Distinct USP25 and USP28 Oligomerization States Regulate Deubiquitinating Activity

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• Deubiquitinating enzymes (DUBs) USP25 and USP28 share domain architecture but have non-redundant functions.
• USP28 stabilizes nuclear proteins like c-MYC, while USP25 regulates inflammatory TRAF signaling.

Purpose of the Study:

• To compare the molecular features and oligomerization states of USP25 and USP28.
• To investigate how structural differences influence the enzymatic activity and cellular function of these DUBs.

Main Methods:

• Structural and biochemical analyses of USP25 and USP28.
• In vitro studies of enzyme dimerization and tetramerization.
• Cellular assays to confirm oligomeric states and assess substrate stabilization.

Main Results:

• Active USP25 and USP28 form distinct dimers with spatially separated catalytic domains.
• USP25, but not USP28, forms an autoinhibited tetramer via a USP25-specific insertion that blocks ubiquitin binding.
• N-terminal regions influence dimer-tetramer equilibrium, while a C-terminal domain does not affect oligomerization.

Conclusions:

• Regions outside the catalytic domain play a crucial role in regulating DUB activity through oligomerization.
• Modulating USP25/USP28 oligomerization affects substrate stabilization, confirming the interplay between structure and function.