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)

Since the water-insoluble crystallins of the lens may be the precursors of cataract, identifying the modifications that differentiate the water-insoluble from the water-soluble crystallins may provide the basis for understanding the chemistry leading to cataract. This investigation of the alpha-crystallins of the water-insoluble urea-soluble portion of 45-year-old normal clear lenses, isolated using gel filtration, ion exchange and reversed phase chromatography, has employed state-of-the-art mass spectrometric techniques to identify and locate the modifications of the water-insoluble alpha-crystallins. Modifications present in the isolated alpha-crystallins were identified by the molecular weights of the modified proteins, by the molecular weights of peptides produced by enzymatic digestion of the proteins, and by the fragmentation patterns produced by collisional activation of the peptides. Modifications that are either unique to the water-insoluble alpha-crystallins or are more prevalent in the water-soluble portion than in the water-soluble part include complete oxidation of the two Cys residues of alpha A-crystallin to form an intra-molecular disulfide bond, partial truncation at both the C-termini and N-termini of alpha A- and alpha B-crystallins, partial oxidation of Met residues to methionine sulfoxide, partial deamidation of several Asn and Gln residues, and evidence of peptide bond cleavage at some of the deamidated residues. Although many reactions have been proposed to contribute to the insolubility of crystallins, this compilation of in vivo post-translational modifications of water-insoluble alpha-crystallins delineates products that are actually present at levels of 5% or more. From these results, it is hypothesized that alpha-crystallin becomes water-insoluble following deamidation of various Asn and Gln residues which cause conformational changes leading to formation of an intra-molecular disulfide bond between the Cys residues of alpha A-crystallin.
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PMID:Modifications of the water-insoluble human lens alpha-crystallins. 906 73

The alpha-crystallins are the most abundant structural proteins of the lens and, because of their chaperone activity, contribute to the solubility of the other crystallins. With aging, the lens crystallins undergo a variety of modifications which correlate with a loss of solubility and the development of cataract. A recent study demonstrating that alpha-crystallins exposed in vitro to FeCl3 and H2O2 exhibit decreased chaperone activity, implicates metal catalyzed oxidations of alpha-crystallins in this loss of solubility. The present study has determined that alpha-crystallins incubated with FeCl3 and H2O2 are modified by the nearly complete oxidation of all methionine residues to methionine sulfoxide, with no other detectable reaction products. The modifications were identified from the molecular weights of peptides formed by enzymatic digestion of the alpha-crystallins and located by tandem mass spectrometric analysis of the fragmentation pattern of the mass spectra of the fragments from peptides with oxidized methionine is loss of 64 Da, which corresponds to loss of CH3SOH from the methionine sulfoxide. These fragments are useful in identifying peptides that include oxidized methionine residues.
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PMID:Identification of hydrogen peroxide oxidation sites of alpha A- and alpha B-crystallins. 925 22

Oxidative damage of the lens causes disulfide bonds between cysteinyl residues of lens proteins and thiols such as glutathione and cysteine, which may lead to cataract. The effect of H2O2 oxidation was determined by comparing bovine lenses incubated with and without 30 mM H2O2. The H2O2 treatment decreased the glutathione and increased the protein-glutathione and protein-cysteine disulfides in the lens. The molecular mass of the gammaB-crystallin isolated from lenses, not treated with H2O2, agreed with the published sequence (Mr 20,966). Some lenses also had a less abundant gammaB-crystallin component 305 Da higher (Mr 21,270), suggesting the presence of a glutathione adduct. The gammaB-crystallins from H2O2 treated lenses had three components, the major one with one GSH adduct, another one with the mass of unmodified gammaB-crystallin, and a third with a mass consistent with addition of two GSH adducts. Mass spectrometric analysis of tryptic peptides of gammaB-crystallins from different lenses indicated that the +305 Da modifications were not at a specific cysteine. For the lenses incubated without H2O2, there was evidence of adducts at Cys-41 and in peptide 10-31, which includes 3 cysteines. Analysis of modified peptide 10-31 by tandem mass spectrometry showed GSH adducts at Cys-15, Cys-18, and Cys-22. In addition, gammaB-crystallins from H2O2-treated lenses had an adduct at Cys-109, partial oxidation at all 7 Met residues, and evidence for two disulfide bonds.
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PMID:Thiolation of the gammaB-crystallins in intact bovine lens exposed to hydrogen peroxide. 998 10

We describe a 5-year-old boy with a unique congenital cataract caused by deposition of numerous birefringent, pleiochroic and macroscopically prismatic crystals. Crystal analysis with subsequent automatic Edman degradation and matrix-associated laser desorption ionization time-of-flight mass spectrometry have identified the crystal-forming protein as gammaD-crystallin (CRYGD) lacking the N-terminal methionine. Sequencing of the CRYGD gene has shown a heterozygous C-->A transversion in position 109 of the inferred cDNA (36R-->S transversion of the processed, N-terminal methionine-lacking CRYGD). The lens protein crystals were X-ray diffracting, and our crystal structure solution at 2.25 A suggests that mutant R36S CRYGD has an unaltered protein fold. In contrast, the observed crystal packing is possible only with the mutant protein molecules that lack the bulky Arg36 side chain. This is the first described case of human cataract caused by crystallization of a protein in the lens. It involves the third known mutation in the CRYGD gene but offers, for the first time, a causative explanation of the phenotype.
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PMID:Link between a novel human gammaD-crystallin allele and a unique cataract phenotype explained by protein crystallography. 1091 66

This investigation of the water-insoluble crystallins from human lenses has used multiple chromatographic separations to obtain proteins of sufficient purity for mass spectrometric analysis. Each fraction was analysed to determine the molecular masses of the constituent proteins as well as peptides in tryptic digests of these proteins. The major components of the water-insoluble crystallins were identified as alphaA- and alphaB-crystallins. In addition, gammaS-, betaB1-, gammaD-, betaA3/A1- and betaB2-crystallins were found, in order of decreasing abundance. Although there was evidence of some backbone cleavage, the predominant forms of alphaA-, alphaB, betaB2-, gammaS- and gammaD-crystallins were the intact polypeptide chains. The major modifications distinguishing the water-soluble crystallins were increased disulfide bonding, oxidation of Met, deamidation of Gln and Asn and backbone cleavage. Of the many reactions hypothesized to lead to crystallin insolubility and cataract, these results most strongly support metal-catalysed oxidation, deamidation and truncation as initiators of conformational changes that favor aggregation.
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PMID:The major in vivo modifications of the human water-insoluble lens crystallins are disulfide bonds, deamidation, methionine oxidation and backbone cleavage. 1093 Mar 24

Human connexin46 (hCx46) forms gap junctional channels interconnecting lens fiber cells and appears to be critical for normal lens function, because hCx46 mutations have been linked to congenital cataracts. We studied two hCx46 mutants, N63S, a missense mutation in the first extracellular domain, and fs380, a frame-shift mutation that shifts the translational reading frame at amino acid residue 380. We expressed wild-type Cx46 and the two mutants in Xenopus oocytes. Production of the expressed proteins was verified by SDS-PAGE after metabolic labeling with [(35)S]methionine or by immunoblotting. Dual two-microelectrode voltage-clamp studies showed that hCx46 formed both gap junctional channels in paired Xenopus oocytes and hemi-gap junctional channels in single oocytes. In contrast, neither of the two cataract-associated hCx46 mutants could form intercellular channels in paired Xenopus oocytes. The hCx46 mutants were also impaired in their ability to form hemi-gap-junctional channels. When N63S or fs380 was coexpressed with wild-type connexins, both mutations acted like "loss of function" rather than "dominant negative" mutations, because they did not affect the gap junctional conductance induced by either wild-type hCx46 or wild-type hCx50.
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PMID:Connexin46 mutations linked to congenital cataract show loss of gap junction channel function. 1094 9

The aim of the study is to screen patients for homocystinuria with and without cataract and analyse for homocystine and methionine. Fifty-eight samples from 29 patients, i.e., plasma and urine collected after overnight fasting were analysed by the screening test for homocystine, and paper chromatography for homocystine and methionine. Out of 29 homocystinuric patients, 24 had cataract. Only one had appreciable amounts of methionine in his serum. He also had mental retardation as expected and belongs to Type I. The other types did not have methionine but had only homocystine. There was no mental retardation or ectopia lentis. So they belonged to Types II, III or IV. As there is excess methionine in Type I, with low cystine, cataract may be due to deficiency of cysteine and reduced glutathione and might be averted by suitable therapy, i.e., high cystine-low methionine diet with B6. In other types with low methionine, cataract may be due to decreased availability of amino acids for the synthesis of lens proteins; the treatment of choice should be B12, and folate with methionine.
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PMID:Homocystinuria with congenital/developmental cataract. 1110 22

Among lens crystallins, gamma-crystallins are particularly sensitive to oxidation, because of their high amount of Cys and Met residues. They have the reputation to induce, upon ageing, lens structural modifications leading to opacities. A combination of small angle X-ray scattering and chromatography was used to study the oxidation of gamma-crystallins. At pH 7.0, all the gamma-crystallins under study were checked to have the same structure in solution. Under gentle oxidation conditions at pH 8.0, human gammaS (hgammaS) and bovine gammaS (bgammaS) formed disulfide-linked dimers, whereas the other bgamma-crystallins did not. Cys20 was shown to be responsible for dimer formation since the C20S mutant only formed monomers. The hgammaS dimers were stable for weeks and did not form higher oligomers. In contrast, monomeric gammaS-crystallins freshly prepared at pH 8.0, and submitted to more drastic oxidation by X-ray induced free radicals, were rapidly transformed into higher oligomers. So, only extensive oxidation causing partial unfolding could be detrimental to the lens and linked to cataract formation. The gammaS-crystallins lack the temperature-induced opacification observed with the other gamma-crystallins and known as cold cataract. The oxidation-induced associative behaviour and cold cataract are therefore demonstrated to be uncoupled.
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PMID:Lens crystallins and oxidation: the special case of gammaS. 1124 46

LEP503 is a novel gene product isolated from lens epithelial cells by a subtractive cDNA cloning strategy. It is highly conserved in different vertebrate species and developmentally regulated in postnatal rat lens, suggesting that LEP503 may be an important lens epithelium gene involved in the processes of lens epithelial cell differentiation. The expression of LEP503 is highly restricted to lens epithelial cells in vivo. To investigate the molecular mechanisms regulating the promoter of the human LEP503, we cloned and characterized the promoter of the human LEP503 gene. The transcription start site was localized to a nucleotide C 22 base pairs (bp) 5' of the initiation methionine codon. By reporter gene transfection experiments, we found that approximately 2.5-kb of LEP503 5'-flanking sequence directed high level luciferase activity in human lens epithelial cells; further deletion analysis revealed positive regulatory element between bp -401 and +22. Mutation analysis in each of the seven potential binding sites for transcription factors within the region between -401 and +22 showed that the AP-1 element at -131 and the Sp1 element at -48 are the most important sites for the tissue-specific expression of LEP503. Consistent with lens epithelial cell-restricted expression of LEP503 mRNA, we found that the approximately 2.5-kb 5'-flanking sequence directed high-level promoter activity in lens epithelial cells but not in other cell types. Understanding the LEP503 promoter will allow us to investigate lens epithelial cell-specific gene regulation and to uncover methods for targeting gene delivery specifically to lens epithelial cells. The LEP503 gene is mapped to human chromosome 1q22, the same location to which zonular pulverulent cataract was previously mapped.
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PMID:Functional analysis of the promoter and chromosomal localization for human LEP503, a novel lens epithelium gene. 1137 38

Singlet oxygen (1O2) is generated by a number of enzymes as well as by UV or visible light in the presence of a sensitizer and has been proposed as a damaging agent in a number of pathologies including cataract, sunburn, and skin cancers. Proteins, and Cys, Met, Trp, Tyr and His side chains in particular, are major targets for 1O2 as a result of their abundance and high rate constants for reaction. In this study it is shown that long-lived peroxides are formed on free Tyr, Tyr residues in peptides and proteins, and model compounds on exposure to 1O2 generated by both photochemical and chemical methods. The yield of these species is significantly enhanced in D2O and decreased by azide. Nuclear magnetic resonance and mass spectroscopic analysis of reaction mixtures, or materials separated by high-performance liquid chromatography, are consistent with the initial formation of an (undetected) endoperoxide that undergoes rapid ring-opening to give a hydroperoxide situated at the C1 ring-position (i.e. para to the phenolic group). In the presence of a free alpha-amino group (e.g. with free Tyr), rapid ring-closure occurs to give an indolic hydroperoxide that decays into the corresponding alcohol, 3a-hydroxy-6-oxo-2,3,3a,6,7,7a-hexahydro-1H-indole-2-carboxylic acid. Hydroperoxides that lack a free alpha-amino group (e.g. those formed on 3-(4-hydroxyphenyl)propionic acid, N-Ac-Tyr and Tyr-containing peptides) are longer-lived, with half-lives of hours to days. These species undergo slow decay at low temperatures to give the corresponding alcohol. Their rate of decay is enhanced at 37 degrees C, or on exposure to UV light or metal ions, and gives rise to reactive radicals, via cleavage of the peroxide bond. These radicals have been characterized by electron paramagnetic resonance spin trapping. These studies demonstrate that long-lived Tyr-derived peroxides are formed on proteins exposed to 1O2 and that these may promote damage to other targets via further radical generation.
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PMID:Singlet oxygen-mediated protein oxidation: evidence for the formation of reactive side chain peroxides on tyrosine residues. 1212 5


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