Ubiquitin–Proteasome-dependent Degradation of a Mitofusin, a Critical Regulator of Mitochondrial Fusion

Abstract

The mitochondrion is a dynamic membranous network whose morphology is conditioned by the equilibrium between ongoing fusion and fission of mitochondrial membranes. In the budding yeast, Saccharomyces cerevisiae, the transmembrane GTPase Fzo1p controls fusion of mitochondrial outer membranes. Deletion or overexpression of Fzo1p have both been shown to alter the mitochondrial fusion process indicating that maintenance of steady-state levels of Fzo1p are required for efficient mitochondrial fusion. Cellular levels of Fzo1p are regulated through degradation of Fzo1p by the F-box protein Mdm30p. How Mdm30p promotes degradation of Fzo1p is currently unknown. We have now determined that during vegetative growth Mdm30p mediates ubiquitylation of Fzo1p and that degradation of Fzo1p is an ubiquitinproteasome-dependent process. In vivo, Mdm30p associates through its F-box motif with other core components of Skp1-Cullin-F-box (SCF) ubiquitin ligases. We show that the resulting SCF Mdm30p ligase promotes ubiquitylation of Fzo1p at mitochondria and its subsequent degradation by the 26S proteasome. These results provide the first demonstration that a cytosolic ubiquitin ligase targets a critical regulatory molecule at the mitochondrial outer membrane. This study provides a framework for developing an understanding of the function of Mdm30p-mediated Fzo1p degradation in the multistep process of mitochondrial fusion.

Deletion of a Novel F-Box Protein, MUS-10, in Neurospora crassa Leads to Altered Mitochondrial Morphology, Instability of mtDNA and Senescence

“…An F-box was identified at the N terminus of the MUS-10 protein (Figure 5), suggesting that it belongs to the F-box protein family whose members are normally components of SCF E3 ubiquitin ligase complexes that direct proteins to the 26S proteasome, ultimately leading to their degradation. These findings are concurrent with the hypothesis that SCF complexes can regulate mitochondrial function (Cohen et al 2008;Deng et al 2008). A YccV-like domain, which has been shown to bind hemimethylated DNA (D'Alencon et al 2003), was also observed in MUS-10, suggesting that it may be capable of interacting with DNA ( Figure 5).…”

Parkin Mediates Proteasome-dependent Protein Degradation and Rupture of the Outer Mitochondrial Membrane

“…Similar OMM rupture has been observed in apoptotic cells (49 -51), but we detected neither activation of caspase-3 nor nuclear fragmentation in these cells (data not shown). The involvement of the ubiquitin-proteasome system including other E3 ligases in OMM protein degradation and quality control has been reported (52)(53)(54)(55)(56)(57). Parkin may also have a role in quality control of mitochondria through turnover of OMM proteins under pathophysiological conditions.…”

Dynamique et morphologie mitochondriales

“…DRP1 semble être le substrat d'autres ubiquitine ligases et ses propriétés (activité, recrutement, stabilité) sont également modifiées par phosphorylation et SUMOylation [23]. Chez la levure, les niveaux de Fzo1 sont contrôlés par un processus de dégradation indépendant ou dépendant du protéasome [24,25]. Chez les mammifères, MFN2 est phosphorylée par la protéine kinase A (PKA), interagit avec une ubiquitine ligase (MITOL/ MARCH5) et son niveau est augmenté par des inhibiteurs du protéasome [10].…”