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In biology, a crystallin is a water-soluble structural protein found in the lens of the eye, accounting for the transparency of the structure. It has also been identified in other places such as the heart  and aggressive breast cancer tumors . Since it has been shown that lens injury may promote nerve regeneration, crystallin has been an area of neural research. So far, it has been demonstrated that crystallin β b2 (crybb2) may be a neurite promoting factor .
The main function of crystallins at least in the lens of the eye is probably to increase the refractive index while not obstructing light. However, this is not their only function. It is becoming increasingly clear that crystallins may have a several metabolic and regulatory functions, both within the lens and in other parts of the body .
Interestingly and perhaps excitingly from an evolutionary perspective, some crystallins are active enzymes. A number of crystallins are related to the serine and tyrosine proteases, and others to quinone oxidoreductases. Whether these crystallins are products of a happy accident of evolution, in that these particular enzymes happened to be transparent, or whether the enzymatic activity is a part of the protective machinery of the lens, is an active research topic.
Crystallins from a vertebrate eye lens are classified into three types: alpha, beta and gamma crystallins. These distinctions are based on the order in which they elute from a gel filtration chromatography column. These are also called ubiquitous crystallins. Beta- and gamma-crystallins are similar in sequence, structure and domains topology, and thus have been grouped together as a protein superfamily called βγ-Crystallins. The α-crystallin superfamily and βγ-crystallins compose the major superfamily of proteins present in the crystalline lens.
In addition to these crystallins there are other taxon-specific crystallins which are only found in the lens of some organisms; these include delta, epsilon, tau, and iota-crystallins. For example, alpha, beta, and delta crystallins are found in avian and reptilian lenses, and the alpha, beta, and gamma families are found in the lenses of all other vertebrates.
- Graw J (1997). The crystallins: genes, proteins and diseases. Biol Chem 378 (11): 1331-48.
- MeSH Crystallins
- Lens Crystallin Crystal Structures by Christine Slingsby, Birkbeck Colleg
- ↑ LUTSCH, G., R. VETTER, U. OFFHAUS, M. WIESKE, H.-J. GRÖNE, R. KLEMENZ, I. SCHIMKE, J. STAHL & R. BENNDORF (1997). Abundance and location of the small heat shock protein HSP25 and αB-crystallin in rat and human heart. Circulation 96 (11): 3466-3476.
- ↑ Jose V. Moyano, Joseph R. Evans, Feng Chen, Meiling Lu, Michael E. Werner, Fruma Yehiely, Leslie K. Diaz, Dmitry Turbin, Gamze Karaca, Elizabeth Wiley, Torsten O. Nielsen, Charles M. Perou and Vincent L. Cryns (2006). αB-Crystallin is a novel oncoprotein that predicts poor clinical outcome in breast cancer. Journal of Clinical Investigation 116: 261-270.
- ↑ Dietmar Fischer, Mitrofanis Pavlidis and Solon Thanos (2000). Cataractogenic Lens Injury Prevents Traumatic Ganglion Cell Death and Promotes Axonal Regeneration Both In Vivo and in Culture. Investigative Ophthalmology and Visual Science 41: 3943-3954.
- ↑ Thomas Liedtke, Jens Christian Schwamborn, Uwe Schröer and Solon Thanos (2007). Elongation of Axons during Regeneration Involves Retinal Crystallin β b2 (crybb2). Molecular & Cellular Proteomics 6: 895-907.
- ↑ Bhat SP (2003). Crystallins, genes and cataract. Progress in drug research. Fortschritte der Arzneimittelforschung. Progrès des recherches pharmaceutiques 60: 205-62.
- ↑ H. Jörnvall, B. Persson, G. C. Du Bois, G. C. Lavers, J. H. Chen, P. Gonzalez, P. V. Rao and J. S. Zigler Jr. (1993). ζ-Crystallin versus other members of the alcohol dehydrogenase super-family. Federation of European Biochemical Societies Letters 322 (3): 240-244.
- ↑ P. Vasantha Rao, C. Murali Krishna and J. Samuel Zigler, Jr. (1992). Identification and Characterization of the Enzymatic Activity of ζ-Crystallin from Guinea Pig Lens. The Journal of Biological Chemistry 267 (1): 96-102.
- ↑ M. Bando, M. Oka, K. Kawai, H. Obazawa, S. Kobayashi and M. Takehana (2006). NADH binding properties of rabbit lens λ-crystallin. Molecular Vision 12: 692-697.
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