title: A bipartite trigger for dislocation directs the proteasomal degradation of an endoplasmic reticulum membrane glycoprotein.
abstract: Polypeptides are organized into distinct substructures, termed protein domains, that are often associated with diverse functions. These modular units can act as binding sites, areas of post-translational modification, and sites of complex multimerization. The human cytomegalovirus US2 gene product is organized into discrete domains that together catalyze the proteasome-dependent degradation of class I major histocompatibility complex heavy chains. US2 co-opts the endogenous ER quality control pathway in order to dispose of class I. The US2 endoplasmic reticulum (ER)-lumenal region is the class I binding domain, whereas the carboxyl terminus can be referred to as the degradation domain. In the present study, we examined the role of the US2 transmembrane domain in virus-mediated class I degradation. Replacement of the US2 transmembrane domain with that of the CD4 glycoprotein completely blocked the ability of US2 to induce class I destruction. A more precise mutagenesis revealed that subregions of the US2 transmembrane domain differ in their ability to trigger class I degradation. Collectively, the data support a model in which US2-mediated class I degradation occurs as a highly regulated process where the US2 transmembrane domain and cytoplasmic tail work in concert to eliminate class I molecules. Host factors, including a signal peptidase complex, probably associate with the US2 molecule in a coordinated fashion to create a predislocation complex to promote the extraction of class I out of the ER. The results imply that the ER quality control machinery may recognize and eliminate misfolded proteins using a similar multistep regulated process.
authors: Mount Sinai School of Medicine, Department of Microbiology, New York, New York 10029, USA.
authors: Vanessa M
authors: VM
authors: Noriega
authors: Domenico
authors: D
authors: Tortorella
mesh_terms: D000595:Amino Acid Sequence; D045744:Cell Line, Tumor; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D006801:Humans; D006868:Hydrolysis; D008969:Molecular Sequence Data; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D014759:Viral Envelope Proteins / Q000737:chemistry / Q000378:metabolism*
chemical_list: C118670:US2 protein, Varicellovirus; D014759:Viral Envelope Proteins; D046988:Proteasome Endopeptidase Complex