Abstract
N-glycosylation of proteins in the endoplasmic reticulum (ER) has a central role in protein quality control. Here we report that N-glycan serves as a signal for degradation by the Skp1-Cullin1-Fbx2-Roc1 (SCF(Fbx2)) ubiquitin ligase complex. The F-box protein Fbx2 (ref. 4) binds specifically to proteins attached to N-linked high-mannose oligosaccharides and subsequently contributes to ubiquitination of N-glycosylated proteins. Pre-integrin beta 1 is a target of Fbx2; these two proteins interact in the cytosol after inhibition of the proteasome. In addition, expression of the mutant Fbx2 Delta F, which lacks the F-box domain that is essential for forming the SCF complex, appreciably blocks degradation of typical substrates of the ER-associated degradation pathway. Our results indicate that SCF(Fbx2) ubiquitinates N-glycosylated proteins that are translocated from the ER to the cytosol by the quality control mechanism.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Animals
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Cell Line
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Cysteine Endopeptidases / metabolism
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Cystic Fibrosis Transmembrane Conductance Regulator / chemistry
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Cystic Fibrosis Transmembrane Conductance Regulator / genetics
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Cystic Fibrosis Transmembrane Conductance Regulator / metabolism
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Endoplasmic Reticulum / metabolism
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Glycoproteins / chemistry*
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Glycoproteins / genetics
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Glycoproteins / metabolism*
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Glycosylation
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Humans
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Integrin beta1 / metabolism
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Leupeptins / pharmacology
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Ligases / chemistry*
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Ligases / metabolism*
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Macromolecular Substances
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Mannose / metabolism
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Mice
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Multienzyme Complexes / antagonists & inhibitors
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Multienzyme Complexes / metabolism
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Polysaccharides / chemistry*
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Polysaccharides / metabolism*
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Proteasome Endopeptidase Complex
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Protein Binding / drug effects
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Protein Precursors / metabolism
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Ribonucleases / chemistry
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Ribonucleases / metabolism
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Substrate Specificity
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Transfection
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Ubiquitin / metabolism*
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Ubiquitin-Protein Ligases
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alpha-Fetoproteins / chemistry
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alpha-Fetoproteins / metabolism
Substances
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CFTR protein, human
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Glycoproteins
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Integrin beta1
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Leupeptins
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Macromolecular Substances
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Multienzyme Complexes
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Polysaccharides
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Protein Precursors
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Ubiquitin
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alpha-Fetoproteins
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Cystic Fibrosis Transmembrane Conductance Regulator
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Ubiquitin-Protein Ligases
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Ribonucleases
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ribonuclease B
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Cysteine Endopeptidases
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Proteasome Endopeptidase Complex
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Ligases
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Mannose
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benzyloxycarbonylleucyl-leucyl-leucine aldehyde