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.
Beta-crystallins, the most heterogeneous, differ by the presence of the C-terminal extension (present in the basic group, none in the acidic group). Beta-crystallins form aggregates of different sizes and are able to self-associate to form dimers or to form heterodimers with other beta-crystallins. This gene, a beta acidic group member, is part of a gene cluster with beta-B1, beta-B2, and beta-B3.[7]
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Bijlsma EK, Delattre O, Juyn JA, et al. (1994). "Regional fine mapping of the beta crystallin genes on chromosome 22 excludes these genes as physically linked markers for neurofibromatosis type 2". Genes Chromosomes Cancer. 8 (2): 112–8. doi:10.1002/gcc.2870080208. PMID7504514. S2CID31532867.
van Rens GL, Geurts van Kessel AH, Bloemendal H (1992). "Localization of the beta A4-crystallin gene (CRYBA4) on human chromosome 22 in the region q11.2→q13.1". Cytogenet. Cell Genet. 61 (3): 180–3. doi:10.1159/000133403. PMID1424806.
