Crystallins are separated into two classes: taxon-specific, or enzyme, and ubiquitous. The latter class constitutes the major proteins of vertebrate eye lens and maintains the transparency and refractive index of the lens. Since lens central fiber cells lose their nuclei during development, these crystallins are made and then retained throughout life, making them extremely stable proteins. Mammalian lens crystallins are divided into alpha, beta, and gamma families; beta and gamma crystallins are also considered as a superfamily. Alpha and beta families are further divided into acidic and basic groups. Seven protein regions exist in crystallins: four homologous motifs, a connecting peptide, and N- and C-terminal extensions. Gamma-crystallins are a homogeneous group of highly symmetrical, monomeric proteins typically lacking connecting peptides and terminal extensions. They are differentially regulated after early development. Four gamma-crystallin genes (gamma-A through gamma-D) and three pseudogenes (gamma-E, gamma-F, gamma-G) are organized in a genomic segment as a gene cluster. Whether due to aging or mutations in specific genes, gamma-crystallins have been involved in cataract formation.
^ abcFu L, Liang JJ (February 2002). "Detection of protein-protein interactions among lens crystallins in a mammalian two-hybrid system assay". The Journal of Biological Chemistry. 277 (6): 4255–60. doi:10.1074/jbc.M110027200. PMID11700327.
Brakenhoff RH, Aarts HJ, Reek FH, Lubsen NH, Schoenmakers JG (December 1990). "Human gamma-crystallin genes. A gene family on its way to extinction". Journal of Molecular Biology. 216 (3): 519–32. doi:10.1016/0022-2836(90)90380-5. PMID2258929.
den Dunnen JT, van Neck JW, Cremers FP, Lubsen NH, Schoenmakers JG (May 1989). "Nucleotide sequence of the rat gamma-crystallin gene region and comparison with an orthologous human region". Gene. 78 (2): 201–13. doi:10.1016/0378-1119(89)90223-0. PMID2777080.
Shiloh Y, Donlon T, Bruns G, Breitman ML, Tsui LC (May 1986). "Assignment of the human gamma-crystallin gene cluster (CRYG) to the long arm of chromosome 2, region q33-36". Human Genetics. 73 (1): 17–9. doi:10.1007/BF00292656. PMID3011643.
den Dunnen JT, Moormann RJ, Cremers FP, Schoenmakers JG (1986). "Two human gamma-crystallin genes are linked and riddled with Alu-repeats". Gene. 38 (1–3): 197–204. doi:10.1016/0378-1119(85)90218-5. PMID4065573.
Andley UP, Mathur S, Griest TA, Petrash JM (December 1996). "Cloning, expression, and chaperone-like activity of human alphaA-crystallin". The Journal of Biological Chemistry. 271 (50): 31973–80. doi:10.1074/jbc.271.50.31973. PMID8943244.
Lampi KJ, Ma Z, Shih M, Shearer TR, Smith JB, Smith DL, David LL (January 1997). "Sequence analysis of betaA3, betaB3, and betaA4 crystallins completes the identification of the major proteins in young human lens". The Journal of Biological Chemistry. 272 (4): 2268–75. doi:10.1074/jbc.272.4.2268. PMID8999933.
Fu L, Liang JJ (February 2002). "Detection of protein-protein interactions among lens crystallins in a mammalian two-hybrid system assay". The Journal of Biological Chemistry. 277 (6): 4255–60. doi:10.1074/jbc.M110027200. PMID11700327.