Crystallin, beta A1 explained

Beta-crystallin A3 is a protein that in humans is encoded by the CRYBA1 gene.^{[1] [2] [3]}

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, encodes two proteins (crystallin, beta A3 and crystallin, beta A1) from a single mRNA, the latter protein is 17 aa shorter than crystallin, beta A3 and is generated by use of an alternate translation initiation site. Deletion of exons 3 and 4 causes the autosomal dominant disease 'zonular cataract with sutural opacities'.^[4]

Further reading

• Hulsebos TJ, Bijlsma EK, Geurts van Kessel AH . Direct assignment of the human beta B2 and beta B3 crystallin genes to 22q11.2----q12: markers for neurofibromatosis 2. . Cytogenet. Cell Genet. . 56 . 3–4 . 171–5 . 1991 . 2055112 . 10.1159/000133080 . etal.
• Basti S, Hejtmancik JF, Padma T . Autosomal dominant zonular cataract with sutural opacities in a four-generation family. . Am. J. Ophthalmol. . 121 . 2 . 162–8 . 1996 . 8623885 . 10.1016/s0002-9394(14)70580-x . etal.
• Werten PJ, Carver JA, Jaenicke R, de Jong WW . The elusive role of the N-terminal extension of beta A3- and beta A1-crystallin. . Protein Eng. . 9 . 11 . 1021–8 . 1997 . 8961355 . 10.1093/protein/9.11.1021 . free .
• Lampi KJ, Ma Z, Shih M . Sequence analysis of betaA3, betaB3, and betaA4 crystallins completes the identification of the major proteins in young human lens. . J. Biol. Chem. . 272 . 4 . 2268–75 . 1997 . 8999933 . 10.1074/jbc.272.4.2268 . etal. free .
• Kannabiran C, Rogan PK, Olmos L . Autosomal dominant zonular cataract with sutural opacities is associated with a splice mutation in the betaA3/A1-crystallin gene. . Mol. Vis. . 4 . 21 . 1998 . 9788845 . etal.
• Srivastava OP, Srivastava K . Characterization of a sodium deoxycholate-activatable proteinase activity associated with betaA3/A1-crystallin of human lenses. . Biochim. Biophys. Acta . 1434 . 2 . 331–46 . 1999 . 10525151 . 10.1016/s0167-4838(99)00183-1.
• Graw J, Jung M, Löster J . Mutation in the betaA3/A1-crystallin encoding gene Cryba1 causes a dominant cataract in the mouse. . Genomics . 62 . 1 . 67–73 . 2000 . 10585769 . 10.1006/geno.1999.5974 . etal.
• Vanita, Sarhadi V . Reis A . A unique form of autosomal dominant cataract explained by gene conversion between beta-crystallin B2 and its pseudogene. . J. Med. Genet. . 38 . 6 . 392–6 . 2001 . 11424921 . 1734905 . 10.1136/jmg.38.6.392 . etal.
• MacCoss MJ, McDonald WH, Saraf A . Shotgun identification of protein modifications from protein complexes and lens tissue. . Proc. Natl. Acad. Sci. U.S.A. . 99 . 12 . 7900–5 . 2002 . 12060738 . 122992 . 10.1073/pnas.122231399 . 2002PNAS...99.7900M . etal. free .
• Strausberg RL, Feingold EA, Grouse LH . Generation and initial analysis of more than 15,000 full-length human and mouse cDNA sequences. . Proc. Natl. Acad. Sci. U.S.A. . 99 . 26 . 16899–903 . 2003 . 12477932 . 139241 . 10.1073/pnas.242603899 . 2002PNAS...9916899M . etal. free .
• Qi Y, Jia H, Huang S . A deletion mutation in the betaA1/A3 crystallin gene (CRYBA1/A3) is associated with autosomal dominant congenital nuclear cataract in a Chinese family. . Hum. Genet. . 114 . 2 . 192–7 . 2004 . 14598164 . 10.1007/s00439-003-1049-7 . 38106334 . etal.
• Reddy MA, Bateman OA, Chakarova C . Characterization of the G91del CRYBA1/3-crystallin protein: a cause of human inherited cataract. . Hum. Mol. Genet. . 13 . 9 . 945–53 . 2004 . 15016766 . 10.1093/hmg/ddh110 . etal. free .
• Ferrini W, Schorderet DF, Othenin-Girard P . CRYBA3/A1 gene mutation associated with suture-sparing autosomal dominant congenital nuclear cataract: a novel phenotype. . Invest. Ophthalmol. Vis. Sci. . 45 . 5 . 1436–41 . 2004 . 15111599 . 10.1167/iovs.03-0760 . etal. free .
• Gerhard DS, Wagner L, Feingold EA . The status, quality, and expansion of the NIH full-length cDNA project: the Mammalian Gene Collection (MGC). . Genome Res. . 14 . 10B . 2121–7 . 2004 . 15489334 . 528928 . 10.1101/gr.2596504 . etal.
• Lapko VN, Cerny RL, Smith DL, Smith JB . Modifications of human betaA1/betaA3-crystallins include S-methylation, glutathiolation, and truncation. . Protein Sci. . 14 . 1 . 45–54 . 2005 . 15576560 . 2253330 . 10.1110/ps.04738505 .
• Takata T, Oxford JT, Brandon TR, Lampi KJ . Deamidation alters the structure and decreases the stability of human lens betaA3-crystallin. . Biochemistry . 46 . 30 . 8861–71 . 2007 . 17616172 . 2597435 . 10.1021/bi700487q .
• Lu S, Zhao C, Jiao H . Two Chinese families with pulverulent congenital cataracts and deltaG91 CRYBA1 mutations. . Mol. Vis. . 13 . 1154–60 . 2007 . 17653060 . etal.

Notes and References

1. Hogg D, Tsui LC, Gorin M, Breitman ML . Characterization of the human beta-crystallin gene Hu beta A3/A1 reveals ancestral relationships among the beta gamma-crystallin superfamily . J Biol Chem . 261 . 26 . 12420–7 . Oct 1986 . 10.1016/S0021-9258(18)67257-6 . 3745196 . free .
2. Sparkes RS, Mohandas T, Heinzmann C, Gorin MB, Zollman S, Horwitz J . Assignment of a human beta-crystallin gene to 17cen-q23 . Hum Genet . 74 . 2 . 133–6 . Nov 1986 . 3770741 . 10.1007/BF00282076 . 7875247 .
3. Web site: Entrez Gene: CRYBA1 crystallin, beta A1.
4. Web site: Entrez Gene: CRYBA1 crystallin, beta A1.