title: The E3 Ubiquitin Ligase TMEM129 Is a Tri-Spanning Transmembrane Protein.
abstract: Misfolded proteins from the endoplasmic reticulum (ER) are transported back into the cytosol for degradation via the ubiquitin-proteasome system. The human cytomegalovirus protein US11 hijacks this ER-associated protein degradation (ERAD) pathway to downregulate human leukocyte antigen (HLA) class I molecules in virus-infected cells, thereby evading elimination by cytotoxic T-lymphocytes. Recently, we identified the E3 ubiquitin ligase transmembrane protein 129 (TMEM129) as a key player in this process, where interference with TMEM129 activity in human cells completely abrogates US11-mediated class I degradation. Here, we set out to further characterize TMEM129. We show that TMEM129 is a non-glycosylated protein containing a non-cleaved signal anchor sequence. By glycosylation scanning mutagenesis, we show that TMEM129 is a tri-spanning ER-membrane protein that adopts an Nexo-Ccytoorientation. This insertion in the ER membrane positions the C-terminal really interesting new gene (RING) domain of TMEM129 in the cytosol, making it available to catalyze ubiquitination reactions that are required for cytosolic degradation of secretory proteins.
authors.affiliation: Medical Microbiology, University Medical Center Utrecht, 3584CX Utrecht, The Netherlands. M.L.vandeWeijer@umcutrecht.nl.
authors.forename: Michael L
authors.initials: ML
authors.lastname: van de Weijer
authors.affiliation: Medical Microbiology, University Medical Center Utrecht, 3584CX Utrecht, The Netherlands. g.h.vanmuijlwijk@uu.nl.
authors.forename: Guus H
authors.initials: GH
authors.lastname: van Muijlwijk
authors.affiliation: Medical Microbiology, University Medical Center Utrecht, 3584CX Utrecht, The Netherlands. L.J.Visser@uu.nl.
authors.forename: Linda J
authors.initials: LJ
authors.lastname: Visser
authors.affiliation: Medical Microbiology, University Medical Center Utrecht, 3584CX Utrecht, The Netherlands. A.I.CorreiadeAlmeidaCosta@umcutrecht.nl.
authors.forename: Ana I
authors.initials: AI
authors.lastname: Costa
authors.affiliation: Medical Microbiology, University Medical Center Utrecht, 3584CX Utrecht, The Netherlands. E.Wiertz@umcutrecht.nl.
authors.forename: Emmanuel J H J
authors.initials: EJ
authors.lastname: Wiertz
authors.affiliation: Medical Microbiology, University Medical Center Utrecht, 3584CX Utrecht, The Netherlands. R.J.Lebbink-2@umcutrecht.nl.
authors.forename: Robert Jan
authors.initials: RJ
authors.lastname: Lebbink
mesh_terms: D004721:Endoplasmic Reticulum / Q000737:chemistry*; D006801:Humans; D007425:Intracellular Membranes / Q000737:chemistry*; D008565:Membrane Proteins / Q000032:analysis* / Q000378:metabolism*; D008954:Models, Biological; D044767:Ubiquitin-Protein Ligases / Q000032:analysis* / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: D008565:Membrane Proteins; C000591994:TMEM129 protein, human; D044767:Ubiquitin-Protein Ligases
keywords: E3 ligase; ER-associated protein degradation; ERAD; RING domain; TMEM129; topology; transmembrane