Structural insights into ubiquitin recognition by USP15 revealed through a covalent activity-based probe

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Biology

Background:

• Ubiquitin-specific protease 15 (USP15) is crucial for immune responses and cancer.
• USP15's mechanisms of ubiquitin recognition and conformational changes are not well understood.

Purpose of the Study:

• To elucidate the structural basis of USP15's ubiquitin engagement and catalytic activity.
• To identify key structural features governing USP15 function.

Main Methods:

• Determined the 2.3 Å crystal structure of the USP15 catalytic domain bound to ubiquitin-propargylamine.
• Characterized the role of the α8 helix and α3-α4 loop through deletion and mutation studies.

Main Results:

• The crystal structure reveals ubiquitin binding induces a conformational switch from an inactive-closed to an active-open state.
• The α8 helix and α3-α4 loop are critical for USP15's structural integrity and ubiquitin binding.
• Deletion of α8 or mutation P331S (destabilizing the α3-α4 loop) abrogates catalytic activity or reduces efficiency.

Conclusions:

• Identified critical structural elements (α8 helix, α3-α4 loop) essential for USP15 enzymatic activity and stability.
• These findings provide insights into USP15 function and potential targets for deubiquitinase inhibition in disease.