Abstract
Proteins internalized into the endocytic pathway are usually degraded. Efficient proteolysis requires denaturation, induced by acidic conditions within lysosomes, and reduction of inter- and intrachain disulfide bonds. Cytosolic reduction is mediated enzymatically by thioredoxin, but the mechanism of lysosomal reduction is unknown. We describe here a lysosomal thiol reductase optimally active at low pH and capable of catalyzing disulfide bond reduction both in vivo and in vitro. The active site, determined by mutagenesis, consists of a pair of cysteine residues separated by two amino acids, similar to other enzymes of the thioredoxin family. The enzyme is a soluble glycoprotein that is synthesized as a precursor. After delivery into the endosomal/lysosomal system by the mannose 6-phosphate receptor, N- and C-terminal prosequences are removed. The enzyme is expressed constitutively in antigen-presenting cells and induced by IFN-gamma in other cell types, suggesting a potentially important role in antigen processing.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Amino Acid Sequence
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Animals
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Base Sequence
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Binding Sites / genetics
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COS Cells
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DNA, Complementary / chemistry
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DNA, Complementary / genetics
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Disulfides / metabolism*
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Endosomes / enzymology
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Endosomes / ultrastructure
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Enzyme Induction / drug effects
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Humans
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Hydrogen-Ion Concentration
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Interferon-gamma / pharmacology
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Lysosomes / enzymology*
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Mannosephosphates / metabolism
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Microscopy, Immunoelectron
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Molecular Sequence Data
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Mutagenesis
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Oxidation-Reduction
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Protein Disulfide Reductase (Glutathione) / biosynthesis
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Protein Disulfide Reductase (Glutathione) / genetics
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Protein Disulfide Reductase (Glutathione) / metabolism
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Protein Processing, Post-Translational
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Sequence Analysis, DNA
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Tumor Cells, Cultured / drug effects
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Tumor Cells, Cultured / enzymology
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Tumor Cells, Cultured / ultrastructure
Substances
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DNA, Complementary
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Disulfides
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Mannosephosphates
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mannose-6-phosphate
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Interferon-gamma
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Protein Disulfide Reductase (Glutathione)