Alpha Crystallin - Classification

Classification

Crystallins from a vertebrate eye lens are classified into three main 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 (such as CRYGC) are similar in sequence, structure and domains topology, and thus have been grouped together as a protein superfamily called βγ-Crystallins. The α-crystallin family and βγ-crystallins compose the major family of proteins present in the crystalline lens. They occur in all vertebrate classes (though gamma-crystallins are low or absent in avian lenses); and delta-crystallin is found exclusively in reptiles and birds.

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.