Substrate binding and sequence preference of the proteasome revealed by active-site-directed affinity probes

Area of Science:

• Biochemistry
• Molecular Biology
• Proteomics

Background:

• The proteasome is a key cellular machine for protein degradation.
• Its distinct proteolytic activities are defined by substrate preferences.
• Understanding proteasome substrate specificity is crucial for cell biology.

Purpose of the Study:

• To investigate the principles governing proteasome substrate hydrolysis.
• To determine the role of peptide length and specific residues in proteasome binding and inhibition.
• To correlate inhibitor modification with specific proteasome subunit activity.

Main Methods:

• Synthesis and use of tripeptide and tetrapeptide vinyl sulfone inhibitors.
• Analysis of inhibitor binding to proteasome subunits using 125I-labeling.
• Assessing the impact of modifications at P4 and C-terminal positions on inhibitory potency.

Main Results:

• Removal of the N-terminal cap abolished binding and inhibition.
• Addition of a P4 amino acid fully restored inhibitory potency.
• Modifications at the P4 position significantly altered beta-subunit modification profiles and distinct proteolytic activities.

Conclusions:

• The P4 position is critical for proteasome substrate recognition and processing.
• Specific beta subunits' proteolytic activities can be assigned based on subunit modification and inhibition patterns.
• Tetrapeptides, unlike tripeptides, may represent a minimal substrate length for proteasome hydrolysis, enabling targeted inhibitor design.