A cholesterol-sensing mechanism unfolds.

Area of Science:

• Biochemistry
• Molecular Biology
• Cellular Metabolism

Background:

• Squalene monooxygenase (SM) synthesizes a key precursor for cholesterol.
• High cholesterol levels in the endoplasmic reticulum (ER) membrane trigger SM degradation.
• The precise molecular signal initiating SM degradation remained unknown.

Purpose of the Study:

• To identify the signal that targets squalene monooxygenase for degradation.
• To elucidate the mechanism by which cholesterol levels regulate SM stability.

Main Methods:

• Investigated the N-terminal domain of squalene monooxygenase.
• Analyzed the structural interconversion of the N-terminal domain in response to cholesterol.
• Characterized the relationship between domain conformation and protein degradation.

Main Results:

• Identified an N-terminal domain in SM that is sensitive to cholesterol levels.
• This domain undergoes a cholesterol-dependent conformational change.
• The domain switches between a membrane-binding helix and a soluble, degradation-prone segment.

Conclusions:

• The N-terminal domain of SM acts as a cholesterol-sensitive degron.
• This represents the first identified instance of a cholesterol-degron collaboration.
• Provides a molecular mechanism for cholesterol-mediated regulation of SM degradation.