Cryo-EM structure of the chain-elongating E3 ubiquitin ligase UBR5

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Biology

Background:

• UBR5 is a nuclear E3 ligase regulating oncogenes like MYC.
• Its structure and substrate engagement mechanisms are poorly understood.
• HECT domain-containing ubiquitin ligases play crucial roles in cellular processes.

Purpose of the Study:

• To determine the cryo-EM structure of human UBR5.
• To investigate UBR5's substrate engagement and ubiquitination mechanisms.
• To characterize UBR5's interactions and enzymatic activity.

Main Methods:

• Cryo-electron microscopy (cryo-EM) for structural determination.
• Biochemical assays to characterize enzymatic activity.
• Identification of interacting proteins.

Main Results:

• The cryo-EM structure reveals an α-solenoid scaffold in an antiparallel dimer, with dynamic catalytic domains.
• UBR5 interacts with the proteasomal nuclear import factor AKIRIN2.
• UBR5 functions as an efficient ubiquitin chain elongator, preferring ubiquitinated substrates.

Conclusions:

• The study provides the first structural insights into human UBR5, a key E3 ligase.
• UBR5's structure and its role as a ubiquitin chain elongator offer explanations for its involvement in various signaling pathways and cancers.
• This work expands the understanding of HECT E3 ligase structure and function.