oxidation and posttranslational modification by reactive small molecules, such as ascorbate or UV filter degradation products, is not observed. Adequate coupling of the metabolically-active cortex, the source of antioxidants such as GSH, to the quiescent nucleus, is crucial especially since it would appear that the cortex remains viable in old lenses, and even possibly in ARN cataract lenses. Therefore it is vital to understand the reason for the onset of the lens barrier. This barrier, which becomes apparent in middle age, acts to impede the flow of small molecules between the cortex and the nucleus. The barrier, rather than nuclear compaction (which is not observed in human lenses), may contribute to the lowered concentration of GSH in the lens nucleus after middle age. By extending the residence time within the lens centre, the barrier also facilitates the decomposition of intrinsically unstable metabolites and may exacerbate the formation of H(2)O(2) in the nucleus. This hypothesis, which is based on the generation of reactive oxygen species and reactive molecules within the nucleus itself, shifts the focus away from theories for cataract that postulated a primary role for oxidants generated outside of the lens. Unfortunately, due to marked variability in the lenses of different species, there appears at present to be no ideal animal model system for studying human ARN cataract.
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PMID:Age-related nuclear cataract-oxidation is the key. 1586 78

Human gammaD crystallin (HgammaD-Crys) is a two domain, beta-sheet eye lens protein that must remain soluble throughout life for lens transparency. Single amino acid substitutions of HgammaD-Crys are associated with juvenile-onset cataracts. Features of the interface between the two domains conserved among gamma-crystallins are a central six-residue hydrophobic cluster, and two pairs of interacting residues flanking the cluster. In HgammaD-Crys these pairs are Gln54/Gln143 and Arg79/Met147. We previously reported contributions of the hydrophobic cluster residues to protein stability. In this study alanine substitutions of the flanking residue pairs were constructed and analyzed. Equilibrium unfolding/refolding experiments at 37 degrees C revealed a plateau in the unfolding/refolding transitions, suggesting population of a partially folded intermediate with a folded C-terminal domain (C-td) and unfolded N-terminal domain (N-td). The N-td was destabilized by substituting residues from both domains. In contrast, the C-td was not significantly affected by substitutions of either domain. Refolding rates of the N-td were significantly decreased for mutants of either domain. In contrast, refolding rates of the C-td were similar to wild type for mutants of either domain. Therefore, domain interface residues of the folded C-td probably nucleate refolding of the N-td. We suggest that these residues stabilize the native state by shielding the central hydrophobic cluster from solvent. Glutamine and methionine side chains are among the residues covalently damaged in aged and cataractous lenses. Such damage may generate partially unfolded, aggregation- prone conformations of HgammaD-Crys that could be significant in cataract.
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PMID:Interdomain side-chain interactions in human gammaD crystallin influencing folding and stability. 1604 26

The alpha-, beta-, and gamma-crystallins are the major structural proteins of mammalian lenses. The human lens also contains tryptophan-derived UV filters, which are known to spontaneously deaminate at physiological pH and covalently attach to lens proteins. 3-Hydroxykynurenine (3OHKyn) is the third most abundant of the kynurenine UV filters in the lens, and previous studies have shown this compound to be unstable and to be oxidized under physiological conditions, producing H2O2. In this study, we show that methionine and tryptophan amino acid residues are oxidized when bovine alpha-crystallin is incubated with 3-hydroxykynurenine. We observed almost complete oxidation of methionines 1 and 138 in alphaA-crystallin and a similar extent of oxidation of methionines 1 and 68 in alphaB-crystallin after 48 h. Tryptophans 9 and 60 in alphaB-crystallin were oxidized to a lesser extent. AlphaA-crystallin was also found to have 3OHKyn bound to its single cysteine residue. Examination of normal aged human lenses revealed no evidence of oxidation of alpha-crystallin; however, oxidation was detected at methionine 1 in both alphaA- and alphaB-crystallin from human cataractous lenses. Age-related nuclear cataract is associated with coloration and insolubilization of lens proteins and extensive oxidation of cysteine and methionine residues. Our findings demonstrate that 3-hydroxykynurenine can readily catalyze the oxidation of methionine residues in both alphaB- and alphaA-crystallin, and it has been reported that alpha-crystallin modified in this way is a poorer chaperone. Thus, 3-hydroxykynurenine promotes the oxidation and modification of crystallins and may contribute to oxidative stress in the human lens.
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PMID:3-Hydroxykynurenine oxidizes alpha-crystallin: potential role in cataractogenesis. 1646 31

Accumulation of methionine sulfoxide (Met(O)) is a significant feature of human cataract and previous studies have shown that methionine sulfoxide reductase A (MsrA), which acts to repair Met(O), can defend human lens cells against oxidative stress induced cell death. A key feature of oxidative stress is increased reactive oxygen species (ROS) in association with loss of mitochondrial function. Here, we sought to establish a potential role for MsrA in the accumulation of ROS in lens cells and the corresponding mitochondrial membrane potential in these cells. Targeted gene silencing was used to establish populations of lens cells expressing different levels of MsrA, and the mitochondrial membrane potential and ROS levels of these cell populations were monitored. Decreased MsrA levels were found to be associated with loss of cell viability, decreased mitochondrial membrane potential, and increased ROS levels in the absence of oxidative stress. These effects were augmented upon oxidative stress treatment. These results provide evidence that MsrA is a major determinant for accumulation of ROS in lens cells and that increased ROS levels in lens cells are associated with a corresponding decrease in mitochondrial membrane potential that is likely related to the requirement for MsrA in lens cell viability.
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PMID:Silencing of the methionine sulfoxide reductase A gene results in loss of mitochondrial membrane potential and increased ROS production in human lens cells. 1693 4


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