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J Immunol. 2013 Aug 15;191(4):1547-55. doi: 10.4049/jimmunol.1301043. Epub 2013 Jul 17.

ERAAP and tapasin independently edit the amino and carboxyl termini of MHC class I peptides.

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Division of Immunology and Pathogenesis, Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA.


Effective CD8(+) T cell responses depend on presentation of a stable peptide repertoire by MHC class I (MHC I) molecules on the cell surface. The overall quality of peptide-MHC I complexes (pMHC I) is determined by poorly understood mechanisms that generate and load peptides with appropriate consensus motifs onto MHC I. In this article, we show that both tapasin (Tpn), a key component of the peptide loading complex, and the endoplasmic reticulum aminopeptidase associated with Ag processing (ERAAP) are quintessential editors of distinct structural features of the peptide repertoire. We carried out reciprocal immunization of wild-type mice with cells from Tpn- or ERAAP-deficient mice. Specificity analysis of T cell responses showed that absence of Tpn or ERAAP independently altered the peptide repertoire by causing loss as well as gain of new pMHC I. Changes in amino acid sequences of MHC-bound peptides revealed that ERAAP and Tpn, respectively, defined the characteristic amino and carboxy termini of canonical MHC I peptides. Thus, the optimal pMHC I repertoire is produced by two distinct peptide editing steps in the endoplasmic reticulum.

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