title: γ-Crystallins of the chicken lens: remnants of an ancient vertebrate gene family in birds.
abstract: 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 promoter had lens-preferred activity similar to that of mouse. Chicken γS was detected by a peptide antibody in lens, but not in other ocular tissues. Low levels of γS and γN 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 γS is well conserved in protein sequence, it has one notable difference in leucine 16, replacing a surface glutamine conserved in other γ-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 γ-crystallins in bird lenses. The conservation of genes for γS- and γN-crystallins suggests they may have been preserved for reasons unrelated to the bulk properties of the lens.
authors.affiliation: Section on Molecular Structure and Functional Genomics, National Eye Institute, National Institutes of Health, Bethesda, MD, USA.
authors.forename: Yingwei
authors.initials: Y
authors.lastname: Chen
authors.affiliation: Section on Molecular Structure and Functional Genomics, National Eye Institute, National Institutes of Health, Bethesda, MD, USA.
authors.forename: Vatsala
authors.initials: V
authors.lastname: Sagar
authors.affiliation: Section on Molecular Structure and Functional Genomics, National Eye Institute, National Institutes of Health, Bethesda, MD, USA.
authors.forename: Hoay-Shuen
authors.initials: HS
authors.lastname: Len
authors.affiliation: Section on Molecular Structure and Functional Genomics, National Eye Institute, National Institutes of Health, Bethesda, MD, USA.
authors.forename: Katherine
authors.initials: K
authors.lastname: Peterson
authors.affiliation: Section on Molecular Structure and Functional Genomics, National Eye Institute, National Institutes of Health, Bethesda, MD, USA.
authors.forename: Jianguo
authors.initials: J
authors.lastname: Fan
authors.affiliation: Section on Molecular Structure and Functional Genomics, National Eye Institute, National Institutes of Health, Bethesda, MD, USA.
authors.forename: Sanghamitra
authors.initials: S
authors.lastname: Mishra
authors.affiliation: USDA, ARS, Southern Plains Area, East College Station, TX, USA.
authors.forename: John
authors.initials: J
authors.lastname: McMurtry
authors.affiliation: Department of Biochemistry and Molecular Biology, School of Medicine, Oregon Health and Science University, Portland, OR, USA.
authors.forename: Phillip A
authors.initials: PA
authors.lastname: Wilmarth
authors.affiliation: Department of Biochemistry and Molecular Biology, School of Medicine, Oregon Health and Science University, Portland, OR, USA.
authors.forename: Larry L
authors.initials: LL
authors.lastname: David
authors.affiliation: Section on Molecular Structure and Functional Genomics, National Eye Institute, National Institutes of Health, Bethesda, MD, USA.
authors.forename: Graeme
authors.initials: G
authors.lastname: Wistow
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D002645:Chickens / Q000235:genetics* / Q000378:metabolism; D002942:Circular Dichroism; D005123:Eye / Q000378:metabolism*; D007908:Lens, Crystalline / Q000737:chemistry / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D005810:Multigene Family; D010802:Phylogeny; D011401:Promoter Regions, Genetic / Q000235:genetics; D020543:Proteome; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012689:Sequence Homology, Nucleic Acid; D013050:Spectrometry, Fluorescence; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014714:Vertebrates / Q000235:genetics* / Q000378:metabolism; D038222:gamma-Crystallins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism
chemical_list: D020543:Proteome; D012333:RNA, Messenger; D038222:gamma-Crystallins
keywords: crystallin; evolution; eye; promoter; protein folding; proteomics