COP9 signalosome
cop9 signalosome
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. It was found in all eukaryotic organisms including human; it was first discovered in plants. Human COP9 signalosome (total size ~350 kDa ) consists of 8 subunits - CSN1/COPS1, CSN2/COPS2, CSN3/COPS3, CSN4/COPS4, CSN5/COPS5, CSN6/COPS6, CSN7/COPS7A & COPS7B and CSN8/COPS8. All are essential for full function of the complex and mutation in some of them is lethal in mice.