Abstract
Some secretory proteins leave the endoplasmic reticulum (ER) by a receptor-mediated cargo capture mechanism, but the signals required for the cargo-receptor interaction are largely unknown. Here, we describe a novel targeting motif that is composed of a high-mannose type oligosaccharide intimately associated with a surface-exposed peptide beta-hairpin loop. The motif accounts for lectin ERGIC-53-assisted ER-export of the lyososomal enzyme procathepsin Z. The second oligosaccharide chain of procathepsin Z exhibits no binding activity for ERGIC-53, illustrating the selective lectin properties of ERGIC-53. Our data suggest that the conformation-based motif is only present in fully folded procathepsin Z and that its recognition by ERGIC-53 reflects a quality control mechanism that acts complementary to the primary folding machinery in the ER. A similar oligosaccharide/beta-hairpin loop structure is present in cathepsin C, another cargo of ERGIC-53, suggesting the general nature of this ER-exit signal. To our knowledge this is the first documentation of an ER-exit signal in soluble cargo in conjunction with its decoding by a transport receptor.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Amino Acid Motifs
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Amino Acid Sequence
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Animals
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Biological Transport
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CHO Cells
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Carbohydrates / chemistry*
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Carrier Proteins / chemistry
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Cathepsin C / chemistry
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Cathepsin K
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Cathepsins / chemistry
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Cricetinae
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Cross-Linking Reagents / pharmacology
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DNA / chemistry
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DNA, Complementary / metabolism
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Electrophoresis, Polyacrylamide Gel
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Endoplasmic Reticulum / metabolism*
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Glycoproteins / chemistry
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Glycoside Hydrolases / pharmacology
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Humans
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Immunoprecipitation
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Lectins / chemistry
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Lectins / metabolism
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Mannose-Binding Lectins / chemistry
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Membrane Proteins / chemistry
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Mice
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Models, Molecular
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Molecular Conformation
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Molecular Sequence Data
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Mutation
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Oligosaccharides / chemistry*
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Polysaccharides / chemistry
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Protein Conformation
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Protein Folding
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Protein Sorting Signals*
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Protein Structure, Secondary
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Sequence Homology, Amino Acid
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Transfection
Substances
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Carbohydrates
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Carrier Proteins
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Cross-Linking Reagents
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DNA, Complementary
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Glycoproteins
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LMAN1 protein, human
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Lectins
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Mannose-Binding Lectins
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Membrane Proteins
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Oligosaccharides
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Polysaccharides
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Protein Sorting Signals
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DNA
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Glycoside Hydrolases
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Cathepsins
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Cathepsin C
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CTSK protein, human
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Cathepsin K
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Ctsk protein, mouse