Structural Insights into the COP9 Signalosome and Its Common Architecture with the 26S Proteasome Lid and eIF3

SummaryThe evolutionary conserved COP9 signalosome (CSN), a large multisubunit complex, plays a central role in regulating ubiquitination and cell signaling. Here we report recombinant insect cell expression and two-step purification of human CSN and demonstrate its functional assembly. We further obtain a three-dimensional structure of both native and recombinant CSN using electron microscopy and single particle analysis. Antibody labeling of CSN5 and segmentation of the structure suggest a likely subunit distribution and the architecture of its helical repeat subunits is revealed. We compare the structure of CSN with its homologous complexes, the 26S proteasome lid and eIF3, and propose a conserved architecture implying similar assembly pathways and/or conserved substrate interaction modes.

► Insect cell expression and purification of active human CSN ► The first 3D structure of CSN by electron microscopy at 25 Å resolution ► CSN structure segmentation and labeling of the active site subunit CSN5 ► Structural comparison of homologous PCI complexes: CSN, 26S proteasome lid, and eIF3