Download MendeleyThe partial dissociation of MHC class I-bound peptides exposes their N terminus to trimming by endoplasmic reticulum aminopeptidase 1.
Papakyriakou, A., Reeves, E., Beton, M., Mikolajek, H., Douglas, L., Cooper, G., Elliott, T., Werner, J.M., James, E.(2018) J Biological Chem 293: 7538-7548
- PubMed: 29599287
- DOI: https://doi.org/10.1074/jbc.RA117.000313
- Primary Citation of Related Structures:
5OQF, 5OQG, 5OQH, 5OQI - PubMed Abstract:
Endoplasmic reticulum aminopeptidase 1 (ERAP1) and ERAP2 process N-terminally extended antigenic precursors for optimal loading onto major histocompatibility complex class I (MHC I) molecules. We and others have demonstrated that ERAP1 processes peptides bound to MHC I, but the underlying mechanism is unknown. To this end, we utilized single-chain trimers (SCT) of the ovalbumin-derived epitope SIINFEKL (SL8) tethered to the H2-K b MHC I determinant from mouse and introduced three substitutions, E63A, K66A, and W167A, at the A-pocket of the peptide-binding groove in the MHC I heavy chain, which interact with the N termini of peptides. These variants significantly decreased SL8-presenting SCT at the cell surface in the presence of ERAP1, but did not affect overall SCT expression, indicating that ERAP1 trims the SL8 N terminus. Comparison of the X-ray crystal structures of WT and three variant SCTs revealed only minor perturbations of the peptide-binding domain in the variants. However, molecular dynamics simulations suggested that SL8 can dissociate partially within a sub-microsecond timescale, exposing its N terminus to the solvent. We also found that the C terminus of MHC I-bound SL8 remains deeply buried in the F-pocket of MHC I. Furthermore, free-energy calculations revealed that the three SCT variants exhibit lower free-energy barriers of N terminus dissociation than the WT K b Taken together, our results are consistent with a previously observed model in which the partial dissociation of bound peptides from MHC I exposes their N terminus to trimming by ERAP1, whereas their C terminus is anchored at the F-pocket.
Organizational Affiliation:
From the Centre for Biological Sciences, Faculty of Natural & Environmental Sciences, University of Southampton, Southampton SO17 1BJ, United Kingdom.
