Peptides accelerate their uptake by activating a ubiquitin-dependent proteolytic pathway

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• The ubiquitin system regulates protein levels via degradation by the 26S proteasome.
• E3 ligases, like Ubr1 in yeast, recognize degradation signals (degrons) on protein substrates.
• Ubr1 is crucial for the N-end rule pathway, degrading proteins with specific N-terminal residues.

Purpose of the Study:

• To investigate the physiological regulation of ubiquitin-dependent pathways by small compounds.
• To elucidate the role of Ubr1 in regulating the degradation of Cup9, a repressor of the peptide transporter Ptr2.
• To understand how dipeptides influence the N-end rule pathway and peptide transport.

Main Methods:

• Studied the N-end rule pathway in Saccharomyces cerevisiae.
• Investigated the interaction between Ubr1, Cup9, and dipeptides.
• Analyzed the allosteric activation of Ubr1 by dipeptides containing destabilizing N-terminal residues.

Main Results:

• Demonstrated that dipeptides with destabilizing N-terminal residues allosterically activate Ubr1.
• Showed that this activation accelerates the degradation of the transcriptional repressor Cup9.
• Identified a positive feedback loop where imported dipeptides enhance peptide transport by de-repressing Ptr2.

Conclusions:

• Small compounds, specifically dipeptides, can allosterically modulate E3 ligase activity in a physiological context.
• This mechanism provides a feedback system to regulate peptide uptake based on intracellular dipeptide levels.
• Suggests that small molecules may be general regulators of other ubiquitin-dependent protein degradation pathways.