Crystallin 322855 220559284 2008-06-20T13:08:31Z DOI bot 6652755 Citation maintenance. You can [[WP:DOI|use this bot]] yourself! Please [[User:DOI_bot/bugs|report any bugs]]. In [[biology]], a '''crystallin''' is a water-soluble structural [[protein]] found in the [[Lens (anatomy)|lens]] of the [[eye]], accounting for the transparency of the structure. It has also been identified in other places such as the heart <ref name="heart-presence-1">{{cite journal |author=LUTSCH, G., R. VETTER, U. OFFHAUS, M. WIESKE, H.-J. GRÖNE, R. KLEMENZ, I. SCHIMKE, J. STAHL & R. BENNDORF |title=Abundance and location of the small heat shock protein HSP25 and αB-crystallin in rat and human heart |journal=Circulation |volume=96 |issue=11 |pages=3466–3476 |year=1997 |url=http://www.circ.ahajournals.org/cgi/content/abstract/96/10/3466 |pmid=9396443}}</ref> and aggressive breast cancer tumors <ref name="tumor-presence-1">{{cite journal |author=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 |title=αB-Crystallin is a novel oncoprotein that predicts poor clinical outcome in breast cancer |journal=Journal of Clinical Investigation |volume=116 |pages=261–270 |year=2006 |url=http://www.jci.org/cgi/content/full/116/1/261 |doi=10.1172/JCI25888}}</ref>. Since it has been shown that lens injury may promote nerve regeneration<ref name="nerve-regeneration-1">{{cite journal |author=Dietmar Fischer, Mitrofanis Pavlidis and Solon Thanos |title=Cataractogenic Lens Injury Prevents Traumatic Ganglion Cell Death and Promotes Axonal Regeneration Both In Vivo and in Culture |journal=Investigative Ophthalmology and Visual Science |year=2000 |volume=41 |pages=3943–3954 |url=http://www.iovs.org/cgi/content/full/41/12/3943 |pmid=11053298}}</ref>, 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 <ref name="neurite-promoting-1">{{cite journal |author=Thomas Liedtke, Jens Christian Schwamborn, Uwe Schröer and Solon Thanos |title=Elongation of Axons during Regeneration Involves Retinal Crystallin β b2 (crybb2) |journal=Molecular & Cellular Proteomics |volume=6 |pages=895–907 |year=2007 |url=http://www.mcponline.org/cgi/content/abstract/6/5/895 |doi=10.1074/mcp.M600245-MCP200 |pmid=17264069}}</ref>. ==Function== The main function of crystallins at least in the [[lens (anatomy)|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 <ref name="pmid12790344">{{cite journal |author=Bhat SP |title=Crystallins, genes and cataract |journal=Progress in drug research. Fortschritte der Arzneimittelforschung. Progrès des recherches pharmaceutiques |volume=60 |issue= |pages=205–62 |year=2003 |pmid=12790344 |doi=}}</ref>. ===Enzyme activity=== Interestingly and perhaps excitingly from an [[evolution|evolutionary]] perspective, some crystallins are active [[enzymes]], while others lack activity but show [[homology]] to other enzymes.<ref name="Enzymatic-activity-1">{{cite journal |author=H. Jörnvall, B. Persson, G. C. Du Bois, G. C. Lavers, J. H. Chen, P. Gonzalez, P. V. Rao and J. S. Zigler Jr. |title=ζ-Crystallin versus other members of the alcohol dehydrogenase super-family |journal=Federation of European Biochemical Societies Letters |volume=322 |issue=3 |pages=240–244 |year=1993 |url=http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6T36-44G8DGD-BD-1&_cdi=4938&_user=10&_orig=search&_coverDate=05%2F17%2F1993&_sk=996779996&view=c&wchp=dGLbVzb-zSkWW&md5=958d25f43cb077a4a568eb0a31d491a6&ie=/sdarticle.pdf |pmid=8486156 |doi=}}</ref><ref name="Enzymatic-activity-2">{{cite journal |author=P. Vasantha Rao, C. Murali Krishna and J. Samuel Zigler, Jr. |title=Identification and Characterization of the Enzymatic Activity of ζ-Crystallin from Guinea Pig Lens |journal=The Journal of Biological Chemistry |volume=267 |issue=1 |pages=96–102 |year=1992 |url=http://www.jbc.org/cgi/reprint/267/1/96.pdf |pmid=1370456 |doi=}}</ref> The crystallins of different groups of organisms are related to a large number of different proteins, with those from birds and reptiles related to [[lactate dehydrogenase]] and [[argininosuccinate lyase]], those of mammals to [[alcohol dehydrogenase]] and [[NADPH:quinone reductase|quinone reductase]], and those of [[cephalopod]]s to [[glutathione S-transferase]] and [[aldehyde dehydrogenase]]. Whether these crystallins are products of a happy accident of evolution, in that these particular enzymes happened to be transparent and highly-soluble, or whether these diverse enzymatic activities are part of the protective machinery of the lens, is an active research topic.<ref>{{cite journal |author=Piatigorsky J |title=Puzzle of crystallin diversity in eye lenses |journal=Dev. Dyn. |volume=196 |issue=4 |pages=267–72 |year=1993 |month=April |pmid=8219350 |doi=10.1002/aja.1001960408}}</ref> The recruitment of protein that originally evolved with one function to serve a second, unrelated function is an example of an [[exaptation]].<ref>Buss, David M., Martie G. Haselton, Todd K. Shackelford, et al. (1998) “[http://www.sscnet.ucla.edu/comm/haselton/webdocs/spandrels.html Adaptations, Exaptations, and Spandrels],” ''[[American Psychologist]]'', 53 (May):533-548.</ref> ==Classification== 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. ==External links== * {{cite journal |author=Graw J |title=The crystallins: genes, proteins and diseases |journal=Biol Chem |volume=378 |issue=11 |pages=1331–48 |year=1997 |pmid=9426193}} * {{MeshName|Crystallins}} * [http://sirtophamhatt.cryst.bbk.ac.uk/bca/CNews/1998/Dec98/eyeln.html Lens Crystallin Crystal Structures] by Christine Slingsby, Birkbeck Colleg ==References== {{reflist}} {{Eye proteins}} [[Category:Proteins]] [[ja:クリスタリン]] [[no:Krystallin]] [[ru:Кристаллин]] [[uk:Кристалін]]