Endoplasmic reticulum chaperones stabilize ligand-receptive MR1 molecules for efficient presentation of metabolite antigens

Hamish E. G. McWilliam, Jeffrey Y. W. Mak, Wael Awad, Matthew Zorkau, Sebastian Cruz-Gomez, Hui Jing Lim, Yuting Yan, Sam Wormald, Laura F. Dagley, Sidonia B. G. Eckle, Alexandra J. Corbett, Haiyin Liu, Shihan Li, Scott J. J. Reddiex, Justine D. Mintern, Ligong Liu, James McCluskey, Jamie Rossjohn, David P. Fairlie, Jose A. Villadangos

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29 Citations (Scopus)


The antigen-presenting molecule MR1 (MHC class I-related protein 1) presents metabolite antigens derived from microbial vitamin B2 synthesis to activate mucosal-associated invariant T (MAIT) cells. Key aspects of this evolutionarily conserved pathway remain uncharacterized, including where MR1 acquires ligands and what accessory proteins assist ligand binding. We answer these questions by using a fluorophore-labeled stable MR1 antigen analog, a conformation-specific MR1 mAb, proteomic analysis, and a genome-wide CRISPR/Cas9 library screen. We show that the endoplasmic reticulum (ER) contains a pool of two unliganded MR1 conformers stabilized via interactions with chaperones tapasin and tapasin-related protein. This pool is the primary source of MR1 molecules for the presentation of exogenous metabolite antigens to MAIT cells. Deletion of these chaperones reduces the ERresident MR1 pool and hampers antigen presentation and MAIT cell activation. The MR1 antigen-presentation pathway thus co-opts ER chaperones to fulfill its unique ability to present exogenous metabolite antigens captured within the ER.

Original languageEnglish
Pages (from-to)24974-24985
Number of pages12
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number40
Publication statusPublished - 6 Oct 2020


  • Fluorescent probe
  • MAIT cells
  • MHC class I-related protein 1 (MR1)
  • Protein trafficking
  • Vitamin B

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