title: Lunapark Is a Component of a Ubiquitin Ligase Complex Localized to the Endoplasmic Reticulum Three-way Junctions.
abstract: The endoplasmic reticulum (ER) network comprises sheets and tubules that are connected by dynamic three-way junctions. Lunapark (Lnp) localizes to and stabilizes ER three-way junctions by antagonizing the small GTPase Atlastin, but how Lnp shapes the ER network is unclear. Here, we used an affinity purification approach and mass spectrometry to identify Lnp as an interacting partner of the ER protein quality control ubiquitin ligase gp78. Accordingly, Lnp purified from mammalian cells has a ubiquitin ligase activity in vitro Intriguingly, biochemical analyses show that this activity can be attributed not only to associated ubiquitin ligase, but also to an intrinsic ubiquitin ligase activity borne by Lnp itself. This activity is contained in the N-terminal 45 amino acids of Lnp although this segment does not share homology to any known ubiquitin ligase motifs. Despite its interaction with gp78, Lnp does not seem to have a broad function in degradation of misfolded ER proteins. On the other hand, the N-terminal ubiquitin ligase-bearing motif is required for the ER three-way junction localization of Lnp. Our study identifies a new type of ubiquitin ligase and reveals a potential link between ubiquitin and ER morphology regulation.
authors.affiliation: From the School of Life Science and Technology, ShanghaiTech University, 100 Haike Rd., Shanghai 201210, China and.
authors.forename: Yupeng
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: the Laboratory of Molecular Biology, NIDDK, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: Ting
authors.initials: T
authors.lastname: Zhang
authors.affiliation: From the School of Life Science and Technology, ShanghaiTech University, 100 Haike Rd., Shanghai 201210, China and.
authors.forename: Huanhuan
authors.initials: H
authors.lastname: Huo
authors.affiliation: the Laboratory of Molecular Biology, NIDDK, National Institutes of Health, Bethesda, Maryland 20892 yihongy@mail.nih.gov.
authors.forename: Yihong
authors.initials: Y
authors.lastname: Ye
authors.affiliation: From the School of Life Science and Technology, ShanghaiTech University, 100 Haike Rd., Shanghai 201210, China and liuyf@shanghaitech.edu.cn.
authors.forename: Yanfen
authors.initials: Y
authors.lastname: Liu
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism; D006367:HeLa Cells; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport; D060285:Receptors, Autocrine Motility Factor / Q000235:genetics / Q000378:metabolism*
chemical_list: D018398:Homeodomain Proteins; C474231:LNPK protein, human; D008565:Membrane Proteins; C555000:AMFR protein, human; D060285:Receptors, Autocrine Motility Factor; C440006:ATL1 protein, human; D019204:GTP-Binding Proteins
keywords: Atlastin; ER three-way junction; Lunapark/Lnp; endoplasmic-reticulum-associated protein degradation (ERAD); gp78; misfolded; protein misfolding; ubiquitin; ubiquitin ligase; ubiquitin-conjugating enzyme (E2 enzyme)