title: Vpu-mediated degradation of CD4 reconstituted in yeast reveals mechanistic differences to cellular ER-associated protein degradation.
abstract: In HIV infected cells, the plasma membrane protein CD4 is removed from the secretory pathway by proteasomal digestion. This crucial step of viral infection occurs at the endoplasmic reticulum and is triggered by the HIV encoded protein Vpu. Here we show that this process can be recapitulated in baker's yeast. The analysis in the yeast system revealed that Vpu-induced breakdown of CD4 occurs independently of the cellular ER-associated protein degradation system. Moreover, our system allows direct comparison between Vpu-mediated turnover and cellular ER-associated protein degradation of CD4. This analysis suggests fundamental mechanistic differences between both pathways: Vpu-induced turnover strictly relies on ubiquitination of CD4 at cytosolic lysine residues prior to export of the substrate from the membrane. In contrast, the cellular ER-associated protein degradation pathway can transport ER-lumenal parts of CD4 into the cytoplasm before ubiquitination and extraction of the membrane anchor.
authors.affiliation: Max-Delbrück-Centrum für Molekulare Medizin, Robert-Rössle-Strasse 10, 13092 Berlin, Germany.
authors.forename: Birgit
authors.initials: B
authors.lastname: Meusser
authors.forename: Thomas
authors.initials: T
authors.lastname: Sommer
mesh_terms: D001692:Biological Transport; D015704:CD4 Antigens / Q000378:metabolism*; D003513:Cycloheximide / Q000494:pharmacology; D003546:Cysteine Endopeptidases / Q000235:genetics / Q000378:metabolism; D003600:Cytosol / Q000737:chemistry; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D015967:Gene Expression Regulation, Viral; D054298:Human Immunodeficiency Virus Proteins; D006801:Humans; D008239:Lysine / Q000378:metabolism; D009097:Multienzyme Complexes / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D011233:Precipitin Tests; D046988:Proteasome Endopeptidase Complex; D014176:Protein Biosynthesis / Q000187:drug effects; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011506:Proteins / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D012694:Serine / Q000378:metabolism; D013379:Substrate Specificity; D014452:Ubiquitins / Q000378:metabolism; D054334:Viral Regulatory and Accessory Proteins / Q000235:genetics / Q000378:metabolism*; D044844:beta-Transducin Repeat-Containing Proteins / Q000378:metabolism; D000086082:Viroporin Proteins
chemical_list: D015704:CD4 Antigens; D003513:Cycloheximide; D003546:Cysteine Endopeptidases; D054298:Human Immunodeficiency Virus Proteins; D008239:Lysine; D009097:Multienzyme Complexes; D046988:Proteasome Endopeptidase Complex; D011500:Protein Synthesis Inhibitors; D011506:Proteins; D012694:Serine; D014452:Ubiquitins; D054334:Viral Regulatory and Accessory Proteins; D044844:beta-Transducin Repeat-Containing Proteins; C514859:vpu protein, Human immunodeficiency virus 1; D000086082:Viroporin Proteins