The E3 Ubiquitin Ligase TMEM129 Is a Tri-Spanning Transmembrane Protein

• Published in: Viruses Vol. 8; no. 11; p. 309
• Main Authors: van de Weijer, Michael L, van Muijlwijk, Guus H, Visser, Linda J, Costa, Ana I, Wiertz, Emmanuel J H J, Lebbink, Robert Jan
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 15.11.2016; MDPI
• Subjects: Antigens; Cytomegalovirus; Cytotoxicity; E3 ligase; Endoplasmic reticulum; Endoplasmic Reticulum - chemistry; Enzymes; ER-associated protein degradation; ERAD; Herpesviridae; Humans; Intracellular Membranes - chemistry; Leukocytes; Membrane Proteins - analysis; Membrane Proteins - metabolism; Models, Biological; Mutagenesis; Proteins; RING domain; TMEM129; topology; transmembrane; Ubiquitin-Protein Ligases - analysis; Ubiquitin-Protein Ligases - metabolism; Ubiquitination; Viruses; United States > US; Netherlands; ERAD; E3 ligase; transmembrane; topology; TMEM129; ER-associated protein degradation; RING domain
• ISSN: 1999-4915; 1999-4915
• DOI: 10.3390/v8110309

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 N -C orientation. 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.