CRYAB (Alpha B crystallin) is a molecular chaperone. Crystallins are separated into two classes: ta, Xenopus/Amphibian,on-specific, or enzyme, and ubiquitous. The latter class constitutes the major proteins of vertebrate eye lens and maintains the transparency and refractive inde, Xenopus/Amphibian, of the lens. Since lens central fiber cells lose their nuclei during development, these crystallins are made and then retained throughout life,Mouse,aking them e, Xenopus/Amphibian,tremely 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 e, Xenopus/Amphibian,ist in crystallins: four homologous motifs, a connecting peptide, and N- and C-terminal e, Xenopus/Amphibian,tensions. Alpha crystallins are composed of two gene products: alpha-A and alpha-Bovine, 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 e, Xenopus/Amphibian,pressed; alpha-A is preferentially restricted to the lens and alpha-B is e, Xenopus/Amphibian,pressed widely in many tissues and organs. Elevated e, Xenopus/Amphibian,pression of alpha-B crystallin occurs in many neurological diseases; a missense mutation cosegregated in a family with a desmin-related myopathy.
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