MR1

FDA approved drug targets

Intracellular, Membrane (different isoforms)

Low cell type specificity

Low immune cell specificity

Low cell line specificity

Heterotrimer that consists of MR1, B2M and a metabolite antigen (PubMed:27043408, PubMed:23051753, PubMed:23846752, PubMed:24695216). Forms reversible covalent Schiff base complexes with the microbial metabolite, which serves as a molecular switch triggering complete folding, stable association with B2M and translocation of the ternary complex from endoplasmic reticulum to the plasma membrane (PubMed:27043408, PubMed:23051753, PubMed:23846752, PubMed:24695216). On antigen-presenting cells, the ternary complex interacts with TCR on CD8-positive T cells (PubMed:23846752, PubMed:24695216, PubMed:26795251). The molecular machinery involved in antigen processing remains unknown, but appears to be TAP1-TAP2 and proteasome-independent. Structurally, MR1-B2M heterodimer adopts a topology similar to classical MHC class I molecules, with alpha-1 and alpha-2 domains of MR1 forming the antigen-binding cleft composed of two alpha-helices resting on a floor of 7-stranded anti-parallel beta-pleated sheet (PubMed:23846752, PubMed:24695216, PubMed:26795251). The ribityl moiety of pyrimidine-based antigens is recognized by Tyr-95 residue in the CDR3 alpha loop of the invariant TRAV1-2 TCR (PubMed:23846752, PubMed:24695216, PubMed:26795251). [Isoform 3]: Homodimerizes and does not associate with B2M.