COP9 signalosome
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COP9 (Constitutive photomorphogenesis 9) signalosome (CSN) is a protein complex with isopeptidase activity. It catalyses the hydrolysis of NEDD8 protein from the cullin subunit of Cullin-RING ubiquitin ligases (CRL). Therefore, it is responsible for CRL deneddylation – at the same time, it is able to bind denedyllated cullin-RING complex and retain them in deactivated form. COP9 signalosome thus serves as a sole deactivator of CRLs.[1] The complex was originally identified in plants,[2][3] and subsequently found in all eukaryotic organisms including human.[4][5] Human COP9 signalosome (total size ~350 kDa) consists of 8 subunits - CSN1, CSN2, CSN3, CSN4, CSN5, CSN6, CSN7 (COPS7A, COPS7B), CSN8. All are essential for full function of the complex and mutation in some of them is lethal in mice.[1]
