The molecular basis for Mucosal-Associated Invariant T cell recognition of MR1 proteins.Lopez-Sagaseta, J., Dulberger, C.L., Crooks, J.E., Parks, C.D., Luoma, A.M., McFedries, A., Van Rhijn, I., Saghatelian, A., Adams, E.J.
(2013) Proc Natl Acad Sci U S A 110: E1771-E1778
- PubMed: 23613577
- DOI: https://doi.org/10.1073/pnas.1222678110
- Primary Citation of Related Structures:
- PubMed Abstract:
Mucosal-associated invariant T (MAIT) cells are an evolutionarily conserved αβ T-cell lineage that express a semi-invariant T-cell receptor (TCR) restricted to the MHC related-1 (MR1) protein. MAIT cells are dependent upon MR1 expression and exposure to microbes for their development and stimulation, yet these cells can exhibit microbial-independent stimulation when responding to MR1 from different species. We have used this microbial-independent, cross-species reactivity of MAIT cells to define the molecular basis of MAIT-TCR/MR1 engagement and present here a 2.85 Å complex structure of a human MAIT-TCR bound to bovine MR1. The MR1 binding groove is similar in backbone structure to classical peptide-presenting MHC class I molecules (MHCp), yet is partially occluded by large aromatic residues that form cavities suitable for small ligand presentation. The docking of the MAIT-TCR on MR1 is perpendicular to the MR1 surface and straddles the MR1 α1 and α2 helices, similar to classical αβ TCR engagement of MHCp. However, the MAIT-TCR contacts are dominated by the α-chain, focused on the MR1 α2 helix. TCR β-chain contacts are mostly through the variable CDR3β loop that is positioned proximal to the CDR3α loop directly over the MR1 open groove. The elucidation of the MAIT TCR/MR1 complex structure explains how the semi-invariant MAIT-TCR engages the nonpolymorphic MR1 protein, and sheds light onto ligand discrimination by this cell type. Importantly, this structure also provides a critical link in our understanding of the evolution of αβ T-cell recognition of MHC and MHC-like ligands.
Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL 60637, USA.