title: The Arabidopsis homolog of the mammalian OS-9 protein plays a key role in the endoplasmic reticulum-associated degradation of misfolded receptor-like kinases.
abstract: The endoplasmic reticulum-associated degradation (ERAD) is a highly conserved mechanism to remove misfolded membrane/secretory proteins from the endoplasmic reticulum (ER). While many of the individual components of the ERAD machinery are well characterized in yeast and mammals, our knowledge of a plant ERAD process is rather limited. Here, we report a functional study of an Arabidopsis homolog (AtOS9) of an ER luminal lectin Yos9 (OS-9 in mammals) that recognizes a unique asparagine-linked glycan on misfolded proteins. We discovered that AtOS9 is an ER-localized glycoprotein that is co-expressed with many known/predicted ER chaperones. A T-DNA insertional atos9-t mutation blocks the degradation of a structurally imperfect yet biochemically competent brassinosteroid (BR) receptor bri1-9, causing its increased accumulation in the ER and its consequent leakage to the cell surface responsible for restoring the BR sensitivity and suppressing the dwarfism of the bri1-9 mutant. In addition, we identified a missense mutation in AtOS9 in a recently discovered ERAD mutant ems-mutagenized bri1 suppressor 6 (ebs6-1). Moreover, we showed that atos9-t also inhibits the ERAD of bri1-5, another ER-retained BR receptor, and a misfolded EFR, a BRI1-like receptor for the bacterial translation elongation factor EF-Tu. Furthermore, we found that AtOS9 interacted biochemically and genetically with EBS5, an Arabidopsis homolog of the yeast Hrd3/mammalian Sel1L known to collaborate with Yos9/OS-9 to select ERAD clients. Taken together, our results demonstrated a functional role of AtOS9 in a plant ERAD process that degrades misfolded receptor-like kinases.
authors.affiliation: Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109-1048, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Su
authors.forename: Yidan
authors.initials: Y
authors.lastname: Liu
authors.forename: Yang
authors.initials: Y
authors.lastname: Xia
authors.forename: Zhi
authors.initials: Z
authors.lastname: Hong
authors.forename: Jianming
authors.initials: J
authors.lastname: Li
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism; D017124:Conserved Sequence; D004269:DNA, Bacterial / Q000235:genetics; D060746:Endoplasmic Reticulum-Associated Degradation; D006023:Glycoproteins / Q000737:chemistry; D006801:Humans; D037102:Lectins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009363:Neoplasm Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D051192:Receptors, Pattern Recognition / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
chemical_list: D029681:Arabidopsis Proteins; D004269:DNA, Bacterial; C545106:EFR protein, Arabidopsis; D006023:Glycoproteins; D037102:Lectins; D009363:Neoplasm Proteins; C098898:OS9 protein, human; D051192:Receptors, Pattern Recognition; C036483:T-DNA; D011494:Protein Kinases; C108270:BRI1 protein, Arabidopsis