Structural basis of CSN-mediated SCF deneddylation

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Cell Biology

Background:

• Cullin-RING ligases (CRLs) are the largest E3 ligase family, crucial for protein ubiquitination.
• The COP9 signalosome (CSN) regulates CRLs through neddylation/deneddylation, impacting CRL activity and substrate receptor exchange.
• Understanding CSN's catalytic mechanism is vital as it's a promising drug target.

Purpose of the Study:

• To elucidate the structural basis of CSN's catalytic mechanism.
• To visualize functional states and intermediates of the CSN-CRL (SCF) complex during deneddylation.
• To inform the rational design of CSN-targeted therapeutics.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was employed to determine high-resolution structures.
• Analysis of distinct functional states of CSN-CRL (SCF) complexes.
• Identification of key intermediates in the CSN deneddylation cycle.

Main Results:

• Distinct functional states of CSN-CRL (SCF) complexes were visualized, including an autoinhibited docking state and a catalytic intermediate.
• Key domain repositioning (CSN5, RBX1, Cullin) for isopeptide bond cleavage was observed.
• Four dissociation intermediates defining CSN release and the role of RBX1 RING stabilization were resolved.
• The CSNAP component was located within a CSN3-CSN8 groove.

Conclusions:

• A mechanistic model for CSN function in CRL deneddylation is proposed.
• Structural insights reveal how CSN regulates CRL activity and substrate receptor dynamics.
• The findings provide a foundation for developing targeted CSN-based therapies.