Alpha-crystallin A chain is a protein that in humans is encoded by the CRYAAgene.[5]
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. Alpha crystallins are composed of two gene products: alpha-A and alpha-B, for acidic and basic, respectively. Alpha crystallins can be induced by heat shock and are members of the small heat shock protein (sHSP also known as the HSP20) family. They act as molecular chaperones although they do not renature proteins and release them in the fashion of a true chaperone; instead they hold them in large soluble aggregates. Post-translational modifications decrease the ability to chaperone. These heterogeneous aggregates consist of 30-40 subunits; the alpha-A and alpha-B subunits have a 3:1 ratio, respectively. Two additional functions of alpha crystallins are an autokinase activity and participation in the intracellular architecture. Alpha-A and alpha-B gene products are differentially expressed; alpha-A is preferentially restricted to the lens and alpha-B is expressed widely in many tissues and organs. Defects in this gene cause autosomal dominant congenital cataract (ADCC).[5]
Hawkins JW, Van Keuren ML, Piatigorsky J, et al. (1987). "Confirmation of assignment of the human alpha 1-crystallin gene (CRYA1) to chromosome 21 with regional localization to q22.3". Hum. Genet. 76 (4): 375–80. doi:10.1007/BF00272448. PMID3610158. S2CID19506423.
Takemoto LJ (1996). "Differential phosphorylation of alpha-A crystallin in human lens of different age". Exp. Eye Res. 62 (5): 499–504. doi:10.1006/exer.1996.0060. PMID8759518.
Prabhakaram M, Katz ML, Ortwerth BJ (1997). "Glycation mediated crosslinking between alpha-crystallin and MP26 in intact lens membranes". Mech. Ageing Dev. 91 (1): 65–78. doi:10.1016/0047-6374(96)01781-2. PMID8910261. S2CID53227438.
Takemoto LJ (1998). "Quantitation of asparagine-101 deamidation from alpha-A crystallin during aging of the human lens". Curr. Eye Res. 17 (3): 247–50. doi:10.1076/ceyr.17.3.247.5218. PMID9543632.
Doss EW, Ward KA, Koretz JF (1998). "Investigation of the 'fines' hypothesis of primary open-angle glaucoma: the possible role of alpha-crystallin". Ophthalmic Res. 30 (3): 142–56. doi:10.1159/000055468. PMID9618718. S2CID46813838.