Association of partially folded lens betaB2-crystallins with the alpha-crystallin molecular chaperone. (33/70)

Age-related cataract is a result of crystallins, the predominant lens proteins, forming light-scattering aggregates. In the low protein turnover environment of the eye lens, the crystallins are susceptible to modifications that can reduce stability, increasing the probability of unfolding and aggregation events occurring. It is hypothesized that the alpha-crystallin molecular chaperone system recognizes and binds these proteins before they can form the light-scattering centres that result in cataract, thus maintaining the long-term transparency of the lens. In the present study, we investigated the unfolding and aggregation of (wild-type) human and calf betaB2-crystallins and the formation of a complex between alpha-crystallin and betaB2-crystallins under destabilizing conditions. Human and calf betaB2-crystallin unfold through a structurally similar pathway, but the increased stability of the C-terminal domain of human betaB2-crystallin relative to calf betaB2-crystallin results in the increased population of a partially folded intermediate during unfolding. This intermediate is aggregation-prone and prevents constructive refolding of human betaB2-crystallin, while calf betaB2-crystallin can refold with high efficiency. alpha-Crystallin can effectively chaperone both human and calf betaB2-crystallins from thermal aggregation, although chaperone-bound betaB2-crystallins are unable to refold once returned to native conditions. Ordered secondary structure is seen to increase in alpha-crystallin with elevated temperatures up to 60 degrees C; structure is rapidly lost at temperatures of 70 degrees C and above. Our experimental results combined with previously reported observations of alpha-crystallin quaternary structure have led us to propose a structural model of how activated alpha-crystallin chaperones unfolded betaB2-crystallin.  (+info)

Novel allele of crybb2 in the mouse and its expression in the brain. (34/70)

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Dual roles for Prox1 in the regulation of the chicken betaB1-crystallin promoter. (35/70)

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A novel nonsense mutation in CRYBB1 associated with autosomal dominant congenital cataract. (36/70)

PURPOSE: To identify the molecular defect underlying an autosomal dominant congenital nuclear cataract in a Chinese family. METHODS: Twenty-two members of a three-generation pedigree were recruited, clinical examinations were performed, and genomic DNA was extracted from peripheral blood leukocytes. All members were genotyped with polymorphic microsatellite markers adjacent to each of the known cataract-related genes. Linkage analysis was performed after genotyping. Candidate genes were screened for mutation using direct sequencing. Individuals were screened for presence of a mutation by restriction fragment length polymorphism (RFLP) analysis. RESULTS: Linkage analysis identified a maximum LOD score of 3.31 (recombination fraction [theta]=0.0) with marker D22S1167 on chromosome 22, which flanks the beta-crystallin gene cluster (CRYBB3, CRYBB2, CRYBB1, and CRYBA4). Sequencing the coding regions and the flanking intronic sequences of these four candidate genes identified a novel, heterozygous C-->T transition in exon 6 of CRYBB1 in the affected individuals of the family. This single nucleotide change introduced a novel BfaI site and was predicted to result in a nonsense mutation at codon 223 that changed a phylogenetically conserved amino acid to a stop codon (p.Q223X). RFLP analysis confirmed that this mutation co-segregated with the disease phenotype in all available family members and was not found in 100 normal unrelated individuals from the same ethnic background. CONCLUSIONS: This study has identified a novel nonsense mutation in CRYBB1 (p.Q223X) associated with autosomal dominant congenital nuclear cataract.  (+info)

Nonsense mutation in the CRYBB2 gene causing autosomal dominant progressive polymorphic congenital coronary cataracts. (37/70)

PURPOSE: We sought to identify the genetic defect in a large, five-generation Chinese family with autosomal dominant progressive polymorphic congenital coronary cataracts and to examine the clinical features in detail. METHODS: Clinical and ophthalmologic examinations were conducted on family members. All members were genotyped with microsatellite markers at loci previously associated with cataracts. Two-point LOD scores were calculated using a linkage package after genotyping. A mutation was detected by direct sequencing and verified by denaturing high-performance liquid chromatography (DHPLC). RESULTS: Clinical observations showed that all affected family members had progressive polymorphic coronary cataracts. Linkage analysis was obtained at markers, D22S303 (LOD score [Z]=2.11, recombination fraction [theta]=0.0) and D22S1167 (Z=1.20, theta=0.0). Haplotype analysis indicated that the cataract gene was closely linked with these two markers. Sequencing the betaB-crystallin gene (CRYBB2) revealed a C --> T transition in exon 6, which changed a codon from Gln to a stop codon (P.Q155X). This mutation cosegregated with all affected individuals and was not observed in any unaffected family member or 100 normal, unrelated individuals. CONCLUSIONS: This study identified a mutation in CRYBB2 in a large Chinese family with autosomal dominant progressive polymorphic congenital coronary cataracts. These results provide evidence that CRYBB2 is a pathogenic gene for congenital cataracts; at the same time, congenital cataracts are a clinically and genetically heterogeneous lens condition.  (+info)

Associations of seroreactivity against crystallin proteins with disease activity and cataract in patients with uveitis. (38/70)

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Deamidation destabilizes and triggers aggregation of a lens protein, betaA3-crystallin. (39/70)

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Patterns of crystallin distribution in porcine eye lenses. (40/70)

PURPOSE: To measure the protein distribution patterns in single young porcine lenses. METHODS: Twenty fresh porcine lenses from 5 to 6 months old animals were fractionated into 8-10 concentric fractions by controlled dissolution in phosphate buffer. Proportions of soluble and insoluble protein were determined by Bradford assay. Water-soluble proteins in all layers were separated into HMW, MMW, and LMW fractions by size-exclusion HPLC and constituents of each class further characterized by SDS gel electrophoresis, as were the water-insoluble proteins. Size-exclusion fractions were further separated by reverse-phase HPLC and the molecular masses of each peak determined by MALDI-TOF mass spectrometry. RESULTS: The major soluble proteins in the porcine lens are beta-crystallins. They comprise around 45% of the total protein in the outer lens decreasing gradually to 35% in the central region. Soluble alpha-crystallins vary from 35% to 22% from outer to inner lens. The proportion of soluble gamma-crystallin levels, substantially lower than that of the other protein classes, increases gradually with progression into the lens center. Insoluble protein levels also increase from outer to inner lens layers. CONCLUSIONS: In the young porcine lens, there is relative constancy in the levels of all three crystallin classes in the outer lens with alpha- and beta-crystallins representing the predominant protein classes. The increase in gamma-crystallin in the inner lens may contribute to the refractive index gradient.  (+info)