Ubiquitin is a regulatory protein found in most tissues of many walled-celled organisms. Originally known as ubiquitous immunopoietic polypeptide, ubiquitin was discovered in 1975 and its mechanism identified by a team including Aaron Ciechanover, Avram Hershko, and Irwin Rose of the Fox Chase Cancer Center, for which they were awarded the Nobel Prize in Medicine in 2004. Ubiquitins act as traffic control agents within the cell, directing other proteins to various compartments within the cell including tagging proteins for destruction.
The word ubiquitin was formed in 1975 from the English adjective ubiquitous which dates only from 1837. Ubiquitous derives from the noun ubiquitary which dates from 1580s from the Latin preposition ubi meaning where and que meaning any, also, ever. Ubiquitary (meaning everywhere) originally referred to the Luthern doctrine that Christ is omnipresent.
Representation of ubiquitin protein, highlighting the secondary structure. α-helices are coloured in blue and β-strands in green. The sidechains of the 7 lysine residues are indicated by orange sticks. The two best-characterised attachment points for further ubiquitin molecules in polyubiquitin chain formation (lysines 48 & 63) are labelled.
Image of ubiquitin protein courtesy rogerdodd under a Creative Commons 3.0 license, used with permission.