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Aberrant intermolecular disulfide bonding in a mutant HLA-DM molecule: implications for assembly, maturation, and

R Busch1, R C Doebele, E von Scheven

  • 1Department of Pediatrics, Stanford University Medical Center, CA 94305, USA. rbusch@leland.stanford.edu

Journal of Immunology (Baltimore, Md. : 1950)
|April 29, 1998
PubMed

Insights

A mutation in HLA-DM (DM) causes misfolding, ER retention, and degradation, impairing antigen presentation. Restoring wild-type DM function resolves these peptide-loading defects.

Area of Science:

  • Immunology
  • Molecular Biology
  • Cell Biology

Background:

  • Human Leukocyte Antigen-DM (HLA-DM) is crucial for MHC class II peptide loading.
  • A specific B cell line (7.12.6) has a mutated DM beta-chain (Cys79Tyr) causing antigen presentation defects.

Purpose of the Study:

  • To investigate the functional consequences of the mutated HLA-DM beta-chain.
  • To understand the molecular mechanisms behind the antigen presentation defect in the 7.12.6 cell line.

Main Methods:

  • Analysis of HLA-DM folding and assembly in EBV-transformed B cells.
  • Peptide loading assays on HLA-DR molecules.
  • Transfection of wild-type DMB to assess functional restoration.
  • Characterization of mutant DM protein stability and localization.

Main Results:

  • The mutated HLA-DM beta-chain leads to defective peptide loading and CLIP accumulation in HLA-DR molecules.
  • Transfection with wild-type DMB restored normal peptide loading.
  • Mutant DM molecules exhibited slow ER exit, rapid degradation, and reduced levels in post-Golgi compartments.
  • Impaired noncovalent alpha-beta dimer formation and increased formation of aberrant disulfide-bonded DM alpha-beta and DM beta-beta homodimers were observed.

Conclusions:

  • The native conformation of HLA-DM is stabilized by a Cys79beta disulfide bond and noncovalent interactions with DM alpha.
  • Misfolding of the DM beta-chain, due to loss of these stabilizing interactions, results in ER retention and degradation, leading to impaired antigen presentation.

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