DCAF8 binds DDB1 via an N-terminal helix-loop-helix motif to assemble CRL4 and promote cell cycle progression

Cullin-RING Ligase 4 (CRL4) complexes achieve substrate specificity through DDB1-CUL4-associated factors (DCAFs), yet how individual DCAFs engage the adaptor protein DDB1 remains incompletely understood. Here, we report the cryo-electron microscopy structure of DCAF8 in complex with DDB1 (2.53 Å) and define the molecular determinants underlying CRL4^DCAF8 assembly and cell cycle progression. Our structure reveals that DCAF8 associates with DDB1 primarily through an N-terminal helix-loop-helix (HLH) motif that inserts into a conserved pocket formed by the BPA and BPC domains of DDB1. Disruption of this interface impairs complex assembly, attenuates CDC25A ubiquitination, and results in cell cycle defects. In contrast, residues within the conserved double DxR box of DCAF8 are positioned away from the DDB1 interface and are dispensable for adaptor binding. Together, these findings define a DCAF8-specific recruitment mechanism within CRL4 ubiquitin Ligase assemblies.