ubiquitin recycling

Definition

Target type: biologicalprocess

Any process involved in the maintenance of an internal steady state of ubiquitin monomers and free ubiquitin chains at the level of the cell by recycling ubiquitin from proteasome-bound ubiquitinated intermediates. [GOC:BHF, GOC:dph, GOC:tb, PMID:19410548]

Ubiquitin recycling is a crucial cellular process that ensures the efficient reuse of ubiquitin, a small protein involved in protein degradation and other cellular processes. Ubiquitin is a highly conserved protein that is attached to target proteins as a polyubiquitin chain, marking them for degradation by the proteasome. After the proteasome degrades the target protein, the ubiquitin chains are removed and recycled for further use.

The process of ubiquitin recycling involves several key steps:

1. **Deubiquitination:** Ubiquitin chains are removed from the target protein by deubiquitinases (DUBs). DUBs are a family of enzymes that specifically cleave the isopeptide bonds between ubiquitin molecules. There are many different DUBs, each with its own substrate specificity.

2. **Ubiquitin refolding:** Once removed from the target protein, ubiquitin molecules may become misfolded due to their interaction with the proteasome or other cellular components. To be recycled, ubiquitin must refold into its native conformation. This process is assisted by molecular chaperones such as Hsp70 and Hsp90.

3. **Ubiquitin conjugation:** The refolded ubiquitin molecules can then be re-conjugated to new target proteins. This process is catalyzed by ubiquitin ligases (E3s), which are enzymes that attach ubiquitin to target proteins. The ubiquitin ligase-mediated conjugation requires the coordinated action of E1 and E2 enzymes, which activate and transfer ubiquitin, respectively.

Ubiquitin recycling is a dynamic process that is tightly regulated by a complex network of enzymes and proteins. This process ensures that ubiquitin is available for protein degradation and other cellular processes. Defects in ubiquitin recycling can lead to the accumulation of misfolded proteins, which can contribute to various diseases, including neurodegenerative disorders and cancer.

Ubiquitin recycling is also a highly regulated process, with several mechanisms in place to prevent the accumulation of free ubiquitin in the cell. For example, ubiquitin can be sequestered in specific cellular compartments or degraded by specific proteases. These mechanisms ensure that ubiquitin levels are tightly controlled and that the recycling process operates efficiently.'
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Proteins (2)

Compounds (15)