Tobacco etch virus protease (TEVp) is a unique endopeptidase with stringent substrate specificity. TEVp has been widely used as a purified protein for in vitro applications, but also as a biological tool directly expressing it in living cells. To adapt the protease to diverse applications, several TEVp mutants with different stability and enzymatic properties have been reported. Herein we describe the development of a novel engineered TEVp mutant designed to be active in the secretory pathway. While wild type TEVp targeted to the secretory pathway of mammalian cells is synthetized as an N-glycosylated and catalytically inactive enzyme, a TEVp mutant with selected mutations at two verified N-glycosylation sites and at an exposed cysteine was highly efficient. This mutant was very active in the endoplasmic reticulum (ER) of living cells and can be used as a biotechnological tool to cleave proteins within the secretory pathway. As an immediate practical application we report the expression of a complete functional monoclonal antibody expressed from a single polypeptide, which was cleaved by our TEVp mutant into the two antibody chains and secreted as an assembled and functional molecule. In addition, we show active TEVp mutants lacking auto-cleavage activity.
Background: CD4 and Tetherin are stabilized through intrachain and interchain disulfide bonds, respectively. Results: CD4 and Tetherin retro-translocate from ER to cytosol with oxidized disulfide bridges as folded and multimeric molecules. Conclusion: Cysteines reduction is not a prerequisite for ER to cytosol dislocation. Significance: Our observations challenge the requirements of reduction and unfolding before dislocation.
Background:The AAA-ATPase VCP/p97 and the deubiquitinase YOD1 are required in the endoplasmic reticulum-associated degradation (ERAD) of misfolded proteins. Results: Three ERAD substrates (NHK-␣1〈⌻, NS1-kLC, and Tetherin) become cytosolically exposed independently of p97 and YOD1, whereas MHC-I␣-and CD4-induced retro-translocation requires them. Conclusion: VCP/p97 and YOD1 have distinct substrate-dependent activities in ERAD. Significance: We demonstrate two different levels of p97 and YOD1 requirements in ERAD.
Translational stalling of ribosome bound to endoplasmic reticulum (ER) membrane requires an accurate clearance of the associated polypeptides, which is not completely understood in mammals. We characterized in mammalian cells the model of ribosomal stalling at the STOP-codon based on proteins tagged at the C-terminus with the picornavirus 2A peptide followed by a termination codon instead of the Proline (2A*). We exploited the 2A* stalling model to characterize the pathway of degradation of ER-targeted polypeptides. We report that the ER chaperone BiP/GRP78 is a new main factor involved. Moreover, degradation of the ER-stalled polypeptides required the activities of the AAA-ATPase VCP/p97, its associated deubiquitinylase YOD1, the ribosome-associated ubiquitin ligase Listerin and the proteasome. In human proteome, we found two human C-terminal amino acid sequences that cause similar stalling at the STOP-codon. Our data suggest that translational stalling at the ER membrane activates protein degradation at the interface of ribosomal-and ERassociated quality control systems.
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