Ubiquitin-proteasome-dependent degradation of a mitofusin, a critical regulator of mitochondrial fusion.
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 ubiquitin-proteasome-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.
Cohen
Mickael M J
MM
Laboratory of Protein Dynamics and Signaling, National Cancer Institute, Frederick, MD 21702, USA.
Leboucher
Guillaume P
GP
Livnat-Levanon
Nurit
N
Glickman
Michael H
MH
Weissman
Allan M
AM
D000332:Aerobiosis; D020816:Amino Acid Motifs; D044783:F-Box Proteins / Q000737:chemistry / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D008239:Lysine / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D024101:Mitochondrial Proteins; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D044843:SKP Cullin F-Box Protein Ligases / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism*; D054875:Ubiquitination
D044783:F-Box Proteins; C481653:Mdm30 protein, S cerevisiae; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D029701:Saccharomyces cerevisiae Proteins; D025801:Ubiquitin; D044843:SKP Cullin F-Box Protein Ligases; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease; C401395:FZO1 protein, S cerevisiae; D020558:GTP Phosphohydrolases; D008239:Lysine