Crystal structure of a TAPBPR–MHC-I complex reveals the mechanism of peptide editing in antigen presentation

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Science  12 Oct 2017:
DOI: 10.1126/science.aao5154

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Central to CD8+ T-cell mediated immunity is the recognition of peptide–major histocompatibility complex class I (pMHC-I) proteins displayed by antigen-presenting cells. Chaperone-mediated loading of high-affinity peptides onto MHC-I is a key step in the MHC-I antigen presentation pathway. However, the structure of MHC-I with a chaperone that facilitates peptide loading has not been determined. We report the crystal structure of MHC-I in complex with the peptide editor TAPBPR (TAP binding protein, related), a tapasin homolog. TAPBPR remodels the peptide-binding groove of MHC-I, resulting in the release of low-affinity peptide. Changes include groove relaxation, modifications of key binding pockets, and domain adjustments. This structure captures a peptide-receptive state of MHC-I and provides insights into the mechanism of peptide editing by TAPBPR and, by analogy, tapasin.

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