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 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.
Arunachalam
B
B
Section of Immunobiology, Howard Hughes Medical Institute, Yale University School of Medicine, P.O. Box 208011, New Haven, CT 06520-8011, USA.
Phan
U T
UT
Geuze
H J
HJ
Cresswell
P
P
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D019556:COS Cells; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D004220:Disulfides / Q000378:metabolism*; D011992:Endosomes / Q000201:enzymology / Q000648:ultrastructure; D004790:Enzyme Induction / Q000187:drug effects; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007371:Interferon-gamma / Q000494:pharmacology; D008247:Lysosomes / Q000201:enzymology*; D008360:Mannosephosphates / Q000378:metabolism; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D016296:Mutagenesis; D010084:Oxidation-Reduction; D011490:Protein Disulfide Reductase (Glutathione) / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D017422:Sequence Analysis, DNA; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000201:enzymology / Q000648:ultrastructure
D018076:DNA, Complementary; D004220:Disulfides; D008360:Mannosephosphates; C027693:mannose-6-phosphate; D007371:Interferon-gamma; D011490:Protein Disulfide Reductase (Glutathione)