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The oxidoreductase ERp57 is an integral component of the peptide loading complex of major histocompatibility complex (MHC) class I molecules, formed during their chaperone-assisted assembly in the endoplasmic reticulum. Misfolded MHC class I molecules or those denied suitable peptides are retrotranslocated and degraded in the cytosol. The presence of ERp57 during class I assembly suggests it may be involved in the reduction of intrachain disulfides prior to retrotranslocation. We have studied the ability of ERp57 to reduce MHC class I molecules in vitro. Recombinant ERp57 specifically reduced partially folded MHC class I molecules, whereas it had little or no effect on folded and peptide-loaded MHC class I molecules. Reductase activity was associated with cysteines at positions 56 and 405 of ERp57, the N-terminal residues of the active CXXC motifs. Our data suggest that the reductase activity of ERp57 may be involved during the unfolding of MHC class I molecules, leading to targeting for degradation.

Original publication




Journal article


The EMBO journal

Publication Date





2655 - 2663


Division of Cell Biology and Immunology, School of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK.


Cell Line, Subcellular Fractions, Animals, Humans, Rats, Disulfides, Cysteine, Insulin, Isomerases, Peptides, Heat-Shock Proteins, Recombinant Proteins, DNA, Complementary, Precipitin Tests, Major Histocompatibility Complex, Amino Acid Motifs, Protein Binding, Protein Folding, Mutation, Time Factors, Protein Disulfide-Isomerases