Enzymatic Reduction of Disulfide Bonds in Lysosomes: Characterization of a Gamma-Interferon-Inducible Lysosomal Thiol Reductase (GILT)

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 o...

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Bibliographic Details
Published in:	Proceedings of the National Academy of Sciences - PNAS 2000-01, Vol.97 (2), p.745-750
Main Authors:	Arunachalam, Balasubramanian, Phan, Uyen T., Geuze, Hans J., Cresswell, Peter
Format:	Article
Language:	eng
Subjects:	Amino Acid Sequence Amino acids Animals Base Sequence Binding Sites - genetics Biological Sciences Cell lines COS Cells Disulfides Disulfides - metabolism DNA, Complementary - chemistry DNA, Complementary - genetics Endosomes - enzymology Endosomes - ultrastructure Enzyme Induction - drug effects Enzymes Gilts Humans Hydrogen-Ion Concentration Immunology Interferon-gamma - pharmacology Lysosomes Lysosomes - enzymology Mannosephosphates - metabolism Microscopy, Immunoelectron Molecular Sequence Data Mutagenesis Oxidation-Reduction Protein Disulfide Reductase (Glutathione) - biosynthesis Protein Disulfide Reductase (Glutathione) - genetics Protein Disulfide Reductase (Glutathione) - metabolism Protein Processing, Post-Translational Proteins Sequence Analysis, DNA Thiols Thioredoxin Tumor Cells, Cultured - drug effects Tumor Cells, Cultured - enzymology Tumor Cells, Cultured - ultrastructure
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Summary:	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-γ in other cell types, suggesting a potentially important role in antigen processing.
ISSN:	0027-8424 1091-6490