Structure of CRL7 reveals coupling with CUL1-RBX1/ROC1 for multi-cullin-RING E3-catalyzed ubiquitin ligation.

Most cullin-RING ubiquitin ligases (CRLs) form homologous assemblies between a neddylated cullin-RING catalytic module and a variable substrate-binding receptor (for example, an F-box protein). However, the vertebrate-specific CRL7 is of interest because it eludes existing models, yet its constituent cullin CUL7 and F-box protein FBXW8 are essential for development, and CUL7 mutations cause 3M syndrome. In this study, cryo-EM and biochemical analyses reveal the CRL7 assembly. CUL7's exclusivity for FBXW8 among all F-box proteins is explained by its unique F-box-independent binding mode. In CRL7, the RBX1 (also known as ROC1) RING domain is constrained in an orientation incompatible with binding E2NEDD8 or E2ubiquitin intermediates. Accordingly, purified recombinant CRL7 lacks auto-neddylation and ubiquitination activities. Instead, our data indicate that CRL7 serves as a substrate receptor linked via SKP1-FBXW8 to a neddylated CUL1-RBX1 catalytic module mediating ubiquitination. The structure reveals a distinctive CRL-CRL partnership, and provides a framework for understanding CUL7 assemblies safeguarding human health.