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Free keywords:
CONJUGATING ENZYME; STRUCTURAL BASIS; CDC34 UBC3; E3 LIGASE; DNA-REPAIR;
SCF; NEDD8; COMPLEX; SUBSTRATE; REVEALSBiochemistry & Molecular Biology; Biophysics; Cell Biology;
Abstract:
E3 ubiquitin ligases, in collaboration with E2 ubiquitin-conjugating enzymes, modify proteins with poly-ubiquitin chains. Cullin-RING ligase (CRL) E3s use Cdc34/UBE2R-family E2s to build Lys48-linked poly-ubiquitin chains to control an enormous swath of eukaryotic biology. Yet the molecular mechanisms underlying this exceptional linkage specificity and millisecond kinetics of poly-ubiquitylation remain unclear. Here we obtain cryogenic-electron microscopy (cryo-EM) structures that provide pertinent insight into how such poly-ubiquitin chains are forged. The CRL RING domain not only activates the E2-bound ubiquitin but also shapes the conformation of a distinctive UBE2R2 loop, positioning both the ubiquitin to be transferred and the substrate-linked acceptor ubiquitin within the active site. The structures also reveal how the ubiquitin-like protein NEDD8 uniquely activates CRLs during chain formation. NEDD8 releases the RING domain from the CRL, but unlike previous CRL-E2 structures, does not contact UBE2R2. These findings suggest how poly-ubiquitylation may be accomplished by many E2s and E3s.
The authors define a NEDD8-activated cullin-RING E3 poly-ubiquitylation mechanism using chemistry, cryo-EM and rapid kinetics. Near-perfect catalytic efficiency is achieved by an E2 'synergy loop' connecting to the E3, donor and acceptor ubiquitins.
