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Published on: November 8, 2016
Yeast SREBP cleavage activation requires the Golgi Dsc E3 ligase complex
Emerson V Stewart1, Christine C Nwosu, Zongtian Tong
1Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
Fission yeast uses a novel Golgi E3 ligase complex (Dsc) for sterol regulatory element binding protein (SREBP) cleavage, involving the ubiquitin-proteasome pathway. This differs from mammalian SREBP activation, suggesting a new protein degradation route.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Mammalian lipid homeostasis relies on sequential proteolysis of sterol regulatory element binding proteins (SREBPs) via Golgi proteases.
- SREBP function is conserved in fungi, but the cleavage mechanism in fission yeast was previously unknown.
Purpose of the Study:
- To elucidate the mechanism of SREBP cleavage in fission yeast.
- To identify the genetic and molecular components involved in SREBP processing in this organism.
Main Methods:
- Genetic screens to identify mutants defective in SREBP cleavage.
- Biochemical assays to characterize protein interactions and pathway components.
- Comparative analysis with mammalian and other yeast systems.
Main Results:
- Four genes (dsc1-4) were identified, encoding components of a transmembrane Golgi E3 ligase complex.
- This Dsc complex shows homology to the Hrd1 E3 ligase involved in ER-associated degradation.
- SREBP cleavage by the Dsc complex requires the E2-conjugating enzyme Ubc4, the Dsc1 E3 ligase, and the proteasome.
- Dsc mutants exhibit genetic interactions with the multivesicular body pathway.
Conclusions:
- Fission yeast utilizes a distinct Golgi-localized E3 ligase complex (Dsc) for SREBP cleavage.
- This process is dependent on the ubiquitin-proteasome system.
- The Dsc complex represents a novel post-ER pathway for protein degradation, distinct from mammalian SREBP activation.
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