Fig. 5 ∣. Comparison of the molecular features of TAPBPR-bound MR1 versus MHC-I.

a, Structural model of L30C-MTSL in the TAPBPR G24-R36 loop. b, Intermolecular ¹H_M-Γ₂ PRE rates (s⁻¹) of ILV^proS methyl resonances corresponding to hpMR1 residues while in complex with TAPBPR^L30C-MTSL. PREs that are too large to measure accurately (> 100 s⁻¹) are plotted at 100 s⁻¹. Error bars were derived from five Monte Carlo fitting procedures. c, Intermolecular ¹H_M-Γ₂ PRE rates (s⁻¹) plotted onto a RosettaCM model of hpMR1–bβ₂m (PDB template 4PJ5, TCR removed). PRE effects are color-coded on the basis of strength: 0–10 s⁻¹ shown in gray, 10–60 s⁻¹ in blue and ≥ 100 s⁻¹ shown in warm pink. ¹H_M-Γ₂ PRE rates are listed in Supplementary Table 5. d, Left, an ensemble of the ten lowest-energy structural models of the Ac-6-FP–hpMR1–bβ₂m–TAPBPR complexes from restrained MD simulations and right, X-ray structure of the H2-D^d–hβ₂m–TAPBPR complex (PDB ID 5WER). e, Superposition of the groove of free (orange) and TAPBPR-bound (green with Ac-6-FP in magenta) MR1 versus H2-D^d. Arrows denote (top) widening of the groove at the α_2-1 helix and (bottom) rearrangement of the pleated β-sheet of the floor of the antigen binding groove. f, Mutant proteins used. Left, mutations on hpMR1 at TAPBPR interacting surfaces, resulting in the hpMR1^IM construct. Right, mutations on TAPBPR at hpMR1 interacting surfaces, resulting in the TAPBPR^TN6 construct. g, Surface expression of mutant MR1^IM was poorly responsive to TAPBPR-TM coexpression. Data are mean ± s.d. from N = 4 independent experiments. Statistical significance was determined by one-way ANOVA with Tukey test: *P < 0.05, ***P < 0.001. A full list of P values is noted in the Methods.