Pulse-SILAC and Interactomics Reveal Distinct DDB1-CUL4-Associated Factors, Cellular Functions, and Protein...

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• Cullin-RING finger ligases are crucial for protein ubiquitination, targeting approximately 20% of cellular proteins for proteasomal degradation.
• The cullin 4 (CUL4)-DNA damage-binding protein 1 (DDB1) complex, a key ubiquitin ligase, utilizes substrate recognition adaptors called DDB1/CUL4-associated factors (DCAFs).
• DCAFs typically contain a WD40 domain and mediate the specificity of the CUL4-DDB1 complex, with over sixty WD40-containing proteins suggested as potential adaptors.

Purpose of the Study:

• To precisely define the association and classification of DCAFs with the DDB1/CUL4 complex.
• To identify novel DCAF partners and potential protein substrates.
• To elucidate the functional roles of DCAFs in regulating CUL4-DDB1 activity and cellular processes.

Main Methods:

• BioID and affinity purification-mass spectrometry were employed to identify and validate DCAFs interacting with DDB1.
• Pulse-stable isotope labeling with amino acids in cell culture (pSILAC) was used to measure changes in protein stability and degradation.
• Bioinformatics and structural analyses were utilized to investigate potential DCAF interactions.

Main Results:

• Seven WD40-containing proteins were confidently identified as DCAFs interacting with the DDB1/CUL4 complex.
• Changes in protein degradation were measured upon expression of each DCAF, revealing their roles in substrate targeting.
• New protein partners and potential substrates for the CUL4-DDB1 ligase were identified.

Conclusions:

• This study provides a high-confidence list of DCAFs, enhancing the understanding of the DDB1/CUL4-DCAF interactome.
• The identified DCAFs play significant roles in regulating CUL4-DDB1 complex activity and substrate specificity.
• Characterization of DCAF-mediated protein targeting and degradation offers new insights into cellular process regulation.