Human UBE2F blocking peptide

Cullin-5 (Cul-5) was originally identified as an arginine vasopressin (AVP) receptor due to its homology to a vasopressin-activated calcium-mobilizing protein 1 (VACM-1). Cul-5 has subsequently gained much attention after being identified as the key component of CRL-5 (Cullin-RING ligase-5) that mediates ubiquitylation and degradation of several key cellular proteins associated with human cancers and viral infections. Structurally, Cul-5 interacts with the Elongin B/C complex, a RING finger protein (RBX2/SAG), and a SOCS protein to form a CRL-5 E3 ubiquitin ligase protein complex. CRL-5, by controlling turnover of a variety of substrates, is implicated in several biological processes and human diseases. Activation of CRL-5 requires Cul-5 neddylation, catalyzed by a neddylation enzyme cascade, consisting of the E1 NEDD8-activating enzyme (NAE), the E2 neddylation conjugating enzyme (UBE2F), and E3 neddylation ligase (RBX2/SAG). RBX2/SAG, therefore, serves as both Cul-5 neddylation E3 and CRL-5 ubiquitylation E3. Here, we review the current knowledge on CRL-5, its activation by the UBE2F-SAG, its regulation of various signaling pathways via substrate degradation, and its implications in human cancers.

Ubiquitin and ubiquitin-like proteins (UBLs) are directed to targets by cascades of El, E2, and E3 enzymes. The largest ubiquitin E3 subclass consists of cullin-RING ligases (CRLs), which contain one each of several cullins (CUL1, -2, -3, -4, or -5) and RING proteins (RBX1 or -2). CRLs are activated by ligation of the UBL NEDD8 to a conserved cullin lysine. How is cullin NEDD8ylation specificity established? Here we report that, like UBE2M (also known as UBC12), the previously uncharacterized E2 UBE2F is a NEDD8-conjugating enzyme in vitro and in vivo. Biochemical and structural analyses indicate how plasticity of hydrophobic E1-E2 interactions and El conformational flexibility allow one El to charge multiple E2s. The E2s; have distinct functions, with UBE2M/RBX1 and UBE2F/RBX2 displaying different target cullin specificities. Together, these studies reveal the molecular basis for and functional importance of hierarchical expansion of the NEDD8 conjugation system in establishing selective CRL activation.