Ubx4 modulates cdc48 activity and influences degradation of misfolded proteins of the endoplasmic reticulum.
Misfolded proteins of the secretory pathway are recognized in the endoplasmic reticulum (ER), retrotranslocated into the cytoplasm, and degraded by the ubiquitin-proteasome system. Right after retrotranslocation and polyubiquitination, they are extracted from the cytosolic side of the ER membrane through a complex consisting of the AAA ATPase Cdc48 (p97 in mammals), Ufd1, and Npl4. This complex delivers misfolded proteins to the proteasome for final degradation. Extraction, delivery, and processing of ERAD (ER-associated degradation) substrates to the proteasome requires additional cofactors of Cdc48. Here we characterize the UBX domain containing protein Ubx4 (Cui1) as a crucial factor for the degradation of polyubiquitinated proteins via ERAD. Ubx4 modulates the Cdc48-Ufd1-Npl4 complex to guarantee its correct function. Mutant variants of Ubx4 lead to defective degradation of misfolded proteins and accumulation of polyubiquitinated proteins bound to Cdc48. We show the requirement of the UBX domain of Ubx4 for its function in ERAD. The observation that Ubx2 and Ubx4 are not found together in one complex with Cdc48 suggests several distinct steps in modulating the activity and localization of Cdc48 in ERAD.
From the Institut für Biochemie, Universität Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany.
Sven M
SM
Alberts
From the Institut für Biochemie, Universität Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany.
Caroline
C
Sonntag
From the Institut für Biochemie, Universität Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany.
Antje
A
Schäfer
From the Institut für Biochemie, Universität Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany. Electronic address: dieter.wolf@ibc.uni-stuttgart.de.
Dieter H
DH
Wolf
D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D016296:Mutagenesis; D029543:Nucleocytoplasmic Transport Proteins / Q000378:metabolism; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination; D000074405:Valosin Containing Protein; D033921:Vesicular Transport Proteins / Q000378:metabolism
D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D047908:Intracellular Signaling Peptides and Proteins; C104361:NPL4 protein, S cerevisiae; D029543:Nucleocytoplasmic Transport Proteins; D029701:Saccharomyces cerevisiae Proteins; C507001:UBX2 protein, S cerevisiae; C542871:UBX4 protein, S cerevisiae; C444652:UFD1 protein, S cerevisiae; D033921:Vesicular Transport Proteins; D000251:Adenosine Triphosphatases; C000614177:CDC48 protein, S cerevisiae; D000074405:Valosin Containing Protein