26S proteasomes and immunoproteasomes produce mainly N-extended versions of an antigenic peptide

EMBO J. 2001 May 15;20(10):2357-66. doi: 10.1093/emboj/20.10.2357.

Abstract

Protein degradation by proteasomes is the source of most antigenic peptides presented on MHC class I molecules. To determine whether proteasomes generate these peptides directly or longer precursors, we developed new methods to measure the efficiency with which 26S and 20S particles, during degradation of a protein, generate the presented epitope or potential precursors. Breakdown of ovalbumin by the 26S and 20S proteasomes yielded the immunodominant peptide SIINFEKL, but produced primarily variants containing 1-7 additional N-terminal residues. Only 6-8% of the times that ovalbumin molecules were digested was a SIINFEKL or an N-extended version produced. Surprisingly, immunoproteasomes which contain the interferon-gamma-induced beta-subunits and are more efficient in antigen presentation, produced no more SIINFEKL than proteasomes. However, the immunoproteasomes released 2-4 times more of certain N-extended versions. These observations show that the changes in cleavage specificity of immunoproteasomes influence not only the C-terminus, but also the N-terminus of potential antigenic peptides, and suggest that most MHC-presented peptides result from N-terminal trimming of larger proteasome products by aminopeptidases (e.g. the interferon-gamma-induced enzyme leucine aminopeptidase).

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Antigens / biosynthesis*
  • Antigens / immunology
  • Egg Proteins / biosynthesis*
  • Egg Proteins / immunology
  • Epitopes, B-Lymphocyte / biosynthesis*
  • Epitopes, B-Lymphocyte / immunology
  • Hybridomas
  • Immunodominant Epitopes / biosynthesis*
  • Immunodominant Epitopes / immunology
  • Mice
  • Ovalbumin / biosynthesis*
  • Ovalbumin / immunology
  • Peptide Biosynthesis*
  • Peptide Fragments
  • Peptide Hydrolases / metabolism*
  • Peptides / immunology
  • Proteasome Endopeptidase Complex*

Substances

  • Antigens
  • Egg Proteins
  • Epitopes, B-Lymphocyte
  • Immunodominant Epitopes
  • OVA-8
  • Peptide Fragments
  • Peptides
  • Ovalbumin
  • Peptide Hydrolases
  • Proteasome Endopeptidase Complex
  • ATP dependent 26S protease