Ubiquitin is a regulatory protein found in eukaryotic organisms that tags other proteins for destruction. It varies little between organisms and is essential for complex cellular function. Ubiquitination involves three types of enzymes and a single organism can contain many different versions. Dysfunctions in Ub-mediated processes can lead to pathological conditions.
Ubiquitin (Ub) protein is a regulatory protein found in the tissues of eukaryotic organisms, which are those that have complex cellular structures surrounded by membranes. Animals, plants and fungi are included in this category. The main role of the ubiquitin protein is to tag other proteins for destruction. When at least four attach to another protein, the cell begins to take it apart.
Composed of a sequence of only 76 amino acids, the protein ubiquitin varies little between organisms. There is only a slight difference between the human version and the one found in yeast, suggesting that its structure is essential for complex cellular function. The amine sequence has been conserved throughout evolutionary history.
Cells are continually building proteins that perform specific functions. Disassembling this type of protein is an effective way to ensure that the process associated with it is stopped. The protein ubiquitin plays a central role in getting rid of proteins that are no longer needed. In a process called ubiquitination, proteins to be recycled are assigned a molecular tag, the protein ubiquitin.
Regulatory proteins that have completed their function are thought to trigger a signal that attracts the protein ubiquitin. Three types of enzymes are required to complete the attachment. E1, or Ub-activating enzymes, put ubiquitin into a reactive state. The attachment to the protein is catalyzed by E2, or Ub conjugating enzymes. A third type of enzyme, E3, works to identify the protein to be removed.
A single organism can contain many different versions of these enzymes. There are more than a dozen variants of the E2 enzyme in yeast, for example. A combination of these variants is thought to facilitate the ubiquitin encoding of proteins associated with specific functions.
A protein identified by four or more tags is fed into the proteasome, a hollow structure that breaks down proteins into individual parts. The ubiquitin protein tag acts like a chemical key to unlock the proteasome. When the disassembly begins, the Ub tags are released and can be reused. The 2004 Nobel Prize in Chemistry was awarded to the discoverers of this process.
The protein ubiquitin plays a central role in many different cellular processes. Dysfunction in Ub-mediated processes can lead to a number of pathological conditions. Certain cancers, immune system disorders and degenerative nerve diseases have been linked to improper Ub function, suggesting possible treatment options or avenues for further research.
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