The Journal of Experimental Medicine
VeriKine-HS Human IFN-Beta
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© The Rockefeller University Press, 0022-1007/1996/12/2251/ $5.00
The Journal of Experimental Medicine, Volume 184, Number 6, December 1, 1996 2251-2260

Articles

Intermediates in the Assembly and Degradation of Class I Major Histocompatibility Complex (MHC) Molecules Probed with Free Heavy Chain–specific Monoclonal Antibodies

Robert P. Machold and Hidde L. Ploegh

From the Center for Cancer Research, Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139

Unassembled (free) heavy chains appear during two stages of the class I MHC molecule's existence: immediately after translation but before assembly with peptide and β2-microglobulin, and later, upon disintegration of the heterotrimeric complex. To characterize the structures of folding and degradation intermediates of the class I heavy chain, three monoclonal antibodies have been produced that recognize epitopes along the H-2Kb heavy chain which are obscured upon proper folding and subsequent assembly with β2-microglobulin (KU1: residues 49-54; KU2: residues 23-30; KU4: residues 193-198). The Kb heavy chain is inserted into the lumen of the endoplasmic reticulum in an unfolded state reactive with KU1, KU2, and KU4. Shortly after completion of the polypeptide chain, reactivity with KU1, KU2 and KU4 is lost synchronously, suggesting that folding of the class I heavy chain is a rapid, cooperative process. Perturbation of the folding environment in intact cells with the reducing agent dithiothreitol or the trimming glucosidase inhibitor N-7-oxadecyl-deoxynojirimycin prolongs the presence of mAb-reactive Kb heavy chains. At the cell surface, a pool of free Kb heavy chains appears after 60–120 min of chase, whose subsequent degradation, but not their initial appearance, is impaired in the presence of concanamycin B, an inhibitor of vacuolar acidification. Thus, free heavy chains that arise at the cell surface are destroyed after internalization.

Address correspondence to Hidde L. Ploegh, Center for Cancer Research, Department of Biology, Massachusetts Institute of Technology, 40 Ames Street, E17-322, Cambridge, MA 02139.

This work was supported by National Institutes of Health grants R01-AI33456-01 and R01-AI07463-17.

1Abbreviations used in this paper: β2m, β2-microglobulin; HA, hemagglutinin; Raf HC, rabbit anti-free haevy serum.


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