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Nat Cell Biol. 2008 Mar;10(3):272-82. doi: 10.1038/ncb1689. Epub 2008 Feb 10.

OS-9 and GRP94 deliver mutant alpha1-antitrypsin to the Hrd1-SEL1L ubiquitin ligase complex for ERAD.

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  • 1Department of Biological Sciences & Bio-X Program, Stanford University, Lorry Lokey Bldg, 337 Campus Drive, Stanford, CA 94305, USA.


Terminally misfolded or unassembled proteins in the early secretory pathway are degraded by a ubiquitin- and proteasome-dependent process known as ER-associated degradation (ERAD). How substrates of this pathway are recognized within the ER and delivered to the cytoplasmic ubiquitin-conjugating machinery is unknown. We report here that OS-9 and XTP3-B/Erlectin are ER-resident glycoproteins that bind to ERAD substrates and, through the SEL1L adaptor, to the ER-membrane-embedded ubiquitin ligase Hrd1. Both proteins contain conserved mannose 6-phosphate receptor homology (MRH) domains, which are required for interaction with SEL1L, but not with substrate. OS-9 associates with the ER chaperone GRP94 which, together with Hrd1 and SEL1L, is required for the degradation of an ERAD substrate, mutant alpha(1)-antitrypsin. These data suggest that XTP3-B and OS-9 are components of distinct, partially redundant, quality control surveillance pathways that coordinate protein folding with membrane dislocation and ubiquitin conjugation in mammalian cells.

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