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The partial dissociation of MHC class I bound peptides exposes their N terminus to trimming by endoplasmic reticulum aminopeptidase 1

DOI: 10.1074/jbc.RA117.000313 DOI Help

Authors: Athanasios Papakyriakou (University of Southampton) , Emma Reeves (University of Southampton) , Mary Beton (University of Southampton) , Halina Mikolajek (University of Southampton) , Leon Douglas (University of Southampton) , Grace Cooper (University of Southampton) , Tim Elliott (University of Southampton) , Jörn M. Werner (University of Southampton) , Edward James (University of Southampton)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Biological Chemistry

State: Published (Approved)
Published: March 2018

Open Access Open Access

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-Kb 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 Kb. 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, while their C terminus is anchored at the F-pocket.

Journal Keywords: H2-Kb; ERAP1; single chain trimer; free energy calculations; peptide trimming; antigen processing; major histocompatibility complex (MHC); X-ray crystallography; antigen presentation; molecular dynamics

Subject Areas: Biology and Bio-materials

Instruments: I04-Macromolecular Crystallography , I24-Microfocus Macromolecular Crystallography

Added On: 04/04/2018 11:04


Discipline Tags:

Life Sciences & Biotech Structural biology

Technical Tags:

Diffraction Macromolecular Crystallography (MX)