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Ubiquitin is a small protein that exists in all eukaryotic cells. It performs its myriad functions through conjugation to a large range of target proteins. A variety of different modifications can occur. The ubiquitin protein itself consists of 76 amino acids and has a molecular mass of about 8.6 kDa.
The ubiquitin-proteasome system is critical to appropriate protein degradation within cells. Dysfunctions of this system can disrupt cellular homeostasis and lead to a host of disorders. In normally functioning cells, the covalent linkage of ubiquitin or ubiquitin-like protein to a target protein changes the target protein's surface.
Ubiquitin-like proteins (UBLs) are a family of small proteins involved in post-translational modification of other proteins in a cell, usually with a regulatory function. The UBL protein family derives its name from the first member of the class to be discovered, ubiquitin (Ub), best known for its role in regulating protein degradation through covalent modification of other proteins.
A ubiquitin ligase (also called an E3 ubiquitin ligase) is a protein that recruits an E2 ubiquitin-conjugating enzyme that has been loaded with ubiquitin, recognizes a protein substrate, and assists or directly catalyzes the transfer of ubiquitin from the E2 to the protein substrate. In simple and more general terms, the ligase enables movement ...
Anaphase-promoting complex (also called the cyclosome or APC/C) is an E3 ubiquitin ligase that marks target cell cycle proteins for degradation by the 26S proteasome. The APC/C is a large complex of 11–13 subunit proteins , including a cullin ( Apc2 ) and RING ( Apc11 ) subunit much like SCF .
FBP then binds to Skp1 of the SCF complex using an F-box motif, bringing the target protein into proximity with the functional E2 ubiquitin-conjugating enzyme. FBP is also essential in regulating SCF activity during the course of the cell cycle. SCF levels are thought to remain constant throughout the cell-cycle.
Ubiquitin is a protein composed of 76 amino acids. In order for ubiquitin to bind to other proteins, it must go through an activation process by E1, an ATP-dependent ubiquitin activating enzyme. The carboxyl terminal (C-terminus) of ubiquitin is linked to the cysteine residue of the E1 protein by a high energy thioester linkage and activated.
Ubiquitin is one of the most conserved proteins known in eukaryotic organisms. Ubiquitin is required for ATP-dependent, non-lysosomal intracellular protein degradation of abnormal proteins and normal proteins with a rapid turnover. Ubiquitin is covalently bound to proteins to be degraded, and presumably labels these proteins for degradation.