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Published on: August 20, 2018
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
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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