Ufd2p synthesizes branched ubiquitin chains to promote the degradation of substrates modified with atypical chains.
Ubiquitination of a subset of proteins by ubiquitin chain elongation factors (E4), represented by Ufd2p in Saccharomyces cerevisiae, is a pivotal regulator for many biological processes. However, the mechanism of Ufd2p-mediated ubiquitination is largely unclear. Here, we show that Ufd2p catalyses K48-linked multi-monoubiquitination on K29-linked ubiquitin chains assembled by the ubiquitin ligase (Ufd4p), resulting in branched ubiquitin chains. This reaction depends on the interaction of K29-linked ubiquitin chains with two N-terminal loops of Ufd2p. Only following the addition of K48-linked ubiquitin to substrates modified with K29-linked ubiquitin chains, can the substrates be escorted to the proteasome for degradation. We demonstrate that this ubiquitin chain linkage switching reaction is essential for ERAD, oleic acid and acid pH resistance in yeast. Thus, our results suggest that Ufd2p functions by switching ubiquitin chain linkages to allow the degradation of proteins modified with a ubiquitin linkage, which is normally not targeted to the proteasome.
State Key Laboratory of Stem Cell and Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China.
Chao
C
Liu
State Key Laboratory of Stem Cell and Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China.
Weixiao
W
Liu
Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA.
Yihong
Y
Ye
State Key Laboratory of Stem Cell and Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China.
Wei
W
Li
D008239:Lysine / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000502:physiology; D011485:Protein Binding; D059748:Proteolysis; D012441:Saccharomyces cerevisiae / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D025801:Ubiquitin / Q000096:biosynthesis*; D044763:Ubiquitin-Conjugating Enzymes / Q000378:metabolism*; D054875:Ubiquitination / Q000502:physiology*
D029701:Saccharomyces cerevisiae Proteins; D025801:Ubiquitin; D044763:Ubiquitin-Conjugating Enzymes; D046988:Proteasome Endopeptidase Complex; C114683:UFD2 protein, S cerevisiae; D008239:Lysine