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. Elevated expression of alpha-B crystallin occurs in many neurological diseases; a;missense mutation cosegregated in a family with a desmin-related myopathy.
CRYAB; crystallin, alpha B; CRYA2; alpha-crystallin B chain; HSPB5; heat shock protein beta-5; rosenthal fiber component; heat-shock 20 kD like-protein; renal carcinoma antigen NY-REN-27; CTPP2; alpha B-crystallin; alpha(B)-crystallin