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Ubiquitins are small proteins (~8 kDa) that post-translationally modify proteins on lysine residues through formation of an isopeptide bond between the carboxylic acid group of the ubiquitin's glycine and the epsilon amino group of the substrate's lysine.
Ubiquitin (Ub) receptors are responsible for the recognition of ubiquitylated proteins. Here the authors describe the crystal structure of the ubiquitylated form of the Ub-receptor Rpn10, which suggest that ubiquitylation of Rpn10 promotes its dissociation from the proteasome.
Signalling by ubiquitin, SUMO and other ubiquitin-like modifiers (UBLs), and crosstalk between these modifications, underlies cellular responses to DNA double-strand breaks (DSBs). Important insights have been gained into the mechanisms by which ubiquitin and UBLs regulate protein interactions at DSB sites to enable accurate repair in mammalian cells, thereby protecting genome integrity.
The eukaryotic 26S proteasome is responsible for degrading virtually any protein with an appropriate ubiquitin signal, and in the process ubiquitin is spared and recycled. Two studies of the proteasome-associated deubiquitinase UBP6 now shed light on how deubiquitination coordinates the cycle of substrate processing.
Ubiquitin and ubiquitin-like proteins have central roles in regulating cellular processes and homeostasis. This Focus examines our understanding of the ubiquitination reaction and the mechanisms by which ubiquitin and related modifications affect protein and cellular functions.