MAIT TCR recognition of MR1–Ac-6-FP. (a) Electron density of Ac-6-FP in omit and final 2Fo-Fc maps of the ternary complex MR1–Ac-6-FP-MAIT original WT (clone A-F7) TCR. Electron density in mesh format, the ligand in ball and stick, MR1 in ribbon representation in white, a Fo-Fc omit map contoured at 3σ (green). (b–d) Structural basis for Ac-6-FP recognition by MR1 and original WT (clone A-F7) MAIT TCR compared with the previously published MR1-6-FP original WT (clone A-F7) MAIT TCR structure (PDB accession no. 4L4T). (b) Superposition of Ac-6-FP and 6-FP and MR1 induced conformational changes. (c) CDR3β conformational changes induced by Ac-6-FP. (d) Contacts between Ac-6-FP and Tyr95α from the CDR3α loop. MR1-6-FP residues are shown in white, pale yellow, and pale orange for the CDR3α and CDR3β loops, respectively, and the 6-FP ligand is shown in cyan. Equivalent residues from the MR1–Ac-6-FP shown in slate, yellow, and orange for the CDR3α and CDR3β loops, respectively and Ac-6-FP in green with contacts between TCR and Ac-6-FP indicated by dashed lines.