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Updated: Dec 27, 2025

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Published on: June 1, 2022
Mitochondrial ClpX activates an essential biosynthetic enzyme through partial unfolding
Julia R Kardon1,2,3, Jamie A Moroco4, John R Engen4
1Department of Biochemistry, Brandeis University, Waltham, United States.
Mitochondrial chaperone mtClpX activates 5-aminolevulinic acid synthase (ALAS) by targeted unfolding. This controlled remodeling, not global unfolding, is crucial for ALAS cofactor incorporation and function.
Area of Science:
- Mitochondrial biology
- Protein quality control
- Enzyme regulation
Background:
- Mitochondria utilize chaperone systems to regulate protein activity and lifespan.
- The AAA+ protein unfoldase, mtClpX, is known to activate ALAS by promoting cofactor incorporation.
- Signals directing substrate-chaperone interactions remain poorly understood.
Purpose of the Study:
- To elucidate the mechanism by which mitochondrial ClpX (mtClpX) activates 5-aminolevulinic acid synthase (ALAS).
- To identify sequence and structural features of ALAS involved in mtClpX interaction and activation.
Main Methods:
- Utilized *Saccharomyces cerevisiae* proteins for biochemical analysis.
- Observed the remodeling of ALAS by mtClpX in real-time.
- Characterized sequence and structural determinants of ALAS for mtClpX binding and action.
Main Results:
- Identified specific sequence and structural features in ALAS that facilitate mtClpX binding and action.
- Demonstrated that mtClpX induces targeted unfolding of ALAS, localized between the binding site and the active site.
- Showed that this localized unfolding is essential for gating cofactor binding to ALAS.
Conclusions:
- mtClpX employs a novel mechanism of targeted substrate unfolding for activation, distinct from canonical global unfolding.
- Substrate-specific features dictate chaperone interaction and remodeling outcome, providing insight into mitochondrial protein quality control.
- This mechanism highlights how chaperones precisely regulate enzyme activity through controlled conformational changes.
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