Dataset Information

?-Crystallins of the chicken lens: remnants of an ancient vertebrate gene family in birds.

ABSTRACT: ?-Crystallins, abundant proteins of vertebrate lenses, were thought to be absent from birds. However, bird genomes contain well-conserved genes for ?S- and ?N-crystallins. Although expressed sequence tag analysis of chicken eye found no transcripts for these genes, RT-PCR detected spliced transcripts for both genes in chicken lens, with lower levels in cornea and retina/retinal pigment epithelium. The level of mRNA for ?S in chicken lens was relatively very low even though the chicken crygs gene promoter had lens-preferred activity similar to that of mouse. Chicken ?S was detected by a peptide antibody in lens, but not in other ocular tissues. Low levels of ?S and ?N proteins were detected in chicken lens by shotgun mass spectroscopy. Water-soluble and water-insoluble lens fractions were analyzed and 1934 proteins (< 1% false discovery rate) were detected, increasing the known chicken lens proteome 30-fold. Although chicken ?S is well conserved in protein sequence, it has one notable difference in leucine 16, replacing a surface glutamine conserved in other ?-crystallins, possibly affecting solubility. However, L16 and engineered Q16 versions were both highly soluble and had indistinguishable circular dichroism, tryptophan fluorescence and heat stability (melting temperature Tm ~ 65 °C) profiles. L16 has been present in birds for over 100 million years and may have been adopted for a specific protein interaction in the bird lens. However, evolution has clearly reduced or eliminated expression of ancestral ?-crystallins in bird lenses. The conservation of genes for ?S- and ?N-crystallins suggests they may have been preserved for reasons unrelated to the bulk properties of the lens.

SUBMITTER: Chen Y

PROVIDER: S-EPMC5576348 | biostudies-literature | 2016 Apr

REPOSITORIES: biostudies-literature

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γ-Crystallins of the chicken lens: remnants of an ancient vertebrate gene family in birds.

Chen Yingwei Y Sagar Vatsala V Len Hoay-Shuen HS Peterson Katherine K Fan Jianguo J Mishra Sanghamitra S McMurtry John J Wilmarth Phillip A PA David Larry L LL Wistow Graeme G

The FEBS journal 20160311 8

γ-Crystallins, abundant proteins of vertebrate lenses, were thought to be absent from birds. However, bird genomes contain well-conserved genes for γS- and γN-crystallins. Although expressed sequence tag analysis of chicken eye found no transcripts for these genes, RT-PCR detected spliced transcripts for both genes in chicken lens, with lower levels in cornea and retina/retinal pigment epithelium. The level of mRNA for γS in chicken lens was relatively very low even though the chicken crygs gene ...[more]

PMID: 26913478

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Project description:Crystallins are transparent, refractive proteins that contribute to the focusing power of the vertebrate eye lens. These proteins are extremely soluble and resist aggregation for decades, even under crowded conditions. Crystallins have evolved to avoid strong interprotein interactions and have unusual hydration properties. Crystallin aggregation resulting from mutation, damage, or aging can lead to cataract, a disease state characterized by opacity of the lens.Different aggregation mechanisms can occur, following multiple pathways and leading to aggregates with varied morphologies. Studies of variant proteins found in individuals with childhood-onset cataract have provided insight into the molecular factors underlying crystallin stability and solubility. Modulation of exposed hydrophobic surface is critical, as is preventing specific intermolecular interactions that could provide nucleation sites for aggregation. Biophysical measurements and structural biology techniques are beginning to provide a detailed picture of how crystallins crowd into the lens, providing high refractivity while avoiding excessively tight binding that would lead to aggregation.Despite the central biological importance of refractivity, relatively few experimental measurements have been made for lens crystallins. Our work and that of others have shown that hydration is important to the high refractive index of crystallin proteins, as are interactions between pairs of aromatic residues and potentially other specific structural features.This Account describes our efforts to understand both the functional and disease states of vertebrate eye lens crystallins, particularly the ?-crystallins. We use a variety of biophysical techniques, notably NMR spectroscopy, to investigate crystallin stability and solubility. In the first section, we describe efforts to understand the relative stability and aggregation propensity of different ?S-crystallin variants. The second section focuses on interactions of these proteins with the holdase chaperone ?B-crystallin. The third, fourth, and fifth sections explore different modes of aggregation available to crystallin proteins, and the final section highlights the importance of refractive index and the sometimes conflicting demands of selection for refractivity and solubility.

Dataset Information

?-Crystallins of the chicken lens: remnants of an ancient vertebrate gene family in birds.

Publications

γ-Crystallins of the chicken lens: remnants of an ancient vertebrate gene family in birds.

Similar Datasets

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