Oral Presentation The 46th Lorne Conference on Protein Structure and Function 2021

Molecular basis underpinning metabolite-mediated T-cell immunity (#20)

Wael Awad 1 , Geraldine Ler 2 , Mariolina Salio 3 , Natacha Veerapen 4 , Jeffrey Mak 2 , Jérôme Le Nours 1 , Gurdyal Besra 4 , James McCluskey 5 , Alexandra Corbett 5 , David Farilie 2 , Jamie Rossjohn 1
  1. Infection and Immunity Program and Department of Biochemistry and Molecular Biology, Biomedicine Discovery Institute, Monash University, Clayton, Victoria, Australia
  2. Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland, Australia
  3. MRC Human Immunology Unit, MRC Weatherall Institute of Molecular Medicine, , University of Oxford, Oxford, UK
  4. Institute of Microbiology and Infection School of Biosciences, University of Birmingham, Birmingham, UK
  5. Department of Microbiology and Immunology, Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia

Mucosal associated invariant T (MAIT) cells are an abundant human T cells subset that are variably activated by small-molecule metabolites presented by the MHC class 1 related molecule, MR1. During infection with riboflavin-producing microorganisms, the microbial metabolite 5-amino-6-D-ribitylaminouracil (5-A-RU) reacts with glycolysis byproducts forming potent ribityl pyrimidine ligands. These pyrimidine intermediates are presented by MR1 on the surface of the antigen-presenting cells encountering the MAIT T-cell receptor (TCR) leading to the activation of the MAIT cells. The most potent MAIT agonist is 5-(2-oxopropylideneamino)-6-D-ribitylaminouracil (5-OP-RU), but the mechanism that underpins this potency remains unclear.

To dissect the molecular basis for the high potency of 5-OP-RU as a MAIT agonist, we chemically synthesized and characterized a large panel of 5-OP-RU analogues, termed “altered metabolite ligands” (AMLs), and investigated functionally and structurally their impact on MAIT recognition. Here, modification of the 5-OP-RU ribityl moiety impacted differentially on MAIT TCR binding affinity, consistent with the ability of AMLs to stimulate MAITs. Through an analysis of 13 MAIT TCR-MR1-AML crystal structures, we show that the propensity of MR1-upregulation on the cell surface was related to the nature of MR1-AML interactions. Further, MR1-AML adaptability and a dynamic compensatory interplay at the TCR-AML-MR1 interface impacted on the affinity of the TCR-MR1-AML interaction, which ultimately underscored the ability of the AMLs to activate MAITs. Therefore, we determined the molecular basis underlying MR1 antigen capture, MAIT TCR recognition and thereby provide insights into MAIT cell antigen potency.

 

1) Awad, W.#, Ler, G.J.M.# et al. (2020). The molecular basis underpinning the potency and specificity of MAIT cell antigens. Nature Immunology 21, 400-411.

2) Salio, M.#, Awad, W.#et al. (2020). Ligand-dependent downregulation of MR1 cell surface expression. PNAS,

3) Awad W, et al. (2020). Atypical TRAV1-2- T cell receptor recognition of the antigen-presenting molecule MR1. Biol. Chem., in press.