Structural and mechanistic insights into the CAND1-mediated SCF substrate receptor exchange

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• SCF (SKP1-CUL1-Fbox) ubiquitin E3 ligases are crucial for regulating cellular pathways via substrate degradation.
• Variable SKP1-Fbox substrate receptor (SR) modules allow SCF ligases to target diverse substrates.
• CAND proteins are vital for the efficient exchange of these SR modules.

Purpose of the Study:

• To elucidate the structural mechanism of CAND1-mediated SR exchange in SCF ubiquitin E3 ligases.
• To understand the molecular interplay between CAND1, SCF, and DCNL1 during SR dynamics.
• To provide a detailed structural model for CAND-SCF regulation.

Main Methods:

• Reconstitution of a human CAND1-driven exchange reaction involving substrate-bound SCF, DCNL1, and SRs.
• Cryo-electron microscopy (cryo-EM) to visualize structural intermediates.
• Functional biochemical assays to complement structural findings.

Main Results:

• High-resolution structures of key intermediates, including a ternary CAND1-SCF complex.
• Detailed visualization of SR- and CAND1-dissociation intermediates.
• Identification of CAND1-induced conformational changes in CUL1/RBX1 that optimize DCNL1 binding.
• Discovery of a dual role for DCNL1 in CAND1-SCF dynamics.
• Structural basis for CAND1 displacement during cullin neddylation.

Conclusions:

• CAND1 binding induces conformational changes in SCF, facilitating SR exchange and DCNL1 interaction.
• DCNL1 plays a multifaceted role in regulating CAND1-SCF complex dynamics.
• Cullin neddylation is a key event that leads to CAND1 displacement, completing the regulatory cycle.
• The study provides a comprehensive structural and functional model for CAND-SCF regulation.