A comprehensive method for detecting ubiquitinated substrates using TR-TUBE

Area of Science:

• Biochemistry
• Molecular Biology
• Proteomics

Background:

• Identifying ubiquitinated protein substrates for ubiquitin ligases is difficult because they are rapidly degraded or deubiquitinated.
• Existing methods using diGly remnant antibodies and mass spectrometry (MS) are insufficient for characterizing the ubiquitin-modified proteome, especially when overexpressing a specific ubiquitin ligase.

Purpose of the Study:

• To develop a robust method for identifying specific ubiquitin ligase substrates.
• To overcome challenges posed by proteasomal degradation and deubiquitination in substrate identification.

Main Methods:

• Exogenously expressed trypsin-resistant tandem ubiquitin-binding entities (TR-TUBE) were used to protect polyubiquitin chains from deubiquitinating enzymes (DUBs) and proteasomal degradation.
• Combined enrichment strategies using TR-TUBE and diGly remnant antibodies followed by MS were employed.
• The method was validated by identifying substrates of the uncharacterized F-box protein, FBXO21.

Main Results:

• TR-TUBE effectively protected ubiquitinated substrates from degradation and deubiquitination.
• Overexpression of ubiquitin ligases in TR-TUBE expressing cells significantly increased substrate-derived diGly peptides.
• The combined TR-TUBE and diGly antibody approach coupled with MS enabled the identification of specific ubiquitin ligase substrates, including those of FBXO21.

Conclusions:

• The developed method using TR-TUBE and diGly antibodies is effective for identifying ubiquitin ligase substrates.
• This approach overcomes limitations of previous methods, enabling better characterization of the ubiquitin-modified proteome.
• The study successfully identified target substrates for the uncharacterized F-box protein FBXO21, advancing our understanding of its function.