CUL5-ARIH2 E3-E3 ubiquitin ligase structure reveals cullin-specific NEDD8 activation

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Mechanisms of Ubiquitylation

Background:

• Ubiquitylation often involves partnerships between distinct E3 ligases.
• ARIH-family E3 ligases (RING-between-RING) target substrates of neddylated cullin-RING E3s.
• ARIH2 is implicated in ubiquitylating substrates of neddylated CUL5-RBX2 E3s, including those targeted by HIV-1 Vif.

Purpose of the Study:

• To elucidate the structural mechanisms of ARIH2 activation by neddylated CUL5-RBX2.
• To compare cullin-specific regulation by NEDD8 in different E3-E3 assemblies.
• To understand how ubiquitin-like proteins induce protein-protein interactions indirectly.

Main Methods:

• Structural analyses
• Biochemical assays
• Comparative structural analysis of E3-E3 assemblies

Main Results:

• Distinct ARIH2 autoinhibition and activation mechanisms revealed upon assembly with neddylated CUL5-RBX2.
• NEDD8 regulates ARIH1 and ARIH2 differently; CUL1-linked NEDD8 directly recruits ARIH1, while CUL5-linked NEDD8 does not bind ARIH2.
• An allosteric mechanism where NEDD8 binding to CUL5 induces structural rearrangements that expose ARIH2-binding sites was identified.

Conclusions:

• NEDD8 activates ARIH2 indirectly through an allosteric mechanism involving CUL5.
• This indirect activation highlights how ubiquitin-like proteins can mediate protein-protein interactions.
• The allosteric specificity of ubiquitin-like protein modifications presents potential therapeutic targeting opportunities.