To generate peptides for presentation by major histocompatibility complex (MHC) class I molecules to T lymphocytes, the immune system of vertebrates has recruited the proteasomes, phylogenetically ancient multicatalytic high molecular weight endoproteases. We have previously shown that many of the proteolytic fragments generated by vertebrate proteasomes have structural features in common with peptides eluted from MHC class I molecules, suggesting that many MHC class I ligands are direct products of proteasomal proteolysis. Here, we report that the processing of polypeptides by proteasomes is conserved in evolution, not only among vertebrate species, but including invertebrate eukaryotes such as insects and yeast. Unexpectedly, we found that several high copy ligands of MHC class I molecules, in particular, self-ligands, are major products in digests of source polypeptides by invertebrate proteasomes. Moreover, many major dual cleavage peptides produced by invertebrate proteasomes have the length and the NH2 and COOH termini preferred by MHC class I. Thus, the ability of proteasomes to generate potentially immunocompetent peptides evolved well before the vertebrate immune system. We demonstrate with polypeptide substrates that interferon γ induction in vivo or addition of recombinant proteasome activator 28α in vitro alters proteasomal proteolysis in such a way that the generation of peptides with the structural features of MHC class I ligands is optimized. However, these changes are quantitative and do not confer qualitatively novel characteristics to proteasomal proteolysis. The data suggest that proteasomes may have influenced the evolution of MHC class I molecules.
Potential Immunocompetence of Proteolytic Fragments Produced by Proteasomes before Evolution of the Vertebrate Immune System
Address correspondence to Dr. K. Eichmann, Max-Planck-Institut für Immunbiologie, Stübeweg 51, 79108 Freiburg, Germany. Phone: 49-761-51-08-541; FAX: 49-761-51-08-545: E-mail: [email protected]
C. Realini and M.C. Rechsteiner were supported by grants from the American Cancer Society and from The National Institutes of Health.
Note added in proof. While this article was in print, the x-ray structure of the yeast 20S proteasome was reported (Groll, M., L. Ditzel, J. Löwe, D. Stock, M. Botchler, H.D. Bartunik, and R. Huber. 1997. Structure of the 20S proteasome from yeast at 2.4 A resolution. Nature (Lond.). 386:463–471). The results are in excellent agreement with the length distribution of proteasomal fragments and with the alterations by IFN-γ–inducible elements described in this paper.
1Abbreviations used in this paper: β2m, β2 microglobulin; aa, amino acid; BTG1, B cell translocation gene 1; Db, H-2Db; hsp, heat shock protein; Kb, H-2Kb; LLnL, N-acetyl-l-leucinyl-l-Leucinal-l-norleucinal; MALDI-Tof-MS, matrix-assisted laser desorption/ionization time of flight mass spectrometry; PA, proteasome activator; SSU, small subunit; TAP, transporter associated with antigen processing.
Gabriele Niedermann, Rudolf Grimm, Elke Geier, Martina Maurer, Claudio Realini, Christoph Gartmann, Jürgen Soll, Satoshi Omura, Martin C. Rechsteiner, Wolfgang Baumeister, Klaus Eichmann; Potential Immunocompetence of Proteolytic Fragments Produced by Proteasomes before Evolution of the Vertebrate Immune System. J Exp Med 21 July 1997; 186 (2): 209–220. doi: https://doi.org/10.1084/jem.186.2.209
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