title: Dimeric Ube2g2 simultaneously engages donor and acceptor ubiquitins to form Lys48-linked ubiquitin chains.
abstract: Cellular adaptation to proteotoxic stress at the endoplasmic reticulum (ER) depends on Lys48-linked polyubiquitination by ER-associated ubiquitin ligases (E3s) and subsequent elimination of ubiquitinated retrotranslocation products by the proteasome. The ER-associated E3 gp78 ubiquitinates misfolded proteins by transferring preformed Lys48-linked ubiquitin chains from the cognate E2 Ube2g2 to substrates. Here we demonstrate that Ube2g2 synthesizes linkage specific ubiquitin chains by forming an unprecedented homodimer: The dimerization of Ube2g2, mediated primarily by electrostatic interactions between two Ube2g2s, is also facilitated by the charged ubiquitin molecules. Mutagenesis studies show that Ube2g2 dimerization is required for ER-associated degradation (ERAD). In addition to E2 dimerization, we show that a highly conserved arginine residue in the donor Ube2g2 senses the presence of an aspartate in the acceptor ubiquitin to position only Lys48 of ubiquitin in proximity to the donor E2 active site. These results reveal an unanticipated mode of E2 self-association that allows the E2 to effectively engage two ubiquitins to specifically synthesize Lys48-linked ubiquitin chains.
authors.affiliation: State Key Laboratory of Reproductive Biology, Institute of Zoology Chinese Academy of Sciences, Beijing, China.
authors.forename: Weixiao
authors.initials: W
authors.lastname: Liu
authors.forename: Yongliang
authors.initials: Y
authors.lastname: Shang
authors.forename: Yan
authors.initials: Y
authors.lastname: Zeng
authors.forename: Chao
authors.initials: C
authors.lastname: Liu
authors.forename: Yanchang
authors.initials: Y
authors.lastname: Li
authors.forename: Linhui
authors.initials: L
authors.lastname: Zhai
authors.forename: Pan
authors.initials: P
authors.lastname: Wang
authors.forename: Jizhong
authors.initials: J
authors.lastname: Lou
authors.forename: Ping
authors.initials: P
authors.lastname: Xu
authors.forename: Yihong
authors.initials: Y
authors.lastname: Ye
authors.forename: Wei
authors.initials: W
authors.lastname: Li
mesh_terms: D000595:Amino Acid Sequence; D002460:Cell Line; D004252:DNA Mutational Analysis; D006801:Humans; D008239:Lysine / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D025821:Polyubiquitin / Q000096:biosynthesis*; D011485:Protein Binding; D011487:Protein Conformation; D055503:Protein Multimerization; D044763:Ubiquitin-Conjugating Enzymes / Q000235:genetics / Q000378:metabolism*
chemical_list: D050505:Mutant Proteins; D025821:Polyubiquitin; C471617:UBE2G2 protein, human; D044763:Ubiquitin-Conjugating Enzymes; D008239:Lysine