Testing the role of gp96 as peptide chaperone in antigen processing.
gp96 is a 96-kDa glycoprotein of the endoplasmic reticulum that is believed to be involved in antigen processing as an intermediate carrier of peptides for presentation by major histocompatibility complex (MHC) class I molecules. This function implies that gp96 carries a large array of different peptides that represent the antigenicity of the cell and can serve all MHC class I molecules. So far, the evidence regarding these peptides is largely indirect and based on experiments where mice immunized with gp96 from tumor or virus-infected cells developed T cellular immune responses with the corresponding specificities. We analyzed by mass spectrometry peptides isolated from gp96 and found a number of different peptides derived from the proteins of different cellular compartments but mostly cytoplasm and nucleus. The sequences of these peptides provide information on the specificity of antigen processing and reveal structural requirements for binding to gp96 that only partially correspond to those of peptides presented by MHC class I molecules. The yield of peptides extracted from gp96 was far substoichiometric with an estimated occupancy of this chaperone of between 0.1% and 0.4%. These results strongly argue against a regular role for gp96 as a peptide chaperone in antigen processing.
Demine
Rodion
R
Charité-University Medicine Berlin, Humboldt University, Clinical Research Group Tumor Immunology, Department of Dermatology and Allergy, D-10098 Berlin, Germany.
Walden
Peter
P
D000595:Amino Acid Sequence; D000818:Animals; D017951:Antigen Presentation / Q000502:physiology*; D000951:Antigens, Neoplasm / Q000502:physiology*; D045744:Cell Line, Tumor; D005805:Genes, MHC Class I / Q000502:physiology; D006801:Humans; D051379:Mice; D018832:Molecular Chaperones / Q000502:physiology*; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000502:physiology*
D000951:Antigens, Neoplasm; D018832:Molecular Chaperones; D010446:Peptide Fragments; C052646:sarcoma glycoprotein gp96 rejection antigens