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Immunopeptidomics: Isolation of Mouse and Human MHC Class I- and II-Associated Peptides for Mass Spectrometry Analysis
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Interaction of HLA-DR with an acidic face of HLA-DM disrupts sequence-dependent interactions with peptides

Achal Pashine1, Robert Busch, Michael P Belmares

  • 1Department of Pediatrics, Stanford University, Stanford, California 94305, USA.

Immunity
|August 23, 2003
PubMed

Insights

Human leukocyte antigen-DM (HLA-DM) edits peptides bound to MHC class II (MHCII) molecules. This study maps the HLA-DM interaction site on MHCII, revealing its role in peptide editing and complex formation.

Area of Science:

  • Immunology
  • Molecular Biology
  • Structural Biology

Background:

  • Human leukocyte antigen-DM (HLA-DM) is crucial for adaptive immunity, editing peptides presented by major histocompatibility complex class II (MHCII) molecules.
  • While crystal structures show HLA-DM resembles MHCII, the precise interaction mechanism and interface remain uncharacterized.

Purpose of the Study:

  • To elucidate the interaction interface between HLA-DM and MHCII.
  • To understand how HLA-DM facilitates peptide editing and loading onto MHCII molecules.

Main Methods:

  • Site-directed mutagenesis was employed to identify key residues on HLA-DM involved in MHCII interaction.
  • Cell-based assays and in vitro peptide loading experiments were used to assess the functional impact of mutations.
  • Biochemical approaches, including the design of soluble fused protein complexes, were utilized to study DM-MHCII interactions.

Main Results:

  • Mutagenesis identified a critical MHCII-interacting surface on HLA-DM.
  • Disrupting this surface impaired HLA-DM function in cellular assays and in vitro peptide loading.
  • Engineered soluble HLA-DM/MHCII complexes demonstrated rapid, sequence-independent peptide release, suggesting reduced MHCII groove selectivity.

Conclusions:

  • The identified surface is essential for HLA-DM's interaction with MHCII and its function in peptide editing.
  • HLA-DM appears to decrease the sequence specificity of the MHCII peptide-binding groove.
  • These findings provide structural and functional insights into the mechanism of MHCII peptide loading.

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