PMID:19060110

Citation	Hong, Z, Jin, H, Tzfira, T and Li, J (2008) Multiple mechanism-mediated retention of a defective brassinosteroid receptor in the endoplasmic reticulum of Arabidopsis. Plant Cell 20:3418-29
Abstract	Endoplasmic reticulum-mediated quality control (ERQC) is a well-studied process in yeast and mammals that retains and disposes misfolded/unassembled polypeptides. By contrast, how plants exert quality control over their secretory proteins is less clear. Here, we report that a mutated brassinosteroid receptor, bri1-5, that carries a Cys69Tyr mutation, is retained in the ER by an overvigilant ERQC system involving three different retention mechanisms. We demonstrate that bri1-5 interacts with two ER chaperones, calnexin and binding protein (BiP), and is degraded by a proteasome-independent endoplasmic reticulum-associated degradation (ERAD). Mutations in components of the calnexin/calreticulin cycle had little effect on the fidelity of the Arabidopsis thaliana ERQC for bri1-5 retention. By contrast, overexpression of bri1-5, treatment with an ERAD inhibitor, RNA interference-mediated BiP silencing, or simultaneous mutations of Cys-69 and its partner Cys-62 can mitigate this quality control, resulting in significant suppression of the bri1-5 phenotype. Thus, bri1-5 is an excellent model protein to investigate plant ERQC/ERAD in a model organism.
Links	PubMed PMC2630446 Online version:10.1105/tpc.108.061879
Keywords	Arabidopsis/drug effects; Arabidopsis/genetics; Arabidopsis/metabolism; Arabidopsis Proteins/genetics; Arabidopsis Proteins/metabolism; Calnexin/metabolism; Endoplasmic Reticulum/genetics; Endoplasmic Reticulum/metabolism; Microscopy, Confocal; Molecular Sequence Data; Protein Binding
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