| Description: | Crystallins are separated into two classes:taxon-specific, or enzyme, and ubiquitous. The latter classconstitutes the major proteins of vertebrate eye lens and maintainsthe transparency and refractive index of the lens. Since lenscentral fiber cells lose their nuclei during development, thesecrystallins are made and then retained throughout life, making themextremely stable proteins. Mammalian lens crystallins are dividedinto alpha, beta, and gamma families; beta and gamma crystallinsare also considered as a superfamily. Alpha and beta families arefurther divided into acidic and basic groups. Seven protein regionsexist in crystallins: four homologous motifs, a connecting peptide,and N- and C-terminal extensions. Gamma-crystallins are ahomogeneous group of highly symmetrical, monomeric proteinstypically lacking connecting peptides and terminal extensions. Theyare differentially regulated after early development. Fourgamma-crystallin genes (gamma-A through gamma-D) and threepseudogenes (gamma-E, gamma-F, gamma-G) are tandemly organized in agenomic segment as a gene cluster. Whether due to aging ormutations in specific genes, gamma-crystallins have been involvedin cataract formation. |
