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Hüttner, S, Veit, C, Schoberer, J, Grass, J and Strasser, R (2012) Unraveling the function of Arabidopsis thaliana OS9 in the endoplasmic reticulum-associated degradation of glycoproteins. Plant Mol. Biol. 79:21-33

In the endoplasmic reticulum, immature polypeptides coincide with terminally misfolded proteins. Consequently, cells need a well-balanced quality control system, which decides about the fate of individual proteins and maintains protein homeostasis. Misfolded and unassembled proteins are sent for destruction via the endoplasmic reticulum-associated degradation (ERAD) machinery to prevent the accumulation of potentially toxic protein aggregates. Here, we report the identification of Arabidopsis thaliana OS9 as a component of the plant ERAD pathway. OS9 is an ER-resident glycoprotein containing a mannose-6-phosphate receptor homology domain, which is also found in yeast and mammalian lectins involved in ERAD. OS9 fused to the C-terminal domain of YOS9 can complement the ERAD defect of the corresponding yeast Δyos9 mutant. An A. thaliana OS9 loss-of-function line suppresses the severe growth phenotype of the bri1-5 and bri1-9 mutant plants, which harbour mutated forms of the brassinosteroid receptor BRI1. Co-immunoprecipitation studies demonstrated that OS9 associates with Arabidopsis SEL1L/HRD3, which is part of the plant ERAD complex and with the ERAD substrates BRI1-5 and BRI1-9, but only the binding to BRI1-5 occurs in a glycan-dependent way. OS9-deficiency results in activation of the unfolded protein response and reduces salt tolerance, highlighting the role of OS9 during ER stress. We propose that OS9 is a component of the plant ERAD machinery and may act specifically in the glycoprotein degradation pathway.

PubMed PMC3332353 Online version:10.1007/s11103-012-9891-4

Amino Acid Sequence; Arabidopsis/drug effects; Arabidopsis/metabolism; Arabidopsis Proteins/chemistry; Arabidopsis Proteins/metabolism; Endoplasmic Reticulum/drug effects; Endoplasmic Reticulum/metabolism; Endoplasmic Reticulum-Associated Degradation/drug effects; Glycoproteins/metabolism; Green Fluorescent Proteins/metabolism; Membrane Glycoproteins/chemistry; Membrane Glycoproteins/metabolism; Molecular Sequence Data; Mutation/genetics; Phenotype; Polysaccharides/metabolism; Protein Binding/drug effects; Protein Structure, Tertiary; Recombinant Fusion Proteins/metabolism; Saccharomyces cerevisiae/drug effects; Saccharomyces cerevisiae/metabolism; Sodium Chloride/pharmacology; Stress, Physiological/drug effects; Unfolded Protein Response/drug effects